Simultaneously Extracted Metals Research Articles

Bioavailability Assessment of Metals from the Coastal Sediments of Tropical Estuaries Based on Acid-Volatile Sulfide and Simultaneously Extracted Metals

Bioavailability assessment is important for evaluating the risks to the local biota, and the combined use of several ecological risk indices in eutrophic environments allows the best analysis of the local reality for decision-making. The relationship between acid volatile sulfide (AVS) concentrations and simultaneously extracted metals (SEM) allows us to infer the metal holding capacity of sediment, with the objective of evaluating the potential bioavailability of trace metals (Cd, Cu, Ni, Pb, and Zn) using ecological risk indices, such as the ΣSEM/AVS model and Adverse Effect Index (AEI), in surface sediments from Guanabara Bay and Sepetiba Bay, Brazil. AVS was determined using a colorimetric method and SEM with ICP-OES. In general, almost all sampling in Sepetiba Bay showed ΣSEM/AVS ratio values above 1. However, all results for the ΣSEM/AVS ratio found for the Guanabara Bay sediments were <1 for both estuaries. After normalization by organic carbon content, a possible toxicity risk for biota was found in Sepetiba Bay. However, the AEI in Guanabara Bay was above 1 for all metals in most samples, also indicating a risk to the biota.

Evaluation of bioaccumulation and toxicity of Tubifex tubifex exposed to contaminated river sediment by potentially toxic elements — A case study of the Middle Black Sea, Turkey

To determine the ecotoxicological assessment of the Black Sea in the seasonal and spatial dimensions, the concentrations of potentially toxic elements (PTEs) in sediment were measured at five sampling sites selected as Kızılırmak (T1), Engiz River (T2), Mert River (T3), Abdal River (T4), and Yeşilırmak (T5). In addition, a 28-day toxicity test was conducted with T. tubifex to evaluate the accumulation and toxicity of the PTEs contamination. The results of PTEs concentration in sediment indicated that the sampling sites are ranked according to the degree of elemental pollution from highly polluted to less polluted as Yeşilırmak > Kızılırmak > Abdal River > Engiz River > Mert River. Both natural and anthropogenic activities including industrial and agricultural effluents, municipal wastewater, and traffic-related pollution were found as the main sources of PTEs. Additionally, the acid volatile sulfide (AVS) – simultaneously extracted metal (SEM) concentrations were measured to determine the potential availability and toxicity of the presence of PTEs. ∑SEM–AVS < 0 were found in 60 % of the samples taken from five different sampling points while ∑SEM– AVS > 0 were observed in 40 % of the samples. Accordingly, the toxicity of PTEs is expected to be limited at 60 % of the samples. The results indicated no mortality in the tested sediment samples. The highest reproduction rate (16.67 ± 1.53) and lowest PTEs content were measured in the Mert River. The results of bioaccumulation factors (BAF) revealed that the most accumulated PTEs were Cu > Zn > Ni > Pb.

Reactive sulfide dynamic models for predicting metal hazardous in sediments of two northern Egyptian Lakes

To track pollution status and bioavailability of Cu, Zn, Cd, Pb, and Ni, the current study's acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) models were compared to previous studies in Edku and Mariut lakes prior to 8 years. Sediment samples were collected in winter and summer 2019 from the two lakes. Metal pollution is higher in the winter than in the summer, according to SEM/AVS models. Metal toxicity is reported to have increased slightly in both lakes. According to risk quotients (RQSEM-PEL and RQSEM-TEL) the two lakes are moderately polluted. The results of the Fe/AVS ratio were in the range of 6.77 to 226.87 and 2.88 to 36.38 μmol/g for Edku and Mariut lakes, respectively. This indicated that [SEM]/[AVS] ratios overestimate the availability of metals. A positive correlation was reported between total organic matter and ∑SEM (r = 0.74 and 0.39 at p < 0.05) in Mariut and Edku lakes, respectively. Multiple-year SEM-AVS studies are recommended.

Comparison of acid volatile sulphide, metal speciation, and diffusive gradients in thin-film measurement for metal toxicity assessment of sediments in Lake Chaohu, China.

