Predictions of sediment toxicity using consensus-based freshwater sediment quality guidelines

Source-risk and uncertainty assessment of trace metals in surface sediments of a human-dominated seaward catchment in eastern China

Current total concentration-based methods for source attribution and risk assessment often overestimate metal risks, thereby impeding the formulation of effective risk management strategies. This study aims to develop a framework for source-specific risk assessment based on metal bioavailability in surface river sediments from a human-dominated seaward catchment in eastern China. Metal bioavailability was quantified using chemical fractionation results, and source apportionment was conducted using the positive matrix factorization (PMF) model. Risk assessment integrated these findings using two indices: the Potential Ecological Risk Index (PERI) and the Mean Probable Effect Concentration Quotient (mPEC-Q), with uncertainty addressed via Monte Carlo simulations. Results indicated that average total concentrations of Cu, Pb, Zn, Cr, Hg, Cd, and As exceeded their respective background levels by 1.63 to 15.00 times. The residual fraction constituted the majority, accounting for 53.84 % to 77.79 % of total concentrations, suggesting significant natural origins. However, source apportionment revealed a predominant contribution from anthropogenic activities, including industrial smelting, agricultural practices, and atmospheric deposition. The contributions were found to vary between 5.35 % and 40.03 % when the total concentration was adjusted to bioavailable content. Total concentration-based PERI/mPEC-Q assessments indicated high/moderate risk levels, decreasing to considerable/low risk levels with bioavailability adjustment. Hg and Cd were identified as priority metals. Further incorporating source appointment parameters into the risk assessment, industrial smelting was identified as the primary contributor, accounting for 66.06 % of total risk by total concentration and 65.63 % by bioavailability. This underscores the role of bioavailability in mitigating risk overestimation. Monte Carlo simulations validated industrial smelting as a major risk contributor. This study emphasizes the importance of considering bioavailability in the source-risk assessment of sediment-metals, crucial for targeted risk management in urbanized catchment areas.

Chronic effects of metal releases from historical mining on threatened crayfish in Madison County Missouri, USA

The Little St. Francis River and its tributaries drain metals-contaminated areas of the Madison County Mines National Priority List Superfund site (MCM) which was designated in 2003 to facilitate remediation of metals contamination within the MCM. One concern for natural resource trustees in the MCM is the potential effects of elevated metals concentrations on the federally threatened St. Francis River crayfish, Faxonius quadruncus, which has a geographic range that is limited to the St. Francis River watershed. A survey of riffle-dwelling crayfish, in-situ cage study, and laboratory toxicity tests were conducted to assess the effects of mining-derived metals on F. quadruncus and other crayfish species in the MCM. Crayfish densities were significantly greater at sites upstream of metals releases from historical mining (henceforth mining releases) compared to densities at sites downstream of mining releases, and metals concentrations in whole-body crayfish, surface water, sediments, macroinvertebrates, fish, and plant material were greater at sites downstream of mining releases compared to sites upstream of mining releases. Crayfish densities were also negatively correlated with consensus-based adverse effects indices, expressed as surface-water toxic units and sediment probable effects quotients. Decreased growth and increased mortality during cage and laboratory studies were likely due to exposure to, and subsequently uptake of, elevated concentrations of metals. Crayfish in all studies were found to bioaccumulate metals, which supports their utility as bioindicators of metals contamination. Study results show that elevated metals concentrations associated with mining releases in the MCM continue to adversely affect biota, including the federally threatened F. quadruncus.

Poison in the water: Arsenic's silent assault on fish health

Arsenic occurs across the world in freshwater and marine environments, menacing the survival of aquatic organisms. Organic and inorganic forms of this substance can be found, in which the inorganic form is more hazardous than the organic form. Most aquatic bodies contain inorganic arsenic species, but organic species are believed to be the dominant form of arsenic in the majority of fish. Natural and anthropogenic both are the sources of water contamination with arsenic. Its bioaccumulation and transfer from one trophic level to another in the aquatic food chain make arsenic a vital environmental issue. Continuous exposure to low concentrations of arsenic in aquatic organisms including fish leads to its bioaccumulation, which may affect organisms of higher trophic levels including large fishes or humans. Humans can be exposed to arsenic through the consumption of fish contaminated with arsenic. Hence, the present review facilitates our understanding about sources of arsenic, its bioaccumulation, food chain transfer, and its effect on the fish health. Also, "Poison in the Water: Arsenic's Silent Assault on Fish Health" serves as a wake-up call to recognize the pressing need to address arsenic contamination in water bodies. By understanding its devastating impact on fish health, we can strive to implement sustainable practices and policies that safeguard our precious aquatic environments and ensure the well-being of both wildlife and human communities that depend on them.

Multiple lines of evidence point to pesticides as stressors affecting invertebrate communities in small streams in five United States regions

Multistressor studies were performed in five regions of the United States to assess the role of pesticides as stressors affecting invertebrate communities in wadable streams. Pesticides and other chemical and physical stressors were measured in 75 to 99 streams per region for 4 weeks, after which invertebrate communities were surveyed (435 total sites). Pesticides were sampled weekly in filtered water, and once in bed sediment. The role of pesticides as a stressor to invertebrate communities was assessed by evaluating multiple lines of evidence: toxicity predictions based on measured pesticide concentrations, multivariate models and other statistical analyses, and previously published mesocosm experiments. Toxicity predictions using benchmarks and species sensitivity distributions and statistical correlations suggested that pesticides were present at high enough concentrations to adversely affect invertebrate communities at the regional scale. Two undirected techniques-boosted regression tree models and distance-based linear models-identified which pesticides were predictors of (respectively) invertebrate metrics and community composition. To put insecticides in context with known, influential covariates of invertebrate response, generalized additive models were used to identify which individual pesticide(s) were important predictors of invertebrate community condition in each region, after accounting for natural covariates. Four insecticides were identified as stressors to invertebrate communities at the regional scale: bifenthrin, chlordane, fipronil and its degradates, and imidacloprid. Fipronil was particularly important in the Southeast region, and imidacloprid, bifenthrin, and chlordane were important in multiple regions. For imidacloprid, bifenthrin, and fipronil, toxicity predictions were supported by mesocosm experiments that demonstrated adverse effects on naïve aquatic communities when dosed under controlled conditions. These multiple lines of evidence do not prove causality-which is challenging in the field under multistressor conditions-but they make a strong case for the role of insecticides as stressors adversely affecting invertebrate communities in streams within the five sampled regions.

Geochemical distribution and environmental assessment of potentially toxic elements in farmland soils, sediments, and tailings from phosphate industrial area (NE Algeria)

This study investigates the extent and spatial distribution of Potentially Toxic Elements (PTEs) in the Djebel Onk phosphate mine area in south-eastern Algeria, as well as the associated risks to human health. Various scales are considered and sampled, including tailing waste (n = 8), surrounding farmland soil (n = 21), and sediments (n = 5). The samples were mineralogically and chemically analyzed using XRD, FTIR, XRF, and ICP-MS techniques. Principal Component Analysis (PCA) was applied after transforming the raw data into centered-log ratios (clr) to identify the dominant factors controlling the distribution of PTEs. Furthermore, pollution assessment was conducted using several indices, including geo-accumulation, pollution load, contamination security indices, and enrichment and contamination factors. The results reveal that the analyzed samples are mostly P-enriched in the mine tailings, farmland soil, and sediments, with P2O5 concentrations ranging from 13.37 wt% to 26.17 wt%, 0.91-21.70 wt%, and 17.04-29.41 wt%, respectively. The spatial distribution of PTEs exhibits clearly a decrease in the contents of CaO, P2O5, Cr, Sr, Cd, and U with increasing distance from the mine discharge site, while other oxides, such as MgO, Al2O3, SiO2, K2O, and Fe2O3, and associated elements (Cu, Co, Pb, and Zn), show an increase. PCA confirms the influence of minerals such as, apatite, dolomite, and silicates on the distribution PTEs. It denoted that the highest contamination level of all PTEs in soils and sediments was observed in the southern part of the plant and mine tailings compared to the northern part. In terms of human health risks, the assessment reveals that the hazard index (HI) values for both non-carcinogenic and carcinogenic risks associated with PTEs in the study area are below 1, suggesting no significant risk. However, regardless of the sample type, the lifetime cancer risk (LCR) values vary from 1.69E-05-2.11E-03 and from 1.03E-04-2.27E-04 for Cr, Ni, As (children) and Cd (adults), respectively, exceeding the safe levels recommended by the United States Environmental Protection Agency. The study highlights that oral ingestion poses the greatest risk, followed by dermal contact and particle inhalation. Importantly, all these indices decrease with increasing distance from the sampling site to the waste discharge point and the factory, which indicates that the phosphate mining activity had caused some extent risks. These findings provide valuable insights for mitigating the adverse health impacts and guiding environmental management efforts.

