Particle bound pollutants in rivers: Results from suspended sediment sampling in Globaqua River Basins

Detangling past and modern zinc anthropogenic source contributions in an urbanized coastal river by combining elemental, isotope and speciation approaches

The accumulation of trace metals in the environmental compartments of coastal rivers is a global and complex environmental issue, requiring multiple tools to constrain the various anthropogenic sources and biogeochemical processes affecting the water quality of these environments. The Valao fluvio-estuarine system (Rio de Janeiro, Brazil) presents a challenging case of a coastal river contaminated by both modern and historical anthropogenic metal sources, located in the land and in the intra-estuary, continuously mixed by tidal cycles. This study employed a combination of spatial distribution analysis of trace metals including gadolinium (Gd), zinc (Zn) isotopic analyses, and X-ray absorption spectroscopy (XAS) to distinguish between these sources. The concentrations of metals in both dissolved (water samples) and surficial sediment compartments (Suspended Particulate Matter and sediment samples) display an overall enrichment trend from upstream to downstream. Multivariate statistical analysis allows to discriminate geogenic elements derived from watershed geology (Ti, K, and Mg) vs anthropogenic contaminants from urban runoff and domestic sewage discharges (Cu, Cr, Pb, Zn, and Gd); and legacy metal contaminants (Zn and Cd) remobilized from ancient metallurgical wastes and transported upstream in the estuary during tidal cycles. The anthropogenic Gd concentration in the dissolved compartment increases along the watercourse, highlighting continuous ongoing sewage discharge. Zinc solid speciation also indicates that Zn contribution from legacy metallurgy waste is primarily associated with sulfide-Zn and Zn-phyllosilicate in the outlet estuary, while in upstream sediments of fluvio-estuarine system, Zn is found bound to organic matter. Zinc isotope systematically reveals a progressive downstream shift to heavier isotope compositions. Upstream, the relatively pristine site and the urbanized section of the river exhibit a relatively uniform δ66/64Zn value (+0.20 ± 0.07 ‰) in suspended particulate matter (SPM) and surficial sediments. These results indicate that domestic sewage discharges contribute to Zn enrichment in sediments of the Valao fluvio-estuarine system but without modifying its isotope signature in sediments. The sediment of the downstream estuarine section shows a heavier δ66/64Zn value (+0.48 ± 0.08 ‰), indicating the strong influence of the intra-estuarine source identified as the historical metallurgic contamination. An integrated view of the geochemical tracers allows thus inferring that the untreated sewage and legacy metallurgical contamination are the primary sources of anthropogenic Zn contamination. It highlights the progressive mixing along the estuarine gradient under tidal dynamics. The influence of the former source continuously expands from the headland towards the estuary.

Systematic underestimation of polycyclic aromatic hydrocarbon aqueous concentrations in rivers

Polycyclic aromatic hydrocarbons (PAHs) are a widespread group of organic contaminants whose presence in water bodies is cause of severe concern. With few exceptions, the majority of PAHs is hydrophobic, presents a high adsorption affinity, and is thus primarily transported within river systems during high-flow events together with suspended particulate matter (SPM). Evidence exists of analytical challenges related to the incomplete extraction of PAHs adsorbed to solids and thus to a potential negative bias in the chemical analysis of PAHs in bulk water samples with high SPM content. Despite this, partly due to the elevated efforts required to collect representative samples containing sufficient SPM for the separate PAH analysis in this matrix, several investigations rely on the analysis of aqueous samples. This study tests the hypothesis that surveys based exclusively on bulk water may lead to a systematic underestimation of the real contamination level and transport of PAHs in rivers. Six high-turbidity events were examined in three Austrian rivers applying time-integrated sampling and simultaneously analyzing PAHs in total bulk water, filtered water, SPM, and supernatant. Despite an unavoidable degree of uncertainty in such challenging sampling scheme, the results indicate that measurements performed with best available standard methods in bulk water samples determined in average only about 40% of the theoretically expected total PAHs concentrations derived from the analyses in SPM. Such deviation has important implications for the reliable assessment of the compliance with environmental quality standards as well as for surveys aimed to estimate riverine loads, validate emission models, and understand the transport dynamics of PAHs in rivers. Whereas the first objective, e.g., in European countries, is alternatively achieved via monitoring in biota, the latter ones require efforts directed to complement monitoring campaigns with separate sampling of SPM, with monitoring of suspended solids transport to appropriately select and interpret the results of water samples and to improve the chemical analysis of PAHs in bulk water samples with high solids content.

Distribution, sources, partition behavior and risk assessment of polycyclic aromatic hydrocarbons (PAHs) in the waters and sediments of Lake Ulansuhai, China

This study represents the first comprehensive investigation of 16 polycyclic aromatic hydrocarbons (PAHs) in the waters and sediments of Lake Ulansuhai. It explores their occurrence, sources, transport behavior, and associated risks to human health and ecosystems. The results revealed that concentrations of ∑PAHs in dissolved phase and sediment with no significant seasonal differences. In contrast, ∑PAHs concentrations in suspended particulate matter were significantly higher during the ice-free period compared to the ice period. Spatially, the northern part of Lake Ulansuhai displayed higher PAHs content. Diagnostic isomeric ratios and PMF models indicated that the PAHs were primarily derived from combustion sources. The distribution of PAHs within water-sediment demonstrated that non-equilibrium status. Fugacity calculations indicated that 2-4 rings PAHs acted as secondary sources of sediment emissions. Toxicity assessment, indicated that PAHs posed no significant carcinogenic risk to humans. Risk quotient values showed that PAHs as low to high ecological risk.

Effect of varying hydrologic regime on seasonal total maximum daily loads (TDML) in an agricultural watershed

Rising hypoxia due to the eutrophication of riverine ecosystems is primarily caused by the transport of nutrients. The majority of existing TMDL models cannot be efficienty applied to represent nutrient concentrations in riverine ecosystems having varying flow regimes due to seasonal differences. Accurate TMDL assessment requires nutrient loads and suspended matter estimation under varying flow regimes with minimal uncertainty. Though a large database can enhance accuracy, it can be resource intensive. This study presents the design of an innovative modeling strategy to optimize the use of existing datasets to effectively represent streamflow-load dynamics while minimizing uncertainty. The study developed an approach to assess TMDLs using six different flux models and kriging techniques (i) to enhance the accuracy of nutrient load estimation under different hydrologic regimes (flow stratifications) and (ii) to derive an optimal modeling strategy and sampling scheme for minimizing uncertainty. The flux models account for uncertainty in load prediction across varying flow strata, and the deployment of multiple load calculation procedures. Further, the proposed flux approach allows the determination of load exceedance under different TMDL scenarios aimed at minimizing uncertainty to achieve reliable load predictions. The study employed a 10-year dataset (2009-2018) consisting of daily flow data (m3/sec) and weekly data (mg/L) for nitrogen (N), phosphorus (P) and total suspended solids (TSS) concentrations in three distinct agricultural sites in+ the Minnesota River Watershed. The outcomes were analyzed geospatially in a Geographic Information System (GIS) environment using the kriging interpolation technique. The study recommends (i) triple stratification of flows to obtain accurate load estimates, and (ii) an optimal sampling scheme for nitrogen and phosphorous with 30.6 % and 49.8 % datapoints from high flow strata. The study outcomes are expected to contribute to the planning of economically and technically sound combinations of best management practices (BMPs) required for achieving total maximum daily loads (TMDL) in a watershed.

Spatial distribution of heavy metals in the sediments of River Ganges, India: Occurrence, contamination, source identification, seasonal variations, mapping, and ecological risk evaluation

Present study analyzed the seasonal and spatial distribution patterns, sources, and ecological risks of seven heavy metals (Cr, Fe, Ni, Cu, Zn, Cd and Pb) in the sediments of River Ganges, finding that the majority of concentrations were lithologic, except for Cd, which was significantly higher than background standards. Elevated values of geochemical indices viz. Igeo, CF, RI, Cd, mCd, HQ, mHQ, and PN suggest moderate to high ecological risk in the benthic environment and its organisms due to the synergistic effect of heavy metals. The PEC-Qmetals revealed 8-10 % toxicity in the upstream and downstream sites, due to the influence of agricultural activities. Multivariate statistical techniques (PCM and PCA) indicated that Cd and Pb predominantly originated from anthropogenic sources, while other metals primarily derived from geological background. These geochemical findings may help to understand the potential risks and recommend strategies to mitigate the effects of metallic contamination in river sediments.