The toxicity of heavy metals in sediments is inseparable from their forms in the environment. Traditional sediment toxicity assessment systems, such as total metals, dissolved metals in pore water, metals extracted by the Community Bureau of Reference procedure, and acid volatile sulphide (AVS)-simultaneously extracted metal (SEM), have their own limitations. This study revealed the horizontal and vertical distribution characteristics of AVS and SEM in Lake Chaohu and three typical groups of two-dimensional profiles of diffusive gradients in thin-film (DGT)-labile S(-II) were obtained at representative sampling sites. There was a positive correlation between DGT-labile S(-II) and AVS due to sulphate-reducing bacteria and a negative correlation due to the high sulphate reduction rate induced by high total organic carbon. Moreover, there was no correlation between DGT-labile S(-II) and AVS when bioturbation was dominant in the sediments. To realise the application of DGT measurement in toxicity assessment of heavy metals in sediment through the sandwich relationship of DGT-labile metals vs. metals speciation vs. sediment toxicity assessment, the key relationship of DGT-labile metals vs. metals speciation was explored. DGT-labile Ni showed potential to reveal this relationship.

A Comparison of Sediment Metal Concentrations as Potential Stressors to Resident Benthic Communities in an Agricultural Waterbody

This study was designed to (1) determine the relationship between the sediment concentrations of eight total metals (As, Cd, Cr, Cu, Pb, Hg, Ni, and Zn) and five simultaneously extracted metals (SEM) (Ni, Cu, Zn, Cd, and Pb) with 11 benthic metrics based on a three-year data set including two seasons per year for an agricultural water body (Cache Slough, California), and (2) rank the importance of individual metals within a metal mixture as potential stressors to resident benthic communities. The total arsenic, lead, and cadmium showed the highest number of statistically significant and ecologically meaningful relationships with benthic metrics. The total copper, nickel, zinc, chromium, and mercury were not reported to show any statistically significant and ecologically meaningful relationships with any of the benthic metrics. There were also no statistically significant and ecologically meaningful relationships between the benthic metrics and the simultaneously extracted (bioavailable) metals. Both stress tolerant and stress sensitive benthic metrics were reported to have the best discriminatory power for detecting the adverse effects from metals. Mixed agreement results were reported when comparing statistically significant and ecologically meaningful benthic metric relationships with the threshold effect level (TEL) exceedances for the various metals.

The potential ecological risks and bioavailability of heavy metals in the sediments of Lake Baiyangdian

