Incorporating contaminant bioavailability into sediment quality assessment frameworks

Improving toxicity prediction of metal-contaminated sediments by incorporating sediment properties

For the purpose of sediment quality assessment, the prediction of toxicity risk-levels for aquatic organisms based on simple environmental measurements is desirable. One commonly used approach is the comparison of total contaminant concentrations with corresponding water and sediment quality guideline values, serving as a Line of Evidence (LoE) based on chemistry-toxicity effects relationships. However, the accuracy of toxicity predictions can be improved by considering the factors that modify contaminant bioavailability. In this study we used paired chemistry-ecotoxicity data sets for sediments to evaluate the improvement in toxicity risk predictions using bioavailability-modified guidelines. The sediments were predominantly contaminated with metals, and measurements of sediment particle size, total organic carbon (TOC) and acid volatile sulfide (AVS) were used to modify hazard quotients (HQ). To further assess the predictive efficacy of the bioavailability-modified guideline models, sediments with differing contamination levels were tested for toxicity to a benthic amphipod's reproduction. To account for differences between laboratory exposure and field exposure scenarios, where the latter creates greater dilution, both static-renewal and flow-through test procedures were employed, and flow-through resulted in lower dissolved metal concentrations in the overlying waters. We also investigated how lower AVS concentration by oxidation modified the toxicity. This study reaffirmed that consideration of factors that influence contaminant bioavailability improves toxicity risk predictions, however the improvements may be modest. The sediment particle size data had the greatest influence on the modified HQ, indicating that higher percentage of fine particle size (<63 μm) contributed most to a lower predicted toxicity. The comparison of the static-renewal and flow-through test results continue to raise important questions about the relevance of static or static-renewal toxicity test results for risk assessment decisions, as both these test designs may cause unrealistically high contributions of dissolved metals in overlying waters to toxicity. Overall, this study underscores the value of incorporating outcomes from simple and routine sediment analysis (e.g., particle size, TOC, and consideration of AVS) to enhance the predictive efficacy of toxicity risk assessments in the context of sediment quality risk assessment.

Application of a Multi-Metal Stable-Isotope-Enriched Bioassay to Assess Changes to Metal Bioavailability in Suspended Sediments

The direct measurement of particulate contaminant bioavailability is a challenging aspect for the environmental risk assessment of contaminated sites. Here, we demonstrated a multi-metal stable-isotope-enriched bioassay to simultaneously measure the bioavailability of Cd, Cu, and Zn in naturally contaminated sediments following differing periods of resuspension treatment. Freshwater filter-feeding clams were pre-labeled with the isotopes ¹¹⁴Cd, ⁶⁵Cu, and ⁶⁸Zn to elevate isotope abundances in their tissues and then exposed to metal-contaminated suspended sediments. The assimilation of sediment-associated metals by clams would decrease the isotope ratios (Cd^114/111, Cu^65/63, and Zn^68/64) in tissues, providing a direct measurement of metal bioavailability. For the sediments tested here, the method revealed bioavailable cadmium and non-bioavailable copper in sediments but was inconclusive for zinc. With a longer resuspension time, the bioavailability of particulate cadmium increased, but that of copper was unaffected. Metal bioavailability predicted using traditional wet-chemical extraction methods was inconsistent with these findings. The study indicated that multi-metal stable-isotope-enriched bioassay provides a new tool for directly assessing metal bioavailability in sediments, and this method is amenable for use in in situ assessments.

Risk assessment for sediment associated heavy metals using sediment quality guidelines modified by sediment properties

Sediment quality guidelines (SQGs) are a fundamental component of sediment quality assessment framework, frequently used in the first tier of assessment to predict the potential risks of contaminants in sediment. A recognized weakness of SQGs concerns the bioavailability of sediment contaminants, which may vary considerably with different physical-chemical properties. To better evaluate the ecological risks and predict the toxicity of the heavy metals (Cd, Cu, Ni, Pb, Zn) in the sediments of Haihe River of China, the risk quotients derived from total metal concentrations and SQG values were modified using multiple linear regressions with sediment properties, i.e. total organic carbon (TOC), acid-volatile sulfide (AVS), and particle size distribution (PSD). Then, the sediment toxicity was tested with the benthic organisms of chironomids and tubificids, and the relationships between the observed toxicity with the modified risk quotients were investigated. We found that the risk quotient modified with TOC and AVS displayed significantly improved relationship with the toxicity (p < 0.001) compared to the original risk quotient without modification (p = 0.062-0.074 > 0.05). Risk assessment indicated that although the heavy metals in the sediments of Haihe River of China are at a relatively low level, potential ecological risks caused by Ni and Zn still exist in some area, especially in the lower reaches along the estuary. The results indicated that the risk quotient and SQG values modified with sediment properties are promising for risk assessment of the metal contaminants in sediments.