Remote sensing-enabled machine learning for river water quality modeling under multidimensional uncertainty

Two fundamental problems have inhibited progress in the simulation of river water quality under climate (and other) uncertainty: 1) insufficient data, and 2) the inability of existing models to account for the complexity of factors (e.g., hydro-climatic, basin characteristics, land use features) affecting river water quality. To address these concerns this study presents a technique for augmenting limited ground-based observations of water quality variables with remote-sensed surface reflectance data by leveraging a machine learning model capable of accommodating the multidimensionality of water quality influences. Total Suspended Solids (TSS) can serve as a surrogate for chemical and biological pollutants of concern in surface water bodies. Historically, TSS data collection in the United States has been limited to the location of water treatment plants where state or federal agencies conduct regularly-scheduled water sampling. Mathematical models relating riverine TSS concentration to the explanatory factors have therefore been limited and the relationships between climate extremes and water contamination events have not been effectively diagnosed. This paper presents a method to identify these issues by utilizing a Long Short-Term Memory Network (LSTM) model trained on Moderate Resolution Imaging Spectroradiometer (MODIS) satellite reflectance data, which is calibrated to TSS data collected by the Ohio River Valley Water Sanitation Commission (ORSANCO). The methodology developed enables a thorough empirical analysis and data-driven algorithms able to account for spatial variability within the watershed and provide effective water quality prediction under uncertainty.

Microplastics could be marginally more hazardous than natural suspended solids - A meta-analysis

Microplastics (MP) are perceived as a threat to aquatic ecosystems but bear many similarities to suspended sediments which are often considered less harmful. It is, therefore pertinent to determine if and to what extent MP are different from other particles occurring in aquatic ecosystems in terms of their adverse effects. We applied meta-regressions to toxicity data extracted from the literature and harmonized the data to construct Species Sensitivity Distributions (SSDs) for both types of particles. The results were largely inconclusive due to high uncertainty but the central tendencies of our estimates still indicate that MP could be marginally more hazardous compared to suspended sediments. In part, the high uncertainty stems from the general lack of comparable experimental studies and dose-dependent point estimates. We therefore argue that until more comparable data is presented, risk assessors should act precautionary and treat MP in the 1-1000 µm size range as marginally more hazardous to aquatic organisms capable of ingesting such particles.

Efficiency of five samplers to trap suspended particulate matter and microplastic particles of different sizes

Suspended particulate matter (SPM) plays a major role in nutrient cycles and for the transport of pollutants within local and transboundary water catchments. Obtaining representative SPM samples from rivers, lakes, inland and coastal waters is crucial for quantitative and qualitative chemical analyses to correctly describe the chemical status of a water body. However, a representative sampling of SPM over time is challenging due to the heterogeneity of SPM particles sizes, their non-uniform distribution in rivers, and a variety of sampling devices being in use. Therefore, we investigated the efficiencies of five different sampling devices commonly used in national and international monitoring programs to collect representative SPM samples. We tested three passive sedimentation-based samplers (SBSs: sedimentation box, SB; sedimentation tank, ST; Raetz Sampler, RS), and two active separation techniques (continuous flow centrifuge, CFC; vacuum filtration, VF) in an experimental laboratory setup using in-house SPM standard suspensions (mineral, organic, and microplastic particles) with defined particle sizes. The mass-based efficiencies of the three examined SBSs were 0-66% for the mineral and organic particles <75 μm, where the mean particle sizes of collected samples were always shifted to bigger sizes compared to the initial suspensions. The efficiencies of the three SBSs to collect microplastic particles <80 μm were <20% due to the lower densities of microplastic compared to organic and mineral particles. In contrast to the SBSs, VF and CFC units showed excellent efficiencies >86% for all tested materials, with similar particle size distributions of the sampled material compared to those of the inlet suspensions. In conclusion, SPM sampling efficiencies of sampling units have to be carefully considered and compared to the respective aims of the monitoring approaches, especially when statements are derived from quantitative results on SPM.

Toxicity risks associated with trace metals call for conservation of threatened fish species in heavily sediment-laden Yellow River

Trace metals and metalloids in aquatic ecosystems may lead to adverse effects on the survival of fish, especially in the sensitive life stages of vulnerable species. It is still unknown whether threatened fish species in the heavily sediment-laden Yellow River are exposed to toxicity risks associated with multiple trace metals. Herein, we analyzed the concentrations of trace metals in aquatic environmental media and fish tissues across the Yellow River mainstream and assessed the level of metal toxicity to threatened fish. Significantly different concentrations of trace metals in fish tissues were measured between at least two categories among near-threatened, vulnerable, endangered, and critically endangered fish. No metal showed a higher concentration in demersal fish than in pelagic fish. Substantially low metal toxicity was observed for the gill of Rhinogobio nasutus (near-threatened) in the upper reaches, as well as for the gill and liver of Silurus lanzhouensis (endangered) in the middle reaches. High contents of suspended sediment in water and high metal concentrations in sediment and suspended matter could influence the survival and reproduction of fish, especially those already with threatened status.

Disproportional erosion of the middle-lower Yangtze River following the operation of the Three Gorges Dam

The operation of the Three Gorges Dam (TGD) modifies downstream flow and sediment regimes, triggering disproportional fluvial responses at different distances downstream. However, our understanding of the downstream geomorphic changes in the middle-lower Yangtze River remains incomplete due to the complexity of the river responses across temporal and spatial scales. Here, we leverage data on discharge, suspended sediment concentration (SSC), riverbed grain size, cross-sectional profiles and high-resolution channel bathymetric maps at different locations downstream of the TGD to investigate geomorphic responses. The results show that the magnitude of fluvial erosion decreases downstream, with the Yichang-Luoshan Reach (the first ~500 km downstream) experiencing the most severe erosion in 2003-2020 (~9.05 × 10⁴ t/km/yr). Local changes in riverbed morphology include channel bar erosion, channel incision (~0.43 m/yr in CS1 near the dam site over 2002-2019), riverbank retreat and bed material coarsening (an increase in D₅₀ from 0.175 to 43.1 mm at Yichang station from 2002 to 2017). Such marked erosion is caused by the sharply reduced SSC in the dominant discharge range (10,000-30,000 m³/s) and the extended duration of this dominant discharge range. The sediment erosive magnitude in the Luoshan-Datong Reach is relatively small (3.85 × 10⁴ t/km/yr) in 2002-2020. The Luoshan-Hukou Reach (~500-1000 km downstream) exhibits moderate channel incision, minor bed material coarsening and moderate mid-channel bar lateral erosion. The Hukou-Datong Reach (below 1000 km downstream) experienced minor geomorphic change without significant evidence of bed material coarsening. The relatively small impact of the TGD on the lower reach from Luoshan to Datong can be mainly attributed to the progressive SSC recovery along the river induced by upstream channel erosion providing sediment replenishment. These findings have significant implications for estimating geomorphic changes in response to upstream damming and thus could inform better river management and ecological assessment in other similar alluvial rivers.

Trace metals exposure in three different coastal compartments show specific morphological and reproductive traits across generations in a sentinel copepod

The effect of exposure from several compartments of the environment at the level of individuals was rarely investigated. This study reports the effect of contaminants from varied compartments like sediment resuspension, elutriation from resuspended sediment (extract) and seawater spiked trace metal mixtures (TM) on morphological and reproductive traits of the pelagic bioindicator copepod Eurytemora affinis. At the population level of E. affinis, lowest survival was observed in dissolved exposures (TM and extract) in the first generation (G1), showing some adaptation in the second generation (G2). An opposite trend for resuspended sediment showed higher sensitivity in survival at G2. At the individual level, prosome length and volume proved to be sensitive parameters for resuspended sediments, whereas clutch size and egg diameter were more sensitive to TM and extract. Although the generation of decontamination (G3, no exposure), showed a significant recovery at the population level (survival % along with clutch size) of E. affinis exposed to resuspended sediment, morphological characteristics like prosome length and volume showed no such recovery (lower than control, p < 0.05). To the contrary, dissolved exposure showed no significant recovery from G1 to G3 on neither survival %, clutch size, egg diameter, prosome volume, but an increase of prosome length (p < 0.05). Such tradeoffs in combatting the stress from varied sources of toxicity were observed in all exposures, from G1 to G3. The number of lipid droplets inside the body cavity of E. affinis showed a significant positive correlation with trace metal bioaccumulation (p < 0.01) along with a negative correlation (p < 0.05) with survival and clutch size in each treatment. This confirms the inability of copepods to utilize lipids under stressful conditions. Our study tenders certain morphological and reproductive markers that show specificity to different compartments of exposure, promising an advantage in risk assessment and fish feed studies.