沉积物是湖泊水体重金属的主要汇集场所，也是湖泊重金属污染研究及整治的重点.本文分析了白洋淀多个淀区沉积物中16种重金属含量水平及垂向分布特征，解析了其中典型有害重金属潜在生态风险，并基于酸可挥发性硫（AVS）及同步可提取金属（SEM）、间隙水溶解态金属、可转化态金属形态分级等研究，对重金属生物可利用性进行了分析.结果表明：沉积物重金属含量均值高低依次为Fe （29630.50 mg/kg）>Ti （3213.07 mg/kg）>Mn （539.44 mg/kg）>Zn （104.01 mg/kg）>V （76.63 mg/kg）>Cr （52.60 mg/kg）>Cu （43.49 mg/kg）>Ni （35.83 mg/kg）>Pb （26.75 mg/kg）>Co （10.32 mg/kg）>As （8.96 mg/kg）>Mo （2.06 mg/kg）>Sb （1.57 mg/kg）>Tl （0.43 mg/kg）>Cd （0.31 mg/kg）>Hg （0.16 mg/kg）；其中，10种重金属在各淀区沉积物中呈现出自北往南逐渐降低的趋势，各金属在不同淀区分布差异性主要由污染输入所致.除北部烧车淀区域外，其余区域重金属潜在生态风险总体处于较低水平.重金属污染主要来源于该区域周边河道，但近10年来污染输入及在沉积物中的富集总体趋于稳定并呈逐渐降低的趋势.入淀污染不仅增加了该区域沉积物中重金属总量，也使得其中可转化态重金属比例较高，大多在30%~90%之间，提升了重金属生物可利用潜力.水生植物等内生性有机质的大量富集导致沉积物还原性较强，AVS含量较高，沉积物中AVS和ΣSEM均值分别为（10.59±6.37）和（2.23±1.53）μmol/g （dw）.Cd、Cu、Ni、Pb、Zn等金属由于高含量还原态硫的固定而生物可利用性较低.然而，As和Hg在这样的高有机质和强还原环境下更容易溶解和释放，是潜在生物可利用性相对较高的金属，在间隙水中的浓度分别达到（17.07±0.23）和（2.39±0.94）μg/L，未来研究及整治中应给予更多关注.;Being the primary sink for heavy metals in lakes, the sediment is the hotspot for the research and remediation of heavy metals in lakes. In the current study, the horizontal and vertical distributions of 16 kinds of heavy metals in the sediment of multiple areas in Lake Baiyangdian were analyzed and based on the concentrations of several typical harmful heavy metals in the sediment, the potential ecological risk was assessed. The bioavailability of heavy metals was further analyzed according to the acid volatile sulfide (AVS), simultaneously extracted metals (SEM), dissolved metals in the pore water, and fractionation of mobile metals. The results showed that the concentrations of heavy metals in the sediment followed the descending order of:Fe (29630.50 mg/kg)>Ti (3213.07 mg/kg)>Mn (539.44 mg/kg)>Zn (104.01 mg/kg)>V (76.63 mg/kg)>Cr (52.60 mg/kg)>Cu (43.49 mg/kg)>Ni (35.83 mg/kg)>Pb (26.75 mg/kg)>Co (10.32 mg/kg)>As (8.96 mg/kg)>Mo (2.06 mg/kg)>Sb (1.57 mg/kg) >Tl (0.43 mg/kg)>Cd (0.31 mg/kg)>Hg (0.16 mg/kg). Among all the heavy metals studied, 10 kinds of the metals in the sediment of the studied areas showed a gradually decreasing trend from north to south of the lake. The variations in the horizontal distribution of metals between different areas were most likely caused by the external pollution input from the north part of the lake. The potential ecological risks of heavy metals in most parts of the lake were generally at low levels except for the Shaochedian area in the north. The inflowing rivers around this area were the main sources of heavy metal pollution. While the pollution input and the accumulation of heavy metals in the sediment have generally stabilized and gradually decreased during the past 10 years, the pollution input not only increased the total amount of heavy metals in the sediment of this area but also led to the high proportion of mobile heavy metals (mostly between 30% and 90%), which increased the bioavailable potential of metals. The massive enrichment of endogenous organic matter from the wither of aquatic plants led to the strong reductive status of the sediment, which thereby resulted in high concentrations of AVS. The average concentrations of AVS and ΣSEM in the sediment of the whole lake were (10.59±6.37) μmol/g(dw) and (2.23±1.53) μmol/g(dw), respectively. Due to the immobilization with a high concentration of sulfides, the bioavailability of Cd, Cu, Ni, Pb, and Zn were generally low. However, As and Hg are much easier to dissolve and release from the sediment under such high organic matter content and strong reducing environment. These two metals had relatively high potential bioavailability with the concentration in the pore water reaching (17.07±0.23)μg/L and (2.39±0.94)μg/L, respectively, which should be given more attention during future research and remediation works.

Sediment toxicity data and excess simultaneously extracted metals from field-collected samples: Comparison to United States Environmental Protection Agency benchmarks.

