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

Samples of coastal sediment were collected from the southern (Victoria Harb our) and the western side (Deep Bay) of Hong Kong to determine the existing or potential impacts of sediment-associated contaminants on the environmen t. The samples were analyzed for the total concentrations of Cd, Cr, Cu, Pb and Zn, ammonia-N, pH, and simultaneously extracted and soluble metals. El utriate sediment toxicity tests (ESTT) were also conducted, using a microal gal 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 N ew Yau Ma Tei typhoon shelter. All the sediment elutriates had inhibitory e ffects on the growth of the microalgae. The lowest 48-h LC50 was obtained i n Tsuen Wan elutriate (42.6%). The results indicated that the percentage re sponse of the microalgae was not directly correlated to heavy metal content s, but showed a positive correlation to the ammonia concentration. The calc ulated 48-h LC50 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 sample s (Kowloon Bay, Rambler Channel, Chai Wan, Sam Ka Tsuen, Causeway Bay, Aldr ich Bay, Old Yau Ma Tei typhoon shelter) was determined. Air-stripped sedim ent 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 w hen compared with the non-air-stripped samples, suggesting that ammonia-N w as one of the major toxicants in the elutriates. The 48-h LC50 (NH3) was ca lculated at. 36.67 +/- 2.47 mg/l. These results suggested that a significan t component of sediment toxicity was a result of elevated ammonia, although there were elevated concentrations of potentially toxic heavy metals. (C) 1999 Elsevier Science Ltd. All rights reserved.