Significant riverine inputs of typical plastic additives-phthalate esters from the Pearl River Delta to the northern South China Sea

Phthalate esters (PAEs) are representative additives used extensively in plastics. In this study, 15 PAEs were investigated at the eight riverine outlets of the Pearl River Delta (PRD). The total concentrations of Σ₁₅PAEs, including both the dissolved and particulate phases, ranged from 562 to 1460 ng/L and 679 ng/L-2830 ng/L in the surface and bottom layers, respectively. Dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) dominated in the dissolved and suspended particulate matter (SPM) phases, respectively, accounting for >50 % and > 80 % of Σ₁₅PAEs. Riverine input of wastewater from the PRD was possibly the primary source of the contamination. Higher levels of PAEs occurred at the eastern outlets than at the western ones. The dissolved and particulate PAEs varied seasonally, with significantly higher concentrations observed in the dry season than in the wet season. However, no significant differences of PAE levels in both phases were observed among low, medium, and high tides. The partitioning results demonstrated that SPM is important in the transportation of pollutants in estuaries, where more hydrophobic DEHP was predominantly transported by the SPM phase, while those more hydrophilic ones were regularly transported by the dissolved phase. The total annual flux of Σ₁₅PAEs through the eight outlets to the SCS reached 1390 tons.

Multimedia distribution of polycyclic aromatic hydrocarbons in the Wang Lake Wetland, China

The Wang Lake Wetland is a highly valued area that is protected due to its high biodiversity. The wetland has a complicated hydrological regime and is subject to frequent human disturbance. We hypothesize that fluctuating hydrology and human activities have varied contributions to the temporal and spatial variations of polycyclic aromatic hydrocarbons (PAHs) in the wetland. Soil (SS), sediment (SD), and water, to acquire dissolved phase (DP) and suspended particulate matter (SPM), samples were collected from eight locations during low- and high-flow periods to elucidate multimedia phase distribution and transport of PAHs. Following the onset of the rainy season, the concentration of SPM-associated PAHs increased significantly, while the DP PAHs remained stable. Individual PAH ratios showed that, although pyrogenic sources are common, petrogenic derived compounds are the main source of PAHs in the Wang Lake Wetland. During the high-flow period, the empirical values for logarithms of the organic carbon-normalized partition coefficients (log K_OC) of individual PAH-congeners were lower than the corresponding field-observed log K_OC values from the SPM-DP and SD-DP systems, reflecting the complexity in evaluating multi-phase PAH partitioning. During the high-flow period, temperature-driven changes may have changed the sediment from a sink to a source for some high molecular weight PAHs. It was determined that human activities governed the PAH loading in the low-flow period, whereas during high-flow conditions, increased rainfall, higher temperatures, and fishery activity are the main factors controlling PAH input to the Wang Lake Wetland.

Performance and mechanism of the in situ restoration effect on VHCs in the polluted river water based on the orthogonal experiment: photosynthetic fluorescence characteristics and microbial community analysis

Volatile halogenated hydrocarbons (VHCs) attracted many attentions due to its toxicity and persistence in the environment. In this research, a novel in situ ecological restoration reactor was applied to the degradation of VHCs in polluted river water. The optimized working condition adaptation of the in situ restoration technique was evaluated through orthogonal tests. The experiments showed that when the water depth was 0.4 m, the HRT was 5 days, and the current velocity was 1 m/s, the optimal removal efficiency of VHCs in the reactor was achieved. And the removal rates of CHCl₃, CCl₄, C₂HCl₃, and C₂Cl₄ reached 70.27%, 70.59%, 67.74%, and 81.82%, respectively. The results showed that both HRT and water depth were significantly related to the removal efficiency of reactor. The physiological state of the plants was analyzed by fitting rapid light curve (RLC) model, which showed that the accumulation of VHCs inhibited the photosynthetic performance of plants. Moreover, the microbial community structures of fillers were tested by high-throughput sequencing, and the findings supported that the microbial community made a great response to adapt to the changes in environment of the reactor. The relative abundance of Rhodocyclaceae increased slightly, which hinted that it had good adaptability to VHCs in polluted river water. The research results confirmed that in situ ecological restoration reactor was a potential approach for removal VHCs in polluted river water.

Macroinvertebrate Assemblages along the Longitudinal Gradient of an Urban Palmiet River in Durban, South Africa

Urban rivers are regarded as unnatural because they drain catchments characterized by impervious surfaces. The present study explored macroinvertebrate communities in relation to water and habitat quality along the longitudinal gradient of an urban Palmiet River in Durban, South Africa. Sampling was conducted across six sites along the river. The water quality has shown a significant variation (ANOVA, p < 0.05) across six sites. Good-quality water was observed at Site 6, whereas Site 5 exhibiting hypertrophic condition. Sites 4 to 1 were all eutrophic; however, nutrient levels showed to decrease from Site 4 down to Site 2 and increased again at Site 1. A similar trend was observed for habitat quality, with Site 6 showing excellent and Site 5 exhibited poor habitat. Coinciding with water and habitat quality, macroinvertebrate diversity and abundance showed significant differences across six sites. Sensitive palaemonids, notonemourids, and amphipods were only observed in the headwaters and have contributed over 50% of the variation in abundance between Site 6 and other sites. The non-metric multidimensional scaling (NMDS) plot has also shown clear discrimination (MANOVA, p < 0.001) for the Average Score Per Taxon (ASPT) across the six sites. Macroinvertebrate communities have shown a clear association between water and habitat quality. These findings affirm the ecological importance of urban rivers as they provide refuge to aquatic biodiversity, with anthropogenic litter providing additional habitats for other taxa. Despite the current conditions supporting biodiversity and the functioning of the river, it is unclear if the system could endure further disturbance.

Phosphorus in soils and fluvial sediments from a Cerrado biome watershed under agricultural expansion

Over the past decades, lands alongside Gurguéia River have witnessed rapid expansion of soybean agriculture which has increased soil degradation and affected nutrient concentration in sediment, especially phosphorus (P). The present study aimed to quantify the P concentration in soils under different land uses (i.e., croplands, grasslands, and cerrado) and fluvial sediments (suspended sediment, channel bank, and riverbed sediments), assessing pollution over the main watercourse in cerrado biome Gurguéia watershed, located in Piauí State, Brazil. In total, 136 composite soil samples at a depth of 0-5 cm, under different land uses, as well as 51 composite fluvial sediment samples were collected over the watershed. The land use change from native cerrado had resulted in an increase of total phosphorus (TP) whose concentration was higher in cropland areas, followed by suspended sediment, channel bank, and riverbed sediments. This high concentration in cropland areas resulted from phosphate fertilizer inputs. The transfer of phosphorus to water bodies was evidenced, since an increase of TP was observed in suspended sediment, channel bank and riverbed  sediments. Mineralogical signatures in sediments were identified by X-ray diffraction analysis which showed the occurrence of kaolinite, illite, smectite, iron oxides, and other minerals in lesser proportions. The presence of 1:1 minerals was higher in riverbed sediments and downstream sampling points, while 2:1 minerals were present in higher proportions in suspended sediment and channel bank sediment, as well as at the upstream and middle sampling points. This finding shows that land use change from cerrado to cropland due to soybean agriculture expansion might increase P discharges from terrestrial to aquatic environments, with sediments being the major carrier of this element.