US Environmental Protection Agency (USEPA) Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Metal Mixtures are based on the principle that metals toxicity to benthic organisms is determined by bioavailable metals concentrations in porewater. One ESB is based on the difference between simultaneously extracted metal (SEM) and acid volatile sulfide (AVS) concentrations in sediment (excess SEM). The excess SEM ESBs include a lower uncertainty bound, below which most samples (95%) are expected to be "nontoxic" (defined as a bioassay mortality rate ≤24%), and an upper uncertainty bound, above which most samples (95%) are expected to be "toxic" (defined as a mortality rate >24%). Samples that fall between the upper and lower bounds are classified as "uncertain." Excess SEM ESBs can, in principle, be improved by normalizing for organic carbon (OC). OC is a binding phase that reduces metals bioavailability. OC normalization should improve the accuracy of bioavailable metal concentration estimates, thus tightening uncertainty bounds. We evaluated field-collected sediments from 13 studies with excess SEM, OC, and bioassay data (n = 740). Use of the OC-normalized excess SEM benchmarks did not improve prediction accuracy. The ESB model predicts OC-normalized excess SEM exceeding the upper benchmark even when toxicity is not observed, because error in the OC normalization model increases at low OC concentrations. To minimize the likelihood of incorrectly identifying nontoxic samples as toxic, we recommend that OC normalization of excess SEM should not be considered for sediments with an OC concentration <1% and is questionable for sediments with an OC concentration of 1%-4%. Additional focused studies are needed to confirm or refine the minimum sediment OC concentrations that are applicable for reducing uncertainty in toxicity predictions due to excess SEM. Integr Environ Assess Manag 2022;18:174-186. © 2021 SETAC.

Metal-sulfide dynamics in a constructed wetland in the Southeastern United States

The Tritium Processing Facility at the Savannah River Site releases effluent containing copper (Cu), zinc (Zn), and lead (Pb) to the H-02 constructed wetland for remediation before the final release. Sediment cores were collected in the wetland cells in both summer and winter. Concentrations of total metals in all sediment layers and acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) in surface sediments were determined. Total metal concentrations suggested most metals removed from surface water were retained by the organic-rich flocculent in the top sediment layers instead of being transported to the deeper sulfide mineral layers. The seasonal difference of AVS and SEM indicated a season-related sulfur cycle and metal removal process in the wetland cells. SEM-Zn was the major contributor to total SEM. Metals accumulating in surface sediments were mainly sequestered in AVS and SEM extractable phases including metal-sulfides and organic matter complexes. The general SEM/AVS ratio was > 1, demonstrating the metals associated with sediments were potentially mobile and/or bioavailable, which becomes a concern for the long-term sustainability of the constructed wetland. The disturbance event in the sediment triggered the release of total metals, which were mostly in particulate form and were not bioavailable. Due to the high levels of reduced ion (Fe) in the sediment, the released particulate metals were likely to form metal-scavenging particulate Fe3+ oxyhydroxides under oxic conditions.

Metal bioavailability during the periodic drying and rewetting process of littoral anoxic sediment

High water-level fluctuations (WLFs) usually lead to the periodic drying and rewetting of littoral sediment, proven to influence the transformation of various sediment contaminants. However, details regarding metal bioavailability variations remain unclear. In this study, oxidation–reduction status transition, metal fraction transformation, and the development of the acid volatile sulfide (AVS) and the simultaneously extracted metals (SEM) were investigated to assess the variations of metal bioavailability in the littoral anoxic sediment during the drying–rewetting process. A series of sediment cores were collected from the littoral area near the mouth of Nanfei River in Lake Chaohu, China, with half of them exposed to dark conditions with an overlying water cover (the control treatment). The other half was dried through the removal of overlying water and then exposed to air and sunlight (the drying treatment). Every 5 days, three of the dried sediment cores were rewetted for 3 days with lake water collected in situ. Various characteristics were analyzed for both the control and drying sediment cores. The drying and rewetting experiment was carried out for 30 days, and the bioavailability of metals was then evaluated thoroughly through data analyses. The periodic drying and rewetting process led to the oxidation of the anoxic sediment with a pronounced increase in oxygen penetration depth and redox potential, and a decrease in AVS concentrations in the drying treatment after 15 days of experimentation. Significant increases in the values of the ratio of SEM and AVS, the difference between SEM and AVS, and the organic carbon normalized difference between ΣSEM and AVS were retrieved for the drying treatment after process completion. The increase of metal bioavailability to aquatic organisms was consequently predicted, with the most significant concerns noted regarding Cd and Pb due to their transformation to less firmly bound fractions. The periodic drying and rewetting process could increase the bioavailability of metals in littoral anoxic sediment. Therefore, this process should be given more attention during future management of water level and remediation of littoral sediment in similar areas.

