Toxic effects of dredged sediments of Hong Kong coastal waters on clams.

The present project is an attempt to study the effects of the sediments collected from various sites on the survival of three indigenous bivalves (Circe scripta, Gafrarium fumidum and Tapes philippinarium). The preliminary trial revealed that T. philippinarium was more sensitive than the other two species in response to the dredged sediment collected from the pollution blackspot: Yau Ma Tei typhoon shelter. A subsequent experiment used T. philippinarium to assess the toxicity of sediments under different dissolved oxygen regimes (7.8, 8.0 and 8.2 mg L-1). Significant correlations (p<0.05) were noted between the mortality rates of the test animals and the total nitrogen and ammonia contents in the seawater.