Acid-volatile sulfide and simultaneously extracted metals in surface sediments of the southwestern coastal Laizhou Bay, Bohai Sea: concentrations, spatial distributions and the indication of heavy metal pollution status

Equilibrium partitioning approach for metal toxicity assessment in tropical estuarine sediment of Bandon Bay, Thailand

An equilibrium partitioning approach (EqPA) was employed to evaluate the metal toxicity and define sediment quality guidelines (SQGs) for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), and mercury (Hg) in the cockle cultivated areas located in Bandon Bay, Thailand. An assessment of metal toxicity using the [∑SEM]-[AVS] and [∑SEM]-[AVS]/foc models indicated no adverse effect on benthic organisms. The normalized total metal concentrations in this area were below the established SQG values for As, Cd, Cu, Ni, Pb, Zn, and Hg, namely respectively 21.3, 0.8, 84.6, 36.0, 34.6, 440.9 mg/kg dry weight, and 49.3 μg/kg dry weight on sand and calcium carbonate free with 1 % total organic carbon basis, suggesting low metal toxicity. This study provides locality adapted SQG values for supporting sediment quality management specifically in Bandon Bay, potentially serving as a model for other coastal areas.

Distribution of acid-volatile sulfides and simultaneously extracted metals in Guanabara Bay: combination of anthropogenic, sedimentological, and geochemical processes

Coastal sedimentary systems are affected by continental and marine metal pollutant inputs associated with different hydrodynamic characteristics and geochemical processes. These include the formation of acid-volatile sulfides (AVS) within sediments, which affects metal bioavailability and associated aquatic biota toxicity risks. Physicochemical changes in these environments in the face of extreme natural or man-made environmental influences can dramatically alter metal bioavailability and toxicity through metal binding and immobilization as insoluble sulfides. Surface sediments from Guanabara Bay, river mouths, and two mangrove areas were collected, and AVS and simultaneously extracted metals Cd, Cu, Fe, Mn, Ni, Pb, and Zn and ΣSEM were determined to assess sediment quality. A severe eutrophication history favored AVS concentrations exceeding or close to the sum-SEM concentrations, demonstrating that AVS play an important role in making trace metals unavailable for assimilation by living organisms, mitigating the risks of contamination for the local biota. This eutrophication-driven sulfide accumulation may attenuate the sediment toxicity in sites heavily polluted by metals, while some fewer eutrophic sites became more exposed to metals in excess to AVS.

Application of high-resolution techniques in the assessment of the mobility of Cr, Mo, and W at the sediment-water interface of Nansi Lake, China

There are few studies on the simultaneous behavior of chromium (Cr), molybdenum (Mo), and tungsten (W) belonging to group VIB of the periodic table. Herein, based on high-resolution dialysis (HR-Peeper) and diffusive gradients in thin films (DGT) technology, the vertical distribution characteristics of DGT-labile and soluble Cr, Mo, and W in two lakes of Nansi Lake (Weishan Lake and Dushan Lake) were analyzed. In addition, the net diffusion fluxes and R-value (CDGT/Csol) were used to evaluate the mobility and release risk of metals at the sediment-water interface. The results showed that the DGT-labile concentrations of the three metal elements (Cr, Mo, and W) in Weishan Lake were higher than those in Dushan Lake, both in overlying water and sediment. This is mainly due to the dredging of the Dushan Lake area, which can permanently remove the polluted sediment in the lake. Meanwhile, the exogenous input is relatively high near the tourist area of Weishan Island. The net diffusion fluxes indicate that the W has a potential release risk of diffusion to the overlying water in Dushan Lake. The release of Cr, Mo, and W is thought to be related to the reductive dissolution of Fe/Mn (hydr)oxides based on Pearson correlation coefficients. The R-values of Cr and W indicate that Cr and W belong to the partial continuity case. The R-value of Mo was lower than the minimum value, meaning that Mo belongs to the single diffusion type and it is difficult for Mo sediments to supply pore water.

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 (RQ_SEM-PEL and RQ_SEM-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.

Developing ecological risk assessment of metals released from sediment based on sediment quality guidelines linking with the properties: A case study for Kaohsiung Harbor

This study aimed to introduce sediment properties (total organic carbon (TOC), acid-volatile sulfides (AVS), particle size distribution) into sediment quality guideline-based risk quotients to assess the potential toxicity of metals (Ni, Cu, Zn, Cr, Cd, and Pb) released from sediments. Sediment was collected at three times points in 20 sampling sites in Kaohsiung Harbor. The Microtox® toxicity test was used to assess the sediment toxicity and the relationship between sediment toxicity and risk quotient estimated based on the metal concentration was constructed. To improve the toxicity prediction and modify the risk quotient according to the sediment properties, stepwise multiple linear regression (MLR) models that have been tested over wide ranges of TOC, AVS, and particle size distribution to determine the key sediment properties. Common multimetal indices, including the pollution load index, modified degree of contamination index, Nemerow pollution index, potential ecological risk index, and total toxic risk index, were compared with sediment toxicity to evaluate the degrees of correlation. By modifying the relationship between metal toxicity and the risk quotient by including TOC and AVS, the prediction showed that sediments in Kaohsiung Harbor were generally of slight acute toxicity to acute toxicity to organisms, with sampling sites near an industrial zone showing a higher probability of high acute toxicity. In particular, the acute risk of adverse effects on aquatic organisms from sediments in the Salt River estuary was significantly higher than that at other sites, which was consistent with the results of assessment based on the multimetal indices. This study suggests that the MLR-based approach may facilitate the adoption of updated site-specific metals standards that more accurately account for the parameters affecting metal bioavailability than metal concentration standard alone.

Magnetic properties of the surface sediments in the Yellow River Estuary and Laizhou Bay, Bohai Sea, China: Implications for monitoring heavy metals

The Yellow River Estuary (YRE) and adjacent Laizhou Bay (LB) encounter eco-environmental risks caused by heavy metals (HMs) pollution. Here magnetic measurements were performed on 239 surface sediment samples from the YRE and LB to establish a rapid and effective method for detecting HMs. Magnetite, maghemite, and hematite coexist in the sediments. The distributions of magnetic minerals are dominated by sediment sources (Yellow River in northern and western LB, and rivers in southern and eastern coastal LB), and the anticlockwise water current. Compared to the background values, Cd content is enriched for all samples, while Co, Cr, Ni, Cu, Zn, and Pb contents are lower for most samples. The low pollution load indexes (PLI) of HMs (< 1-1.56) indicate the unpolluted to moderately polluted status, while the muddy area is the most polluted. The principal component analysis indicates that Co, Cr, Ni, Cu, and Zn are mainly from natural weathering substances, while Cd and Pb are anthropogenic. Contents of fine-grained sediments and magnetic particles are positively correlated to Co, Ni, Cu, Zn, and PLI. The high-risk Co, Ni, Cu, and Zn regions can be quickly delineated with the frequency-dependent susceptibility.

