Phytoestrogens in the environment, II: Microbiological degradation of phytoestrogens and the response of fathead minnows to degradate exposure

Phytoestrogens are endocrine active compounds derived from plants, including the isoflavones genistein and daidzein, and their methylated derivatives biochanin A and formononetin. These compounds have been detected at the μg/L level in the effluents of plant-processing industries and municipal treatment plants and at the ng/L level in surface waters worldwide. The present study assessed the persistence of genistein and daidzein in natural aquatic systems, specifically riverine samples. Initial concentration, temperature, sample location, and time of sample collection varied. Genistein and daidzein were found to be readily biodegradable at all tested concentrations, at both 10°C and 20°C, in samples collected during different seasons, and in samples from 3 different rivers. In addition, organismal responses in larval and sexually mature fathead minnows (Pimephales promelas) were quantified following exposure to microbiologically degraded phytoestrogens (genistein, daidzein, and formononetin). Products of the microbiological degradation of parent phytoestrogens did not affect larval survival, growth, or predator avoidance. Female adult fathead minnows exposed to these degradation products produced significantly fewer eggs than those exposed to a control, but no other morphological, physiological, or behavioral changes were observed with male or female minnows. The present research suggests that although phytoestrogens are not likely to persist in aquatic systems, they may pseudo-persist if discharges are continuous; in addition, caution should be exercised with respect to high-concentration effluents because of the potentially antiestrogenic effects of phytoestrogen degradates. Environ Toxicol Chem 2014;33:560-566.