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 μg/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 μg/L) than that of those with no UV exposure (EC 50 = 153 μg/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 μg/g dry weight [dw]) and 21 ng/clam (or 2300 μg/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 μg/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. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 567–577 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10093