Improved prediction of sediment toxicity using a combination of sediment and overlying water contaminant exposures

The choice of sediment quality assessment methodologies can strongly influence assessment outcomes and management decisions for contaminated sites. While in situ (field) methods may potentially provide greater realism, high costs and/or complex logistics often prevent their use and assessment must rely on laboratory-based methods. In this study, we utilised static-renewal and flow-through ecotoxicology tests in parallel on sediments with a wide range of properties and varying types and concentrations of contaminants. The prediction of chronic effects to amphipod reproduction was explored using multiple linear regression (MLR). The study confirmed the considerable over-estimation of the risk of toxicity of contaminated sediments in field locations when assessments rely on the results of laboratory-based static and static-renewal tests. Improved prediction of toxicity risks was achieved using a combination of contaminant exposure measures from sediment and overlying water. Existing sediment and water quality guideline values (GVs) were effective for predicting risks posed by sediments containing mixtures of common metal and organic contaminants. For 17 sediments with paired data sets from static-renewal and flow-through tests, the best prediction of toxicity to reproduction was achieved using a 2-parameter MLR that included hazard quotients for sediment contaminants and toxic units for dissolved metals (r² = 0.892). The inclusion of particle size, organic carbon and acid-volatile sulfide did not improve toxicity predictions, despite these parameters being recognised as modifying contaminant bioavailability. The use of dilute-acid-extractable metal concentrations in place total recoverable metal concentrations did not improve the predictions. The study also confirmed that sediments existing within the estuarine and marine bays of Sydney Harbour pose significant risks of adverse effects to benthic organisms.

Remediation criteria for gasworks-impacted sediments: Assessing the effects of legacy hydrocarbons and more recent metal contamination

Historical contamination of sediments from industries that commenced before environmental regulations were commonplace is prevalent in many large cities. This contamination is frequently overlain and mixed with more recent urban contamination. The remediation of contaminated sites is often a very expensive exercise and the final remediation criteria often reflect a trade-off between protecting human and ecological health and the finances of those deemed responsible for the site clean-up. In this study, we describe an assessment of estuarine sediments impacted historically by contamination from a gasworks site. The major historical sediment contaminants included polycyclic aromatic hydrocarbons (PAHs) and other petroleum-related hydrocarbons (TRHs). Elevated concentrations of metals exist throughout the city region due to historical pollution and ongoing urban stormwater discharges. Equilibrium partitioning models were used to consider the influence on the bioavailability of PAHs of both natural sedimentary organic carbon and forms of black carbon (pyrogenic carbon - coal tars, charcoal). The strongest predictor of the observed sublethal toxicity to amphipod and copepod reproduction was a combination of total PAHs and metals (primarily Cu, Pb and Zn). Total PAHs was the strongest predicting variable for toxicity to organism survival. While high total PAH concentrations were attributed to the former gas works, high background concentrations of metals existed throughout much of this region of the estuary. Thus, without remediation at the estuary-scale, resuspension of the surrounding sediments by tidal currents and boat movements is predicted to re-contaminate remediated areas with sediments that may continue to cause chronic toxicity due to metals. The assessment indicated that remedial actions that remove or isolate sediments that caused toxicity to benthic organism survival would lead to significant improvements in ecosystem health, but toxicity to organism reproduction may remain at similar levels that exist throughout much of this region of the estuary due to high metal concentrations.

Diagnosis of complex mixture toxicity in sediments: Application of toxicity identification evaluation (TIE) and effect-directed analysis (EDA)

