Biodegradation of Endocrine Disrupting Wastewater Micro-Constituents in Stream Systems

Over the last decade, the Emerging Contaminants Project of the U.S. Geological Survey Toxics Substances Hydrology Program has employed novel analytical methods and conducted nationalscale surveys in order to assess the environmental occurrence of a number of contaminants of “emerging” concern. In light of the apparent widespread occurrence of these “emerging” contaminants, the U.S. Geological Survey research focus has been extended to include their fate and transport in a variety of environmental settings.For example, the potential for in situ biodegradation of the endocrine disrupting alkylphenol surfactant compounds, 4-nonylphenols, has been investigated in three, hydrologically-distinct, wastewater treatment plant impacted streams in the United States. Biodegradation of 4-nonylphenol was assessed in water and sediment microcosm mineralization studies using [U-ring-14C] 4-n-nonylphenol as a model substrate. Microcosms prepared with sediment collected upstream of the wastewater treatment plant outfalls and incubated under oxic conditions showed rapid and complete mineralization of [U-ring-14C] 4-n-nonylphenol to 14CO2 in all three systems. In contrast, no mineralization of [U-ring-14C] 4-n-nonylphenol was observed in these sediments under anoxic (methanogenic) conditions. The initial linear rate of [U-ring-14C] 4-n-nonylphenol mineralization in sediments from upstream and downstream of the respective outfalls was inversely correlated with the biochemical oxygen demand of the stream bed sediments. These results suggest that wastewater treatment plant procedures that maximize the delivery of dissolved oxygen while minimizing the biochemical oxygen demand in stream receptors, favor efficient biodegradation of 4-NP contaminants in wastewater-impacted stream environments.Results of this and other studies indicate that wastewater micro-constituents can undergo significant biodegradation in surface waters and, consequently, that in situ biodegradation can be an important component of the management of these contaminants in the environment. However, the efficiency and circumstances of biodegradation can vary significantly between stream systems and between compound classes. Likewise, the potentials for in situ biodegradation of a large number of wastewater micro-constituents remain untested. Continued assessment of the potential for wastewater micro-constituent biodegradation is required to develop best management practices for individual surface-water systems and for specific compound classes. A strong understanding of the “assimilative capacity” of surface-water receptors for wastewater micro-constituents will provide a scientific foundation for “up-front technical input” during the development of regulatory contaminant criteria and maximum load polices.