A novel use for the continuous-flow serial diluter: Aquatic toxicity testing of contaminated sediments in suspension

Testing the toxicity of contaminated sediments is crucial to evaluating environmental risks because hydrophobic chemicals readily sorb to particulate matter. The 96-h median lethal concentration (96-h LC50) for creosote-contaminated sediments was determined with spot (Leiostomus xanthurus), a saltwater fish common to estuarine areas of the eastern United States. Fish were exposed to suspended sediment in a flow-through 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 suspended sediment in all treatments was 20 mg/l, on a dry-weight basis. Mean total resolvable polycyclic aromatic hydrocarbon (PAH) concentrations tested were 110, 250, 560, 1400, and 3300 μg PAH/l. Sediment concentration varied <24% and PAH concentration varied <36%. The 96-h LC50 was 1740 μg PAH/l (95% confidence INTERVAL = 1480−2060 μg PAH/l). This result compares favorably with results from tests using other species of fish and exposure methods. Other reported methods, however, have not demonstrated the constancy or ease of dosage administration for 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 hydrophobic chemicals to fish.