Determining causality of sediment toxicity is of great importance in aquatic risk assessment, but there are tremendous challenges due to joint toxicity of trace pollutants in complex sediment matrices. Two approaches, namely toxicity identification evaluation (TIE) and effect-directed analysis (EDA) have been developed. Conventional sediment TIEs take the advantage of environmental relevance by using whole organism bioassays; however, they suffer from lack of effective methods for specifically identifying major contributors as it typically only evaluates contaminant class rather than specific contaminants. Alternatively, EDA is a powerful tool in identifying causes of sediment toxicity with sophisticated fractionation and chemical analysis of targeted and non-targeted non-polar organic toxicants, but it is not always environmentally relevant due to the use of in-vitro bioassays and exhaustive solvent extraction. An integrated TIE and EDA method would provide an environmentally relevant and toxicant specific approach to effectively determine causality of sediment toxicity by combining the merits of the two methods. Bioavailability-based extraction and dosing techniques are recommended to be incorporated into the integrated method to improve the accuracy of toxicity diagnosis. Besides considering bioavailability in the integrated TIE and EDA approach, the premise of adverse outcome pathways should also be considered. Generally speaking, both TIE and EDA have focused on adverse effects at cellular and organism levels. The addition of trait-based approaches in screening multiple toxicological endpoints helps to extend effects on cellular and organism levels to population level, and provides a better understanding of potential impacts to the community and ecosystem. The outcome pathway underlies the critical role of determining causality in interpreting impacts of complex mixtures to benthic community and aquatic ecosystem.

The role of passive sampling in monitoring the environmental impacts of produced water discharges from the Norwegian oil and gas industry

Stringent and periodic iteration of regulations related to the monitoring of chemical releases from the offshore oil and gas industry requires the use of ever changing, rapidly developing and technologically advancing techniques. Passive samplers play an important role in water column monitoring of produced water (PW) discharge to seawater under Norwegian regulation, where they are used to; i) measure aqueous concentrations of pollutants, ii) quantify the exposure of caged organisms and investigate PW dispersal, and iii) validate dispersal models. This article summarises current Norwegian water column monitoring practice and identifies research and methodological gaps for the use of passive samplers in monitoring. The main gaps are; i) the range of passive samplers used should be extended, ii) differences observed in absolute concentrations accumulated by passive samplers and organisms should be understood, and iii) the link between PW discharge concentrations and observed acute and sub-lethal ecotoxicological end points in organisms should be investigated.

Strategies for Transferring Mixtures of Organic Contaminants from Aquatic Environments into Bioassays

Mixtures of organic contaminants are ubiquitous in the environment. Depending on their persistence and physicochemical properties, individual chemicals that make up the mixture partition and distribute within the environment and might then jointly elicit toxicological effects. For the assessment and monitoring of such mixtures, a variety of cell-based in vitro and low-complexity in vivo bioassays based on algae, daphnids or fish embryos are available. A very important and sometimes unrecognized challenge is how to combine sampling, extraction and dosing to transfer the mixtures from the environment into bioassays, while conserving (or re-establishing) their chemical composition at adjustable levels for concentration-effect assessment. This article outlines various strategies for quantifiable transfer from environmental samples including water, sediment, and biota into bioassays using total extraction or polymer-based passive sampling combined with either solvent spiking or passive dosing.

Determination of 1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene and related compounds in marine pore water by automated thermal desorption-gas chromatography/mass spectrometry using disposable optical fiber

A method is described for determination of ten DDT-related compounds in marine pore water based on equilibrium solid-phase microextraction (SPME) using commercial polydimethylsiloxane-coated optical fiber with analysis by automated thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS). Thermally cleaned fiber was directly exposed to sediments and allowed to reach equilibrium under static conditions at the in situ field temperature. Following removal, fibers were rinsed, dried and cut into appropriate lengths for storage in leak-tight containers at -20°C. Analysis by TD-GC/MS under full scan (FS) and selected ion monitoring (SIM) modes was then performed. Pore-water method detection limits in FS and SIM modes were estimated at 0.05-2.4ng/L and 0.7-16pg/L, respectively. Precision of the method, including contributions from fiber handling, was less than 10%. Analysis of independently prepared solutions containing eight DDT compounds yielded concentrations that were within 6.9±5.5% and 0.1±14% of the actual concentrations in FS and SIM modes, respectively. The use of optical fiber with automated analysis allows for studies at high temporal and/or spatial resolution as well as for monitoring programs over large spatial and/or long temporal scales with adequate sample replication. This greatly enhances the flexibility of the technique and improves the ability to meet quality control objectives at significantly lower cost.