Use of Multivariate Statistical Techniques to Study Spatial Variability and Sources Apportionment of Pollution in Rivers Flowing into the Laizhou Bay in Dongying District

Spatial variability and source apportionment of river pollution flowing into the Bohai Sea are of great significance to the pollution liability and development of control strategies to reduce the terrestrial discharge of pollution in the ocean. In this study, ten water quality variables from 14 monitoring sites in rivers flowing into Laizhou Bay were obtained to investigate the spatial variation and pollution sources in Dongying District from 2018–2019. The survey area was divided into a low pollution (LP) zone and a high pollution (HP) zone by cluster analysis based on ten indicators. Principle component analysis/factor analysis with a geographic information system was performed to identify the four main pollution sources in the survey area. Compared with the positive matrix factorization model, the absolute principal component score-multiple linear regression (APCS-MLR) model was more appropriate for the source apportionment of pollution in the surface water of Dongying District. The point source pollution of domestic sewage (23.6%) was the most crucial pollution source of water in the LP zone, followed by non-point pollution from agricultural activity (16.4%). The contribution rate in the HP zone analyzed by the APCS-MLR model followed a decreasing order: point source pollution from domestic sewage (28.5%) > non-point pollution source of overland runoff (14.8%) > point source pollution of hybrid wastewater (12.4%) > point source pollution from industries sewage (10.6%). Therefore, the spatial distribution and sources of pollution in the investigated area should be considered while developing control measures to reduce the discharge of pollution to Laizhou Bay.

Tissue distribution and bioaccumulation of organophosphate esters in wild marine fish from Laizhou Bay, North China: Implications of human exposure via fish consumption

Despite organophosphate esters (OPEs) are ubiquitous in the environment, limited information is available about their tissue-specific accumulation potential in marine fish and exposure risks. Ten fish species from the coastal area of Laizhou Bay, North China, were sampled and analyzed to investigate tissue levels, bioaccumulation, and human exposure risks of 20 OPEs. Seventeen OPEs were detected in fish tissues with total concentration ranging from 6.6-107 ng/g dry weight. The average log bioaccumulation factor (BAF) values of OPEs ranged from 2.8 to 4.4 in livers, 2.3-3.8 in muscles, 2.5-3.9 in gills, and 2.8-4.4 in kidneys. The log BAF values of OPEs significantly increased with increasing their log K_OW values (r = 0.55-0.63, p < 0.001). The estimated daily intake of OPEs ranged from 1.7-12.0 and 3.1-22.1 ng/kg bw/d for rural and urban residents, respectively. The hazard quotients of OPEs were in the range of 4 × 10 ^-5 to 6.7 × 10 ^-4 and 7 × 10 ^-5 to 1.2 × 10 ^-3 for rural and urban residents, respectively. Results showed that the human health risks of OPEs associated with fish consumption is at low level.

Effects of soil particle size on the adsorption, distribution, and migration behaviors of heavy metal(loid)s in soil: a review

In recent years, toxic pollution from heavy metal(loid)s in soil has become a severe environmental problem worldwide. The migration and transformation of heavy metal(loid)s in soil have become hot topics in the field of environmental research. Soil particle size plays an important role in influencing the environmental behavior of heavy metal(loid)s in soil. This review collates and synthesizes the research on the adsorption, distribution, and migration of heavy metal(loid)s in soil particles. There is no unified method for soil particle separation, since the purposes of different studies are different. Regardless of adsorption or distribution characteristics, fine soil particles generally exhibit a higher capacity to combine heavy metal(loid)s; however, certain studies have also observed a contrary phenomenon, according to which heavy metal(loid)s were more enriched in coarser particles. The adsorption and distribution of heavy metal(loid)s in soil particles were essentially determined by the physicochemical properties of the soil particles. Land use obviously affected the distribution of heavy metal(loid)s in the soil particles. Organic matter had an important influence on the distribution and availability of heavy metal(loid)s in agricultural and forest soils, while for urban soils and sediments, clay minerals or metal (hydr)oxides may play the dominant role. Preferential surface migration of fine particles during erosion processes did not always lead to the enrichment of heavy metal(loid)s in the lost soil. Further research should be conducted to explore the relationships among the soil aggregates, organic matter, heavy metal(loid)s, and soil microorganisms; the association between the distribution and availability of heavy metal(loid)s and the properties of soil particles; and the migration patterns of heavy metal(loid)s in soil particles at different scales.

Spatial distribution of phthalate acid esters in sediments of the Laizhou Bay and its relationship with anthropogenic activities and geochemical variables

Spatial distribution and ecological risks of phthalate acid esters (PAEs) in sediments of the Laizhou Bay were investigated, and the relationships of PAEs with human activities and geochemical variables were studied in this work. Thirteen detectable PAEs were widespread occurrence, and the total PAE concentrations ranged from 813.1 to 11,975.6 μg/kg dry weight in sediments of the Laizhou Bay. Di-(2-ethylhexyl) phthalate (DEHP) and di-butyl phthalate (DBP) were predominant and accounted for 51.9% of ΣPAEs. The major sources of PAEs with their characteristic PAE congeners or composition could be classified as riverine runoff from catchments of the Yellow River and the rivers Xiaoqing & Zhimai, and direct discharge from the west coast and Binhai Zone, according to continuous PAE spatial distribution patterns generated by GIS techniques. The concentrations of most PAEs gradually decreased from west inshore to east offshore in inverted S shapes, which was consistent with the tide field of the Laizhou Bay. There are negative correlations between sediment depth and all PAEs, and nine PAEs exhibited negative correlations with salinity using Pearson correlation analysis. Depth and salinity exerted negative influence on PAEs (contributions of 55.8% and 32.0%, respectively) according to redundancy analysis. The DBP concentrations of 15.1% sites exceeded the ERLs and only one site had the DEHP concentration exceeded environmental risk limits. The DBP risk quotient values of 11.3% (for algae), 3.8% (for crustaceans) and 43.4% (for fish) sites exceeded 1, and most of these sites are near to four major sources. These results might benefit the implementation of effective environmental management and remediation practices.

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.