Source apportionment and source-specific risk assessment of bioavailable metals in river sediments of an anthropogenically influenced watershed in China

Integrated source analysis and risk assessment of metals facilitate the development of targeted risk management strategies. However, previous studies usually addressed total concentration rather than bioavailability, and consequently overestimated metal risk, especially natural source-related risk. In this study, a source-specific risk assessment was conducted by integrating the source analysis of bioavailable metals in surface sediments. Moreover, risk assessment was performed using two bioavailability-based indices: the total availability risk index (TARI) and a modified index of mean probable effect concentration quotients (mPEC-Q). A representative river watershed in eastern China was selected as the study area. Findings revealed that the total concentrations of Pb, Cu, Zn, Cr, and Ni in the sediments were 1.4-2.2 times higher than the local soil background values. Using a modified community bureau of reference (BCR) sequential extraction procedure, the dominant fraction for Pb, Cu, Zn, and Cr in the studied area was found to be the residual fraction, constituting 53.63-62.44% of the total concentrations. This suggested that a significant portion of the metals potentially originated from natural sources. Nevertheless, the concentration enrichment ratio (CER) indicated that anthropogenic sources contributed significantly, accounting for 67.84-87.68% of bioavailable metals. The positive matrix factorization (PMF) model further identified three different sources of bioavailable metals, with a descending concentration contribution sequence of industrial sources (37.61%), mixed traffic and natural sources (33.17%), and agricultural sources (29.22%). Both the TARI and mPEC-Q index values indicated that the bioavailable metals generally posed a moderate risk, and Ni was the priority pollutant. Industrial sources contributed the most to the total risk, although the contribution from TARI-based assessment (37.27%) was lower than that from the mPEC-Q assessment (46.43%). This study provides an example of the consideration of metal bioavailability in the context of source-specific risk assessments to develop more reasonable management strategies.

Effect of past century mining activities on sediment properties and toxicity to freshwater organisms in northern Sweden

The release of toxic metals from local mining activities often represents a severe environmental hazard for nearby lake ecosystems. Previous studies on the impact of mining have primarily focused on single lakes, with less emphasis on spatial and temporal recovery patterns of multiple lakes within the same catchment, but with different hydrological connection and distance to the pollutant source. This knowledge gap prevents us from assessing the real environmental risk of abandoned mines and understanding ecosystem recovery. This study explores the intensity and spatial patterns of sediment contamination and the potential for ecosystem recovery in three lakes in close vicinity of a lead (Pb) and zinc (Zn) mine in Sweden that has been inoperative for >20 years. Dated (²¹⁰Pb and ¹³⁷Cs) sediment cores from each lake were used to reconstruct temporal patterns in trace element deposition and relate those with past mining activities. Results show that all lakes were affected by mining, indicated by increasing Pb and Zn concentrations and decreasing organic matter content, at the onset of mining. However, the extent and timing of mining impact differed between lakes, which was partly ascribed to differences in the historical use of tailings and settling ponds. Assessment of toxicity levels in sediments, based on normalized Probable Effect Concentration Quotient (PEC-Q) to organic matter content, provided more consistent results with the historical mining than conventional methods, showing a decreasing impact in lakes once the operations ceased. Still, sediment Pb concentrations were > 10 times higher than pre-mining values, evidencing the urgent need for remediation actions in the study lakes. This study highlights the importance of considering spatial heterogeneity in metal deposition, sediment organic matter content, and hydrological connectivity with tailings when risk assessments are performed in mining-impacted lakes. The use of normalized PEC-Q in toxic assessments is also recommended.

Ecological risk assessment and sources identification of heavy metals in surface sediments of a river-reservoir system

Heavy metal contamination of river water and sediments is a global issue affecting ecological health. To reveal heavy metals' ecological risks and biological toxicity in the middle and lower Han River (MLHR), sediment samples collected in this area were analyzed based on a modified ecological risk assessment method (NIRI) and a biological toxicity assessment method. Also, Spearman correlation analysis and Positive Matrix Factorization (PMF) methods were applied to identify the potential sources of heavy metals. The results indicated that the heavy metal content significantly exceeded the background concentrations in Hubei Province. The average potential risk of heavy metals at sampling sites was: Cd > Hg > As > Pb > Cu > Zn. Consequently, high biological toxicity occurred along the MLHR due to the heavy metal enrichment. River damming and water diversion significantly enhanced the hydrologic regime variations and ecological risk in the MLHR. Moreover, two possible pollution sources of the MLHR were identified: one is a combined source of traffic pollution, agricultural pollution, and partial industrial pollution consisting of five heavy metals, Pb, Hg, Zn, Cu, and As, the other is an industrial pollution source dominated by Cd and As. This study provides insights into sediment heavy metal pollution management and ecological risk control in the MLHR and similar rivers worldwide.

Transport of toxic metals in the bottom sediments and health risk assessment of Corbicula fluminea (Asiatic clam) collected from Laguna de Bay, Philippines

Laguna de Bay, the 3rd largest lake in Southeast Asia, is the most significant source of freshwater fish in the Philippines. With decades of unregulated discharge of industrial, domestic, and agricultural wastewaters into the lake, this study investigates the apportionment of heavy metals from the bottom sediments and its impact on the toxicity of Corbicula fluminea (Asiatic clam), a popular food item in the markets. The sediment samples from the western part of the lake contained higher Cd, Cu, Pb, and Zn and lower As and Cr concentrations compared to the eastern part. There were positive correlations for As, Cr, Cu, Pb, and Zn and negative correlations for Cd and Ni concentrations noted between sediments and C. fluminea. Human health risk associated with the consumption of C. fluminea collected from Laguna de Bay was attributed to the following heavy metals: Cu > As > Zn > Cd > Pb > Cr > Ni. Interestingly, the observed trend in toxicities of the shellfish was consistent with the transport phenomenon of heavy metals facilitated by the counterclockwise direction of the bottom current. This study strongly suggests the re-evaluation of the waste management plan in the industrial zones and policies regulating the sale of the shellfish harvest.

Risk-Based Prioritization of Organic Chemicals and Locations of Ecological Concern in Sediment From Great Lakes Tributaries

With improved analytical techniques, environmental monitoring studies are increasingly able to report the occurrence of tens or hundreds of chemicals per site, making it difficult to identify the most relevant chemicals from a biological standpoint. For the present study, organic chemical occurrence was examined, individually and as mixtures, in the context of potential biological effects. Sediment was collected at 71 Great Lakes (USA/Canada) tributary sites and analyzed for 87 chemicals. Multiple risk-based lines of evidence were used to prioritize chemicals and locations, including comparing sediment concentrations and estimated porewater concentrations with established whole-organism benchmarks (i.e., sediment and water quality criteria and screening values) and with high-throughput toxicity screening data from the US Environmental Protection Agency's ToxCast database, estimating additive effects of chemical mixtures on common ToxCast endpoints, and estimating toxic equivalencies for mixtures of alkylphenols and polycyclic aromatic hydrocarbons (PAHs). This multiple-lines-of-evidence approach enabled the screening of more chemicals, mitigated the uncertainties of individual approaches, and strengthened common conclusions. Collectively, at least one benchmark/screening value was exceeded for 54 of the 87 chemicals, with exceedances observed at all 71 of the monitoring sites. Chemicals with the greatest potential for biological effects, both individually and as mixture components, were bisphenol A, 4-nonylphenol, indole, carbazole, and several PAHs. Potential adverse outcomes based on ToxCast gene targets and putative adverse outcome pathways relevant to individual chemicals and chemical mixtures included tumors, skewed sex ratios, reproductive dysfunction, hepatic steatosis, and early mortality, among others. The results provide a screening-level prioritization of chemicals with the greatest potential for adverse biological effects and an indication of sites where they are most likely to occur. Environ Toxicol Chem 2022;41:1016-1041. Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Environmental Assessment Impact of Acid Mine Drainage from Kizel Coal Basin on the Kosva Bay of the Kama Reservoir (Perm Krai, Russia)

The Kosva Bay is permanently affected by acid mine drainage (AMD) from Kizel Coal Basin in the Perm Krai of Russia. This discharge is released in the middle part of the Kosva River from the abandoned mines. This study investigates the current trace element (TE) concentrations for Zn, Cu, Pb, Ni, Cr, Cd, As, and Hg and the mineral composition, major oxides, grain size of sediments, and acute toxicity using two test organisms within the site of AMD downstream from the Kosva River and up to the Kosva Bay of Kama Reservoir. The objectives of this study were to analyze the quality of sediment and level pollution of Kosva Bay using pollution and ecotoxicological indices. The environmental indices, namely the contamination factor (CF), the geoaccumulation index (Igeo), and the potential ecological risk factor (Eri), indicate contamination by Cr and Pb in sediments at the site of AMD, with the highest values for Cr, Cu, and As in the Kosva Bay sediments downstream of abandoned coal mines. The results of Igeo and CF average values in bay of sediments showed different degrees of contamination, from moderate contamination to considerable contamination, respectively. According to the potential ecological risk index (RI) values, the Kosva Bay sediments exhibited low to moderate risk, and As and Cd have the highest contribution rate. According to LAWA and the Polish geochemical classification of sediments, sediments of the bay correspond to the highest levels (IV–III classes) for Cr, Ni, and Hg. Based on the SQGC, Hg, Cd, Cr, and Ni are the most probable for resulting in adverse effects on aquatic organisms in this study. The results of this study indicate that complex pollution and ecotoxicological indices must be supported by ecotoxicologal tests. High precipitation totals, low evaporation rates, and flow regulation stream by the Shirokovsky Reservoir located upstream from abandoned coal mines provide significant fluctuations in streamflow, which is probably the most important factor controlling the distribution and mobility of TE in the studied sediments.