A tiered assessment framework to evaluate human health risk of contaminated sediment

For sediment contaminated with bioaccumulative pollutants (e.g., PCBs and organochorine pesticides), human consumption of seafood that contain bioaccumulated sediment-derived contaminants is a well-established exposure pathway. Historically, regulation and management of this bioaccumulation pathway has focused on site-specific risk assessment. The state of California (United States) is supporting the development of a consistent and quantitative sediment assessment framework to aid in interpreting a narrative objective to protect human health. The conceptual basis of this framework focuses on 2 key questions: 1) do observed pollutant concentrations in seafood from a given site pose unacceptable health risks to human consumers? and 2) is sediment contamination at a site a significant contributor to seafood contamination? The first question is evaluated by interpreting seafood tissue concentrations at the site, based on health risk calculations. The second question is evaluated by interpreting site-specific sediment chemistry data using a food web bioaccumulation model. The assessment framework includes 3 tiers (screening assessment, site assessment, and refined site assessment), which enables the assessment to match variations in data availability, site complexity, and study objectives. The second and third tiers use a stochastic simulation approach, incorporating information on variability and uncertainty of key parameters, such as seafood contaminant concentration and consumption rate by humans. The framework incorporates site-specific values for sensitive parameters and statewide values for difficult to obtain or less sensitive parameters. The proposed approach advances risk assessment policy by incorporating local data into a consistent region-wide problem formulation, applying best available science in a streamlined fashion.

Evaluating cost when selecting performance reference compounds for the environmental deployment of polyethylene passive samplers

A challenge in environmental passive sampling is determining when equilibrium is achieved between the sampler, target contaminants, and environmental phases. A common approach is the use of performance reference compounds (PRCs) to estimate target contaminant sampling rates and indicate degree of sampler equilibrium. One logistical issue associated with using PRCs is their sometimes exorbitant cost. To address PRC expense, this investigation 1) compared the performance of inexpensive PRCs (deuterated PAHs) and expensive PRCs ((13) C-labeled PCBs) to estimate dissolved PCB concentrations in freshwater and marine deployments, and 2) evaluated the use of smaller quantities of PRC relative to regular amounts used for estimating dissolved PAH and PCB concentrations. Saltwater and freshwater site average differences between total dissolved PCB concentrations calculated using the 2 classes of PRCs was 34 pg/L (20%) and 340 pg/L (51%), respectively, and in some deployments, statistical differences in PCB concentrations generated by the 2 types of PRCs were detected. However, no statistical differences were detected between total dissolved PAH and PCB for the 3 quantities of PRCs. In both investigations, individual dissolved PCB congeners and PAH compounds demonstrated comparable behavior as those expressed as total PCB or PAH dissolved concentrations. This research provides evidence that in some applications passive sampling using inexpensive and smaller quantities of PRCs can yield cost savings of approximately 75%. This approach appears most promising in the marine water column and when focusing on dissolved concentrations of low and medium molecular weight congeners or total PCBs.

Passive sampling in contaminated sediment assessment: building consensus to improve decision making

Contaminated sediments pose an ongoing, pervasive, global challenge to environmental managers, because sediments can reflect a legacy of pollution that can impair the beneficial uses of water bodies. A formidable challenge in assessing the risks of contaminated sediments has been the elucidation and measurement of contaminant bioavailability, expressed as the freely dissolved concentration (Cfree ) in interstitial water, which serves as a surrogate measure of the substances' chemical activity. Recent advances in passive sampling methods (PSMs) enable Cfree of sediment-associated contaminants to be quantified at trace levels, thereby overcoming current limitations of predictive models. As a result, PSMs afford the opportunity for a paradigm shift from traditional practice that can effectively reduce uncertainty in risk assessment and bolster confidence in the science used to support management of contaminated sediments. This paper provides a brief overview of the 5 subsequent papers in this series that review literature on PSM use in sediments for both organic and metal(loid) contaminants, outline the technical rationale for using PSMs as a preferred basis for risk assessment over conventional chemical analyses, describe practical considerations for and uncertainties associated with laboratory and field deployment of PSMs, discuss management application of PSMs, including illustrative case studies in which PSMs have been used in decision making, and highlight future research and communication needs.

Passive sampling methods for contaminated sediments: state of the science for metals

"Dissolved" concentrations of contaminants in sediment porewater (Cfree ) provide a more relevant exposure metric for risk assessment than do total concentrations. Passive sampling methods (PSMs) for estimating Cfree offer the potential for cost-efficient and accurate in situ characterization of Cfree for inorganic sediment contaminants. In contrast to the PSMs validated and applied for organic contaminants, the various passive sampling devices developed for metals, metalloids, and some nonmetals (collectively termed "metals") have been exploited to a limited extent, despite recognized advantages that include low detection limits, detection of time-averaged trends, high spatial resolution, information about dissolved metal speciation, and the ability to capture episodic events and cyclic changes that may be missed by occasional grab sampling. We summarize the PSM approaches for assessing metal toxicity to, and bioaccumulation by, sediment-dwelling biota, including the recognized advantages and limitations of each approach, the need for standardization, and further work needed to facilitate broader acceptance and application of PSM-derived information by decision makers.