Sediment quality of the Bohai Sea and the northern Yellow Sea indicated by the results of acid-volatile sulfide and simultaneously extracted metals determinations

The surface sediments from the Bohai Sea (BS) and the northern Yellow Sea (NYS) were analyzed for acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) to assess the sediment quality. The results indicated that >60% of the samples were found to have possible adverse effects on aquatic life in the BS based on the difference between the concentrations of AVS ([AVS]) and SEM ([SEM]), and the corresponding percentage in the NYS was <25%. Nevertheless, there was no indication of adverse effects for all the BS and the NYS samples when the total organic carbon (TOC) concentration was introduced in the sediment quality evaluation with [AVS] and [SEM]. The grain size composition, TOC, water content and pH all had significant influence on the distribution of [SEM] and the [SEM]/[AVS] ratios; while, in contrast, the distribution of [AVS] could be mainly determined by the redox condition of sediment.

Application of diffusive gradients in thin films (DGT) and simultaneously extracted metals (SEM) for evaluating bioavailability of metal contaminants in the sediments of Taihu Lake, China

The toxicities of heavy metals in sediments are related to their bioavailability, which is critical for deriving reliable sediment quality guidelines. To evaluate the bioavailability of the metals (Cd, Cu, Ni, Pb and Zn), sediments were collected from Taihu Lake, one of the largest and most important freshwater lakes in China. Concentrations of simultaneously extracted metals (1-M HCl extraction, CSEM) in the sediments, metals released from sediment to pore waters and accumulated by diffusive gradients in thin films (DGT, CDGT), and dissolved metals in the overlying water (COLW) were measured separately. Sediment toxicity was assessed with tubificids (Monopylephorus limosus) and chironomids (Chironomus kiiensis and Chironomus tentans). Significant relationships existed between the total metal concentrations and CSEM, CDGT, and COLW measurements (r2 = 0.43–0.95, n = 27, p < 0.001), with stronger relationships with CSEM (r2 = 0.91–0.95) than CDGT (r2 = 0.56–0.85) and COLW (r2 = 0.43–0.71). Risk quotients were derived by dividing CSEM by sediment quality guideline values (SQGVs), and by dividing both CDGT and COLW by water quality criteria (WQC). Toxicity of the sediments to the three species was better explained by the CSEM-based risk quotient than those derived from CDGT and COLW. The study indicated that DGT piston probes deployed face down in sediments did not accumulate metals in proportion to the bioavailable metal fraction that caused toxicity to these freshwater benthic organisms, and that single measurements of metals in overlying waters are not adequate for predicting risks of toxicity from sediments. The measurement of CSEM was determined to be effective for assessing the risk posed by the metals in the Taihu Lake sediments, but offered limited improvement over measurement of total metal concentrations.

Integrated assessment of sediment quality in a coastal lagoon (Maluan Bay, China) based on AVS-SEM and multivariate statistical analysis

Total metal concentrations and acid-volatile sulfide (AVS) measurements coupled with simultaneously extracted metals (SEM) were determined in heterogeneous sediments from Maluan Bay, China. Zn was the predominant component of SEM, while Cd was the least. In sediment cores, AVS increased with sediment depth, followed by a decrease with large variation, while SEM fluctuated. Multiple empirical sediment quality guidelines (SQGs) and equilibrium partitioning (EqP) approaches were applied to assess the contamination degree, sediment quality and potential risks associated with bioavailable metals, indicating that not all sediments with [SEM]-[AVS] > 0 were capable of causing toxicity because TOC is also an important metal-binding phase. In order to screen out the physicochemical variability and the complexity and large variance of datasets, multivariate statistical techniques were utilized to comprehensively reveal pollution status by visualized factor scores. Collectively, this study favors the integrative utilization of multifarious methods to scientifically diagnose the pollution characterization for sustainable coastal management.

