A NOVEL USE FOR THE CONTINUOUS-FLOW SERIAL DILUTER - AQUATIC TOXICITYTESTING OF CONTAMINATED SEDIMENTS IN SUSPENSION

Testing the toxicity of contaminated sediments is crucial to evaluatin g environmental risks because hydrophobic chemicals readily sorb to pa rticulate matter. The 96-h median lethal concentration (96-h LC(50)) f or creosote-contaminated sediments was determined with spot (Leiostomu s xanthurus), a saltwater fish common to estuarine areas of the easter n United States. Fish were exposed to suspended sediment in a flow-thr ough system. A continuous-flow serial diluter was used to produce five concentrations of creosote. Sediment without creosote added was used to maintain a constant sediment concentration throughout the dilution process and for a vehicle control. The nominal concentration of suspen ded sediment in all treatments was 20 mg/l, on a dry-weight basis. Mea n total resolvable polycyclic aromatic hydrocarbon (PAH) concentration s tested were 110, 250, 560, 1400, and 3300 mu g PAH/l. Sediment conce ntration varied <24% and PAH concentration varied <36%. The 96-h LC(50 ) was 1740 mu g PAH/l (95% confidence interval = 1480-2060 mu g PAH/l) . This result compares favorably with results from tests using other s pecies of fish and exposure methods. Other reported methods, however, have not demonstrated the constancy or ease of dosage administration f or a range of concentrations as the system used here. Exposing fish to suspended sediments contaminated with hydrophobic compounds may be an appropriate method for assessing the environmental risk of hydrophobi c chemicals to fish.