Xuelu Gao

Heavy metal pollution status in surface sediments of the coastal Bohai Bay

Bohai Bay, the second largest bay of Bohai Sea, largely due to the huge amount of pollutants discharged into it annually and its geohydrologic condition, is considered to be one of the most polluted marine areas in China. To slow down, halt and finally reverse the environmental deterioration of Bohai Sea, some researchers have proposed to connect it with Jiaozhou Bay in the western coast of Southern Yellow Sea by digging an interbasin canal through Shandong Peninsula. In order to assess the heavy metal pollution and provide background information for such a large geoengineering scheme, surface sediments from 42 stations covering both riverine and marine regions of the northwestern coast of Bohai Bay were analyzed for heavy metal content and fractionation (Cd, Cr, Cu, Ni, Pb and Zn). Three empirically derived sediment quality guidelines were used to assess the pollution extent of these metals. The studied metals had low mobility except for Cd at all stations and Zn at some riverine stations. Although a high mobility of Cd was observed, it could hardly cause a bad effect on the environment owing to its low total concentrations. Anthropogenic influence on the accumulation of studied heavy metals in sediments of Bohai Bay was obvious, but their contents were relatively lower to date comparing with some other marine coastal areas that receive important anthropogenic inputs. Taking as a whole, surface sediments of northwestern Bohai Bay had a 21% probability of toxicity based on the mean effects range-median quotient.

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.

Concentration and fractionation of trace metals in surface sediments of intertidal Bohai Bay, China

Surface sediments from intertidal Bohai Bay were sampled for the geochemical and environmental assessment of six trace metals (Cd, Cr, Cu, Ni, Pb and Zn). Results indicate that sediment grain size plays an important role in controlling the distribution and fractionation of them. Metal concentrations in clayey silt sediments are all clearly higher than in sand and silty sand ones. Cd and Pb in clayey silt sediments are more mobile than in sand and silty sand ones. 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. According to the mean probable effects level quotient, the combination of studied metals may have a 21% probability of being toxic. The sediments with high fraction of clay and silt have been contaminated by trace metals to various degrees, among which Cr contributes the most to contamination.

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.

Geochemistry of organic carbon and nitrogen in surface sediments of coastal Bohai Bay inferred from their ratios and stable isotopic signatures

Total organic carbon (TOC), total nitrogen (TN) and their δ(13)C and δ(15)N values were determined for 42 surface sediments from coastal Bohai Bay in order to determine the concentration and identify the source of organic matter. The sampling sites covered both the marine region of coastal Bohai Bay and the major rivers it connects with. More abundant TOC and TN in sediments from rivers than from the marine region reflect the situation that most of the terrestrial organic matter is deposited before it meets the sea. The spatial variation in δ(13)C and δ(15)N signatures implies that the input of organic matter from anthropogenic activities has a more significant influence on its distribution than that from natural processes. Taking the area as a whole, surface sediments in the marine region of coastal Bohai Bay are dominated by marine derived organic carbon, which on average accounts for 62±11% of TOC.

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

Surface sediments were collected from the coastal waters of southwestern Laizhou Bay and the rivers it connects with during summer and autumn 2012. The acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) were measured to assess the sediment quality. The results showed that not all sediments with [SEM]-[AVS]>0 were capable of causing toxicity because the organic carbon is also an important metal-binding phase in sediments. Suppose the sediments had not been disturbed and the criteria of US Environmental Protection Agency had been followed, heavy metals in this area had no adverse biological effects in both seasons except for few riverine samples. The major ingredient of SEM was Zn, whereas the contribution of Cd - the most toxic metal studied - to SEM was <1%. The distributions of AVS and SEM in riverine sediments were more easily affected by anthropogenic activity compared with those in marine sediments.

Assessment of sediment quality in two important areas of mariculture in the Bohai Sea and the northern Yellow Sea based on acid-volatile sulfide and simultaneously extracted metal results

The surface sediments from Laizhou Bay (LB) and the coastal sea around Zhangzi Island (ZI) were analyzed for acid-volatile sulfide (AVS) and simultaneously extracted metals (SEMs) to assess the sediment quality. These two areas, especially LB, are important mariculture bases in China and are significantly affected by the Yellow River. The concentrations of AVS ([AVS]) and SEM ([SEM]) varied in the ranges 0.71-11.03 and 0.10-0.74 μmol g(-1) 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.

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.

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.

Chemical speciation of 12 metals in surface sediments from the northern South China Sea under natural grain size.

pling programme, the calculated dilution suggested that even a substantial bulk water release was highly unlikely to pose a significant threat to the surrounding environment. However, if the results had suggested much higher levels of toxicity (precisely how toxic would have been determined by producing a median lethal effect, LC50, value from a dilution series) this would have alerted the salvage team to take specific precautions to minimise the release from the holds into the environment and may have informed alternative control operations such as the removal of the hold water to a tanker or via a controlled release. It is in this way that this approach could play an important part in understanding the potential effects of shipping accidents and in informing the salvage and mitigation activities. In the context of the MSC Napoli incident the use of this approach provided important assurance to the environment group, conservationists and the general public that the release of the hold contents (58,000 tonnes of water was pumped overboard during the refloating of the vessel) was unlikely to result in significant detriment to the surrounding biota. The opportunity to deploy a toxicity test method to the assessment of cargo-mediated hazard assessment in a real incident has allowed the value of such an approach to be confirmed. This approach could be applied to the hazard assessment of water within any enclosed or semi-enclosed vessel in the event of an incident at sea provided that access is available for sampling. This clearly has applications to shipping accidents but may also be applied to other scenarios. It is recommended that the approach be developed into a more standardised methodology for deployment at short notice in emergency response situations. A range of other short-term bioassays or screening tests (e.g. to assess endocrine disruption, genotoxicity etc.) could be used in this context dependent on the perceived nature of the hazard. For optimum value the method should be used in conjunction with appropriate hydrodynamic models to assess dilution factors in the vicinity of the incident.