Expanding the Sediment Transport Tracking Possibilities in a River Basin through the Development of a Digital Platform—DNS/SWAT

Simulation of stochastic and variable sediment transport processes within models still poses a big challenge, especially in mountainous areas. Since sediment transport, including erosion and deposition, remains an unceasing problem in many areas, sediment modeling is perceived as a possible solution. This article combines a review of the selected sediment models with a presentation of the effects of several years of research using the DNS digital platform in the Western Carpathians. The review focuses on the main advantages and gaps in selected modeling tools with particular emphasis on one of the most popular: SWAT. The description of the digital platform—DNS is an example of how to answer these gaps by combining subsequent models, methods, and databases using their best features. To accentuate the benefits of such an approach, the effects of combining subsequent models (AdH/PTM) and methods (fingerprinting) on a common digital DNS space are presented, on the example of the Raba River (basin). In this way, both unique possibilities of estimating the amount of contamination carried with sediment particles and their sources, as well as sequencing of sedimentation in the reservoir, taking into account its subsequent zones, were obtained.

Transport of Potentially Toxic Elements in Solid Particulate Matter during Flash Flood Events in Upper and Lower Stretch of the Sava River

During extreme hydrological conditions such as flood events, sediments and alluvial soils may become re-suspended. As a consequence, the concentration of solid particulate matter (SPM) in the water column increases. As sediments represent a sink for the contaminants, when such perturbation occurs, the toxic substances may be re-dissolved into the water, causing harmful effects to the freshwater habitat. The purpose of this study was to evaluate the release of potentially toxic elements associated to SPM during flash floods. Two sampling sites on the Sava River were chosen: Litija (Slovenia), where the river has still the characteristics of an alpine river, and in Belgrade (Serbia), where Sava is a lowland river with a flat riverbed, slower flow and bigger quantities of fine-grained sediment. The results of the study showed a good correlation between the SPM mass concentration and water level/discharge. At both sampling sites, elevated concentrations of As, Cd, Cr, Cu, Pb, Ni and Zn were determined in SPM, indicating a moderate level of contamination at Litija and a high level at Belgrade. The results demonstrated that during the two investigated flash flood events limited the dissolution of PTE from SPM-bearing particles.

Following the Occurrence and Origin of Titanium Dioxide Nanoparticles in the Sava River by Single Particle ICP-MS

Titanium dioxide nanoparticles (TiO2NPs) are widely produced and used NPs in different applications. To evaluate the risk from anthropogenic TiO2NPs, more information is needed on their occurrence in the environment. For the first time, this study reports the levels of TiO2NPs in waters and sediments at selected sampling sites along the Sava River using inductively coupled plasma mass spectrometry in single particle mode (spICP-MS). The highest concentrations of TiO2NPs were determined in river water at Vrhovo (VRH), Jasenovac (JAS), and Slavonski Brod (SLB) sampling locations impacted by urban, agricultural, and/or industrial activities, suggesting that these NPs are likely of anthropogenic origin. The results further showed that hydrological conditions and sediment composition significantly influence the levels of TiO2NPs in river water at most locations. Moreover, the Ti/Al elemental concentration ratios of NPs in water and sediments at JAS were higher than the natural background ratios, further confirming their anthropogenic origin. The outcome of this study provides first information on the presence of (anthropogenic) TiO2NPs in different environmental compartments of the Sava River, contributing to more reliable risk assessments and better regulation of TiO2NPs emissions in the future.

Tissue-specific distribution and bioaccumulation pattern of trace metals in fish species from the heavily sediment-laden Yellow River, China

The Yellow River is one of the largest contributors to the global riverine sediment flux from the land to the ocean. Tissue-specific bioaccumulation of trace metals in fish from heavily sediment-laden rivers remains unclear to date. The concentrations and distributions of trace metals in water, suspended matters, sediments, and various fish tissues were investigated in the mainstem of the Yellow River were investigated. The concentrations of most metals in abiotic media were high in the Gan-Ning-Meng of upstream and downstream segments, and were highest in fine-sized suspended matters. The highest concentrations of most metals were in the gill and liver, followed by the gonad, and lowest in the muscle, and there were a significant overall differences among the tissues. The concentrations of metals in some tissues (e.g., muscle and gill) significantly differed among regions and feeding habits. The highest values of the bioaccumulation factor for suspended matters (BF_SPM) were observed in the midstream region (e.g., reaching to 19.0 for Se in the liver). This was determined by metal type and tissue specificity, food composition, and concentration of metals in abiotic media. The results highlight the significance of suspended matters for the distribution of trace metals in abiotic and biotic media.

Dilution of PAHs loadings of particulate matter in air, dust and rivers in urban areas: A comparative study (Tehran megacity, Iran and city of Tübingen, SW-Germany)

PAHs (polycyclic aromatic hydrocarbons) in urban areas are usually bound to particles. Concentrations are different in different compartments (airborne particles, street dust, suspended sediments in rivers and channels). This study follows concentrations of PAHs from particles in air to street dust and finally suspended sediments in the city of Tehran, Iran compared to Tübingen, Germany. Data sets are based on own investigations (PAHs on suspended sediments), or taken from literature studies (PAHs in street dust and airborne particles). Based on a cross-comparison of concentrations of PAHs on particles, and their congener distribution patterns, the occurrence, interrelation (exchange and mixing processes), as well as possible dilution processes among PAHs in the different particle classes are disentangled. Results show that for Tehran and Tübingen PAHs in airborne particles are very high (in the range of 500 mg kg^-1). However, in street dust and suspended sediments PAHs concentrations on particles are around 100 times lower. Surprisingly concentrations in street dust and suspended sediments are 5 to 10 times lower in Tehran (average 0.5 mg kg^-1) than in Tübingen (average 5 mg kg^-1). Since it is unlikely that PAHs emissions are lower in the Tehran megacity, an effective dilution of the atmospheric signal by uncontaminated (background) particles is hypothesized. Uncontaminated particles may stem from wind erosion of bare surfaces, construction and sand mining sites or even dust from the desert areas, which are frequent in arid climate in Tehran.

Long-Term Leaching Behavior of Organic and Inorganic Pollutants after Wet Processing of Solid Waste Materials

The recycling of mineral materials is a sustainable and economical approach for reducing solid waste and saving primary resources. However, their reuse may pose potential risks of groundwater contamination, which may result from the leaching of organic and inorganic substances into water that percolates the solid waste. In this study, column leaching tests were used to investigate the short- and long-term leaching behavior of “salts”, “metals”, and organic pollutants such as PAHs and herbicides from different grain size fractions of construction & demolition waste (CDW) and railway ballast (RB) after a novel treatment process. Specifically, silt, sand and gravel fractions obtained after a sequential crushing, sieving, and washing process (“wet-processing”) of very heterogeneous input materials are compared with respect to residual contamination, potentially limiting their recycling. Concentrations in solid fractions and aqueous leachate were evaluated according to threshold values for groundwater protection to identify relevant substances and to classify materials obtained for recycling purposes according to limit values. For that, the upcoming German recycling degree was applied for the first time. Very good agreement was observed between short and extensive column tests, demonstrating that concentrations at L/S 2 ratios are suitable for quality control of recycling materials. Different solutes showed a characteristic leaching behavior such as the rapid decrease in “salts”, e.g., SO₄²⁻ and Cl⁻, from all solid fractions, and a slower decrease in metals and PAHs in the sand and silt fractions. Only the gravel fraction, however, showed concentrations of potential pollutants low enough for an unlimited re-use as recycling material in open technical applications. Sand fractions may only be re-used as recycling material in isolated or semi-isolated scenarios. Leaching from heterogeneous input materials proved harder to predict for all compounds. Overall, column leaching tests proved useful for (i) initial characterization of the mineral recycling materials, and (ii) continuous internal (factory control) and external quality control within the upcoming German recycling decree. Results from such studies may be used to optimize the treatment of mixed solid waste since they provide rapid insight in residual pollution of material fractions and their leaching behavior.