Bioaccumulation and Trophic Transfer of Emerging Organophosphate Flame Retardants in the Marine Food Webs of Laizhou Bay, North China

Despite the increase in production, usage, and discharge of organophosphate flame retardants (OPFRs), little information is available about their bioaccumulation and trophic transfer in the marine food web. In this study, seawater, sediment, and marine species (10 fish and 9 invertebrate species) collected from Laizhou Bay, North China, were analyzed to investigate the levels, bioaccumulation, and biomagnification of OPFRs in a marine food web. Of 20 OPFRs screened for, 17 were quantifiable in seawater, sediment, and organisms. The ∑OPFRs concentrations ranged from 0.2 to 28.4 ng/L in seawater, 0.1-96.9 ng/g dry weight in sediment, and 21.1-3510 ng/g lipid weight in organisms. Benthic fish accumulated more OPFRs than pelagic fish and invertebrates. A linear and significant increase of bioaccumulation factors with increasing lipophilicity of OPFRs was observed (R² = 0.63, p < 0.05), and the biota-sediment accumulation factors increased with hydrophobicity up to log K_OW = 4.59 and then decreased with increase in log K_OW. Trophic magnification factors of OPFRs ranged from 1.06 to 2.52, indicating biomagnification potential of OPFRs in a marine food web. This study provides important insight into the biomagnification potential of OPFRs and suggests further investigation on this group of chemicals.

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.

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.

Nutrient distribution and structure affect the behavior and speciation of arsenic in coastal waters: A case study in southwestern coast of the Laizhou Bay, China

The effects of nutrient distribution and structure on the behavior and speciation of dissolved inorganic arsenic (DIAs) in coastal waters were analyzed based on the data of 48 surface water samples collected in the southwestern coast of Laizhou Bay and its adjacent rivers (SWLZB). The concentration of DIAs in the SWLZB ranged from 0.016 to 0.099 μmol l^-1 and generally decreased from west to south. The inshore waters exhibited higher DIAs level than the open ocean. The As⁵⁺/As³⁺ ratio was significantly positively correlated with the concentration of TDN, NO₃-N, PO₄-P, DSi, Chl-a and DO. The concentration of DIAs was strongly correlated with the concentration of PO₄-P and DSi, suggesting that adsorption/desorption was an important process for regulating the total DIAs concentration. The results indicated that the distribution of nutrients might well be an important environmental factor affecting the speciation and behavior of DIAs in surface water of the SWLZB.

Distribution and Risk Assessment of Heavy Metals in Sediment from Bohai Bay, China

Sediment core and porewater samples from the Western coastal tidal flat in Bohai Bay, China, were collected for meals and physical-chemical properties analysis. The vertical distribution characteristics of eight metals along the core was investigated based on 137Cs and 210Pb radionuclide dating. The chemical fractions of six metals (Cu, Pb, Zn, Ni, Mn and Cd) were also measured based on the modified European Community Bureau of Reference (BCR) sequential extraction procedures to better understand the mobility and bioavailability of these metals in the sediment. In addition, geoaccumulation index (Igeo) and risk assessment code (RAC) are used to assess risk status of these metals in the environment. 210Pb measurement indicates a sedimentation rate of about −1.87 cm∙year−1. The metals Cu, Zn, Pb and Ni show similar vertical distributions throughout the core, while Mn and Cd show different distribution patterns. Ni, Cu, Pb and Zn are strongly associated with the residual fraction while Mn and Cd are dominant in the acid-soluble fraction. According to the estimated diffusive fluxes, the Zn ions were the most mobilized, followed by Cu, Ni, Pb, and to a lesser extent Cd. The result of Igeo shows that Ni in sediments does not reflect any pollution, and Cu, Pb and Zn are in a level from unpolluted to modest polluted throughout the core. Mn and Cd have obvious anthropogenic sources. Based on the RAC, Cd and Mn pose a high to very high risk to the local environment, respectively, due to the significant percentage of exchangeable fraction. Clay content is significantly positively correlated with Ni, Cu, Al and Fe, and Cu, Pb, Zn and Ni might originate from the same sources or be influenced by similar geochemical processes. River runoff and atmospheric deposition are important sources for heavy metals, and since 1998, domestic sewage discharge might have had an important influence on the source of heavy metals (except for Cd and Mn).

Interactive effects of single, binary and trinary trace metals (lead, zinc and copper) on the physiological responses of Kandelia obovata seedlings

Heavy metals are considered important environmental contaminants, and their mixture toxicity on plants has complex mutual interactions. The interactive effects of heavy metals on growth, photosynthetic parameters, lipid peroxidation and compatible osmolytes were studied in Kandelia obovata grown for 5 months in sediment treated with combinations of lead (Pb), zinc (Zn) and copper (Cu). The results showed no significant reduction of biomass under heavy metal stresses, except for decreased root biomass under higher Pb + Cu treatment, indicating high tolerance of K. obovata to heavy metal stress. Only the photosynthetic parameters, including net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (T_r), decreased with increasing concentration of treatments (except for Pb + Cu and Pb + Zn + Cu). Trinary treatment (Pb + Zn + Cu) increased biomass and the photosynthetic parameters when compared to the external addition of binary metals. In the roots, biomass and soluble sugar content were lower under binary than trinary treatments, indicating that the combination of Zn and Cu exhibited improved effects of alleviating toxicity than each of them alone in Pb-containing combined treatments. In the leaves, Zn-containing combined treatments significantly decreased malondialdehyde (MDA), soluble sugar and proline content in low concentration, while Pb + Cu treatments significantly increased these parameters (P < 0.05). The correlation analysis showed that leaf MDA and proline content were negatively correlated with Zn concentration (P < 0.05). Zn could alleviate the effects of combined heavy metal stress, and Pb + Cu treatment showed synergistic effects in leaves. The positive correlations between MDA content and the osmotic parameters showed that osmotic stress and lipid membranes oxidation exist simultaneously under multiple heavy metal stresses. Therefore, biomass, T_r, leaf MDA, leaf proline content and soluble sugar content could indicate metal mixture toxicity to mangrove seedlings.