Sediment Sources and Sealed-Pavement Area Drive Polycyclic Aromatic Hydrocarbon and Metal Occurrence in Urban Streams

Metals and polycyclic aromatic hydrocarbons (PAHs) are common pollutants in urban streambed sediment, yet their occurrence is highly variable and difficult to predict. To investigate sources of PAHs and metals to streambed sediment, we sampled pavement dust, soil, and streambed sediment in 10 urban watersheds in three regions of the United States and applied a fallout-radionuclide-based sediment-source analysis to quantify the pavement dust contribution to stream sediment (%dust). We also mapped the area of sealcoated pavement in each watershed (%sealed) to investigate the role of coal-tar pavement sealant (CTS) as a PAH source. Median total and carbon-normalized total PAH concentrations were significantly higher in streambed sediment in the Northeast (54.3 mg/kg and 2.71 mg/gOC) and Southeast (5.37 mg/kg and 1.36 mg/gOC), where CTS is commonly used, than in the Northwest (2.11 mg/kg and 0.071 mg/gOC), where CTS is rarely used. Generalized additive models indicated that %sealed and in some cases %dust significantly affected total PAH concentrations in streambed sediments. The %dust was a significant variable for common urban metals: Cu, Pb, and Zn. These findings advance our quantitative understanding of the role of pavement dust as a source and a vector of contaminants to urban streams.

Development of current ambient background threshold values for sediment quality parameters in U.S. lakes on a regional and statewide basis

For the first time, background threshold values have been developed for a large suite of sediment quality parameters from 969 lakes spanning the conterminous United States (U.S.). These values provide a statistical basis for estimating current ambient background, which refers to chemical and physical (e.g., grain size) concentrations derived from natural and/or widespread diffuse anthropogenic sources (e.g., nonpoint sources like atmospheric deposition and land runoff). Surficial sediment quality data, collected based on the randomized, probability-based sampling design of the 2017 National Lakes Assessment (NLA) study, were utilized for this effort. These data included 16 metal(loid)s, 25 polycyclic aromatic hydrocarbons (PAHs), 53 polychlorinated biphenyl (PCB) congeners, 27 legacy organochlorine pesticides and metabolites, total organic carbon (TOC), and grain size parameters. The data were analyzed based on different geographic areas, including: 10 U.S. Environmental Protection Agency (EPA) Regions, two major ecoregions bisecting the State of Minnesota (i.e., Temperate Plains and Upper Midwest), and for Minnesota. Hypothesis testing of 47 sediment quality parameters was performed on three geographic areas bisecting Minnesota, and there were many statistically significant (p < 0.05) differences between geographic pairs that included Minnesota. Background threshold values were calculated for parameters with >20% detects using 95% one-sided upper tolerance limit (UTL) with 95% coverage (UTL95-95) values. The UTL95-95 represents the value below which 95% of the population values are expected to fall with 95% confidence. These values were compared to matching sediment quality guidelines for the protection of benthic organisms, both with and without potential outliers removed. Applications and limitations of the UTL95-95 values are discussed. Jurisdictions within the continental U.S. could use these same publicly available sediment quality data to calculate UTL95-95 values for specific geographic areas, and other countries could design similar probabilistic field studies to determine current ambient background of sediment quality parameters in lake sediments.

Mobilization mechanisms and toxicity risk of sediment trace metals (Cu, Zn, Ni, and Pb) based on diffusive gradients in thin films: A case study in the Xizhi River basin, South China

Identifying the mobilization mechanisms and predicting the potential toxicity risk of metals in sediment are essential to contamination remediation in river basins. In this study, a sequential extraction procedure and diffusive gradients in thin film (DGT) were employed to investigate the mobilization mechanisms, release characteristics, and potential toxicity of sediment metals (Cu, Zn, Ni, and Pb). Acid-soluble and reducible fractions were the dominant geochemical species of Cu, Zn, Ni, and Pb in sediments, indicating high mobility potentials for these metals under reducing conditions. In summer, the sediment acted as a source of water-column metals due to mineralization of organic matter and reductive dissolution of iron/manganese oxides in surface sediments, and the formation of metal sulfide precipitates markedly lowered DGT-labile metal concentrations with depth, while localized sulfide oxidation was responsible for fluctuating labile metal concentrations. Stable distribution patterns of labile metals resulted from the weak reducing conditions of sediment in winter, when the sediment shifted to a metal sink. The interstitial water criteria toxicity unit (IWCTU), calculated from DGT measurements, indicated no and low-to-moderate toxic risk of sediments in summer and winter seasons, respectively, and Pb was the major contributor to the predicted toxic effects in the soft interstitial water.

Estuarine sediment toxicity testing with an indigenous subtropical amphipod

This study reports on a sediment toxicity test developed with a native amphipod strain of Ptilohyale barbicornis where sediments from 10 estuarine stations along the western coastline of Taiwan were evaluated with respect to trace metals and PAHs. The test was validated by determining dose-response relationships for aqueous copper, and cadmium and sodium dodecyl sulfate as well as copper-spiked sediment, showing a sensitivity of P. barbicornis indicating its capability serving as a toxicity test species. A significant negative correlation between growth effects after 28 days of exposure to field-collected contaminated sediments and PAHs concentrations was observed. Similarly, the chronic toxicity test showed that growth was mostly inhibited compared to controls, body lengths in particular being significantly different from controls (p < 0.05). Various estuarine sediment pollutants in the quality guidelines can be further evaluated using P. barbicornis to understand their comprehensive biological effects and ecological risks.

Metal pollution assessment in surface sediments of Namak Lake, Iran

Desiccation of the Namak Lake (NL) can result in the release of fine-grained dust contaminated with heavy metals, while there is little information available on the propagation of metals in the bed sediments of this lake. In this study, contamination of metals in the surface sediments of the NL was analyzed and the pollution status of sediments was assessed using geo-accumulation index (I_geo), enrichment factor (EF), the consensus-based sediment quality guidelines (CBSQGs), and mean probable effect concentration quotient (mPECQ). Results indicated that metal concentrations at the southern part were higher than at the middle and northern parts of the lake. Possible reasons are (i) pollution loads mainly entered the lake through the rivers at the west and northwest, but accumulated at the southern parts, (ii) hard layer of salt covering the bottom of the NL at the northern part suppresses adsorption of metals to the sediment, and (iii) the muddy nature of sediments at the southern part makes it easier for metals to be absorbed. EF results showed that sediments at the southern part of the lake were moderately enriched with lead (Pb). The low I_geo values suggested no pollution with the metals, and CBSQG values showed that the sediments of the NL were not toxic, while the mPECQ index suggested a toxicity probability of less than 25%. Cluster analysis classified the metals into two clusters. In general, the results showed that metal pollution in the surface sediments of NL was generally low although the concentration of Pb at the southern part of the lake was worrisome.

Primary Sources of Polycyclic Aromatic Hydrocarbons to Streambed Sediment in Great Lakes Tributaries Using Multiple Lines of Evidence

Polycyclic aromatic hydrocarbons (PAHs) are among the most widespread and potentially toxic contaminants in Great Lakes (USA/Canada) tributaries. The sources of PAHs are numerous and diverse, and identifying the primary source(s) can be difficult. The present study used multiple lines of evidence to determine the likely sources of PAHs to surficial streambed sediments at 71 locations across 26 Great Lakes Basin watersheds. Profile correlations, principal component analysis, positive matrix factorization source-receptor modeling, and mass fractions analysis were used to identify potential PAH sources, and land-use analysis was used to relate streambed sediment PAH concentrations to different land uses. Based on the common conclusion of these analyses, coal-tar-sealed pavement was the most likely source of PAHs to the majority of the locations sampled. The potential PAH-related toxicity of streambed sediments to aquatic organisms was assessed by comparison of concentrations with sediment quality guidelines. The sum concentration of 16 US Environmental Protection Agency priority pollutant PAHs was 7.4-196 000 µg/kg, and the median was 2600 µg/kg. The threshold effect concentration was exceeded at 62% of sampling locations, and the probable effect concentration or the equilibrium partitioning sediment benchmark was exceeded at 41% of sampling locations. These results have important implications for watershed managers tasked with protecting and remediating aquatic habitats in the Great Lakes Basin. Environ Toxicol Chem 2020;39:1392-1408. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Determining the effects of past gold mining using a sediment palaeotoxicity model

Ore processing techniques used in Yellowknife's largest mining operation, Giant Mine, is responsible for the atmospheric release of approximately 20,000 t of particulate arsenic trioxide and other heavy metal(loids). This rapid deposition of heavy metal(loids) may have caused ecological disturbances to aquatic food webs. Here we use ²¹⁰Pb and ¹³⁷Cs dated lake sediment cores from 20 lakes within a 40 km radius of Yellowknife to examine the spatial-temporal distribution of arsenic, antimony and lead. Further, we model the toxicity of the sediment to aquatic biota pre-, during, and post-mining using palaeotoxicity modelling, enrichment factor assessment, and comparisons to national sediment quality guidelines. We found that metal(loid) profiles in sediment peaked during the height of mining operations. These peak metal(loid) concentrations were highest in lakes near the mine's roaster stack, and decreased with distance from the historic mine. Palaeotoxicity modelling of lake sediment archives indicate that there is no significant difference in the mean predicted toxicity of pre- and post-mining samples (p = 0.14), however mining activities in the region significantly increased the predicted toxicity of sediments to aquatic organisms during mining operations (p < 0.001). In the years since roasting processes ceased, the mean palaeotoxicity of all lakes has decreased significantly (p < 0.05), indicating a projected pattern of biological recovery. Importantly, some lakes remain at an elevated risk, indicating that aquatic ecosystems in Yellowknife may continue to have lingering effects on aquatic biota despite the closure of the mine two decades ago.