Estimating metal loading into the sea from tidal rivers using total suspended solids and water quality models

Metals are mainly transported with suspended sediments in tidal rivers, and it is difficult to describe the transformation process of metals. Freely dissolved metals and suspended metals (including acid-soluble, reducible, oxidizable, and residual metals) were separately analyzed according to a sequential extraction scheme. The regression of the observed suspended metals and total suspended solids (TSS) concentrations allowed us to couple the two pollutant types. TSS is a highly dynamic parameter, and a model can be developed to simulate TSS transport. Thus, a method including the following five steps was proposed to estimate the loadings of metals entering the sea using TSS concentrations and water quality models: (1) collecting and observing basic information on the hydrological conditions, pollution sources, and water quality of the studied river; (2) obtaining a regression model between the suspended metals and TSS and analyzing the potential of establishing a suspended metal flux model; (3) introducing a model describing the fluxes of water-soluble metals into the sea; (4) establishing a calculation model to determine the fluxes of suspended metals into the sea; and (5) characterizing the fluxes of metals into the sea. The method was programmed, and metal concentrations and fluxes could be characterized quickly when the basic river data were sufficient. In addition, if regional development scenarios could be set, metal loadings in all scenarios could be predicted through the procedure developed herein, and some effective suggestions on regional sustainable development might be proposed for decision makers. Integr Environ Assess Manag 2022;18:198-208. © 2021 SETAC.

Maize plant (Zea mays) uptake of organophosphorus and novel brominated flame retardants from hydroponic cultures

The root uptake and root-shoot translocation of seven organophosphorus flame retardants (OPFRs) and four novel brominated flame retardants (NBFRs) were assessed in this investigation using hydroponic grown maize plants (Zea mays). Three initial liquid concentrations for each considered compound were examined (i.e., 0.3 μg L^-1, 3 μg L^-1, 30 μg L^-1). The results indicated that the 30 μg L^-1 treatments were phytotoxic, as they resulted in a significant decrease in shoot dry weight. Plant-driven removal of the tested FRs decreased with the increasing initial spiking level and were reportedly higher for the NBFRs (range 42%-10%) than OPFRs (range 19%-7%). All the considered FRs were measured in the roots (range 0.020-6.123 μg g^-1 dry weight -DW-) and shoots (range 0.012-1.364 μg g^-1 DW) of the tested plants, confirming that there was uptake. Linear relationships were identified between the chemical concentrations in the plant parts and the tested hydroponic concentrations. Root concentration factors were positively correlated with the specific lipophilicity (i.e., logK_ow) of the tested FRs and were determined to be higher for the NBFRs than the OPFRs. The NBFRs had a higher root uptake rate than the OPFRs, and this trend was more significant with the increasing treatment concentrations. Shoot/root concentration factors were found to be lower than the unity value for 10 of the 11 tested compounds. These results can be related to the specific molecular configurations and the occurrence of different functional groups in the tested compounds. The results will help to improve risk assessment procedures and fine tune our understanding of human receptor responses to the ingestion of maize crops grown on agricultural sites irrigated with water contaminated by FRs.

Identification of suspended particulate matters as the hotspot of polycyclic aromatic hydrocarbon degradation-related bacteria and genes in the Pearl River Estuary using metagenomic approaches

Bacterial degradation is unequivocally considered as an important way for the cleanup of polycyclic aromatic hydrocarbon (PAHs) in the aquatic environment. However, the diversity and distribution of PAH-degrading bacterial communities and PAH degradation-related genes (PAHDGs) in ambient environment need to be investigated. In this study, bacteria in the water of the Pearl River Estuary (PRE) were initially separated as the particle-attached bacteria (PAB) and free-living bacteria (FLB), and were further characterized using metagenomic approaches. Proteobacteria (80.1 %) was identified as the most abundant PAH-degrading phylum in the PRE water, followed by Bacteroidetes, Actinobacteria, and Firmicutes. A substantial difference in the community structure was observed between PAH-degrading PAB and FLB. Both of PAH-degrading bacteria and PAHDGs were enriched on the suspended particulate matters (SPMs), with the range of enrichment factor (EF) from 7.84 × 10⁴ to 6.64 × 10⁶ (PAH-degrading bacteria) and from 1.14 × 10³ to 1.76 × 10⁵ (PAHDGs). The levels of PAH-degrading bacteria 16 S rRNA genes and PAHDGs on the SPMs were both significantly correlated with those in the aqueous phase (AP) in the PRE water (p < 0.05), indicating a dynamic distribution of PAH-degrading bacteria between these two phases. The total PAH concentrations on the SPMs of the PRE water were also significantly correlated with the total PAHDG levels in the PAB (p < 0.05). Our results suggested that the SPMs could be the important compartment for the elimination of PAHs from the aquatic environment.

Metallic contamination of global river sediments and latest developments for their remediation

This review article represents the comparative study of heavy metal concentration in water and sediments of 43 important global rivers. The review is a solitary effort in the area of heavy metal contamination of river-sediments during last ten years. The interpretation of heavy metal contamination in sediments has been verified with different indices, factors, codes and reference guidelines, which is based on geochemical data linked to background value of metals. It is observed that health hazards arise due to dynamics of movement of metals between water and sediments, which is primarily influenced by several factors such as physical, chemical, biological, hydrological and environmental. Also, the reason behind accumulation and assimilation of heavy metals on river water system is explained with appropriate mechanisms. Several factors e.g. pH, ORP, organic matter etc. are mainly involved in the distribution, accumulation and assimilation of metals in the sediment phase to water phase. Remediation technologies such as in-situ and ex-situ have been discussed for the removal of heavy metals from contaminated sediments. We have also compared the performance efficiencies of the technologies adopted by different researchers during the period 2003 to 2019 for the removal of metal bound sediments. Many researchers have preferred in-situ over ex-situ remediation due to low cost and time saving remediation effects. In this work we have also incorporated the safety measures and strategies which can prevent the metal accumulation in sediments of river system.

Modeling of the Suspended Solid Removal of a Granular Media Layer in an Upflow Stormwater Runoff Filtration System

Upflow granular media filtration devices are widely used for stormwater runoff treatment. However, the system performance is not well characterized due to the irregular removal of suspended solid (SS) in the pretreatment (sedimentation) chamber and, hence, its irregular input to the media layer. In this regard, the performance of the granular media layer of an upflow filtration system is investigated herein by the use of various models. Due to the significant variation in the SS concentration of the influent and effluent to and from the media layer, the deep bed filtration model, the k-C* model, and the porous media capture model provide limited descriptions of the system performance. By contrast, the performance is well described using the kinetic model, the modified k-C* model using a specific deposit, and the modified porous media capture model using a specific deposit. The parameters of the latter models are shown to be in good correlation with the filtration velocity, SS removal, and specific deposit. The results suggest that modeling using a specific SS deposit can provide an accurate description of the granular media layer performance under a highly variable influent SS concentration.

Evaluation of solids removal and optimisation of backwashing for an upflow stormwater filtration system utilising novel floating fibrous media

Although filtration devices are already widely used for stormwater runoff treatment, there are much to be improved to ensure the required performance. Additionally, the performance of a device should be verified before on-site installation. In this context, an upflow filtration system using novel high porosity floating fibrous media formed into spherical shape was proposed and evaluated for solid capture and backwashing. At filtration velocities of 20-40 m/h, the maximum head loss was about 2 cm even under a solid load of 30 kg/m², and suspended solid (SS) removal efficiency was >96% throughout 300 min. A considerable amount of SS was removed in the pretreatment chamber, so the load on the media was reduced. Several models were tried to describe the solid capture in the media. The coefficients of solid attachment/detachment showed good correlations with filtration velocity. Other parameters indicated a variation of solid capture and permeability, which is unique to the media in this study. The backwashing with air and water for 1-2 min each showed good head loss recovery under the SS load up to 550-600 kg/m², and the SS discharge was more efficient when the stagnant water was drained before water backwashing. The results in this study suggest the high potential of the combination of fibrous media and upflow filtration system for the efficient control of the nonpoint source pollutants in stormwater runoff.