Metals in mangrove ecosystems and associated biota: A global perspective

Mangrove forests prevalent along the intertidal regions of tropical and sub-tropical coastlines are inimitable and dynamic ecosystems. They protect and stabilize coastal areas from deleterious consequences of natural disasters such as hurricanes and tsunamis. Although there are reviews on ecological aspects, industrial uses of mangrove-associated microorganisms and occurrence of pollutants in a region-specific manner, there is no exclusive review detailing the incidence of metals in mangrove sediments and associated biota in these ecosystems on a global level. In this review, mangrove forests have been classified in a continent-wise manner. Most of the investigations detail the distribution of metals such as zinc, chromium, arsenic, copper, cobalt, manganese, nickel, lead and mercury although in some cases levels of vanadium, strontium, zirconium and uranium have also been studied. Seasonal, tidal, marine, riverine, and terrestrial components are seen to influence occurrence, speciation, bioavailability and fate of metals in these ecosystems. In most of the cases, associated plants and animals also accumulate metals to different extents and are of ecotoxicological relevance. Levels of metals vary in a region specific manner and there is disparity in the pollution status of different mangrove areas. Protecting these vulnerable ecosystems from metal pollutants is important from environmental safety point of view.

Calculation of Thallium's toxicity coefficient in the evaluation of potential ecological risk index: A case study

As a common pollutive metal element, Tl is very biotoxic. The potential ecological risk index (RI) proposed by Håkanson is one of the commonest methods for evaluation of ecological risk of a metal in sedimentary environment of a water body. According to the calculation principle proposed by Håkanson, the toxicity coefficient of Tl was calculated, and determined as 10 in this paper. In addition, the environmental risk of Tl in the surface sediment of the Beijing-Hangzhou Grand Canal (Zaozhuang Section) was evaluated by RI method, enrichment factor method, etc. The South-to-North Water Diversion Project which benefits four billion people is the largest inter-basin water transfer project in China. The Zaozhuang Section is a significant water conveyance line of this project. We found that the Tl concentrations were 0.46-0.70 μg g^-1 with the mean value of 0.61 μg g^-1 and were higher than the local background value. The highest contents of Tl occurred in the middle of Zaozhuang section and Tai'erzhuang District, but the enrichment degree of it was much higher in the entrance of Nansihu Lake. The grain size and Al oxides/hydroxides were main factors which controlled the distribution of Tl. Analysis of enrichment factors indicated that Tl in sediments possessed obvious source of human activities which were mainly from combustion of fossil fuels such as coal and mining of mineral resources. As a whole, however, the research region has low Tl content, so Tl has a small probability of environmental pollution.

Presence of arsenic, mercury and vanadium in aquatic organisms of Laizhou Bay and their potential health risk

This study aims at describing and interpreting concentrations of arsenic (As), mercury (Hg) and vanadium (V) in seven species of fish, three species of shellfish, one species of crab and two species of shrimp from the typical estuary-bay ecosystem. Arsenic, Hg and V differed among species, and the highest As, Hg and V were observed in shellfish. The stable nitrogen (δ¹⁵N) and carbon (δ¹³C) isotopes were determined to investigate the trophic interactions between fluctuating environment and aquatic species. Arsenic concentrations in samples were found negatively correlated with δ¹⁵N, implying biodilution effect of As through the food web, while Hg concentrations in samples were positively correlated with δ¹⁵N, indicating their biomagnification effect. The estimated daily intake values of Hg and V in this study were all below the oral reference dose. However, elevated As intakes of some aquatic organisms suggested a potential risk for frequent consumers.

Fast assessment of bioaccessible metallic contamination in marine sediments

A fast (16min) procedure to assess the bioaccessible metallic fraction of Cd, Cr, Cu, Ni, Pb and Zn simultaneously extracted (SEM) from marine sediments plus an indirect approach to determine acid volatile sulfides (AVS) are presented. For the extraction process magnetic agitation was compared with ultrasonic stirring (using a bath and a probe), and several stirring times were assayed. The proposed SEM procedure uses an ultrasonic probe and 1mL of HCl. It dramatically minimizes the turnaround time and the residues. AVS were evaluated as the difference between the amounts of sulphur in the solid residue after the extraction and total sulphur in the original sample. These procedures are fast, easy to implement and cost-effective to assess the potential risk posed by metals in marine sediments. They were tested using several CRMs and applied to sediments from two Galician Rias (NW Spain); their SEM-AVS differences indicated no biological risk.

Impact of pyrene and cadmium co-contamination on prokaryotic community in coastal sediment microcosms

Acute ecological impacts of co-contamination of polycyclic aromatic hydrocarbons (PAHs) and heavy metals on diversity and composition of coastal benthic prokaryotes were unclear. We took pyrene (Pyr) and cadmium (Cd) as the representatives and mimicked an eight-week exposure of moderate and high levels of Pyr, Cd and their mixtures. 16S rRNA amplicon sequencing was used to investigate interaction of the contaminants in temporal succession of prokaryotes. Generally, concentrations of Pyr and HCl-extractable Cd in the sediments were stable over time. Effects and interaction of Pyr and Cd on prokaryotic α-diversity were temporally- and dose-dependent with a decreasing trend in richness and Shannon index under various contamination regimes, particularly in the single-Cd contaminated groups at the early stage. Temporal variability and Pyr-induced pattern in prokaryotic composition were observed. However, Pyr and Cd showed a persistent interaction in prokaryotic composition after 7 days, altering successional trajectories of communities. The communities under Pyr contamination regardless of Cd could be at a developing stage for an active PAH-degrading community with appearance of a pioneer Cycloclasticus phylotype, persistently showing a strong correlation with Pyr level. The associations of phylotypes and Cd level were short-lived and weak, corresponding to the overall resistance of prokaryotic composition to Cd. In the high-throughput sequencing era, using microcosm experiment, we renewed the knowledge about how prokaryotes vary in terms of α-diversity, composition and specific taxa in response to co-contamination of model contaminants at a temporal scale.

Metals in the Scheldt estuary: From environmental concentrations to bioaccumulation

To investigate the relationship between metal concentrations in abiotic compartments and in aquatic species, sediment, suspended matter and several aquatic species (Polychaeta, Oligochaeta, four crustacean species, three mollusc species and eight fish species) were collected during three seasons at six locations along the Scheldt estuary (the Netherlands-Belgium) and analysed on their metal content (Ag, Cd, Co, Cr, Cu, Ni, Pb, Zn and the metalloid As). Sediment and biota tissue concentrations were significantly influenced by sampling location, but not by season. Measurements of Acid Volatile Sulphides (AVS) concentrations in relation to Simultaneously Extracted Metals (SEM) in the sediment suggested that not all metals in the sediment will be bound to sulphides and some metals might be bioavailable. For all metals but zinc, highest concentrations were measured in invertebrate species; Ag and Ni in periwinkle, Cr, Co and Pb in Oligochaete worms and As, Cd and Cu in crabs and shrimp. Highest concentrations of Zn were measured in the kidney of European smelt. In fish, for most of the metals, the concentrations were highest in liver or kidney and lowest in muscle. For Zn however, highest concentrations were measured in the kidney of European smelt. For less than half of the metals significant correlations between sediment metal concentrations and bioaccumulated concentrations were found (liver/hepatopancreas or whole organism). To calculate the possible human health risk by consumption, average and maximum metal concentrations in the muscle tissues were compared to the minimum risk levels (MRLs). Concentrations of As led to the highest risk potential for all consumable species. Cadmium and Cu posed only a risk when consuming the highest contaminated shrimp and shore crabs. Consuming blue mussel could result in a risk for the metals As, Cd and Cr.

