A preliminary risk assessment of trace elements accumulated in fish to the Indo-Pacific Humpback dolphin (Sousa chinensis) in the northwestern waters of Hong Kong

In order to assess the potential risks associated with consumption of contaminated prey items to the Indo-Pacific Humpback dolphin (Sousa chinensis), fish species (Collichthys lucida, Pseudosciaena crocea, Johnius sp., Thryssa sp., Mugil sp. and Trichiurus sp.) representing the main food items of the dolphin were collected from the northwestern waters of Hong Kong, including the Sha Chau and Lung Kwu Chau Marine Park, which form the main habitat of the dolphin in Hong Kong. Within these waters, there are several potential sources of pollution including significant inputs from the Pearl River catchment, several major sewage outfalls and a series of mud pits that receive contaminated dredged sediments. Concentrations of thirteen trace elements (Ag, As, Cd, Co, Cr, Cs, Cu, Hg, Mn, Ni, Se, V, and Zn) in the fish tissue were analyzed by inductively coupled plasma mass spectrometer (ICP-MS). An assessment of the risks of adverse effects on the dolphin due to consumption of tainted fish was undertaken using two toxic reference benchmarks, namely the reference dose (RfD) and toxicity reference value (TRV). The risk quotient (RQ) calculated for each element showed that the risks from consumption of fish were generally low and within safe limits. The risks associated with arsenic, cadmium and mercury were, however, elevated. The highest calculated RQ was associated with total arsenic; however, the majority of arsenic in marine organisms tends to be in the non-toxic organic form, and the actual risk to the dolphin due to this metalloid is likely to be lower.