Multivariate criteria applied in the performance of Tifton 85 grass in a constructed wetland: effects of organic, nutritional, and sodium loads from swine wastewater

The purpose of this study was to analyze the effects of the application of multivariate criteria of principal components and hierarchical clustering as a mechanism for monitoring the performance of Tifton 85 grass (Cynodon spp.) planted in horizontal subsurface flow constructed wetland reactor (HSSF-CW) under different organic (OLR), nutritional and sodium loads of swine wastewater (SW). The HSSF-CW planted with Tifton 85 grass was used as a swine wastewater after treatment applying organic loading rates between 26.1 (1st cut) and 360.6 kg ha^-1 day^-1 COD (8th cut). The maximum performances of HSSF-CW consisted of 52.0 t ha^-1 of productivity and 24.0% of crude protein, with the application of 59.7, 64.2, and 31.2 kg ha^-1 day^-1 of TKN, P_T, and K⁺, respectively. The eleven original variables generated four new components, with PC₄ accounting for 94.0% of total variance, a condition strengthened with four data groupings greater than 48% similarity and three data groupings greater than 95% similarity between the variables. There was a strong association between of nitrogen, phosphorus, and potassium concentration by the hierarchical grouping and the intermediate cuts and lower temperatures.

Climate change impacts on contaminant loads delivered with sediment yields from different land use types in a Carpathian basin

Soil runoff and sediment transport are considered as an important vector for particle-bound contaminant transfer from source to receiving waters. Under changing climate conditions and rapid basin development, identification of sediment origins is critical for planning further action to reduce erosion effects, and further pollution to surface waters. The goal of this study was to distinguish sediment sources in a Carpathian basin (Wolnica River, southern Poland) and to perform source-oriented contaminant load estimations. Sediment yields (SYLD) and land use specific sediment yields (LUSY) were modeled with the use of the Macromodel DNS/SWAT (Discharge-Nutrients-Sea/Soil and Water Assessment Tool). Sorting of sediment sources was performed by the fingerprinting method using variability of the geochemical composition of soils (Pb, Zn, Cd, Cu, Mn, Ni, Fe, Hg, total N and P, Σ16 PAHs, and 137Cs) of four land use (LU) types: arable lands (A), grasslands (G), residential areas (R), and forests (F). Statistical analysis revealed six metals (Pb, Zn, Cd, Cu, Ni, and Hg) as fingerprint properties providing the best source discrimination in this basin. The contribution of particular land use origin assessed with the use of the mixing model varied in the range of 20-30%. Finally, estimation of land use specific contaminant loads in suspended sediments was performed as a result of a modeling and sediment fingerprinting combination. The final estimates revealed yearly LUSY values varying between 716 t/y for A, 12 t/y for F, and metal loads from 31 kg/y for Zn to values below 100 g/y for Cd and Hg. Long-term predictions (2046-2055) of the metal loads revealed an increase by 75% under the combined RCP 8.5 climate change and land use scenarios. These findings are of great value for land management in the Carpathian basins, especially with regards to the predicted increase of forest cover which significantly alters contaminant signals conveyed through the system.

Priority and emerging organic microcontaminants in three Mediterranean river basins: Occurrence, spatial distribution, and identification of river basin specific pollutants

There is a worldwide growing use of chemicals by our developed, industrialized, and technological society. More than 100,000 chemical substances are thus commonly used both by industry and households. Depending on the amount produced, physical-chemical properties, and mode of use, many of them may reach the environment and, notably, the aquatic receiving systems. This may result in undesirable and harmful side-effects on both the human and the ecosystem's health. Mediterranean rivers are largely different from Northern and Central European rivers in terms of hydrological regime, climate conditions (e.g. air temperature, solar irradiation, precipitation), and socio-economics (e.g. land use, tourism, crop types, etc.), with all these factors leading to differences in the relative importance of the environmental stressors, in the classes and levels of the pollutants found and their environmental fate. Furthermore, water scarcity might be critical in affecting water pollution because of the lowered dilution capacity of chemicals. This work provides raw chemical data from different families of microcontaminants identified in three selected Mediterranean rivers (the Sava, Evrotas, and Adige) collected during two sampling campaigns conducted in 2014 and 2015 in three different matrices, namely, water, sediments, and biota (fish). More than 200 organic micropollutants were analyzed, including relevant groups like pharmaceuticals, personal care products, perfluorinated compounds, pesticides, pyrethroid insecticides, flame retardants, and persistent organic pollutants. Data obtained were summarized with some basic statistics for all compound families and matrices analyzed. Observed occurrence and spatial patterns were interpreted both in terms of compound physical-chemical properties and local environmental pressures. Finally, their spatial distribution was examined and their ecotoxicological risk in the water phase was assessed. This allowed locating, at each basin, the most polluted sites ("hot spots") and identifying the respective river basin specific pollutants (RBSPs), prioritizing them in terms of the potential ecotoxicological risk posed to the aquatic ecosystems.

Quantitative assessment of metal contamination and associated pollution risk in sediments from the Mara River in Tanzania

For most rivers in sub-Saharan Africa, information about pollution indices related to sediments is sparse. Sedimentological research of rivers that empty into Lake Victoria is highly patchy and wide apart. The present study determined the levels and associated risk of As, Cd, Cr, Hg, and Pb in sediments collected from four different sites along the Mara River that empties into Lake Victoria in Tanzania. Samples were collected in the dry and rainy months in 2019. Pollution indices, namely geo-accumulation index (I_geo), enrichment factor (EF), contamination factor (CF), modified contamination degree (mCd), pollution load index (PLI), potential ecological risk factor (E_rⁱ), and potential ecological risk index (RI) were used to evaluate the influence of heavy metal contamination in sediments. Dry month mean concentrations, in milligram per kilogram, of heavy metals were as follows: As (11.04 ± 0.13), Cr (1.02 ± 0.29), Cd (0.43 ± 0.05), and Hg (0.01) in the dry month. Respective sediment heavy metal concentrations for the rainy month were 22.22 ± 0.05 mg As/kg, 3.84 ± 0.34 mg Pb/kg, 1.53 ± 0.15 mg Cd/kg, 1.43 mg Cr/kg, and 0.03 mg Hg/kg. Generally, the risk indices showed high values in the rainy month and low values in the dry month, especially for As and Cd-an indication of anthropogenic influence. Correlation coefficient analysis for Pb and Cd showed a strong positive correlation (r = 0.99, p < 0.01)-this may suggest a similar source or similar transport behavior. Special attention needs to be paid with regard to rainy season As and Cd enrichment in the study area.

Hydro-climatic drivers of land-based organic and inorganic particulate micropollutant fluxes: The regime of the largest river water inflow of the Mediterranean Sea

Land-based micropollutants are the largest pollution source of the marine environment acting as the major large-scale chemical sink. Despite this, there are few comprehensive datasets for estimating micropollutant fluxes released to the sea from river mouths. Hence, their dynamics and drivers remain poorly understood. Here, we address this issue by continuous measurements throughout the Rhône River basin (∼100,000 km²) of 1) particulate micropollutant concentrations (persistant organic micropollutants: polychlorobiphenyls [PCBi] and polycyclic aromatic hydrocarbons [PAHs]; emerging compounds: glyphosate and aminomethylphosphonic acid [AMPA]; and trace metal elements [TME]), 2) suspended particulate matter [SPM], and 3) water discharge. From these data, we computed daily fluxes for a wide range of micropollutants (n = 29) over a long-term period (2008-2018). We argue that almost two-thirds of annual micropollutant fluxes are released to the Mediterranean Sea during three short-term periods over the year. The watershed hydro-climatic heterogeneity determines this dynamic by triggering seasonal floods. Unexpectedly, the large deficit of the inter-annual monthly micropollutant fluxes inputs (tributaries and the Upper Rhône River) compared to the output (Beaucaire station) claims for the presence of highly contaminated missing sources of micropollutants in the Rhône River watershed. Based on a SPM-flux-averaged micropollutant concentrations mass balance of the system and the estimates of the relative uncertainty of the missing sources concentration, we assessed their location within the Rhône River catchment. We assume that the potential missing sources of PAHs, PCBi and TME would be, respectively, the metropolitan areas, the alluvial margins of the Rhône River valley, and the unmonitored Cevenol tributaries.

Genotoxic effect of heavy metals on Astyanax lacustris in an urban stream

Uncontrolled urbanization growth contributes to the pollution of aquatic environments. Heavy metals released by domestic and industrial effluents can negatively affect aquatic organisms. This study aimed to evaluate the effect of environmental pollutants, such as metals, on fish DNA damage, in stretches of an urban stream. Specimens of the Neotropical fish, Astyanax lacustris, were exposed in situ for 96 h along the Antas stream, a Brazilian aquatic system deteriorated by anthropogenic factors. Water and sediment samples were collected simultaneously for physicochemical and heavy metal analyses. The comet assay was performed as a biomarker of genotoxicity. Fish located downstream had a higher frequency of DNA damage than in the reference site. We found concentrations of Cr and Ni above acceptable levels in sediment samples. Generally, Ba, Mn, Mg, Zn, Cr, and Ni were the elements most associated with genotoxic damage. Water and sediment of the Antas stream showed genotoxic potential in A. lacustris according to the urbanization gradient, demonstrating the importance to prevent the release of environmental pollutants, especially heavy metals in urban areas.

