The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three, hydrologically-distinct, waste-water treatment plant (WWTP) impacted streams in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring-¹⁴C] 4-n-NP as a model test substrate. Microcosms prepared with sediment, collected upstream of the WWTP outfalls, and incubated under oxic conditions showed rapid and complete mineralization of [U-ring-¹⁴C] 4-n-NP to ¹⁴CO₂ in all three systems. In contrast, no mineralization of [U-ring-¹⁴C] 4-n-NP was observed in these sediments under anoxic (methanogenic) conditions. The initial linear rate of [U-ring-¹⁴C] 4-n-NP mineralization in sediments from upstream and downstream of the respective WWTP outfalls was inversely correlated with the biochemical oxygen demand (BOD) of the stream bed sediments. These results suggest that the net supply of dissolved oxygen to stream bed sediments is a key determinant of the rate and extent of 4-NP biodegradation in stream systems. In the stream systems considered in this study, concentrations of dissolved oxygen in the overlying water column (8-10 mg/L) and in the bed sediment pore water (1-3 mg/L at a depth of 10 cm below the sediment/water interface) were consistent with active in situ 4-NP biodegradation. These results suggest that WWTP procedures which maximize the delivery of dissolved oxygen while minimizing BOD releases to stream receptors, favor efficient biodegradation of 4-NP contaminants in waste-water-impacted stream environments.

Keywords: Biodegradation; Endocrine-disruption; Nonylphenol; Oxic; Streams