HUMIC ACIDS REDUCE THE PHOTO-INDUCED TOXICITY OF ANTHRACENE TO FISH AND DAPHNIA

The effects of dissolved humic materials (DHM) on the photo‐induced toxicity of anthracene to fathead minnows Pimephales promelas and daphnia Daphnia magna were studied in a laboratory system under simulated sunlight. In the fathead minnow toxicity tests, four concentrations of anthracene (0, 6.6, 13.1 and 19.1 μ g/L) and five concentrations of DHM (0, 0.5, 1.0, 3.0 and 6.0 mg C/L) were achieved. In the daphnia toxicity tests, four concentrations of anthracene (0, 5.58, 10.49 and 21.03 μ g/L) and four concentrations of DHM (0, 0.8, 2.7 and 6.9 mg C/L) were achieved. DHM significantly reduced acute photo‐induced toxicity in both organisms. Median lethal times (LT50) were directly related to DHM concentration and inversely related to water anthracene concentration across the tested ranges of each variable. The presence of DHM also reduced anthracene bioaccumulation, and LT50 values for both fish and daphnia were inversely related to body anthracene concentration. Findings presented in this study demonstrate that the photo‐induced toxicity of anthracene is primarily a fugacity‐dependent phenomenon, that selective attenuation of the active wavelengths of solar ultraviolet radiation by DHM also results in a decreased level of acute toxicity and that a common mode of acute photo‐induced toxicity between fish and daphnia exists. Copyright © 1990 SETAC