Ecotoxicological characteristics and ecological risk assessment of trace elements in the bottom sediments of the Rożnów reservoir (Poland)

The bottom sediments in catchment areas behind dams play a significant role in water ecosystems. On the other hand, the structure of sediments makes them a natural geosorbent, in which pollutants introduced to the aquatic environment accumulate. The use of biotests is recognised as an important approach for the assessment of the quality of bottom sediments, as the chemical analysis of sediment samples alone does not provide evidence of the impact of contaminants on biota. The aim of the study was to apply the chemical and ecological indices to determine the potential risk posed by trace elements in the bottom sediments and to evaluate sediment toxicity using organisms belonging to two taxonomic groups, i.e., plants (Phytotoxkit) and crustaceans (Rapidtoxkit). The 46 sediment samples were taken from the Rożnów Dam Reservoir in Southern Poland. The mean concentration of the trace elements in the sediments was 5.22 mg As; 0.26 mg Cd; 63.23 mg Cr; 28.65 mg Cu; 37.11 mg Ni; 11.15 mg Pb; 69.69 mg Zn and 0.09 mg Hg ∙ kg^-1 d.m. The mean probable effect concentration quotient (PECq) value among different sampling sites ranged between 0.04 and 0.33 suggested moderate potential toxicity to the biological communities in bottom sediments. The Ni was potentially the most toxic element for biota in the Rożnów Reservoir. The sensitivity of organisms formed the following order: Thamnocephalus platyurus >Lepidium sativum >Sinapis alba >Sorghum saccharatum. For the plants, the stimulating effect of bottom sediments on root growth was often indicated, while a toxic effect was demonstrated for T. platyurus in 80% of the samples. However, the correlation analysis and PCA results showed that trace elements that originated from similar sources were associated to the toxicity of sediments towards T. platyurus, while ecotoxicity for plants could not be explained by the content of trace elements in bottom sediments. T. platyurus is a good indicator for predicting the toxicity of bottom sediments from the Rożnów Reservoir. However, our study found that both chemical and ecotoxicological analyses are important for a comprehensive evaluation of the quality of bottom sediments.

Methods of Assessment of Metal Contamination in Bottom Sediments (Case Study: Straszyn Lake, Poland)

The concentrations of six metals (Zn, Cu, Pb, Ni, Cr, and Cd) were investigated in bottom sediments of Straszyn Lake (North Poland). This study was designed to determine a total content of metals and to assess their mobility and bioavailability. The sequential extraction was used to fractionate metals into five fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter, and residual. The evaluation of sediments contamination degree by metals was performed by applying the geochemical quality guidelines, the pollution load index, and the geo-accumulation index (I_geo). The assessment based on these methods demonstrated that sediments were polluted with Cr and the sediments quality guidelines confirmed these results. Moreover, the average concentrations of Cu, Ni, and Cr were respectively 3.4, 3.9, and 21.2 times higher than their background values. According to ecological risk index and risk assessment code Cd was the most important factor affecting the ecological environment of the Straszyn Lake. The metal speciation analysis demonstrated that the mean percentage of metals in the exchangeable and carbonate fractions decreased in the following order: Cd (59.1%) > Zn (19.8%) = Ni (19.8%) > Pb (16.6%) > Cu (3.3%) > Cr (2.7%). The very strong correlation calculated between all the metals indicated their common origin.

Evidence for unmonitored coal ash spills in Sutton Lake, North Carolina: Implications for contamination of lake ecosystems

Coal combustion residuals (CCRs, also known as "coal ash") contain high concentrations of toxic and carcinogenic elements that can pose ecological and human health risks upon their release into the environment. About half of the CCRs that are generated annually in the U.S. are stored in coal ash impoundments and landfills, in most cases adjacent to coal plants and waterways. Leaking of coal ash ponds and CCR spills are major environmental concerns. One factor which may impact the safety of CCRs stored in impoundments and landfills is the storage area's predisposition to flooding. The southeastern U.S., in particular, has a large number of coal ash impoundments located in areas that are vulnerable to flooding. In order to test for the possible presence of CCR solids in lake sediments following Hurricane Florence, we analyzed the magnetic susceptibility, microscopic screening, trace element composition, and strontium isotope ratios of bottom sediments collected in 2015 and in 2018 from Sutton Lake in eastern North Carolina and compared them to a reference lake. The results suggest multiple, apparently previously unmonitored, CCR spills into Sutton Lake from adjacent CCR storage sites. The enrichment of metals in Sutton Lake sediments, particularly those with known ecological impact such as As, Se, Cu, Sb, Ni, Cd, V, and Tl, was similar to or even higher than those in stream sediments impacted by the Tennessee Valley Authority (TVA) in Kingston, Tennessee, and the Dan River, North Carolina coal ash spills, and exceeded ecological screening standards for sediments. High levels of contaminants were also found in leachates extracted from Sutton Lake sediments and co-occurring pore water, reflecting their mobilization to the ambient environment. These findings highlight the risks of large-scale unmonitored spills of coal ash solids from storage facilities following major storm events and contamination of nearby water resources throughout the southeastern U.S.

Environmental Risk of Metal Contamination in Sediments of Tropical Reservoirs

Reservoir sediment can work as both sink and source for contaminants. Once released into the water column, contaminants can be toxic to biota and humans. We investigate potential ecological risk to benthic organisms by metals contamination in six reservoirs in Southeast Brazil. Results of the bioavailable fraction of copper (Cu), chromium (Cr), cadmium (Cd), lead (Pb), zinc (Zn), and iron (Fe) in sediment samples are presented. Considering Cu, Cd, and Zn concentrations, about 6% of the samples exceeded the threshold effect levels of sediment quality guidelines. The comparison to sediment quality guidelines is conservative because we used a moderate metal extraction. Control of contaminant sources in these reservoirs is key because they are sources of water and food. The mixture toxicity assessment showed an increased incidence of toxicity to aquatic organisms showing that mixture toxicity should be taken into account in sediment assessment criteria.

Characterizing toxicity of metal-contaminated sediments from the Upper Columbia River, Washington, USA, to benthic invertebrates

Sediments from the Upper Columbia River, Washington, USA, are contaminated with metals from smelting operations. We conducted short-term and long-term tests with the midge Chironomus dilutus and the amphipod Hyalella azteca and short-term tests with the freshwater mussel Lampsilis siliquoidea with 54 sediments from the Upper Columbia River to characterize thresholds for toxicity of metals to benthic invertebrates. Test sediments were screened for toxicity by comparisons with low-metal reference sediments. Toxic effects on amphipods occurred primarily in sediments from the upstream (riverine) reach, and toxic effects on midges occurred in sediments from both the upstream reach and the downstream (reservoir) reach. Little toxicity was observed in mussel tests. Toxicity thresholds (20% effect concentrations [EC20s]) for metals in sediment and porewater were estimated from logistic concentration-response models. Copper (Cu) concentrations in the simultaneously extracted metal fraction of sediments and bioavailable Cu in porewater, as characterized by biotic ligand models, had consistent associations with toxicity endpoints. Concentration-response models for sediment Cu produced EC20s for 6 endpoints, with long-term amphipod survival and reproduction being the most sensitive. A logistic regression model fitted to an endpoint sensitivity distribution for sediment Cu predicted that approximately one-half of the sediments tested would be toxic to at least one endpoint and that approximately 20% of test sediments would be toxic to more than half of the endpoints. These results indicate that sediments from the upstream reach of the Upper Columbia River, which contain high concentrations of metals associated with slags, cause a wide range of toxic effects in laboratory tests and are likely to have adverse effects on benthic invertebrate communities. Environ Toxicol Chem 2018;37:3102-3114. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Palaeotoxicity: reconstructing the risk of multiple sedimentary pollutants to freshwater organisms

'Real-world' contaminant exposure of sediment-dwelling biota is typically long-term, low-level and to multiple pollutants. However, sediment quality guidelines, designed to protect these organisms, relate only to single contaminants. This study uses radiometrically dated sediment cores from 7 English lakes with varying contamination histories to reconstruct temporal changes in likely risk to biota (herein termed 'palaeotoxicity'). The Probable Effects Concentration Quotient (PEC-Q) approach was used to combine sediment concentrations from multiple contaminants (trace metals; PCBs; PBDEs) to determine risk allocated to metals and persistent organic pollutants (POPs) separately as well as combined (PEC-Q Mean-All). Urban-influenced lakes were considerably more contaminated, exceeding PEC-Q thresholds of 0.5 and 2.0 over long durations (some since the nineteenth century). This has been mainly due to metals (principally lead) and by factors of up to 10 for individual metals and by > 2 for PEC-Q Mean-Metals. In 6 out of 7 lakes, considerable reductions in risk associated with trace metals are observed since emissions reductions in the 1970s. However, at all lakes, PEC-Q Mean-POPs has increased sharply since the 1950s and at 5 out of 7 lakes now exceeds PEC-Q Mean-Metals. These organic pollutants are therefore now the dominant driver behind elevated contaminant risk to sediment-dwelling biota and recent temporal trends in PEC-Q Mean-All remain above threshold values as a result. Finally, PEC-Q Mean-All values were compared to standard biological toxicity tests for surface sediments at each site. While chironomid growth and daphniid reproduction were significantly reduced compared to controls at 5 out of 7, and all lakes, respectively, the scale of these reductions showed only limited quantitative agreement with predicted risk.

