Phototoxicity of anthracene and pyrene to glochidia of the freshwater mussel Utterbackia imbecillis.

The acute toxicity of photoactivated anthracene and pyrene to the glochidial larvae of the paper pondshell (Utterbackia imbecillis) was characterized in the laboratory using two sets of experiments. Acute toxicity tests designed to determine the overall sensitivity of glochidia to anthracene and pyrene were conducted under simulated sunlight (ultraviolet [UV]-A = 70+/-0.5 microW/cm2 [mean +/- standard deviation]). The median lethal concentration (LC50) and median lethal dose (LD50) of anthracene at 24 h were 1.93 (95% CI, 0.87-3.02) microg/L and 1.94 (1.87-2.00) microg/g glochidia, respectively. The LC50 and LD50 for pyrene at 24 h were 2.63 (2.38-2.90) microg/L and 6.36 (5.82-6.94) microg/g glochidia, respectively. Acute toxicity tests designed to delineate the relationship between the rate of mortality and UV intensity were conducted under one of four different UV intensities (UV-A = 15, 31, 50, and 68 microW/cm2). Regression analyses revealed that time to death decreased as tissue residue concentrations and UV intensity increased for both compounds. Based on measured tissue residues, anthracene was 1.5-fold more potent than pyrene and 3-fold more potent than fluoranthene. The lower potency of fluoranthene is in agreement with previously developed structure-activity relationships; however, these relationships predict equal potency between anthracene and pyrene. These findings suggest that glochidia of freshwater mussels are sensitive to photoactivated anthracene and pyrene at environmentally relevant concentrations, that the time-dependent mortality of glochidia can be accurately predicted through evaluating the product of tissue residue and light intensity, and that species-dependent factors may alter the predicted relative potencies of anthracene and pyrene.