Passive sampling methods for contaminated sediments: risk assessment and management

This paper details how activity-based passive sampling methods (PSMs), which provide information on bioavailability in terms of freely dissolved contaminant concentrations (Cfree ), can be used to better inform risk management decision making at multiple points in the process of assessing and managing contaminated sediment sites. PSMs can increase certainty in site investigation and management, because Cfree is a better predictor of bioavailability than total bulk sediment concentration (Ctotal ) for 4 key endpoints included in conceptual site models (benthic organism toxicity, bioaccumulation, sediment flux, and water column exposures). The use of passive sampling devices (PSDs) presents challenges with respect to representative sampling for estimating average concentrations and other metrics relevant for exposure and risk assessment. These challenges can be addressed by designing studies that account for sources of variation associated with PSMs and considering appropriate spatial scales to meet study objectives. Possible applications of PSMs include: quantifying spatial and temporal trends in bioavailable contaminants, identifying and evaluating contaminant source contributions, calibrating site-specific models, and, improving weight-of-evidence based decision frameworks. PSM data can be used to assist in delineating sediment management zones based on likelihood of exposure effects, monitor remedy effectiveness, and, evaluate risk reduction after sediment treatment, disposal, or beneficial reuse after management actions. Examples are provided illustrating why PSMs and freely dissolved contaminant concentrations (Cfree ) should be incorporated into contaminated sediment investigations and study designs to better focus on and understand contaminant bioavailability, more accurately estimate exposure to sediment-associated contaminants, and better inform risk management decisions. Research and communication needs for encouraging broader use are discussed.

Passive sampling methods for contaminated sediments: state of the science for organic contaminants

This manuscript surveys the literature on passive sampler methods (PSMs) used in contaminated sediments to assess the chemical activity of organic contaminants. The chemical activity in turn dictates the reactivity and bioavailability of contaminants in sediment. Approaches to measure specific binding of compounds to sediment components, for example, amorphous carbon or specific types of reduced carbon, and the associated partition coefficients are difficult to determine, particularly for native sediment. Thus, the development of PSMs that represent the chemical activity of complex compound-sediment interactions, expressed as the freely dissolved contaminant concentration in porewater (Cfree ), offer a better proxy for endpoints of concern, such as reactivity, bioaccumulation, and toxicity. Passive sampling methods have estimated Cfree using both kinetic and equilibrium operating modes and used various polymers as the sorbing phase, for example, polydimethylsiloxane, polyethylene, and polyoxymethylene in various configurations, such as sheets, coated fibers, or vials containing thin films. These PSMs have been applied in laboratory exposures and field deployments covering a variety of spatial and temporal scales. A wide range of calibration conditions exist in the literature to estimate Cfree , but consensus values have not been established. The most critical criteria are the partition coefficient between water and the polymer phase and the equilibrium status of the sampler. In addition, the PSM must not appreciably deplete Cfree in the porewater. Some of the future challenges include establishing a standard approach for PSM measurements, correcting for nonequilibrium conditions, establishing guidance for selection and implementation of PSMs, and translating and applying data collected by PSMs.

The use of sediment toxicity identification evaluation methods to evaluate clean up targets in an urban estuary

The Ballona Creek Estuary (BCE) in Los Angeles, California, is in a highly urbanized watershed, is contaminated by a variety of chemicals, and has prevalent sediment toxicity. Sediment cleanup targets for BCE have been established for Cu, Cd, Pb, Zn, chlordane, DDTs, PCBs, and PAHs, based on sediment quality guidelines. A sediment toxicity identification evaluation (TIE) was conducted to examine how these targets corresponded to toxicity observed with the estuarine amphipod Eohaustorius estuarius. Whole sediment and porewater TIEs were used to identify the cause of toxicity. Passive samplers were deployed to determine the bioavailable fraction of contaminants. Spiked sediment tests were conducted to determine the thresholds of toxicity for selected constituents. Toxicity was found to be widespread but temporally and spatially variable. Whole sediment and porewater TIEs both indicated pyrethroid pesticides were the most likely contaminant group contributing to the toxicity. Concentrations of the chemicals listed for cleanup were found to often exceed target values but were not observed at concentrations likely to cause toxicity. Bioavailable fractions of the target chemicals quantified using passive samplers did not exceed toxicity thresholds. Spiked sediment tests established 10 day LC50s for 4,4' DDE, 4, 4' DDT, α-chlordane, and cyfluthrin at >3050 μg/g, 266 μg/g, >2120 μg/g, and 0.33 μg/g organic carbon (OC), respectively. The cyfluthrin LC50 was within the range of concentrations observed in the estuary sediments, but LC50s for the other 3 chemicals were orders of magnitude greater than observed levels. The combination of TIE, sediment chemistry and the results from spiked sediment exposures indicate pyrethroid pesticides are more likely the cause of the observed toxicity than any of the contaminants targeted for cleanup. The results of this study indicate the importance of using a TIE approach to determine chemicals of concern and dose-response information to set cleanup targets, rather than using sediment quality guidelines. Integr Environ Assess Manag 2014;10:260-268. © 2013 SETAC.

