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 coastal ecosystems and related risk assessment have become an important topic for marine environment conservation. Copper is a pollutant that has drawn increasing concerns, and long-term direct or indirect exposure to high copper levels, mainly through drinking water and food, can cause adverse effects on human health. It is crucial to understand the trends and health implications of copper levels in popular seafood species, such as oysters. Unlike toxic heavy metals such as mercury, copper is essential for oysters’ growth and development but can inhibit their immune response to exotic stress when goes above normal levels. This study investigated the long-term oyster copper levels in coastal waters of northern South China Sea, in order to help improve sustainable aquaculture of oysters and marine environment conservation in China. Cultured oysters collected from 23 harbors or estuaries along the coast of northern South China Sea during 1989-2015 were examined for spatiotemporal trends of copper levels. Health risk assessment analysis was used to quantify copper exposure to human health through oyster consumption.
Results/Conclusions
Overall, oyster copper levels in this study ranged from 0.9 mg/kg to 1897.0 mg/kg with an average of 210.0±143.6 mg/kg. Oyster copper levels in coastal waters of northern South China Sea showed an overall decline from 1989 to 2015, remained relatively low since 1996, and slightly increased after 2010. Oyster copper levels in Guangdong coastal waters were significantly higher with more variation than in Guangxi and Hainan coastal waters, and the long-term trends of oyster copper levels in Guangdong dominated the overall trends of oyster copper levels in coastal waters of northern South China Sea. Within Guangdong Province, oyster copper levels were highest in Pearl River estuary, followed by west Guangdong and east Guangdong coastal waters. The low risk ratio of copper exposure was 0.12 in 1989-1990, increased to 0.37 in 1991-1995, remained between 0.67 and 0.85 during 1996-2010, and decreased to 0.54 in 2011-2015. Results suggested that the risk of copper exposure to human health through oyster consumption increased during 2011-2015 compared to 2006-2010. It is recommended that the human daily intake of cultured oysters in the study area should reduce by half to minimize copper exposure. The interacting effects between metals in aquatic environment also deserve more attention.