Use of Chemical Indicators and Bioassays in Bottom Sediment Ecological Risk Assessment

This study is was designed to assess the ecological risk associated with chemical pollution caused by heavy metals and PAHs on the basis of their ecotoxicological properties in sediments collected from the Rzeszów dam reservoir (Poland). The sediment samples were collected from three sampling stations: S1-inlet, backwater station, S2-middle of reservoir, S3 outlet, near the dam. The sediments' toxicity was evaluated using a battery of bioassays (Phytotoxkit, Phytotestkit, Ostracodtoxkit F, and Microtox). The highest content of metals (120.5 mg Zn; 22.65 mg Pb; 8.20 mg Cd ∙ kg-1 dw) and all PAHs (∑9361 μg ∙ kg-1 dw) in sediments was found at station S1. The lowest content of metals (86.72 mg Zn; 18.07 mg Cu; 17.20 mg Pb; 3.62 mg Cu; 28.78 mg Ni; 30.52 mg Cr ∙ kg-1 dw) and PAHs (∑4390 μg ∙ kg-1 dw) was found in the sediment from station S2. The ecological risk assessment of the six metals and eight PAHs revealed a high potential toxicity in sediments from stations S1 (PECq = 0.69) and S3 (PECq = 0.56) and a low potential toxicity in sediments from station S2 (PECq = 0.38). The studies also showed the actual toxicity of sediments for the test organisms. The sediment pore water was least toxic compared to the whole sediment: solid phases > whole sediment > pore water. The most sensitive organism for metals and PAHs in bottom sediments was Lepidium sativum, and in pore water-Sorghum saccharatum. The concentration of metals and PAHs in bottom sediments generally did not affect the toxicity for other organisms. Clay content and organic C content are likely to be important factors, which control heavy metal and PAH concentrations in the sediments. Data analysis by PCA found the same origin of metals as well as PAHs-mainly anthropogenic sources. The obtained information demonstrated the need to integrate ecotoxicological and chemical methods for an appropriate ecological risk assessment.

Polycyclic aromatic hydrocarbons (PAHs) in surface sediments near a mining site in Okobo-Enjema, Nigeria: concentrations, source apportionment and risk assessment

PAHs are pollutants of serious environmental and human health concerns. PAH studies in environmental compartments may assist in designing PAH control measures. The levels of selected PAHs in surface sediment samples of a stream near a mining site at Okobo-Enjema, Nigeria, were investigated. The data were used to determine the possible sources of the PAHs and to assess the potential health risk of the PAHs to humans which was evaluated based on the sediment quality, contamination level and cancer risk guidelines. Sediment samples were collected in replicates at various locations in the stream. A mixture of acetone, dichloromethane and n-hexane was used to extract the PAH compounds by sonication. The extracts were cleaned-up, concentrated and quantitatively analyzed using gas chromatography-mass spectrometry. The results indicated 14, 10 and 4 out of the 16 target PAHs were detected at various sampling stations. The total concentrations of the PAHs ranged from 0.09 to 1.2 mg/kg dry weight. High molecular weight PAHs dominated over the low molecular weight compounds at distances nearer to the coal mine. The PAH contamination came from pyrogenic and petrogenic sources. The results suggested that there was no eco-toxicological risk for organisms in the sediments beyond 400 m from the coal mine. The sediments were highly contaminated at ≤400 m from the coal mine; moderately contaminated at between 400 and 500 m from the mine; and lowly contaminated at beyond 500 m from the mine. The cancer risk is low on ingestion and skin contact with the sediments.

Toxicities and risk assessment of heavy metals in sediments of Taihu Lake, China, based on sediment quality guidelines

The occurrence, toxicities, and ecological risks of five heavy metals (Pb, Cu, Cd, Zn and Ni) in the sediment of Taihu Lake were investigated in this study. To evaluate the toxicities caused by the heavy metals, the toxicities induced by organic contaminants and ammonia in the sediments were screened out with activated carbon and zeolite. The toxicities of heavy metals in sediments were tested with benthic invertebrates (tubificid and chironomid). The correlations between toxicity of sediment and the sediment quality guidelines (SQGs) derived previously were evaluated. There were significant correlations (p<0.0001) between the observed toxicities and the total risk quotients of the heavy metals based on SQGs, indicating that threshold effect level (TEL) and probable effect level (PEL) were reliable to predict the toxicities of heavy metals in the sediments of Taihu Lake. By contrast, the method based on acid volatile sulfides (AVS) and simultaneously extracted metals (SEM), such as ∑SEM/AVS and ∑SEM-AVS, did not show correlations with the toxicities. Moreover, the predictive ability of SQGs was confirmed by a total predicting accuracy of 77%. Ecological risk assessment based on TELs and PELs showed that the contaminations of Pb, Cu, Cd and Zn in the sediments of Taihu Lake were at relatively low or medium levels. The risks caused by heavy metals in the sediments of northern bay of the lake, which received more wastewater discharge from upper stream, were higher than other area of the lake.

Concentration, sources and risk assessment of PAHs in bottom sediments

The aims of the study were to investigate the concentration, sources and ecological risk of PAHs (polycyclic aromatic hydrocarbons) in bottom sediments collected from nine reservoirs located in south-eastern Poland. The concentration of ∑PAHs in sediments ranged from 150 to 33,900 μg kg^-1. The total PAH concentration in the bottom sediments was arranged in the following order: Rybnik > Rzeszów > Brzóza Królewska > Brzóza Stadnicka > Besko > Chechło > Ożanna > Głuchów > Narożniki. BAP was the major compound in sediments from the Besko, Brzóza Stadnicka and Rzeszów reservoirs; FLT in the sediments from the Rybnik, Narożniki, Ożanna and Brzóza Królewska reservoirs; and FLN from the Głuchów and Chechło reservoirs. The major inputs of PAHs were of pyrolytic origin. However, petrogenic sources of PAHs occurred especially in the Chechło and Głuchów reservoirs. The ecological risk assessment indicated that non-adverse effects on the benthic fauna may occur for sediments from the Głuchów, Narozniki and Ożanna reservoirs, while slightly adverse effects were found for sediments from the Brzóza Królewska, Besko, Brzóza Stadnicka and Chechło reservoirs. The other sediments showed moderate (Rzeszów reservoirs) and strong effect (Rybnik reservoir) on biological communities. Individual PAHs such as NAP, PHE, FLT, PYR, BAA, CHR and BAP in sediments from the Rybnik reservoir and BAP in sediments from the Rzeszów reservoirs indicated a higher possibility of occurrence of an adverse ecological effect. PCA analysis found slight difference between the reservoirs in the profile of variable PAHs. Only the sediments from the Rybnik and Chechło reservoirs differ considerably from this grouping.

Sediment quality benchmarks for assessing oil-related impacts to the deep-sea benthos

Paired sediment contaminant and benthic infaunal data from prior studies following the 2010 Deepwater Horizon (DWH) oil spill in the Gulf of Mexico were analyzed using logistic regression models (LRMs) to derive sediment quality benchmarks for assessing risks of oil-related impacts to the deep-sea benthos. Sediment total polycyclic aromatic hydrocarbon (PAH) and total petroleum hydrocarbon (TPH) concentrations were used as measures of oil exposure. Taxonomic richness (average number of taxa/sample) was selected as the primary benthic response variable. Data are from 37 stations (1300-1700 m water depth) in fine-grained sediments (92%-99% silt-clay) sampled within 200 km of the DWH wellhead (most within 40 km) in 2010 and 32 stations sampled in 2011 (29 of which were common to both years). Results suggest the likelihood of impacts to benthic macrofauna and meiofauna communities is low (<20%) at TPH concentrations of less than 606 mg kg^-1 (ppm dry weight) and 700 mg kg^-1 respectively, high (>80%) at concentrations greater than 2144 mg kg^-1 and 2359 mg kg^-1 respectively, and intermediate at concentrations in between. For total PAHs, the probability of impacts is low (<20%) at concentrations of less than 4.0 mg kg^-1 (ppm) for both macrofauna and meiofauna, high (>80%) at concentrations greater than 24 mg kg^-1 and 25 mg kg^-1 for macrofauna and meiofauna, respectively, and intermediate at concentrations in between. Although numerical sediment quality guidelines (SQGs) are available for total PAHs and other chemical contaminants based on bioeffect data for shallower estuarine, marine, and freshwater biota, to our knowledge, none have been developed for measures of total oil (e.g., TPH) or specifically for deep-sea benthic applications. The benchmarks presented herein provide valuable screening tools for evaluating the biological significance of observed oil concentrations in similar deep-sea sediments following future spills and as potential restoration targets to aid in managing recovery. Integr Environ Assess Manag 2017;13:840-851. Published 2017. This article is a US Government work and is in the public domain in the USA.