Sources and health risks of PM2.5-bound polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in a North China rural area

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) are typical persistent organic pollutants (POPs), which have high toxicity, bioaccumulation and long-distance transfer capability. Daily variation, sources of PCBs and OCPs in PM_2.5 are rarely explored in polluted rural area. Here, the sources and health risks of the PCBs and OCPs were evaluated for 48 PM_2.5 samples collected in winter 2017 in Wangdu, a heavy polluted rural area in the North China Plain. The average diurnal and nocturnal concentrations of Σ₁₈PCBs and Σ₁₅OCPs were 1.74-24.37 and 1.77-100.49, 11.67-408.81 and 16.89-865.60 pg/m³, respectively. Hexa-CBs and penta-CBs accounted for higher proportions (29.0% and 33.6%) of clean and polluted samples, respectively. Hexachlorobenzene (HCB) was the dominant contributor to OCPs with an average concentration of 116.17 pg/m³. Hexachlorocyclohexane (ΣHCHs) and dichlorodiphenyltrichloroethane (ΣDDTs) were the other two main classes in OCPs with the average concentrations of 4.33 and 15.89 pg/m³, respectively. β-HCH and p,p'-DDE were the main degradation products of HCHs and DDTs, respectively. The principal component analysis and characteristic ratio method indicated both waste incineration and industrial activities were the main sources of PCBs, contributing 76.8% and 12.7%, respectively. The loadings of OCPs were attributed to their application characteristics and the characteristic ratio method reflected a current or past use of OCPs. Health risk assessment showed that the respiratory exposure quantity of doxin-like PCBs (DL-PCBs) and the lifetime cancer risk from airborne OCPs exposure was negligible, while the other exposure modes may pose a risk to human bodies.

Analyzing Particle-Associated Pollutant Transport to Identify In-Stream Sediment Processes during a High Flow Event

Urban areas are a leading source of polycyclic aromatic hydrocarbons (PAHs) that result from combustion processes and are emitted into rivers, especially during rain events and with particle wash-off from urban surfaces. In-stream transport of suspended particles and attached PAHs is linked strongly to sediment turnover processes. This study aimed to identify particle exchange processes that contribute to the transport of suspended particles during flood events. An urban high-flow signal was tracked in high temporal resolution at two sampling sites in the Ammer River (South-western Germany). Samples were analyzed for turbidity, total suspended solids concentrations (TSS), particle-size distribution, organic carbon, and PAH. Maximum discharge and the highest TSS occurred nearly simultaneously at the upstream sampling site, whereas a temporally shifted course was observed for downstream. The total load of particles was similar, yet a decrease of PAH mass (~28%) and an increase of the particulate organic carbon (POC) content (~3.5%-points) occurred. Coarser particles (≥26 µm) dominated at the beginning of the event at both sampling sites. The signal of remobilized riverbed sediment increases downstream and leads to well-established, robust linear correlations between TSS and PAHs. This study highlights that riverbed sediment acts as intermediate storage for contaminated particles from upstream sources that shape, together with the fresh urban input, the “particle signature” of suspensions moving through catchments during high discharge conditions.

A preliminary pan-European assessment of pollution loads from urban runoff

Acknowledging the difficulty of modelling pollution conveyed by urban runoff, this contribution presents a first pan-European quantification of loads from this diffuse source. We estimate annual loads of 5-days biochemical oxygen demand (BOD₅), nitrogen (N), phosphorus (P) and total suspended solids (TSS) using a simple event mean concentration (EMC) model initially proposed by Heaney et al., 1976. On a European scale, this yields discharges corresponding to untreated wastewater of about 31 million population equivalents (PE) for BOD₅, about 18.5 million PE for N and P and about 280 million for TSS. These represent 51% of the pollution coming from treated wastewater for BOD₅, 15% for N and P and 461% for TSS. Although the model applied for the assessment was developed more than 40 years ago, the results are consistent with those obtained using more recent parameterizations, except for a tendency to underestimate P loads. Although lack of data on pollution from urban runoff makes model verification impossible, and the uncertainty on EMC models is known to be very high, urban runoff emerges as a significant source of pollution, and should be properly addressed as such. Reducing runoff volume from urban areas through improved water retention is not only key to pollution control, but also a no-regret option thanks to its co-benefits, especially when incorporated at early stages of planning and design.

Simulating heavy metal concentrations in an aquatic environment using artificial intelligence models and physicochemical indexes

Although heavy metal monitoring campaigns are established worldwide, it is still difficult to model heavy metals in aquatic environments with limited monitoring data. In this study, surface water physicochemical indexes and heavy metal concentrations were measured in a drinking water source in the Taihu Lake region, China. Afterwards, indexes including water temperature, pH, suspended matter, turbidity, and total nitrogen, nitrate nitrogen, ammonia nitrogen, total phosphorous, orthophosphate and permanganate index were used to simulate dissolved, particulate and total heavy metal concentrations using artificial neural network (ANN) and support vector machine (SVM) models. Sensitivity analysis showed that simulated heavy metal concentrations were most sensitive to pH. Thereafter, quick simulation models based on five sensitive parameters (pH, suspended matter, water temperature, total phosphorus and permanganate index) allowed for quick simulations of heavy metal concentrations were built. Both ANN and SVM quick simulation models simulated particulate heavy metal concentrations well with most Nash-Sutcliffe efficiency coefficients >0.8. Models performed worse when simulating dissolved and total heavy metal concentrations. Results demonstrate that artificial intelligence models like ANN and SVM are alternative ways to simulate heavy metal concentrations with limited monitoring data. Furthermore, sensitivity analysis may help to identify key factors affecting heavy metal behavior, and to improve environmental monitoring campaigns and management strategies.

Hydrophobic organic compounds in drinking water reservoirs: Toxic effects of chlorination and protective effects of dietary antioxidants against disinfection by-products

This study investigated formation and genotoxicities of disinfection by-products (DBPs) during chlorination of hydrophobic organic compounds (HOCs) extracted from six drinking water reservoirs around the Pearl River Delta region, China. Chemical analyses firstly showed that after chlorination aromatic HOCs (including polycyclic aromatic hydrocarbons, PAHs) decreased but DBPs (including chlorinated PAHs) increased, while genotoxicity assays revealed that the chlorination increased DNA damage in human Caco-2 cells. Although the link between DBPs and the genotoxicity was weak (insignificant correlations, p ≥ 0.05), we observed that chlorination of HOCs from more contaminated reservoirs in general resulted in higher genotoxicity. Secondly, remedial effects of catalase and dietary antioxidants (i.e. vitamin C and epigallocatechin gallate) in protecting cells against DBPs genotoxicity were detected. After 1 h treatment by the antioxidants, the DNA damage in Caco-2 cells (due to previous exposure to DBPs) significantly decreased (p < 0.05) in 7 out of a total of 18 treatments (38.9%). This is the first study demonstrating that catalase, vitamin C and epigallocatechin gallate protected human cells in vitro against DNA damage upon exposure to chlorinated genotoxic DBPs.