An evaluation on the bioavailability of heavy metals in the sediments from a restored mangrove forest in the Jinjiang Estuary, Fujian, China

The bioavailability of heavy metals in restored mangrove wetland sediments at the Jinjiang Estuary was assessed through acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM). The results indicated that the SEM distributions were more even than the AVS in the restored regions, and the AVS acted as an important carrier for SEM. SEM-Zn was a major part (61.4–70.6%) of ∑SEM, whereas the most toxic metal, Cd, accounted for approximately 0.2%. The possible adverse effects increased in the surface and subsurface sediments (0–20 cm), with no potential bioavailability in deeper layers. This was probably due to the higher AVSs binding to heavy metal ions in the restored regions compared to the mudflat (control group). The conclusions were also similar when taking TOC concentrations into account. Mangrove wetland restoration has significant effects on the bioavailability of heavy metals in sediments. According to the thresholds for metal toxicity on benthic organisms in sediments, Pb, Cu and Ni had potential adverse effects on benthic organisms in this restored wetland.

An alternative approach to bioaccumulation assessment of methyl-Hg, total-Hg, Cd, Pb, Zn in bivalve Anomalocardia brasiliana from Rio de Janeiro bays

We present an alternative approach for establishing in situ bioaccumulation assessment of methyl-Hg (MeHg), total-Hg, Cd, Pb and Zn in bivalve Anomalocardia brasiliana from four bays of Rio de Janeiro presenting varying degrees of eutrophication, acid volatile sulfides (2–55 μmol g−1), simultaneously extracted metals (SEM) and total metals (TM) in sediments. Using metal concentrations of composite samples from three size classes of bivalve and their incorporation rates (IR = metal concentration / total length), which depend on exposure time, we calculated asymptotic IR and respective consequent metal concentrations. Both IR and the metal concentration presented inverse relationships with total length (excepting MeHg) and bay contamination. Lead and zinc concentrations were above Brazilian legal criteria in the most anoxic and contaminated bay, suggesting significant metal bioavailability (SEM/TM between 8% and 63%).

Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] - [AVS])/foc, and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

How useful are geochemical and mineralogical indicators in assessing trace metal contamination and bioavailability in a post-restoration Mediterranean lagoon?

Tunis's Lake North (LNT), located on the Mediterranean Sea, and Tunisia's most important lagoon due to its economic value and its strategic position within the city, has recently undergone a vast sanitation project. To study the lagoon's level of metal pollution, three sediment cores were taken and the sediments were analyzed for trace and major elements, acid volatile sulfides (AVS), total organic carbon (TOC), and minerals. Results showed that TOC concentrations (0.2-3.1%) decreased following the lagoon's restoration. In addition, in comparison to historical data, concentrations of Cu (16-69.5μgg-1), Zn (60.6-191.4μgg-1), and Pb (13-100.9μgg-1) also decreased. Enrichment factor calculation with respect to the crust and local background showed that the sediment had long been contaminated by human pollution and especially by Pb, Zn, and Cu. The AVS to simultaneously extracted metal (SEM) ratio revealed values generally less than 1 indicating no sediment toxicity risks. Statistics revealed a detrital origin for certain metals and a diagenetic origin for FeS2 and carbonate minerals.

Recovery of ostracod with known ages in differently textured sediments and comparison of toxicity of heavily contaminated sediments with ostracod Heterocypris incongruens and amphipod Hyalella azteca

The recovery of 1-, 4-, 6,-, and 8-d-old ostracods (Heterocypris incongruens) from sediments with different texture has been evaluated. The recovery of ostracods at all ages has been in agreement with the acceptability criterion of 80% of survival for sediment tests. The recovery of ostracods has turned out to be equal to or more than 80% for sand and silt sediments, respectively. The comparison of survival rates between ostracods and amphipods has shown good convergence in the tests of heavily contaminated sediments (R2=0.75, p<0.05). The sediment quality criteria (TEC) have been exceeded mostly for total petroleum hydrocarbons (100% samples), Cr (100%), Ni (87%), Cu (87%), Pb (47%), and Cd (53%). The content of acid volatile sulfides (AVS) has been significantly higher than that of simultaneously extracted metals (SEM). The obtained results have indicated that, metals (Cu, Zn, Cd, Ni, and Pb) are non-bioavailable. Only one sample has exceeded TEC for PAHs (dibenz[a,h]anthracene). It was observed that, no significant correlation between the effect of toxicity and the chemical content.