Primary sources and toxicity of PAHs in Milwaukee-area streambed sediment

High concentrations of polycyclic aromatic hydrocarbons (PAHs) in streams can be a significant stressor to aquatic organisms. To understand the likely sources and toxicity of PAHs in Milwaukee-area streams, streambed sediment samples from 40 sites and parking lot dust samples from 6 sites were analyzed for 38 parent PAHs and 25 alkylated PAHs. Diagnostic ratios, profile correlations, principal components analysis, source-receptor modeling, and mass fractions analysis were used to identify potential PAH sources to streambed sediment samples, and land-use analysis was used to relate streambed sediment PAH concentrations to different urban-related land uses. On the basis of this multiple lines-of-evidence approach, coal-tar pavement sealant was indicated as the primary source of PAHs in a majority of streambed sediment samples, contributing an estimated 77% of total PAHs to samples, on average. Comparison with the probable effect concentrations and (or) the equilibrium partitioning sediment benchmark indicates that 78% of stream sediment samples are likely to cause adverse effects to benthic organisms. Laboratory toxicity tests on a 16-sample subset of the streambed sites using the amphipod Hyalella azteca (28-d) and the midge Chironomus dilutus (10-d) measured significant reductions in 1 or more biological endpoints, including survival, in 75% of samples, with H. azteca more responsive than C. dilutus. Environ Toxicol Chem 2017;36:1622-1635. © 2016 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

Assessment of hazard metrics for predicting field benthic invertebrate toxicity in the Detroit River, Ontario, Canada

Numerical sediment quality guidelines (SQGs) are frequently used to interpret site-specific sediment chemistry and predict potential toxicity to benthic communities. These SQGs are useful for a screening line of evidence (LOE) that can be combined with other LOEs in a full weight of evidence (WOE) assessment of impacted sites. Three common multichemical hazard quotient methods (probable effect concentration [PEC]-Q_avg , PEC-Q_met , and PEC-Q_sum ) and a novel (hazard score [HZD]) approach were used in conjunction with a consensus-based set of SQGs to evaluate the ability of different scoring metrics to predict the biological effects of sediment contamination under field conditions. Multivariate analyses were first used to categorize river sediments into distinct habitats based on a set of physicochemical parameters to include gravel, low and high flow sand, and silt. For high flow sand and gravel, no significant dose-response relationships between numerically dominant species and various toxicity metric scores were observed. Significant dose-response relationships were observed for chironomid abundances and toxicity scores in low flow sand and silt habitats. For silt habitats, the HZD scoring metric provided the best predictor of chironomid abundances compared to various PEC-Q methods according to goodness-of-fit tests. For low flow sand habitats, PEC-Q_sum followed by HZD, provided the best predictors of chironomid abundance. Differences in apparent chironomid toxicity between the 2 habitats suggest habitat-specific differences in chemical bioavailability and indicator taxa sensitivity. Using an IBI method, the HZD, PEC-Q_avg , and PEC-Q_met approaches provided reasonable correlations with calculated IBI values in both silt and low flow sand habitats but not for gravel or high flow sands. Computation differences between the various multi-chemical toxicity scoring metrics and how this contributes to bias in different estimates of chemical mixture toxicity scores are discussed and compared. Integr Environ Assess Manag 2017;13:410-422. © 2016 SETAC.

Changing agricultural practices: potential consequences to aquatic organisms

Agricultural practices pose threats to biotic diversity in freshwater systems with increasing use of glyphosate-based herbicides for weed control and animal waste for soil amendment becoming common in many regions. Over the past two decades, these particular agricultural trends have corresponded with marked declines in populations of fish and mussel species in the Upper Conasauga River watershed in Georgia/Tennessee, USA. To investigate the potential role of agriculture in the population declines, surface waters and sediments throughout the basin were tested for toxicity and analyzed for glyphosate, metals, nutrients, and steroid hormones. Assessments of chronic toxicity with Ceriodaphnia dubia and Hyalella azteca indicated that few water or sediment samples were harmful and metal concentrations were generally below impairment levels. Glyphosate was not observed in surface waters, although its primary degradation product, aminomethyl phosphonic acid (AMPA), was detected in 77% of the samples (mean = 509 μg/L, n = 99) and one or both compounds were measured in most sediment samples. Waterborne AMPA concentrations supported an inference that surfactants associated with glyphosate may be present at levels sufficient to affect early life stages of mussels. Nutrient enrichment of surface waters was widespread with nitrate (mean = 0.7 mg NO3-N/L, n = 179) and phosphorus (mean = 275 μg/L, n = 179) exceeding levels associated with eutrophication. Hormone concentrations in sediments were often above those shown to cause endocrine disruption in fish and appear to reflect the widespread application of poultry litter and manure. Observed species declines may be at least partially due to hormones, although excess nutrients and herbicide surfactants may also be implicated.

Spatial distribution of trace elements and ecotoxicity of bottom sediments in Rybnik reservoir, Silesian-Poland

The aim of study was to integrate chemical analyses and toxicity bioassays in order to assess the environmental risk connected with the presence of trace elements in the sediments. This study examined the ecological significance of trace elements in bottom sediments by applying a set of complementary sediment quality assessment methods sediment quality guidelines (SQGs) (mean probable effect concentration quotient (PECQ)), potential ecological risk index (PERI), contamination degree (C d) and two bioassays: the bacterial luminescence inhibition test with Vibrio fischeri on sediment elutriates and the direct contact test with the ostracod crustacean Heterocypris incongruens. The samples were collected from 50 stations of Rybnik reservoir. The reservoir is a region with enormous concentration of industry, mainly hard coal mining, electric power industry, and transportation. Despite the high diversity in metal concentration in the sediments, the spatial distribution of trace elements in the sediments was very similar. Moreover, the strong positive correlations between individual pairs of trace elements indicate that they may derive from a similar source and move together. According to mean PECQs, 68 % of the samples were potentially non-toxic and 32 % of the samples were potentially toxic. PERI values suggested that 70 % of the sediment sampling sites exhibited low ecological risk from metal pollution while 24 % of the samples had severe and serious risk. Based on our combined evaluation, we believe that Cd and Cu in the sediment samples frequently caused adverse biological effects. Higher toxic responses were observed in the Microtox test than in the Ostracodtoxkit test. All the sediment samples were found toxic to V. fischeri, and 96 % of the samples had effect percentages >50 %. For H. incongruens, 12 % of the sediments were not toxic and 44 % had effect percentages >50 %. In order to perform a complex assessment of the environmental impact of metal pollution, both chemical and ecotoxicological analysis should be carried out.

Development and application of freshwater sediment-toxicity benchmarks for currently used pesticides

Sediment-toxicity benchmarks are needed to interpret the biological significance of currently used pesticides detected in whole sediments. Two types of freshwater sediment benchmarks for pesticides were developed using spiked-sediment bioassay (SSB) data from the literature. These benchmarks can be used to interpret sediment-toxicity data or to assess the potential toxicity of pesticides in whole sediment. The Likely Effect Benchmark (LEB) defines a pesticide concentration in whole sediment above which there is a high probability of adverse effects on benthic invertebrates, and the Threshold Effect Benchmark (TEB) defines a concentration below which adverse effects are unlikely. For compounds without available SSBs, benchmarks were estimated using equilibrium partitioning (EqP). When a sediment sample contains a pesticide mixture, benchmark quotients can be summed for all detected pesticides to produce an indicator of potential toxicity for that mixture. Benchmarks were developed for 48 pesticide compounds using SSB data and 81 compounds using the EqP approach. In an example application, data for pesticides measured in sediment from 197 streams across the United States were evaluated using these benchmarks, and compared to measured toxicity from whole-sediment toxicity tests conducted with the amphipod Hyalella azteca (28-d exposures) and the midge Chironomus dilutus (10-d exposures). Amphipod survival, weight, and biomass were significantly and inversely related to summed benchmark quotients, whereas midge survival, weight, and biomass showed no relationship to benchmarks. Samples with LEB exceedances were rare (n=3), but all were toxic to amphipods (i.e., significantly different from control). Significant toxicity to amphipods was observed for 72% of samples exceeding one or more TEBs, compared to 18% of samples below all TEBs. Factors affecting toxicity below TEBs may include the presence of contaminants other than pesticides, physical/chemical characteristics of sediment, and uncertainty in TEB values. Additional evaluations of benchmarks in relation to sediment chemistry and toxicity are ongoing.

Bioavailability of Polycyclic Aromatic Hydrocarbons and their Potential Application in Eco-risk Assessment and Source Apportionment in Urban River Sediment

Traditional risk assessment and source apportionment of sediments based on bulk polycyclic aromatic hydrocarbons (PAHs) can introduce biases due to unknown aging effects in various sediments. We used a mild solvent (hydroxypropyl-β-cyclodextrin) to extract the bioavailable fraction of PAHs (a-PAHs) from sediment samples collected in Pearl River, southern China. We investigated the potential application of this technique for ecological risk assessments and source apportionment. We found that the distribution of PAHs was associated with human activities and that the a-PAHs accounted for a wide range (4.7%-21.2%) of total-PAHs (t-PAHs), and high risk sites were associated with lower t-PAHs but higher a-PAHs. The correlation between a-PAHs and the sediment toxicity assessed using tubificid worms (r = -0.654, P = 0.021) was greater than that from t-PAH-based risk assessment (r = -0.230, P = 0.472). Moreover, the insignificant correlation between a-PAH content and mPEC-Q of low molecular weight PAHs implied the potential bias of t-PAH-based risk assessment. The source apportionment from mild extracted fractions was consistent across different indicators and was in accordance with typical pollution sources. Our results suggested that mild extraction-based approaches reduce the potential error from aging effects because the mild extracted PAHs provide a more direct indicator of bioavailability and fresher fractions in sediments.

Spatial distribution and toxicity assessment of heavy metals in sediments of Liaohe River, northeast China

Twenty-four surface sediment samples were collected from Liaohe River in June 2014 for the analysis of total concentrations of Cu, Pb, Zn, Cd, Ni, Fe, and Mn. The spatial distribution of heavy metals in Liaohe River was site specific, with Hun River as the most polluted river mainly affected by industrial and human activities. The contents of acid-volatile sulfide (AVS) and simultaneously extracted metals (SEMs) in Liaohe River varied significantly, ranging from 0.03 to 19.4 μmol/g and 0.14 to 10.8 μmol/g, respectively. Sulfate-reducing bacteria (SRB) community size, organic matter and sulfate availability, and sediment redox status may be the main factors affecting the AVS distribution. Among all the acid-extracted metals, Zn was dominant in all samples, whereas much more toxic Cd contributed less than 1.0 % to the total SEMs. Sediment quality guidelines (SQGs) and AVS-SEM models were used to predict the sediment toxicity. Results revealed that only a small portion of sites exhibited potential metal toxicity to aquatic biota, while adverse effects should rarely occur in majority of sites. Comparison of the two assessment methods showed inconsistent results, indicating that each method had its own limitations. The combination of different methods will be more convincing as to the sediment quality assessment.