Occurrence, spatial-temporal distribution and ecological risks of pharmaceuticals and personal care products response to water diversion across the rivers in Nanjing, China

Water diversion projects have been continuously used to alleviate water quality issues that arise during urbanization. However, studies about whether it has possible effects on the status of pharmaceutical and personal care products (PPCPs) are limited. In this study, the occurrence trends and spatial-temporal distribution characteristics of 50 PPCPs were investigated in surface water, suspended particulate matter (SPM) and sediments in Nanjing urban rivers under the background of the water diversion project from the Yangtze River to the Qinhuai River. In the four field campaigns that were embarked on April to July 2018, a total of 40, 38 and 24 PPCPs were detected in surface water, SPM and sediments, respectively, with overall concentrations of 138-1990 ng/L, 3214-33,701 ng/g and 12.1-109 ng/g dry weight (dw) among nine sampling sites. The excessive concentration of caffeine (20.6-905 ng/L) may be evidence of the direct discharge of untreated sewage and an obvious indicator of the overall concentrations of PPCPs. The PPCPs contamination levels in surface water were increased along with the direction of the water diversion in urban runoff, and decreased by 8-31% due to the increase in volume attributable to the water diversion. The distribution coefficients (K_d) of pollutants in the SPM-water phases (3.0-5.6 L/kg) were two orders of magnitude higher than those in the sediment-water phases (0.3-3.3 L/kg). And the positive correlations between their log K_ow and SPM-water log K_d values indicated SPM was the important carrier determining the fate of organic UV filters. Furthermore, the results of ecological risk assessment demonstrated that although the increase in the volume of water caused by the water diversion reduced the overall ecological risks of PPCPs in urban rivers, the current contamination level still represents high risks to algae and fish.

Behaviour of metals in an urban river and the pollution of estuarine environment

The high pollutant loads discharged from cities pose risks to urban waterways, and in turn the estuarine environments, making it challenging to improve urban liveability. Past studies on the behaviour of pollutants in rivers have largely investigated their transport along the waterway, primarily focusing on the movement of water and sediment. However, the current approaches in pollutant transport modelling provide limited insights into how pollutant transfer between water and sediment phases influences their transport from the upstream towards the estuarine environment. This research study firstly identified typical patterns of metal loads along an urban river in a highly populated city in China. The outcomes were then used to conceptualise metal transfer between water and sediment phases. It was noted that physico-chemical characteristics of water and sediments play a key role in metal transfer between the two phases, and the dominant transfer path (sediment to water/water to sediment) is different between different metals, independent of their origin (crustal, anthropogenic or marine-related). Several scenarios were derived from the conceptualisation of metal behaviour. These in turn were then used to develop real-world scenarios of metal transport in rivers based on the field data. The conceptualisation of metal behaviour confirmed that each metal is likely to have a dominant phase of transport (sediment/water), which is influenced by the dominant transfer path of that metal between water and sediments.

Designing field-based investigations of organic micropollutant fate in rivers

Organic micropollutants in rivers are emitted via diffuse and point sources like from agricultural practice or wastewater treatment plants (WWTP). Extensive laboratory and field experiments have been conducted to understand emissions and fate of these pollutants in freshwaters. Nevertheless, data is often difficult to compare since common protocols for appropriate approaches are largely missing. Thus, interpretation of the observed changes in substance concentrations and of the underlying fate of these compounds downstream of the chemical input into the river is still challenging. To narrow this research gap, (1) process understanding and (2) measurement approaches for field-based investigations are critically reviewed in this article. The review includes, on the one hand, processes that change the volume of the water (hydrological processes) and, on the other hand, processes that affect the substance mass within the water (distribution and transformation). Environmental boundary conditions for the purpose of better comparability of different attenuation studies, as well as promising state-of-the-art measurement approaches from different disciplines, are presented. This overview helps to develop a tailored procedure to assess turnover mechanisms of organic micropollutants under field conditions. In this respect, further research needs to standardize interdisciplinary approaches to increase the informative value of collected data.

Nutrient uptake by constructed floating wetland plants during the construction phase of an urban residential development

This study investigated plant growth, nutrient partitioning and total nutrient uptake by tall sedge (Carex appressa) plants in two large-scale Constructed Floating Wetlands (CFW1 and CFW2). These CFWs were installed to treat stormwater runoff discharging into a newly-constructed 2.6-ha lake during the construction phase of a 45-ha residential development. Nutrient concentrations of C. appressa shoot above the mat, biomass within the mat, and roots below the mat were analysed 0, 12 and 16 months after planting. Extensive root growth was evident after 12 and 16 months. Some nutrients (nitrogen, phosphorus, sulphur) were distributed almost evenly among the above-, within-, and below-mat components, while others (aluminium, copper, iron, manganese) were concentrated in or on the roots. Given the low concentrations of nutrients within the water column, large amounts of nutrients were removed from stormwater by the plants. Total nitrogen uptake was 20.20 ± 2.88 kg in CFW1 and 15.00 ± 2.07 kg in CFW2 over the 16-month study period. Total potassium uptake was 12.59 ± 1.64 kg in CFW1 and 7.20 ± 1.56 kg in CFW2. Phosphorus uptake was low as a consequence of low phosphorus availability in the water. High aluminium, iron and manganese concentrations were found in the roots, demonstrating that C. appressa removed and sequestered large quantities of these water pollutants from urban stormwater runoff. For example, total aluminium uptake was 7.82 ± 1.73 kg in CFW1 and 5.62 ± 0.75 kg in CFW2. This study demonstrated multiple benefits of CFWs for stormwater treatment in the early stages of an urban development.

Distribution and adsorption of metals on different particle size fractions of sediments in a hydrodynamically disturbed canal

Sediment resuspension widely occurs in environments with hydrodynamic disturbances, where particles are sieved into different grain size groups. The particles of different grain size exhibit heterogeneity of their physical, chemical or biological features. This research addressed the association of metals on size fractional particles sieved by sediment resuspension in a canal of Taihu basin, a highly urbanized and human-impacted area. Surface sediment samples were collected from upstream to downstream sections of the canal to analyze the concentrations and fractionation of lead (Pb), zinc (Zn), and copper (Cu). One sediment sample was sieved into five different particle size groups (50-150 μm, 30-50 μm, 10-30 μm, 5-10 μm and <5 μm) through the wet sedimentation method. The strong adsorption ability of metals on fine particles is attributed to enrichment with organic matter and iron/aluminum (Fe/Al) oxides, with the increase in Pb, Zn, and Cu concentrations from 34.2 mg/kg, 263 mg/kg, and 32.5 mg/kg of 50-150 μm size group particles to 71.4 mg/kg, 698 mg/kg, and 137 mg/kg of <5 μm size group particles, respectively. The fine particles showed stronger sorption ability on Pb than Zn and Cu, with the Freundlich isotherm constant (K_f) values of the adsorption isotherms in the <10 μm size particle group ranging from 3.7 to 5.9 g/kg for Zn and Cu versus from 11 to 18 g/kg for Pb, probably causing difference on metals accumulation and releasing risk among metals in the downstream lakes with changeable environments.

Distribution, Sources, and Water Quality Assessment of Dissolved Heavy Metals in the Jiulongjiang River Water, Southeast China

In this study, the concentration of eight dissolved heavy metals (Ti, Cr, Mn, Fe, Ni, Mo, Sb, and Ba) in 42 water samples from the Jiulongjiang River, southeast China, were determined by inductively coupled plasma mass spectrometry (ICP-MS). Multivariate statistical methods, including correlation analysis (CA) and factor and principal component analysis (FA/PCA), were analyzed to identify the sources of the elements. Water quality index (WQI) and health risk assessment, including hazard quotient (HQ) and hazard index (HI), were used to evaluate water quality and the impacts on human health. Our results were compared with the drinking water guidelines reported by China, the World Health Organization (WHO), and the United States Environmental Protection Agency (US EPA), revealing that Ti, Mn, and Sb were not within approved limits at some sites and might be the main pollutants in the drainage basin. Based on the spatial distributions, Ti, Mn, Fe, Ni, and Mo showed good similarity, indicating that they might come from similar sources along the river. The CA results also showed that Ti, Mn, Fe, Ni, and Mo had a high correlation coefficient. The FA/PCA results identified three principal components (PC) that accounted for 79.46% of the total variance. PC 1 suggested that a mixed lithogenic and urban land source contributed to Ti, Mn, Fe, Ni, and Mo; PC 2 showed that Cr, Ni, and Mo were influenced by the discharge of industrial effluents; Sb had a strong loading on PC 3, which was controlled by mining activities. The results of the WQI indicated that the water in the Jiulongjiang River was basically categorized as excellent water, but the water quality levels in site W5 and N4 were poorer due to urban land use. Hazard quotient and HI values showed that Sb was a potential threat to human health, indicating that preventive actions should be considered in regard to mining activities in the upper reaches of Beixi stream.