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 in all three systems, and incubated under oxic conditions demonstrated substantial mineralization of [U-ring-¹⁴C] 4-n-NP to ¹⁴CO₂.  In contrast, no mineralization of [U-ring-¹⁴C] 4-n-NP was observed in these sediments under anoxic (methanogenic) conditions.  The 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.