Concentrations And Environmental Indication Significance Of Trace Elements In Major Marine Bivalves From The Northern China And In Surface Sediments Of The Bohai Sea And The Yellow Sea

Marine sediment is a major sink for trace elements; the coastal zone, one of the most active regions of land-ocean interaction in the world, is a geographic space of interaction between terrestrial and aquatic ecosystems that is crucial for the survival of a large variety of plants, animals and aquatic organisms. In recent years, huge amounts of trace elements are entering the coastal environment as contaminants in anthropogenic-related processes by the ways of untreated industrial wastewater, municipal sewage effluent, surface run-off and so on. Trace elements have potential toxicity and threat to eco-systems, therefore, contamination of trace elements in the environment is of major concern.Trace elements in major marine bivalves from the northern China and in the surface sediments of the Bohai Sea and the Yellow Sea were studied to obtain a visual representation of spatial or interspecific variations in the concentrations of these elements in samples. The foucs of this research is on the following issues:1) 159 samples of nine edible bivalve species(Argopecten irradians, Chlamys farreri, Crassostrea gigas, Lasaea nipponica, Meretrix meretrix, Mytilus edulis, Ruditapes philippinarum, Scapharca subcrenata and Sinonovacula constricta) were randomly collected from eight local seafood markets in six cities(Dalian, Qingdao, Rizhao, Weifang, Weihai and Yantai) along the northern coastal areas of China for the investigation of trace element contamination and risk assessment. The trace element concentrations in the edible tissues of collected bivalve species were analyzed with ICP-MS and HG-AFS, and then their pollution status was assessed based on a variety of evaluation standards. The human risk assessment for people in the northern China was conducted using the provisional tolerance weekly intake(PTWI), acceptable daily intake(ADI), and reference dose(Rf D) previously established by the United States Environmental Protection Agency(USEPA) and the Joint FAO/World Health Organization(WHO) Expert Committee on Food Additives(JECFA) to provide consumers with better knowledge of contamination problems associated with seafood consumption.2)The surface sediments from the Bohai Sea and the Yellow Sea were analyzed for acid-volatile sulfide(AVS) and simultaneously extracted metals(SEM) to assess the sediment quality. Two methods [SEM]-[AVS] and([SEM]-[AVS])/fOC established by the United States Environmental Protection Agency(USEPA) were adopted for the assessment of trace metal biotoxicity.3) Surface sediments from the coastal zone of the Bohai Bay were sampled for the geochemical and environmental assessment of six trace metals(Cd, Cr, Cu, Ni, Pb and Zn). Two sediment quality guidelines and two geochemical normalization methods(index of geoaccumulation and enrichment factor) were used to judge the potential risk and accumulation of metals.Results of trace elements in major marine bivalves from the northern China and in surface sediments of the Bohai Sea and the Yellow Sea showed:1) As, Cr, Hg, and Pb in all collected bivalve species had comparable levels while Cd, Cu, and Zn exhibited apparent differences in different bivalve species. Cd in Chlamys farreri and Cu in Crassostrea virginica exhibited apparent higher levels than other bivalve species. The concentrations of the essential trace elements were higher than those of the non-essential trace elements, with Zn concentrations being the highest. There were significant correlations between some elements(Cd-Pb, Cd-Zn, Cu-Zn). Risk assessment indicated that we should pay special attention to human health risks associated with Cd and Cu exposure via consumption of marketed bivalves. Human health risks associated with the exposure to the other studied trace elements(As, Cr, Hg, Pb and Zn) via consumption of marketed bivalves were negligible. However, care must be taken considering that most coastal residents regularly consume large quantities of bivalves.2) The average concentrations of eight potential harmful elements(PHEs), namely Ag, Be, Co, Ni, Sb, Se, Tl and V, in the edible tissues of the sampled bivalves followed the order of Se > Ni > V > Co > Ag > Sb > Be > Tl. The recorded average concentrations of Ag, Be, Co, Ni, Sb, Se, Tl and