Dissolved and particulate copper exposure induces differing gene expression profiles and mechanisms of toxicity in the deposit feeding amphipod Melita plumulosa

Uptake of metals via ingestion is an important route of exposure for many invertebrates, and it has been suggested that the toxic response to metals accumulated via food differs from that of metals accumulated via the dissolved phase. To test this hypothesis, the deposit-feeding epibenthic amphipod Melita plumulosa was exposed to nontoxic or reproductively toxic concentrations of copper via the overlying water, via ingestion of sediment, or via a combination of the two. Rates of copper uptake from the two exposure routes were predicted using a biokinetic model. Gene expression profiles were measured via microarray analysis and confirmed via quantitative polymerase chain reaction. Differences in expression profiles were related to the exposure route more than to individual or combined rates of copper uptake. Chitinase and digestive protease transcript expression levels correlated to the copper uptake rate from sediment, rather than from the dissolved phase or combined total uptake rate. Overall, this study supports the hypothesis that metals accumulated via ingestion have a different mode of toxic action than metals taken up from water. Consequently, guidelines that only consider dissolved metal exposure, including equilibrium-partitioning-based guidelines, may underestimate the potential effects from deposited or resuspended metal-contaminated sediments.

Incorporating bioavailability into management limits for copper in sediments contaminated by antifouling paint used in aquaculture

Although now well embedded within many risk-based sediment quality guideline (SQG) frameworks, contaminant bioavailability is still often overlooked in assessment and management of contaminated sediments. To optimise management limits for metal contaminated sediments, we assess the appropriateness of a range methods for modifying SQGs based on bioavailability considerations. The impairment of reproduction of the amphipod, Melita plumulosa, and harpacticoid copepod, Nitocra spinipes, was assessed for sediments contaminated with copper from antifouling paint, located below aquaculture cages. The measurement of dilute acid-extractable copper (AE-Cu) was found to provide the most useful means for monitoring the risks posed by sediment copper and setting management limits. Acid-volatile sulfide was found to be ineffective as a SQG-modifying factor as these organisms live mostly at the more oxidised sediment water interface. SQGs normalised to %-silt/organic carbon were effective, but the benefits gained were too small to justify this approach. The effectiveness of SQGs based on AE-Cu was attributed to a small portion of the total copper being present in potentially bioavailable forms (typically<10% of the total). Much of the non-bioavailable form of copper was likely present as paint flakes in the form of copper (I) oxide, the active ingredient of the antifoulant formulation. While the concentrations of paint-associated copper are very high in some sediments, as the transformation of this form of copper to AE-Cu appears slow, monitoring and management limits should assess the more bioavailable AE-Cu forms, and further efforts be made to limit the release of paint particles into the environment.

Addition of contaminant bioavailability and species susceptibility to a sediment toxicity assessment: application in an urban stream in China

Sediments collected from an urban creek in China exhibited high acute toxicity to Hyalella azteca with 81.3% of sediments being toxic. A toxic unit (TU) estimation demonstrated that the pyrethroid, cypermethrin, was the major contributor to toxicity. The traditional TU approach, however, overestimated the toxicity. Reduced bioavailability of sediment-associated cypermethrin due to sequestration explained the overestimation. Additionally, antagonism among multiple contaminants and species susceptibility to various contaminants also contributed to the unexpectedly low toxicity to H. azteca. Bioavailable TUs derived from the bioavailability-based approaches, Tenax extraction and matrix-solid phase microextraction (matrix-SPME), showed better correlations with the noted toxicity compared to traditional TUs. As the first successful attempt to use matrix-SPME for estimating toxicity caused by emerging insecticides in field sediment, the present study found freely dissolved cypermethrin concentrations significantly improved the prediction of sediment toxicity to H. azteca compared to organic carbon normalized and Tenax extractable concentrations.