An Analysis of Multiple Stressors on Resident Benthic Communities in a California Agricultural Stream

This 3-year study (2015-2017) was designed to characterize benthic communities (macroinvertebrates) and physical habitat in an agriculturally dominated waterbody in the Central Coast area of California (Santa Maria River). Benthic communities as represented by various metrics that represent richness, composition, tolerance/intolerance and trophic measures were used as response variables for the various stressors described below. Concurrent water quality evaluations, physical sediment parameters (grain size and total organic carbon [TOC]), pyrethroids, bulk metals—including simultaneously extracted metals (SEM) and acid volatile sulfides (AVS) ratios—and nutrients were measured. The relationship of various benthic metrics to physical habitat metrics, pyrethroids, metals, nutrients and sediment characteristics was evaluated for the 3-year data set. Total physical habitat scores in this watershed were considered to be poor. Samples collected for various sediment chemistry measurements were from depositional areas (fine grain areas primarily silt and clay) where hydrophobic chemicals such as pyrethroids could be found if sources exist. Dominant benthic taxa collected were generally considered to be tolerant to moderately tolerant of environmental stressors and rated as impaired based on a benthic index. Potentially toxic sediment concentrations of arsenic, cadmium and nickel were reported at various sites based on a comparison with existing threshold effect levels. Pyrethroid concentrations interpreted by using a highly protective toxics units approach with a laboratory sensitive taxon ( Hyalella) suggested potential toxicity at various sites. Nutrient concentrations could not be interpreted within the context of potential impairment because the State of California has not developed nutrient criteria. The results of the stepwise linear regression models comparing benthic metrics with all environmental variables showed that TOC was the most important variable shaping the benthic communities. In contrast, pyrethroids, metals and physical habitat were not shown to be significant factors shaping benthic communities. The summary multivariate canonical correlation analysis indicated that less stressed, more diverse benthic communities tended to be associated more with TOC-rich finer sediments and lower concentrations of phosphorous-based nutrients, and more stressed, less diverse benthic communities tended to be associated with less organically rich, somewhat less fine sediments and higher phosphorous concentrations.

Risk assessment of heavy metals in Vembanad Lake sediments (south-west coast of India), based on acid-volatile sulfide (AVS)-simultaneously extracted metal (SEM) approach.

Contamination of estuarine system due to heavy metals is a severe issue in tropical countries, especially in India. For the evaluation of the risk due to heavy metals, the current study assessed spatial and temporal variation of acid-volatile sulfide (AVS), simultaneously extracted metal (SEM), and total metal concentration as toxicity indicator of aquatic sediments in Vembanad Lake System (VLS), India. Surface sediment samples collected from 12 locations from the northern portion of VLS for 4years during different seasons. The results suggest, in post-monsoon season, 91% of the sampling locations possessed high bioavailability of metals and results in toxicity to aquatic biota. The average seasonal distribution of SEM during the period of observations was in the order post-monsoon > pre-monsoon > monsoon (1.76 ± 2.00 > 1.35 ± 0.60 > 0.80 ± 0.54μmol/g). The concentration of individual metals on ∑SEM are in the order SEM Zn > SEM Cu> SEM Cd ≈ SEM Pb > SEM Hg. Considering annual ΣSEM/AVS ratio, 83% of the sites cross the critical value of 'One,' reveals that active sulfide phase of the sediment for fixing the metals is saturated. The molar ratio (differences between SEM and AVS) and its normalized organic carbon ratio reveals that in the post-monsoon season, about 42% of the sites are in the category of adverse effects are possible. The study suggests the toxicity and mobility of the metals largely depend on the available AVS, and the current situation may pose harm to benthic organisms.

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

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