Characterization and risk assessment of PAH-contaminated river sediment by using advanced multivariate methods

This study applied advanced multivariate methods and risk assessment to evaluate the characteristics of polycyclic aromatic hydrocarbons (PAHs) in the sediment of the severely polluted Erjen River in Taiwan. High-molecular-weight PAHs (HPAHs) dominated in the rainy season. The ecological risk of PAHs in the sediment was low, whereas the total health risk through ingestion and dermal contact was considerably high. The SOM (self-organizing map) analysis clustered the datasets of PAH-contaminated sediment into five groups with similar concentration levels. Factor analysis identified major factors, namely coal combustion, traffic, petrogenic, and petrochemical industry factors, accounting for 88.67% of the variance in the original datasets. The major tributary and the downstream of the river were identified as PAH-contamination hotspots. The PMF (positive matrix factorization) was combined with toxicity assessment to estimate the possible apportionment of sources and the associated toxicity. Spills of petroleum-related products, vehicle exhaust, coal combustion, and exhaust from a petrochemical industry complex constituted respectively 12%, 6%, 74%, and 86% of PAHs in the sediment, but contributed respectively 7%, 15%, 22%, and 56% of toxicity posed by PAHs in the sediment. To improve the sediment quality, best management practices should be adopted to eliminate nonpoint sources of PAHs flushed by storm water into the major tributary and the downstream of the Erjen River. The proposed methodologies and results provide useful information on remediating river PAH-contaminated sediment and may be applicable to other basins with similar properties that are experiencing resembled river environmental issues.

Relative sensitivity of an amphipod Hyalella azteca, a midge Chironomus dilutus, and a unionid mussel Lampsilis siliquoidea to a toxic sediment

The objective of the present study was to evaluate the relative sensitivity of test organisms in exposures to dilutions of a highly toxic sediment contaminated with metals and organic compounds. One dilution series was prepared using control sand (low total organic carbon [TOC; <0.1%, low binding capacity for contaminants]) and a second dilution series was prepared using control sediment from West Bearskin Lake, Minnesota, USA (high TOC [∼10% TOC, higher binding capacity for contaminants]). Test organisms included an amphipod (Hyalella azteca; 10-d and 28-d exposures), a midge (Chironomus dilutus; 20-d and 48-d exposures started with <1-h-old larvae, and 13-d and 48-d exposures started with 7-d-old larvae), and a unionid mussel (Lampsilis siliquoidea; 28-d exposures). Relative species sensitivity depended on the toxicity endpoint and the diluent. All 3 species were more sensitive in sand dilutions than in West Bearskin Lake sediment dilutions. The <1-h-old C. dilutus were more sensitive than 7-d-old C. dilutus, but replicate variability was high in exposures started with the younger midge larvae. Larval biomass and adult emergence endpoints of C. dilutus exhibited a similar sensitivity. Survival, weight, and biomass of H. azteca were more sensitive endpoints in 28-d exposures than in 10-d exposures. Weight and biomass of L. siliquoidea were sensitive endpoints in both sand and West Bearskin Lake sediment dilutions. Metals, ammonia, oil, and other organic contaminants may have contributed to the observed toxicity.

Toxicity of sediments from lead-zinc mining areas to juvenile freshwater mussels (Lampsilis siliquoidea) compared to standard test organisms

Sediment toxicity tests compared chronic effects on survival, growth, and biomass of juvenile freshwater mussels (28-d exposures with Lampsilis siliquoidea) to the responses of standard test organisms-amphipods (28-d exposures with Hyalella azteca) and midges (10-d exposures with Chironomus dilutus)-in sediments from 2 lead-zinc mining areas: the Tri-State Mining District and Southeast Missouri Mining District. Mussel tests were conducted in sediments sieved to <0.25 mm to facilitate recovery of juvenile mussels (2-4 mo old). Sediments were contaminated primarily with lead, zinc, and cadmium, with greater zinc and cadmium concentrations in Tri-State sediments and greater lead concentrations in southeast Missouri sediments. The frequency of highly toxic responses (reduced 10% or more relative to reference sites) in Tri-State sediments was greatest for amphipod survival (25% of samples), midge biomass (20%), and mussel survival (14%). In southeast Missouri sediments, the frequency of highly toxic samples was greatest for mussel biomass (25%) and amphipod biomass (13%). Thresholds for metal toxicity to mussels, expressed as hazard quotients based on probable effect concentrations, were lower for southeast Missouri sediments than for Tri-State sediments. Southeast Missouri sites with toxic sediments had 2 or fewer live mussel taxa in a concurrent mussel population survey, compared with 7 to 26 taxa at reference sites. These results demonstrate that sediment toxicity tests with juvenile mussels can be conducted reliably by modifying existing standard methods; that the sensitivity of mussels to metals can be similar to or greater than standard test organisms; and that responses of mussels in laboratory toxicity tests are consistent with effects on wild mussel populations.

Characterization of heavy-metal-contaminated sediment by using unsupervised multivariate techniques and health risk assessment

This study characterized the sediment quality of the severely contaminated Erjen River in Taiwan by using multivariate analysis methods-including factor analysis (FA), self-organizing maps (SOMs), and positive matrix factorization (PMF)-and health risk assessment. The SOMs classified the dataset with similar heavy-metal-contaminated sediment into five groups. FA extracted three major factors-traditional electroplating and metal-surface processing factor, nontraditional heavy-metal-industry factor, and natural geological factor-which accounted for 80.8% of the variance. The SOMs and FA revealed the heavy-metal-contaminated-sediment hotspots in the middle and upper reaches of the major tributary in the dry season. The hazardous index value for health risk via ingestion was 0.302. PMF further qualified the source apportionment, indicating that traditional electroplating and metal-surface-processing industries comprised 47% of the health risk posed by heavy-metal-contaminated sediment. Contaminants discharged from traditional electroplating and metal-surface-processing industries in the middle and upper reaches of the major tributary must be eliminated first to improve the sediment quality in Erjen River. The proposed assessment framework for heavy-metal-contaminated sediment can be applied to contaminated-sediment river sites in other regions.

Spatial distribution and potential ecologic risk assessment of heavy metals in the sediments of the Nansi Lake in China

The contamination levels and ecological risks of heavy metals in the sediments of the Nansi Lake were investigated. The contents of Cd, Cr, Cu, Pb, Zn, Ni, and Co in the surface sediments collected at 20 sites ranged from 0.08 to 1.12, 58.92 to 135.62, 38.09 to 78.65, 24.51 to 53.95, 110.51 to 235.36, 11.30 to 65.40, and 4.12 to 20.14 mg/kg, respectively. The results of partitioning analysis revealed that the proportions of soluble and exchangeable fraction were less than 1 %, the proportions of carbonate, amorphous oxides, organic matter, and crystalline oxides fraction were less than 10 %, and 10.52 % of Cd was associated with carbonate. The average proportions in the residual fraction ranged from 48.62 % for Cu to 73.76 % for Ni, indicating low mobility and bioavailability. The geoaccumulation index (I geo), relative enrichment factor (REF), sediment pollution index (SPI), and potential effect concentration quotient (PECQ) values of the heavy metals in the sediments were not in agreement with each another. The average REF values of Cd and Zn were higher than those of other metals. However, the average PECQ values were higher for Cr and Ni than those of other metals, indicating that these two metals would cause higher adverse biological effects. Therefore, it is suggested that future management and pollution control might focus on Cd, Zn, Cr, and Ni in the sediments of the Nansi Lake.

Separating the effects of water physicochemistry and sediment contamination on Chironomus tepperi (Skuse) survival, growth and development: a boosted regression tree approach

More comprehensive ecological risk assessment procedures are needed as the unprecedented rate of anthropogenic disturbances to aquatic ecosystems continues. Identifying the effects of pollutants on aquatic ecosystems is difficult, requiring the individual and joint effects of a range of natural and anthropogenic factors to be isolated, often via the analysis of large, complicated datasets. Ecotoxicologists have traditionally used multiple regression to analyse such datasets, but there are inherent problems with this approach and a need to consider other potentially more suitable methods. Sediment pollution can cause a range of negative effects on aquatic animals, and these are used as the basis for toxicity bioassays to measure the biological impact of pollution and the success of remediation efforts. However, experimental artefacts can also lead to sediments being incorrectly classed as toxic in such studies. Understanding the influence of potentially confounding factors will help more accurate assessments of sediment pollution. In this study, we analysed standardised sediment bioassays conducted using the chironomid Chironomus tepperi, with the aim of modelling the impact of sediment toxicants and water physico-chemistry on four endpoints (survival, growth, median emergence day, and number of emerging adults). We used boosted regression trees (BRT), a method that has a number of advantages over multiple regression, to model bioassay endpoints as a function of water chemistry, sediment quality and underlying geology. Endpoints were generally influenced most strongly by water quality parameters and nutrients, although some metals negatively influenced emergence endpoints. Sub-lethal endpoints were generally better predicted than lethal endpoints; median emergence day was the most sensitive endpoint examined in this study, while the number of emerging adults was the least sensitive. We tested our modelling results by experimentally manipulating sediment and observing the impact on C. tepperi endpoints. For survival, experimental observations were accurately predicted by models, which highlighted the importance of conductivity and dissolved oxygen for this endpoint. In comparison, experimental median emergence day was poorly modelled, most likely due to the influence of a wider range of predictors identified as being important influences on this endpoint in models. To demonstrate how BRT model results compare to more traditional techniques, we analysed survival data using multiple regression. Both models yielded similar results, but boosted regression trees offer important advantages over multiple regression. Our results illustrate how boosted regression trees can be used to analyse complex ecotoxicological datasets, and reinforces the importance of water chemistry in sediment toxicology.

