Phytoestrogen distribution and degradation in natural and engineered systems

Abstract

Phytoestrogens are plant-derived hormonally active compounds known to cause varied reproductive, immunosuppressive and behavioral effects in fish. Environmentally relevant concentrations of phytoestrogens have been identified in numerous industrial and wastewater effluents, but their presence in surface water has received little attention. Additionally, no work has been performed to assess the degradability of phytoestrogens in surface waters or to determine which microbial communities may be responsible for their degradation. Given the fundamental questions that exist regarding phytoestrogens in the environment, the objectives of this research were three-fold: 1) Determine the degradation capacity of genistein, a potent and common phytoestrogen species, in surface waters under a variety of environmental conditions, 2) Monitor the temporal and spatial fluctuations of 6 phytoestrogen species in wastewater-impacted and unimpacted surface waters, 3) Examine if genistein, like similarly structured steroidal estrogens, is capable of being degraded cometabolically by nitrifying organisms. Triplicate batch reactors with triplicate negative controls were used to investigate genistein degradation in both surface water and enriched nitrifying cultures. Grab samples were collected from impacted and unimpacted surface waters to identify temporal and spatial phytoestrogen patterns. Genistein degradation rates in surface water samples were found to vary significantly and depended on initial concentration, incubation temperature, season of water collection, and surface water source. Overall genistein degraded rapidly and variably, with the time to 50% degradation ranging from 15 to 70 hours. In reactors amended with 100 μg/L genistein, an enrichment period during which there was no or little degradation was followed by a period of rapid genistein degradation (zero-order), suggesting that genistein may be degraded intentionally as an energy source rather than incidentally via some cometabolic pathway. Experiments with nitrifying organisms indicated that genistein was not cometabolically degraded by nitrifying organisms, but it was degraded by organisms that were enriched under nitrifying conditions. Temporal and spatial studies detected several phytoestrogen species in surface waters at low nanogram per liter concentrations with no discernible temporal or spatial pattern. This research suggests that like genistein, phytoestrogens in general may be readily degraded in surface waters. It also suggests that phytoestrogens are not likely to cause widespread ecological harm, but caution should be taken as numerous compounds in this class exist and only a limited number of surface waters were sampled for phytoestrogen presence.