Spatial variation of microbial communities in sediments along the environmental gradients from Xiaoqing River to Laizhou Bay

The Laizhou Bay is famous for aquaculture, but has been subject to eutrophication and contamination for years. High concentrations of nutrients from the Xiaoqing River are considered as the main cause for significant eutrophication in the west of Laizhou Bay. Here we present results of the research on sedimentary microbial assemblages along this spatial gradient between riverine and marine environments by high-throughput sequencing. The predominant phyla/classes of bacteria and fungi clustered the samples into two distinct provinces, while discriminant taxa of each province were strongly associated with spatial factors and inorganic nitrogen. Spatial variation of bacterial communities was mainly related with the distribution of phosphates, suggesting a phosphate-limitation pattern for the bacterial communities. Alpha- and beta-diversity of fungal communities exhibited a significant correlation with water depth. We consider the distinct distributional gradients of bacterial and fungal communities partly explain the different roles in the biogeochemical processes of coastal sediment.

Assessing PAHs pollution in Shandong coastal area (China) by combination of chemical analysis and responses of reproductive toxicity in crab Portunus trituberculatus

The concentrations of PAHs in seawater and sediments were measured at three selected sites (S1, S2, and S3) along the coastal area of Shandong (China) in April, May, and June, 2015, which ranged from 29.72 to 123.88 ng/L and 82.62 to 232.63 ng/g, respectively. Meanwhile, the reproductive toxicity responses in crab Portunus trituberculatus were also evaluated to assess the pollution of PAHs during the sampling period. Chemical analysis showed that S3 was the most PAH-contaminated area while S1 was the least, and the biochemical parameters concerned with reproduction were efficiently responded to the three sites, especially in S3 (p < 0.05). Moreover, the principal component analyses (PCA) showed that parameters for DNA alkaline unwinding, protein carbonyl content, and lipid peroxidation levels in two genders, 17β-estradiol in female, testosterone and TESK2 gene expression in male crabs, were closely correlated with the concentrations of PAHs (2 + 3 rings, 4 rings, and 5 + 6 rings), which were considered to be good candidate indicators to assess the environmental pollutions resulting from PAHs in the coastal area of Shandong, China.

Occurrence, speciation and transportation of heavy metals in 9 coastal rivers from watershed of Laizhou Bay, China

The occurrence, speciation and transport of heavy metals in 9 coastal rivers from watershed of Laizhou Bay were investigated. The largest dissolved concentrations of Cd, Cu and Zn in water were 6.26, 2755.00, 2076.00 μg/L, respectively, much higher than several drinking water guidelines. The greatest concentrations of Cu, Zn, Cr, Ni, Pb and Cd in sediments were 1462, 1602, 196, 67.2, 63.5 and 1.41 mg/kg, dw, respectively. Correlation and principal component analysis was also conducted to determine the extent between the concentrations of metals in water and sediment, as well as relevant parameters. Throughout the river stretch, most of Cr Zn, Cr, Ni and Pb bound to residual fraction, however, Cd was preferentially bound to the exchangeable phase. Among the 9 rivers, Yellow river account for 72.5%, 67.5%, 55.4%, 59.4%, 79.4% and 85.5% for Cr, Ni, Cu, Zn. Cd and Pb, respectively. The combined potential ecological risk indexes were used to evaluate potential risks. The majority of sampling sites from watershed of Laizhou Bay have moderate ecological risk from metals. The government should pay more attention to the ecological risk of river ecosystem which flow to Laizhou Bay.

Characteristics of cadmium remobilization in tributary sediments in Three Gorges Reservoir using chemical sequential extraction and DGT technology

The Three Gorges Reservoir (TGR) is the largest reservoir in China. Cadmium (Cd) is a primary pollutant in the TGR, and its speciation and bioavailability have attracted extensive attention since TGR submergence. In this study, Chelex-100 DGT (diffusive gradient in thin films) and the sequential extraction method were used to investigate the bioavailable Cd in sediments obtained from a typical tributary (Meixi) and mainstream (Yangtze) in the TGR. The total Cd concentrations in sediments of the four stations were also determined. In comparison to the concentrations of labile Cd measured by DGT (C_DGT-Cd) in four profiles, CJ and MX-upstream/downstream were at potential risk for Cd release from surface sediments using the apparent diffusion flux across the interface numerical model. The order of C_DGT-Cd in surface sediments was as follows: CJ > MX-downstream > MX-upstream > MX-midstream. Additionally, a positive correlation was demonstrated between C_DGT-Cd and Cd in the exchangeable fraction (F1) in the surface sediments, indicating that Cd in the exchangeable fraction was readily captured by DGT. A negative correlation was observed between C_DGT-Cd and C_DGT-Fe, C_DGT-Mn in the sediment-water-interface (SWI), suggesting that Fe/Mn oxides did not control the release of labile-Cd from sediments. Furthermore, a positive correlation existed between the C_DGT-Cd in the surface sediments and Cd in the oxidizable fraction (F3), illustrating that Cd sorbed or bound with organic matter or sulfide was labile and released into the water phase from the surface sediments. A dark area was found in the AgI gel, which further demonstrated that Cd simultaneously was released with sulfide in this area.

Assessing the remobilization of Antimony in sediments by DGT: A case study in a tributary of the Three Gorges Reservoir

The Three Gorges Reservoir (TGR) is one of the world's largest man-made hydropower projects, which has posed great challenges to the aquatic environment of the Yangtze River since the impoundment of water. As a non-essential toxic metalloid, information on the bioavailability of Antimony (Sb) in TGR sediments is lacking. Four sediment cores were collected from a tributary and the mainstream in the TGR to investigate the distribution and remobilization of Sb using the diffusive gradients in thin films (DGT) technique. The results showed that the concentrations of Sb obtained by DGT (CDGT-Sb) at all of the sampling stations were low (below 0.30 μg/L), compared to the relatively high Sb concentrations in the sediments. The lateral and vertical distributions of CDGT-Sb revealed different tendencies in overlying water and sediments at all of the sampling sites in the TGR, which may be attributed to anthropogenic impacts, the heterogeneity of sediments and the unevenness of the sediment-water interface (SWI) during the deployment of DGT probes. In addition, CDGT-Sb in the surface sediments were lower than those in the overlying water, and concentration gradients were found near the SWI, demonstrating that Sb has the potential to diffuse from the overlying water into the sediment. In the sediment cores, different peaks were discovered in the DGT probes and the remobilization of Sb simultaneously appeared in the vicinity of -10 cm. Correlation analysis showed that CDGT-Sb had no or negative correlation with CDGT-Fe and CDGT-Mn in all of the DGT probes, suggesting that the release of Sb was unassociated with Fe and Mn in the sediments in the study area.