Bioavailability-based chronic toxicity measurements of permethrin to Chironomus dilutus

Compared with acute toxicity, chronic exposures to low levels of contaminants are more environmentally relevant, but fewer data are available. In the present study, sediment toxicity of the pyrethoid permethrin to Chironomus dilutus was determined. The whole-life-cycle toxicity testing was conducted with the endpoints covering survival, growth, emergence, and reproduction. Permethrin caused 50% lethality in C. dilutus at 1.83 ± 1.13 µg/g organic carbon (OC) and 1.20 ± 0.55 µg/g OC after exposures of 20 d (before pupation) and 58 d (the end of the testing), respectively. The 5% and median effect concentrations (EC5 and EC50) represented the marginal and toxic levels of the sublethal effects, respectively, and effect data were all normalized to the controls before Probit analysis. The EC5s for growth, emergence, and reproduction were 0.034 ± 0.006 µg/g OC, 0.016 ± 0.008 µg/g OC, and 0.009 ± 0.008 µg/g OC, respectively; the respective EC50s were 1.09 ± 0.56 µg/g OC, 0.838 ± 0.077 µg/g OC, and 0.039 ± 0.105 µg/g OC. In addition, a 24-h Tenax extraction was employed to better assess permethrin bioavailability. Ultimately, response spectra with a series of endpoints were developed for permethrin using either OC-normalized bulk sediment concentrations or bioavailability-based Tenax extractable concentrations as the dose metric. The development of bioavailability-based chronic toxicity endpoints for sediment-associated permethrin would provide valuable benchmarks for evaluating ecological risk of this contaminant and contributing to improve sediment management policies.

Assessing and managing sediment contamination in transitional waters

Sediment contamination remains a global problem, particularly in transitional waters such as estuaries and coastal lagoons, which are the recipients of chemicals from multiple near- and far-field sources. Although transitional waters are highly productive ecosystems, approaches for assessing and managing their sediment contamination are not as well developed as in marine and fresh waters. Further, although transitional waters remain defined by their variable and unique natural water quality characteristics, particularly salinity, the biota inhabiting such ecosystems, once thought to be defined by Remane's "paradox of brackish water", are being redefined. The purpose of the present paper is to build on an earlier but now dated (>12years old) review of methods to assess sediment contamination in estuaries, extending this to all transitional waters, including information on integrative assessments and on management decision-making. The following are specifically discussed: chemical assessments; bioindicators; biomarkers; and, biological surveys. Assessment and management of sediment contamination in transitional waters need to be focused on ecosystem services and, where appropriate and possible, be proactive rather than reactive when uncertainty has been suitably reduced.

Assessing bioavailability and toxicity of permethrin and DDT in sediment using matrix solid phase microextraction

Matrix solid phase microextraction (matrix-SPME) was evaluated as a surrogate for the absorbed dose in organisms to estimate bioavailability and toxicity of permethrin and dichlorodiphenyltrichloroethane (DDT) in laboratory-spiked sediment. Sediments were incubated for 7, 28, and 90 days at room temperature to characterize the effect of aging on bioavailability and toxicity. Sediment toxicity was assessed using two freshwater invertebrates, the midge Chironomus dilutus and amphipod Hyalella azteca. Disposable polydimethylsiloxane fibers were used to estimate the absorbed dose in organisms and to examine bioavailability and toxicity. The equilibrium fiber concentrations substantially decreased with an increase in sediment aging time, indicating a reduction in bioavailability. Based on median lethal fiber concentrations (fiber LC50), toxicity of permethrin was not significantly different among the different aging times. Due to the substantial degradation of DDT to dichlorodiphenyldichloroethane (DDD) in sediment, sediment toxicity to C. dilutus increased, while it decreased for H. azteca with extended aging times. A toxic unit-based fiber LC50 value represented the DDT mixture (DDT and DDD) toxicity for both species. Significant linear relationships were found between organism body residues and the equilibrium fiber concentrations for each compound, across aging times. The study suggested that the matrix-SPME fibers mimicked bioaccumulation in the organisms, and enabled estimation of body residues, and could potentially be used in environmental risk assessment across matrices (e.g. sediment and water) to measure bioavailability and toxicity of hydrophobic pesticides.

