Degradation of nonylphenol ethoxylates in estuarine sediment under aerobic and anaerobic conditions

Nonylphenol ethoxylate (NPEO) surfactants and their metabolites are ubiquitous contaminants of the aquatic environment. Despite considerable interest in the environmental fate of these compounds due to concerns over toxicity and estrogenic activity, the pathways of NPEO degradation in sediments have not previously been reported, in spite of the fact that sediment appears to be an important sink for these compounds in the environment. In the present work, we have examined the rates and pathways of NPEO degradation in batch sediment slurry experiments using radiolabeled NPEO mixtures. Results suggest that NPEOs are more persistent in sediments under anaerobic conditions than in the presence of oxygen. In addition, it was illustrated that NPEO degradation proceeds via separate pathways in oxic and anoxic sediment. Discernible metabolites were identified and an overall mass balance for NPEO degradation in oxic and anoxic sediment was achieved. In contrast with previous studies, no evidence was observed for net production of nonylphenol from NPEOs during aerobic or anaerobic degradation. The observed relative rates at which NPEO ethoxymers disappeared in the sediment slurry experiments were consistent with previous reports for these compounds in sediment and other environmental media, although the absolute rates measured were somewhat faster than those reported for field sediments.