Characterization of surface sediments from the Beijing-Hangzhou Grand Canal (Zaozhuang section), China: assessment of beryllium enrichment, biological effect, and mobility

The South-to-North Water Diversion Project is one of the world's largest water diversion projects, benefiting seven million people in China. The Zaozhuang section of the Beijing-Hangzhou Grand Canal is an important part of this project. This paper investigated the enrichment, biological effect, and mobility of beryllium (Be) in surface sediments of the Zaozhuang section. Results showed that high values were found in Tai'erzhuang District, Zaozhuang city, and the areas near the inlet of the Nansihu Lake, which might have been influenced by local human activities including metallurgy, burning of fossil fuels, and transportation. Four geochemical fractions of Be were obtained: acid-soluble fraction, reducible fraction, oxidizable fraction, and residual fraction. The non-residual fractions (the sum of the first three) accounted for 72.5 ∼ 96.1 % of the total amount of Be. Acid-soluble fraction might be mainly influenced by human activities, with the strongest mobility and bio-availability, accounting for 4.1 ∼ 44.7 % of the total amount, with an average of 20.2 %. Enrichment factor (EF) showed minor to moderate enrichment in some regions; adverse effect index (AEI) also showed that there were high levels of Be in some regions, which might have negative impacts on organisms. Generally, mobility, EF, and AEI of elements are carried out separately. But the results of this study indicated that a comprehensive assessment on the enrichment, mobility, and biological effects of Be caused by human activities is necessary in understanding the environmental risks of Be.

Trace metal bioavailability in sediments from a reference site, Ribeira Bay, Brazil

Surface sediments were collected near potential contamination sources impacting Ribeira Bay (Brazil), a system considered as a 'reference site' for trace metals. Physicochemical properties (pH and Eh), grain size and concentrations of total organic carbon (TOC), total phosphorus (TP), acid-volatile sulfides (AVS) and simultaneously-extracted metals (Fe, Mn, Cd, Cu, Ni, Pb and Zn) were analyzed. Although relatively low metal concentrations were found, correlations of Zn and Ni with high TP levels suggested an association with sewage inputs, while other metals presented associations with specific geochemical carriers (TOC, Fe and Mn compounds). AVS levels exceeding those of the sums of Cd, Cu, Ni, Pb and Zn (ΣSEM) by at least one order of magnitude and TOC-normalized differences between ΣSEM and AVS ((ΣSEM-AVS)/fOC) near to or below than -200μmolgOC(-1) indicated that there were sufficient AVS and TOC levels to control trace metal bioavailability in sediment pore water.

Assessment of sediment quality based on acid-volatile sulfide and simultaneously extracted metals in heavily industrialized area of Asaluyeh, Persian Gulf: concentrations, spatial distributions, and sediment bioavailability/toxicity

Sediment samples from the coastal area of Asaluyeh harbor were collected during autumn and spring 2015. The acid-volatile sulfide (AVS) and simultaneously extracted metals (SEMs) were measured to assess the sediment quality and potential ecological risks. The average concentrations (and relative standard deviation (RSD)) of AVS in the industrial sediments were 12.32 μmol/g (36.91) and 6.34 μmol/g (80.05) in autumn and spring, respectively, while in the urban area, these values were 0.44 μmol/g (123.50) and 0.31 μmol/g (160.0) in autumn and spring, respectively. The average concentrations of SEM (and RSD) in the industrial sediments were 15.02 μmol/g (14.38) and 12.34 μmol/g (20.65) in autumn and spring, respectively, while in the urban area, these values were 1.10 μmol/g (43.03) and 1.06 μmol/g (55.59) in autumn and spring, respectively. Zn was the predominant component (34.25-86.24 %) of SEM, while the corresponding value for Cd, much more toxic ingredient, was less than 1 %. Some of the coastal sediments in the harbor of Asaluyeh (20 and 47 % in autumn and spring, respectively) had expected adverse biological effects based on the suggested criterion by United States Environmental Protection Agency (USEPA), while most stations (80 and 53 % in autumn and spring, respectively) had uncertain adverse effects.

Assessment of metal toxicity and development of sediment quality guidelines using the equilibrium partitioning model for the Three Gorges Reservoir, China

The impoundment of the Three Gorges Reservoir (TGR) in China influences the quality of the water supply. Surface sediment samples from the TGR mainstream and three tributaries were collected. Acid volatile sulfide (AVS), simultaneously extractable metals (SEMs), and the fraction of organic carbon (f(oc)) were used to assess the toxicity of heavy metals. Sediment quality guidelines (SQGs) were established using the equilibrium partitioning approach. The results showed that the surface sediments were found to be oxic or suboxic. AVS concentrations in sediments were relatively low, below SEM concentrations. The [SEM] - [AVS] model indicated that all sediments possibly have adverse effects on aquatic life. However, ([SEM] - [AVS])/f(oc) predicted no adverse biological effects in some areas of the Meixi and Caotang Rivers, while adverse effects to aquatic life were uncertain for the other sediments. The partitioning coefficients, water quality criteria, and residual metals in the sediments were the main factors influencing the SQGs for the TGR, while the metals bound to AVS had a negligible effect. The normalized TGR SQGs were all much higher than the existing standards except for cadmium and copper. The differences might be attributed to the approaches used for derivation of SQGs and the physical and chemical characteristics of the sediments.

Influence of Sedimentation Rate on the Metal Contamination in Sediments of Bohai Bay, China

Metal concentration in marine sediments is influenced by sedimentation rate. In this study, the metal concentration in sediments of Bohai Bay, China, was adjusted by sedimentation rate, which was derived from the radionuclide dating method. The results showed that the sedimentation rate of Bohai Bay sediments increased from 0.3 to 0.55 g/a over time, especially in the last 30 years since the economic reform in China. The sequence of metal concentrations (mg/kg) is: Cr(97.41) > Zn(73.14) > Cu(20.59) > Pb(16.42) > Cd(0.49). Through the adjustment, the change of metal concentration in sediment cores increased obviously from bottom to surface sediments. It indicated that the increasing sedimentation rate of Bohai Bay in recent years diluted the metal concentration in the sediment.