Pesticide Toxicity Index--a tool for assessing potential toxicity of pesticide mixtures to freshwater aquatic organisms

Pesticide mixtures are common in streams with agricultural or urban influence in the watershed. The Pesticide Toxicity Index (PTI) is a screening tool to assess potential aquatic toxicity of complex pesticide mixtures by combining measures of pesticide exposure and acute toxicity in an additive toxic-unit model. The PTI is determined separately for fish, cladocerans, and benthic invertebrates. This study expands the number of pesticides and degradates included in previous editions of the PTI from 124 to 492 pesticides and degradates, and includes two types of PTI for use in different applications, depending on study objectives. The Median-PTI was calculated from median toxicity values for individual pesticides, so is robust to outliers and is appropriate for comparing relative potential toxicity among samples, sites, or pesticides. The Sensitive-PTI uses the 5th percentile of available toxicity values, so is a more sensitive screening-level indicator of potential toxicity. PTI predictions of toxicity in environmental samples were tested using data aggregated from published field studies that measured pesticide concentrations and toxicity to Ceriodaphnia dubia in ambient stream water. C. dubia survival was reduced to ≤50% of controls in 44% of samples with Median-PTI values of 0.1-1, and to 0% in 96% of samples with Median-PTI values >1. The PTI is a relative, but quantitative, indicator of potential toxicity that can be used to evaluate relationships between pesticide exposure and biological condition.

Sediment quality evolution (2001-2011) in the Ebro River basin (Spain)

Spatio-temporal variations in sediment quality (20 sample sites) of the Ebro River basin between 2001 and 2011 have been assessed. The self-organizing map classified the sediment samples according to similarities in their chemical compositions. Its powerful visualization tools helped establish the main pollution contribution on each sample. Most of the samples showed low values of the mean-probable effect concentration quotient through time. However, six samples presented several quality issues related to some trace elements or polycyclic aromatic hydrocarbons. Finally, geoaccumulation index values calculated using estimates of background trace element concentrations suggested anthropogenic influences in more than half of the samples.

Regional models for sediment toxicity assessment

The present study describes approaches to improve the performance of empirical models developed from a large nationwide data set to predict sediment toxicity from chemistry for regional applications. The authors developed 4 multiple chemical (PMax ) models selected from individual chemical models developed using 1) a previously published approach applied to the nationwide data set; 2) a broader array of response and explanatory variables (e.g., different normalization approaches and toxicity classifications) applied to the nationwide data set; 3) a data set from the New York/New Jersey, USA, region; and 4) both nationwide and regional data sets. The models were calibrated using the regional data set. Performance was tested using an independent data set from the same region. The performance of the final PMax model developed using the calibration process substantially improved over that of the uncalibrated PMax model developed using the nationwide data set. The improvements were achieved by selecting the best performing individual chemical models and eliminating those that performed poorly when applied together. Although the best performing PMax model included both nationwide and region-specific models, the performance of the PMax model derived using only nationwide models was nearly as good. These results suggest that calibrating nationwide models to a regional data set may be both a more efficient and effective approach for improving model performance than developing region-specific models. This article is a US Government work and is in the public domain in the USA.

Anthropogenic pollution and variability of manganese in alluvial sediments of the Yellow River, Ningxia, northwest China

Heavy metal pollution of sediments is a global concern and can be a serious problem in heavily industrialized parts of the world. Pollution by manganese is particularly common due to its ubiquitous natural occurrence, ease of mobilization, and extensive association with industry. In Ningxia, China, manganese pollution of Yellow River alluvial sediments was assessed by comparing manganese concentrations in 35 sediment samples with background values derived from similar sediments obtained at sites considered remote from potential sources of contamination. Natural background values of manganese were found to range from 192 to 323 mg/kg for surface sediments, and from 220 to 325 and 283 to 394 mg/kg for subsurface sediments at depths of 45–50 and 95–100 cm, respectively. In the study area, manganese content ranged from 565 to 1,363 mg/kg, indicating anthropogenic pollution extending to a depth of at least 1 m in the study area. All 35 samples were found to exceed the threshold effect concentration (TEC) of 460 mg/kg, below which adverse effects on sediment-dwelling organisms are not expected to occur, and one sample (T12) was found to exceed the probable effect concentration (PEC) of 1,100 mg/kg. PEC defines the threshold above which adverse effects are likely to be observed. Variogram analysis of the surface sediment manganese data revealed adherence to a Gaussian model, and ordinary kriging was used to generate a manganese distribution map. Analysis of the high nugget effect ratio indicates high, small-scale variations that are consistent with potential emissions from an adjacent electrolytic manganese plant.

Chlorinated pesticides in stream sediments from organic, integrated and conventional farms

To determine if current sheep/beef farming practices affect pesticide residues in streams, current-use and legacy chlorinated pesticides were quantified in 100 sediment samples from 15 streams on the South Island of New Zealand. The study involved five blocks of three neighboring farms, with each block containing farms managed by organic, integrated and conventional farming practices. Significantly higher concentrations of dieldrin, ∑ endosulfans, ∑ current-use pesticides, and ∑ chlorinated pesticides were measured in sediments from conventional farms compared to organic and integrated farms. However, streams in the latter two farming categories were not pesticide-free and sometimes contained relatively high concentrations of legacy pesticides. Comparison of measured pesticide concentrations with sediment quality guidelines showed that, regardless of farming practice, mean pesticide concentrations were below the recommended toxicity thresholds. However, up to 23% of individual samples contained chlorpyrifos, endosulfan sulfate, ∑ DDT, dieldrin, or ∑ chlordane concentrations above these thresholds.

Contamination and ecological risk assessment of toxic trace elements in the Xi River, an urban river of Shenyang city, China

The objectives of this study were to assess the enrichment, contamination, and ecological risk posed by toxic trace elements in the sediments of the Xi River in the industrialized city of Shenyang, China. Surface sediment and sediment core were collected; analyzed for toxic trace elements; and assessed with an index of geoaccumulation (Igeo), enrichment factor (EF) value, potential ecological risk factor (Er), ecological risk index (RI), and probable effect concentration quotient (PECQ). Elemental concentrations (milligram per kilogram) were 8.5-637.9 for As, 6.5-103.9 for Cd, 12.2-21.9 for Co, 90.6-516.0 for Cr, 258.1-1,791.5 for Cu, 2.6-19.0 for Hg, 70.5-174.5 for Ni, 126.9-1,405.8 for Pb, 3.7-260.0 for Sb, 38.4-100.4 for V, and 503-4,929 for Zn. The Igeo, EF, Er, and PECQ indices showed that the contamination of Cd and Hg was more serious than that of As, Cr, Cu, Ni, Pb, Sb, and Zn, whereas the presence of Co and V might be primarily from natural sources. The Igeo index for Cr and Ni might underestimate the degree of contamination, potentially as a result of high concentrations of these elements in the shale. The RI index was higher than 600, indicating a notably high ecological risk of sediment for the river. The average PECQ for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn ranged from 1.4 to 4.1 for surface sediment and from 5.2 to 9.6 in the sediment cores, indicating a high potential for an adverse biological effect. It was concluded that the sediment in the Xi River was severely contaminated and should be remediated as a hazardous material.

Effects of historical lead-zinc mining on riffle-dwelling benthic fish and crayfish in the Big River of southeastern Missouri, USA

The Big River (BGR) drains much of the Old Lead Belt mining district (OLB) in southeastern Missouri, USA, which was historically among the largest producers of lead-zinc (Pb-Zn) ore in the world. We sampled benthic fish and crayfish in riffle habitats at eight sites in the BGR and conducted 56-day in situ exposures to the woodland crayfish (Orconectes hylas) and golden crayfish (Orconectes luteus) in cages at four sites affected to differing degrees by mining. Densities of fish and crayfish, physical habitat and water quality, and the survival and growth of caged crayfish were examined at sites with no known upstream mining activities (i.e., reference sites) and at sites downstream of mining areas (i.e., mining and downstream sites). Lead, zinc, and cadmium were analyzed in surface and pore water, sediment, detritus, fish, crayfish, and other benthic macro-invertebrates. Metals concentrations in all materials analyzed were greater at mining and downstream sites than at reference sites. Ten species of fish and four species of crayfish were collected. Fish and crayfish densities were significantly greater at reference than mining or downstream sites, and densities were greater at downstream than mining sites. Survival of caged crayfish was significantly lower at mining sites than reference sites; downstream sites were not tested. Chronic toxic-unit scores and sediment probable effects quotients indicated significant risk of toxicity to fish and crayfish, and metals concentrations in crayfish were sufficiently high to represent a risk to wildlife at mining and downstream sites. Collectively, the results provided direct evidence that metals associated with historical mining activities in the OLB continue to affect aquatic life in the BGR.