Accumulation and Toxicity of Metals in Hong Kong Oysters under Intermittent Exposure and Turbid Estuarine Environments

In Southern China (including Hong Kong), estuaries have been extensively exploited for their rich resources. They are home to numerous shellfish aquaculture activities due to their abundant food supplies and close proximity to human activity. However, estuaries are extremely dynamic with their physico-chemical conditions influenced by tidal action, including salinity, dissolved organic carbon (DOC), dissolved oxygen, redox conditions, and total suspended solids. Concomitantly, estuaries are often the most contaminated coastal systems due to the uncontrolled releases of industrial effluents. These dynamic coastal environments coupled with increasing metal pollution in estuaries have presented great challenges to shellfish living in the estuary. The estuarine oyster, namely Crassostrea hongkongensis, has been widely farmed in Southern China estuaries. In recent years, the oysters have been found to be contaminated with different metals due to their hyper-accumulating capacity for many toxic metals. However, we know very little about how oysters handle the metal challenges in such dynamic and turbid estuarine environments. In the present project, I propose to study the bioaccumulation and toxicity of metals in oysters under fluctuating conditions typical of estuarine environments. Specifically, we will 1) study metal bioaccumulation and toxicity in oysters under intermittent exposure; 2) study metal bioaccumulation in oysters under high suspended sediment loads and illustrate the exposure of metals in the highly dynamic food environments that vary both in quality and quantity; and 3) study metal bioaccumulation and toxicity in oysters under varying exposures in the field using a transplantation approach. The impact and significance of this project are threefold. First, it will help us understand the bioaccumulation and toxicity of metals in oysters under highly dynamic estuarine environments. Traditional ecotoxicological studies tend to focus on constant exposure, but exposure can be very dynamic and fluctuating in estuarine environments. A study of intermittent exposure may provide important information for our understanding of the basic ecotoxicology of oysters in a real estuarine environment setting, as well as for better refinement of water quality criteria. Second, the project can provide information on the adaptation of oysters to estuarine environments. Very little knowledge is currently available on the relationship between oyster physiology (e.g., particle selection and feeding physiology) and metal bioaccumulation and toxicity. Third, results generated from this study can be important for managers and governments in developing strategies to reduce the toxic metal levels in oysters. This project is also important amid the increasing concern for seafood safety in Hong Kong.