Toxicological assessment of coastal sediments in Hong Kong using a flagellate, Dunaliella tertiolecta

Abstract

Samples of coastal sediment were collected from the southern (Victoria Harbour) and the western side (Deep Bay) of Hong Kong to determine the existing or potential impacts of sediment-associated contaminants on the environment. The samples were analyzed for the total concentrations of Cd, Cr, Cu, Pb and Zn, ammonia-N, pH, and simultaneously extracted and soluble metals. Elutriate sediment toxicity tests (ESTT) were also conducted, using a microalgal flagellate, Dunaliella tertiolecta. In the first experiment, a total of six sediment samples were collected from the inner and outer areas of Deep Bay, inside Tuen Mun typhoon shelter, Rambler Channel, Tsuen Wan and the New Yau Ma Tei typhoon shelter. All the sediment elutriates had inhibitory effects on the growth of the microalgae. The lowest 48-h LC 50 was obtained in Tsuen Wan elutriate (42.6%). The results indicated that the percentage response of the microalgae was not directly correlated to heavy metal contents, but showed a positive correlation to the ammonia concentration. The calculated 48-h LC 50 of ammonia toxicity was 18.67±1.4 mg/l. In the second experiment, the toxicity of ammonia-N from a total of seven sediment samples (Kowloon Bay, Rambler Channel, Chai Wan, Sam Ka Tsuen, Causeway Bay, Aldrich Bay, Old Yau Ma Tei typhoon shelter) was determined. Air-stripped sediment elutriates reduced the total ammonia contents from 14.41–37.39 to 8.47–22.08 mg/l which significantly reduced the toxic effect on the microalgae when compared with the non-air-stripped samples, suggesting that ammonia-N was one of the major toxicants in the elutriates. The 48-h LC 50 (NH 3) was calculated at 36.67±2.47 mg/l. These results suggested that a significant component of sediment toxicity was a result of elevated ammonia, although there were elevated concentrations of potentially toxic heavy metals.