Oyster As, Cd, Cu, Hg, Pb and Zn levels in northern South China Sea: Long-term spatiotemporal trends and health risk assessment

Lifei Wang, Department of Biological Sciences, University of Toronto Scarborough, Toronto, ON, Canada, Xuefeng Wang, College of Fisheries, Guangdong Ocean University, Zhanjiang, China and Xiaoping Jia, South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, China

Background/Question/Methods
Estuarine and coastal ecosystems are usually considered as vulnerable because of the complex biogeochemical processes and the anthropogenic disturbances through a variety of pollution. Among environmental pollutants, heavy metal contaminants in estuarine and coastal ecosystems have drawn increasing concerns in marine environmental conservation. Long-term direct or indirect exposure to high heavy metal levels, mainly through food and drinking water, can cause adverse effects on human health. It is crucial to understand the interacting effects and health implications of different heavy metals in popular seafood species, such as oysters. This study investigated the long-term spatiotemporal trends and health risk assessment of oyster As, Cd, Cu, Hg, Pb and Zn levels in the coastal waters of northern South China Sea. Cultured oysters sampled from 23 estuaries and harbors along the coast of northern South China Sea during 1989-2015 were examined for the spatiotemporal trends of the six heavy metal levels. Metal pollution Index (MPI) and target hazard quotient (THQ) were used for quantifying the exposure of the six heavy metals to human health through oyster consumption. Principal component analysis (PCA) was used for assessing the relative importance of the six metals in oyster heavy metal distribution patterns in the northern South China Sea.
Results/Conclusions
Overall, the As, Cd, Cu, Hg, Pb and Zn levels of oysters in the coastal waters of northern South China Sea showed an overall decline from 1989 to 2015, remained relatively high (MPI=2.42~3.68) during 1989-2000, gradually decreased since 2000, and slightly increased after 2010. Oyster heavy metal levels were highest in the Pearl River Estuary (MPI=1.20~5.52), followed by west Guangdong, east Guangdong, Guangxi, and Hainan coastal waters. This pattern is probably because the Pearl River Estuary has the fastest growth of industry and economics among the five zones in this study for the past two decades, and it should be considered as a hotspot for seafood safety monitoring in southern China. Principal component analysis (PCA) indicated that Cu, Zn and Cd were the most important metals in the long-term spatiotemporal distributions of oyster heavy metal levels in the northern South China Sea. Health risk assessment suggested that the risk of the six heavy metals to human health through oyster consumption were relatively high during 1989-2005 (THQ=1.01~5.82), significantly decreased since 2005 (THQ<1), and slightly increased after 2010.