Chemical contaminants discharged into estuaries and coastal areas often attach to sediment particles and are deposited on the sea bed. These contaminant-laden sediments may pose potential threats to coastal ecosystems, the sustainability of aquatic resources, and human health (via the food chain). In this project, we tried to develop two estuarine sediment toxicity tests from a selection of three species: two sediment-dwelling amphipods (Leptocheirus plumulosus and Ptilohyale plumicornis) and a bivalve mollusk (Meretrix lusoria). In the first screening, salinity tolerances of those species were compared in order to determine which ones could be appropriate test organisms for the estuarine environment. The effects of reference toxicants, two trace metals (copper and cadmium), and one organic toxicant, sodium dodecyl sulfate (SDS), were studied on selected organisms cultured in the laboratory. Confounding factors in the estuarine environment (e.g., sediment grain size, feeding demand, salinity tolerance, organism size, and organic matter content) that could contribute to toxicity in two of the test organisms were determined from optimal test survival conditions. Appropriate species must be selected for the purpose of developing standardized estuarine sediment toxicity tests for use in future estuarine sediment dredging, remediation, and cost-benefit assessment of the ecological environment. Local species Ptilohyale plumicornis was collected from the southern estuary and confirmed and the hard clam Meretrix lusoria and an internationally common amphipod species, Leptocheirus plumulosus, were reared in the lab. Test lengths (shell length) of Ptilohyale plumicornis, Leptocheirus plumulosus, and Meretrix lusoria are recommended at 2.5-4.5 mm, 2-4 mm, and about 2 cm as well as salinities of 19, 20, and 22‰, respectively, in toxicity tests. Ptilohyale plumicornis acute (96 h) LC50 values in increasing order were 2.00±0.12 mg/L for Cd, 2.35±0.20 mg/L for Cu, and 7.99±1.55 mg/Lmg/L for SDS. Leptocheirus plumulosus acute (96 h) LC50 values in increasing order were 2.58±0.51 mg/L for Cd, 3.26±0.59 mg/L for Cu, and 5.00±1.78mg/L for SDS. Meretrix lusoria 96-h LC50 values for copper, cadmium, and SDS were 0.09±0.03, 0.96±0.26, and 10.95±2.77 mg/L, respectively. Local amphipod Ptilohyale plumicornis is suitable for sandy sediment toxicity tests based on a previous confounding-factors investigation, and its body size and salinity levels used in our sediment toxicity tests are consistent with other aquatic toxicity tests as were the 25 oC water temperature and a feeding frequency of three times per week. Using Meretrix lusoria as the biomonitoring species for developing standardized estuarine sediment toxicity tests, culture conditions recommended are 22‰ salinity, 25 oC water temperature, no feeding during the 10-d exposure period, sandy sediments, and 2-3 cm shell length.

Sediment toxicity, Estuaries, Amphipods, Bivalve molluscs, Sensitivity