V were 133.57±211.05 ng/g, 11.54±4.74 ng/g, 0.16±0.10 μg/g, 0.65±0.60 μg/g, 13.92±10.66 ng/g, 0.80±0.29 μg/g, 1.85±0.55 ng/g and 0.33±0.12 μg/g, respectively. On average, among different locations and bivalve species, Se had the highest tissue concentrations, followed by Ni, V, Co, Ag, Sb and Be, while the Tl levels were the lowest. Among the eight PHEs quantified in this study, Ag, Be, Co, Ni, Sb, Se, V and Tl had no clear spatial differences among all the locations generally. Care must be taken considering that Ni would be the risky factor and most coastal residents regularly consume large quantities of bivalves.3) The concentrations of AVS([AVS]) and SEM([SEM]) in the surface sediments from the Laizhou Bay(LB) and the coastal sea around the Zhangzi Island(ZI) varied in the ranges 0.71-11.03 and 0.10-0.74 μmol/g dry weight, respectively. [AVS] was generally low in the river outlet area and increased in the seaward direction in LB. [AVS] was significantly and positively correlated with TOC. [SEM] was significantly and positively correlated with TOC, the water content of sediment and the fine sediment fraction and it was significantly and negatively correlated with coarse sediment fraction. The obtained results suggest that the surface sediments of LB and ZI were of high quality and not likely to cause negative effects on their ecosystems.4) AVS and SEM exhibited different spatial patterns in the surface sediments of NYS and BS. The concentrations of AVS ranged from 0.279 to 5.131 μmol/g in the surface sediments of NYS, while the corresponding concentrations of the surface sediments from BS were found varied within the range of 0.570 to 3.994 μmol/g.The SEM concentrations of the surface sediments from NYS ranged from 0.086 to 1.264 μmol/g, while the corresponding data in BS ranged from 0.538 to 1.462 μmol/g. [AVS] was significantly and positively correlated with the fine fraction, and negative correlation with coarse fraction and Eh in the surface sediments of NYS and BS. [AVS] and [SEM] were significantly and positively correlated with TOC in surface sediments of NYS. [SEM]/[AVS] was smaller than one in 10 of the 13 surface sediments of NYS, while only 5 of the 13 surface sediments of BS had [SEM]/[AVS]<1, indicating that the surface sediments of NYS were of higher quality and less likely to cause negative effects on their ecosystems than those in BS. Significant correlations were observed between AVS and other parameters in the surface sediments of NYS but not in the surface sediments of BS indicating that this phenomenon was complex in the surface sediments of BS might be due to common anthropogenic activities. A comparison of the results based on two different criteria by USEPA for sediment quality assessment showed that they were sometimes contradictory. Therefore, a single approach to quality assessment might be insufficient. It was preferable to do a comparison of the results based on different criteria for sediment quality assessment.5) Except for Cr, the mean concentration of which is apparently higher than that in UCC, the mean concentrations of the other elements in surface sediments of the intertidal Bohai Bay are comparable to their corresponding values in UCC. For all the metals studied, their total concentrations in sand and silty sand sediments are much lower than in clayey silt sediments. On average, their total concentrations in sand and silty sand sediments are 0.08, 43.6, 9.7, 15.3, 19.9 and 39.5 μg/g for Cd, Cr, Cu, Ni, Pb and Zn, respectively, and the corresponding values in clayey silt sediments are 0.17, 97.3, 40.5, 42.5, 32.2 and 111 μg/g, respectively. For each metal except Cd, its total concentrations in clayey silt sediments or in sand and silty sand sediments are very similar, and its coefficient of variation is usually <10%. Surface sediment quality was assessed according to USEPA(United States Environmental Protection Agency, 2004) standards, but the results were also compared with USEPA(United States Environmental Protection Agency) guidelines for sediment quality. A comparison of the results based on different criteria for sediment quality assessment shows that they are sometimes contradictory. Therefore, a single approach to quality assessment may be insufficient to get accurate scientific conclusions. The research suggests that a comparison of the results based on different criteria will be more convincing and effective.