The use of selected genotoxicity assays in Hong Kong coastal waters

Abstract

In Hong Kong, discharges of domestic and industrial wastewater and disposal of contaminated mud into coastal waters have resulted in high levels of persistent organic contaminants in the water column, biota and bottom sediments. In addition, the multi-billion dollar Strategic Sewage Disposal Scheme will release the wastewater from some 3.5 million people into the South China Sea, even though the impact of this discharge on the coastal environment is virtually unknown. Although the acute toxicity of the effluent has been tested by government regulators using mortality-based bioassays, the sublethal effects of many of the pollutants, including environmental carcinogens, have not been studied, and nor have their potential environmental risks been assessed. Changes to biological systems in response to toxic exposure have been widely used as “biomarkers” in order to provide an early warning of potential hazards. The objective of the present study was to examine the efficiency and efficacy of using selected genotoxicity assays, namely the electrochemical detection of 8-hydroxy-2-deoxyguanosine levels in cellular DNA, the DNA alkaline gel electrophoresis assay for DNA strand breaks, and micronuclei, as an early-warning surveillance system for environmental carcinogens in Hong Kong coastal waters. Green-lipped mussels (Perna viridis) were transplanted to the study sites including Kat O, Tap Mun, Tsim Sha Tsui, Sai Wan Ho and Ma Wan and retrieved after 4, 8, 12, 16 and 30 days. The bioaccumulation of organic pollutants including the PAHs, OC pesticides and PCBs was observed. However, the selected genotoxicity assays were not well correlated with the concentrations of organic pollutants in the organisms, except for polluted sites (Tsim Sha Tsui and Sha Wan Ho) where micronuclei were positively correlated with organic pollutants. Another case study in Tolo Harbour also showed the relationships between the organic pollutants and genotoxic biomarkers were not significant, possibly due to other environmental and physiological factors. In addition, the improper timing of sampling might cause the absence of significant responses in the selected genotoxic biomarkers. Therefore, further studies are required to validate the effectiveness of these biomarkers under field conditions. These studies might include a more frequent sampling schedule, a better understanding of the interactions between the environmental and physiological factors in the Hong Kong marine environment, and monitoring of changes in biotransformation and DNA repair enzymes in green-lipped mussels.