Heavy metals in surface sediments of the intertidal Laizhou Bay, Bohai Sea, China: Distributions, sources and contamination assessment

Surface sediments from the intertidal zone of the southwestern Laizhou Bay were analyzed for heavy metals to seek their concentrations, distributions, pollution status, potential ecological risks and possible sources. The concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were in the ranges of 4.65-9.65, 0.11-0.28, 25.85-42.75, 7.57-21.29, 0.022-0.054, 12.85-25.35, 9.65-17.65 and 38.22-73.81μgg(-1) dry sediment weight, respectively. Cd and Hg presented a status of no pollution to moderate pollution and moderate to considerable potential ecological risks; they were enriched to some extent at some sampling stations, while the other studied metals were not. The combined effects of the studied metals in the sediments made them have a 21% probability of being toxic to biota. The results indicated that As, Cr, Cu, Zn, Ni and Pb were mainly from natural contribution, while a significant portion of Cd and Hg was likely from anthropogenic discharges in addition to natural inputs.

The risk assessment of heavy metals in Futian mangrove forest sediment in Shenzhen Bay (South China) based on SEM-AVS analysis

The risks of heavy metal in Futian mangrove forest sediment were assessed using the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) methods. The results indicated that AVS distributions were more variable than the SEM distributions at all 16 sampling sites. The positive correlation between AVS and SEM indicated that their similar formative and existing conditions and that AVS acted as an important carrier for SEM. The major SEM component was Zn (69.7.3-94.2%), whereas the Cd contribution (the most toxic metal present) to SEM was no more than 1%. The possible adverse effects caused by heavy metals at ten sampling sites may be due to higher levels of SEMs, rather than AVSs. The total organic carbon (TOC) was an important metal-binding phase in the sediments. Taking into account the TOC concentration, there were no adverse effects due to heavy metals in any of the Futian mangrove forest sediments.

Distribution, enrichment and sources of thallium in the surface sediments of the southwestern coastal Laizhou Bay, Bohai Sea

The concentrations of thallium (Tl) in the surface sediments of the southwestern coastal Laizhou Bay and the rivers it connects were determined. In riverine sediments, the Tl concentrations ranged from 0.34 to 0.76 μg g(-1) in summer; in autumn, the corresponding data were 0.35-1.08 μg g(-1). In marine sediments, the Tl concentrations ranged from 0.36 to 0.58 μg g(-1) in summer; and from 0.30 to 0.56 μg g(-1) in autumn. The grain size, Al and Fe oxides were major factors affecting Tl distribution. Tl in the surface sediments of the studied area was mainly from the natural input with the non-natural input as a subsidiary source. The low concentrations of Tl made it hard to cause potential negative environmental effects in this area.

Sediment quality of the SW coastal Laizhou Bay, Bohai Sea, China: a comprehensive assessment based on the analysis of heavy metals

Historically, the Bohai Sea is one of the most important fishing grounds in China. Yet, surrounded by one of the biggest economic rims of China, its ecological functions have been declining rapidly in recent two decades under the heavy anthropogenic impacts. The Laizhou Bay is the smallest one of the three main bays in the Bohai Sea. Owing to the rich brine deposits, chemical industries using brine as raw materials are booming in the southern coast of the Laizhou Bay, the scale of which ranks as the largest one in China. In order to monitor and assess the environmental quality, surface sediments were collected from the coastal waters of southwestern Laizhou Bay and the rivers it connects with during summer and autumn in 2012, and analyzed for heavy metals. Several widely adopted methods were used in the overall assessment of heavy metal pollution status and potential ecological risks in these sediments, and the data were analyzed to infer the main sources of the pollutants. The results showed that the remarkably high concentrations of heavy metals were almost all recorded in a small number of riverine sites. Cr, Cu, Ni and Zn were the main environmental threat according to the sediment quality guidelines. The marine area was generally in good condition with no or low risk from the studied metals and adverse effects on biota could hardly occur. Natural sources dominated the concentrations and distributions of Cu, Ni, Pb and Zn in the marine area. Our results indicated that heavy metal pollution was not a main cause of the ecological degradation of the Laizhou Bay at present.

Assessing metal toxicity in sediments using the equilibrium partitioning model and empirical sediment quality guidelines: a case study in the nearshore zone of the Bohai Sea, China

Surface sediments were collected from five nearshore (wastewater discharges, aquaculture facilities and a seaport) sites in Bohai Bay and Laizhou Bay, China. The equilibrium partitioning (EqP) model and empirical sediment quality guidelines (SQGs) were applied to assess the potential metal toxicity in the collected sediments. The results show that, based on the EqP model, 35% of stations exhibited potential metal toxicity. Several metals (Cu, Ni and Cr) exceeded the empirical SQGs (9-93% of the time), however these guidelines may not be suitable for use in the Bohai Sea owing to the background concentrations. The EqP model is a more useful method for assessing potential metal toxicity in Bohai Sea sediment than the empirical SQGs. Additionally, we have provided new understanding about methods for assessing sediment metal toxicity in the Bohai Sea that may be useful in other coastal areas in China.

Coastal surface sediment quality assessment in Leizhou Peninsula (South China Sea) based on SEM-AVS analysis

Surface sediments from the coastal area of the Leizhou Peninsula in the South China Sea were collected and analyzed and the potential ecological risks in the area were assessed based on acid-volatile sulfide (AVS) model. The AVS levels are between 0.109 and 55.6 μmol g(-1), with the average at 4.45 μmol g(-1). The high AVS-concentration zones include the aquaculture areas of Liusha Bay and the densely populated areas of Zhanjiang Bay. The simultaneously extracted metals (SEM) range from 0.026 μmol g(-1) to 8.61 μmol g(-1), with the average at 0.843 μmol g(-1). Most of high SEM-concentration stations were located in ports or aquaculture zones. Most of the coastal surface sediments of the Leizhou Peninsula (90%) had no adverse biological effects according to the criterion proposed by USEPA (2005); while adverse effects were uncertain in some stations (8%); even in 2 stations (2%) adverse biological effects may be expected.

