Sensitivity of juvenile Macomona liliana (bivalvia) to UV-photoactivated fluoranthene toxicity.

This study assessed the sensitivity of Macomona liliana (bivalvia, tellinacea) to UV-photoactivated fluoranthene toxicity. Juvenile clams (0.5-2.0 mm) were exposed to a range of aqueous fluoranthene concentrations (5-500 microg/L) for 96 h, after which the clams' ability to rebury in control sediment was determined. Survivors of these fluoranthene-only toxicity tests were then exposed in clean seawater to UV radiation from a solar radiation-simulating light source for 1 h. The differences between EC(50) values before and after UV exposure provided a measure of phototoxicity of the bioaccumulated fluoranthene. Fluoranthene tissue burdens corresponding to the EC(50) values were determined by exposing a second batch of clams to (14)C-radiolabeled fluoranthene. A third experiment quantified the kinetics of fluoranthene uptake and elimination in water-only exposures. Fluoranthene phototoxicity was found to depend on the dose of fluoranthene and the duration of UV exposure. Exposure of animals to 1 h of UV radiation resulted fluoranthene toxicity that was 3 times higher (EC(50) = 46 microg/L) than that of those with no UV exposure (EC(50) = 153 microg/L). The corresponding critical body burden (i.e., fluoranthene tissue concentration at which 50% of the clams failed to rebury) was 6 ng/clam (or 700 microg/g dry weight [dw]) and 21 ng/clam (or 2300 microg/g dw) for UV-exposed and UV-unexposed animals, respectively. First-order uptake and elimination coefficients, determined in the kinetics experiment, were 0.825 Lg(-1) h(-1) and 0.059 h(-1), respectively, indicating rapid uptake and a short fluoranthene tissue half-life of approximately 12 h for M. liliana. Compared with other bivalve species of similar size, M. liliana appeared to be more than 1 order of magnitude less sensitive to UV-activated fluoranthene toxicity, although these differences may be a result in part of differences in the UV exposure regime. Nonetheless, the majority of M. liliana exposed to a fluoranthene concentration of 50 microg/L displayed evidence of UV-photoactivated toxicity within 30-60 min of irradiation, and prolonging UV exposure more than 2 h killed all clams. These results demonstrate that even short UV exposures, as perhaps encountered during normal feeding or byssus-drifting behavior, may significantly increase toxicity to juvenile M. liliana possessing elevated fluoranthene tissue concentrations.