Comparison of national and regional sediment quality guidelines for classifying sediment toxicity in California

A number of sediment quality guidelines (SQGs) have been developed for relating chemical concentrations in sediment to their potential for effects on benthic macroinvertebrates, but there have been few studies evaluating the relative effectiveness of different SQG approaches. Here we apply 6 empirical SQG approaches to assess how well they predict toxicity in California sediments. Four of the SQG approaches were nationally derived indices that were established in previous studies: effects range median (ERM), logistic regression model (LRM), sediment quality guideline quotient 1 (SQGQ1), and Consensus. Two approaches were variations of nationally derived approaches that were recalibrated to California-specific data (CA LRM and CA ERM). Each SQG approach was applied to a standardized set of matched chemistry and toxicity data for California and an index of the aggregate magnitude of contamination (e.g., mean SQG quotient or maximum probability of toxicity) was calculated. A set of 3 thresholds for classification of the results into 4 categories of predicted toxicity was established for each SQG approach using a statistical optimization procedure. The performance of each SQG approach was evaluated in terms of correlation and categorical classification accuracy. Each SQG index had a significant, but low, correlation with toxicity and was able to correctly classify the level of toxicity for up to 40% of samples. The CA LRM had the best overall performance, but the magnitude of differences in classification accuracy among the SQG approaches was relatively small. Recalibration of the indices using California data improved performance of the LRM, but not the ERM. The LRM approach is more amenable to revision than other national SQGs, which is a desirable attribute for use in programs where the ability to incorporate new information or chemicals of concern is important. The use of a consistent threshold development approach appeared to be a more important factor than type of SQG approach in determining SQG performance. The relatively small change in classification accuracy obtained with regional calibration of these SQG approaches suggests that further calibration and normalization efforts are likely to have limited success in improving classification accuracy associated with biological effects. Fundamental changes to both SQG components and conceptual approach are needed to obtain substantial improvements in performance. These changes include updating the guideline values to include current use pesticides, as well as developing improved approaches that account for changes in contaminant bioavailability.

Transitioning sediment quality assessment into regulations: Challenges and solutions in implementing California's sediment quality objectives

Development and promulgation of sediment quality criteria represents a substantial challenge for water quality agencies. Unlike water quality programs that rely on individual chemical thresholds to assess water quality, the complex processes affecting contaminant bioavailability in sediments preclude the use of contaminant concentrations to independently assess impacts or identify cause. Various multiple line of evidence approaches (e.g., sediment quality triad) have been developed for sediment quality assessment, but such frameworks are rarely fully incorporated into statewide regulatory programs due to a lack of standardized and validated tools. In 2003, California's State Water Resources Control Board (State Water Board) initiated development of sediment quality criteria and an assessment framework that required the developers to resolve many challenging technical and policy related issues to the satisfaction of stakeholders, scientists, and the general public. The first part of this multiyear effort has been completed and resulted in the development and validation of an integrated collection of tools, thresholds, and a data interpretation framework for assessing sediment contamination impacts on benthic community condition. The State Water Board's narrative sediment quality criteria and assessment framework became effective in 2009, following US Environmental Protection Agency approval. The results of this effort are described in a series of 6 articles published in this issue of Integrated Environmental Assessment and Management. The articles describe: 1) a multiple line of evidence framework for data integration and assessment, 2) calibration and evaluation of sediment quality guidelines for predicting toxic responses, 3) development and evaluation of sediment quality guidelines with respect to benthic macrofauna responses, 4) selection of toxicity test methods and thresholds, 5) identification and characterization of benthic community assemblages, 6) the effect of sampling methods on benthic community assessment, and 7) recommendations on improving the assessment of contaminant exposure in sediment quality assessment. This collection of articles illustrates the steps needed to improve the scientific foundation for sediment quality assessment in regulatory applications.

Use of solid phase microextraction to estimate toxicity: relating fiber concentrations to toxicity--part I

Use of solid-phase microextraction (SPME) fibers as a dose metric for toxicity testing was evaluated for hydrophobic pesticides to the midge Chironomus dilutus and the amphipod Hyalella azteca. Test compounds included p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), p,p'-dichlorodiphenyldichloroethane (p,p'-DDD), p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE), permethrin, bifenthrin, tefluthrin, and chlorpyrifos. Acute water toxicity tests were determined for 4- and 10-d exposures in both species. Median lethal and sublethal concentrations were expressed both on a water concentration (LC50 and EC50) and on an equilibrium SPME fiber concentration (LC50(fiber) and EC50(fiber)) basis. A significant log dose-response relationship was found between log fiber concentration and organism mortality. It has been shown in the literature that equilibrium SPME fiber concentrations reflect the bioavailable concentrations of hydrophobic contaminants, so these fiber concentrations should be a useful metric for assessing toxic effects from the bioavailable contaminant providing a framework to expand the use of SPME fibers beyond estimation of bioaccumulation.