Rare earth elements in intertidal sediments of Bohai Bay, China: concentration, fractionation and the influence of sediment texture

Surface sediments from intertidal Bohai Bay were assessed using a four-step sequential extraction procedure to determine their concentrations of rare earth elements (REEs) and the chemical forms in which those elements were present. The normalized ratios La/Gd and La/Yb showed that LREE contents were not significantly higher than the middle REEs or HREE contents. A negative Ce anomaly and positive Eu were observed in sand and silty sand sediments, whereas no significant Ce or Eu anomaly was found in clayey silt sediments. Residual fraction of REEs accounted for the majority of their total concentrations. Middle REEs were more easily leached than other REEs, especially in clayey silt sediment. REEs contents in the surface sediment from the intertidal Bohai Sea were consistent with data from the upper continental crust and China shallow sea sediments, indicating that they were generally unaffected by heavily anthropogenic effects from adjacent areas.

Assessment of heavy metal impact on sediment quality of the Xiaoqinghe estuary in the coastal Laizhou Bay, Bohai Sea: inconsistency between two commonly used criteria

Surface sediments in the Xiaoqinghe estuary, southwestern coastal Laizhou Bay, were examined to assess the bio-toxic risk of heavy metals (Cd, Cu, Ni, Pb and Zn) with the effects range-low and effects range-median guidelines (ERL-ERMs) and the concentration ratio of simultaneously extractable metals to acid volatile sulfides ([SEM]/[AVS]). Based on the ERL-ERM guidelines, bio-toxic effect caused by Cu, Ni, Pb and Zn could be expected in the riverine surface sediments of the Xiaoqinghe estuary; and the surface sediments in the marine area were in good quality and only Ni might cause bio-toxic effect occasionally. The AVS-SEM guidelines revealed that no bio-toxic effect could be caused by any of the studied metals in both the riverine and marine sediments, since there were excess sulfides in surface sediments which could form water-insoluble substances with free metal ions and reduce the bioavailability of heavy metals.

Geochemical characteristics of phosphorus in surface sediments of two major Chinese mariculture areas: the Laizhou Bay and the coastal waters of the Zhangzi Island

Phosphorus (P) in surface sediments of the Laizhou Bay (LB) and the coastal waters around the Zhangzi Island (ZI) was analyzed. Six forms of P were separated - exchangeable or loosely sorbed P (Ads-P), aluminum-bound P (Al-P), iron-bound P (Fe-P), authigenic apatite plus CaCO3-bound P plus biogenic apatite (Ca-P), detrital apatite plus other inorganic P (De-P) and organic P (OP). The average contents of P in the LB were in the order: De-P>OP>Ca-P>Fe-P>Ads-P>Al-P; in the ZI, the corresponding order was De-P>OP>Fe-P>Ca-P>Ads-P>Al-P. Due to the high nutrient loadings from the surrounding rivers, TP contents in sediments of the LB were higher than in those of the ZI. The potential bio-available P (Ads-P and OP) accounted for 14.7% and 24.2% of TP in sediments of the LB and the ZI, respectively.

Impact of laver treatment practices on the geoenvironmental properties of sediments in the Ariake Sea

Since the 1970s, the catch of Tairagi and Agemaki shellfish that inhabit the shallow sediments of the Ariake Sea of Japan has fallen dramatically. This is partly accounted for by the Isahaya land reclamation dike project and by the increasingly frequent local red tides. A recent survey of local fisherman suggested that the decline in the shellfish harvest may also be due to the practice of laver treatment in the tidal flats of the Ariake Sea. We carried out field and laboratory investigations to determine whether the practice changes the geoenvironmental properties of the fine-grained sediments in the tidal flats. There were notable changes in the salt concentration, pH, and sulfide content between the sediments exposed to a laver treating agent and those without laver treatment. Based on these differences, we identified potential mechanisms by which the laver treating agent was transported into the sediments and influenced the sulfide levels.

Integrated assessment of heavy metal pollution in the surface sediments of the Laizhou Bay and the coastal waters of the Zhangzi Island, China: comparison among typical marine sediment quality indices

The total concentrations and chemical forms of heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) in the surface sediments of the Laizhou Bay and the surrounding marine area of the Zhangzi Island (hereafter referred to as Zhangzi Island for short) were obtained and multiple indices and guidelines were applied to assess their contamination and ecological risks. The sedimentary conditions were fine in both of the two studied areas according to the marine sediment quality of China. Whereas the probable effects level guideline suggested that Ni might cause adverse biological effects to occur frequently in some sites. All indices used suggested that Cd posed the highest environmental risk in both the Laizhou Bay and the Zhangzi Island, though Cd may unlikely be harmful to human and ecological health due to the very low total concentrations. The enrichment factor (EF) showed that a substantial portion of Cr was delivered from anthropogenic sources, whereas the risk assessment code (RAC) indicated that most Cr was in an inactive state that it may not have any adverse effect either. Moreover, the results of EF and geoaccumulation index were consistent with the trend of the total metal concentrations except for Cd, while the results of RAC and potential ecological risk factor did not follow the same trend of their corresponding total metal concentrations. We also evaluated the effects of using different indices to assess the environmental impact of these heavy metals.

Pollution status of the Bohai Sea: an overview of the environmental quality assessment related trace metals

It is well recognized that the ecosystem of the Bohai Sea is being rapidly degraded and the Sea has basically lost its function as a fishing ground. Billions of funds have been spent in slowing down, halting and finally reversing the environmental deterioration of the Bohai Sea. Although trace metals are routinely monitored, the data with high temporal resolution for a clear understanding of biogeochemical processes in the ecosystem of the Bohai Sea are insufficient, especially in the western literature. In this review, status of trace metal contamination in the Bohai Sea is assessed based on a comprehensive review of their concentrations recorded in the waters, sediments and organisms over the past decades. Studies show that metal contamination in the Bohai Sea is closely associated with the fast economic growth in the past decades. Concentrations of trace metals are high in coastal areas especially in the estuaries. Alarmingly high metal concentrations are observed in the waters, sediments and organisms from the western Bohai Bay and the northern Liaodong Bay, especially the coasts near Huludao in the northernmost area of the Bohai Sea, which is being polluted by industrial sewage from the surrounding areas. The knowledge of the speciation and fractionation of trace metals and the influence of submarine groundwater discharge on the biogeochemistry of trace metals in the Bohai Sea is far from enough and related work needs to be done urgently to get a better understanding of the influence of trace metals on the ecosystem of the Bohai Sea. A clear understanding of the trace metal pollution status of the Bohai Sea could not be achieved presently for lack of systematic cooperation in different research fields. It is quite necessary to apply the environmental and ecological modeling to the investigation of trace metals in the Bohai Sea and then provide foundations for the protection of the environment and ecosystem of the Bohai Sea.