Distribution and fate of neutral alkylphenol ethoxylate metabolites in a sewage-impacted urban estuary

Abstract

The distribution and fate of neutral metabolites of the alkylphenol ethoxylate (APEO) surfactants in an urbanized estuarine environment were examined utilizing a recently developed, highly sensitive LC-MS method. Results indicated that short ethoxyl-chain APEOs and alkylphenols (APs) were present in surficial sediments throughout the estuary at concentrations roughly correlated to the organic carbon content of the sediment and that the APEO mixture was dominated by nonylphenol ethoxylate (NPEOs) metabolites (0.05-30 microg/g), with lesser amounts of octylphenol ethoxylate metabolites (OPEOs)(<0.005-0.09 microg/ g) and halogenated nonylphenols (<0.001-0.03 microg/g). NPEO metabolites in surface water (0.22-1.05 microg/L) were also present at higher concentrations than OPEO metabolites (0.007-0.040 microg/L). APEO metabolite concentrations in both sediment and water showed a strong correlation with conventional sewage tracers, affirming a wastewater source of these contaminants. APEO distributions in surface waters within the estuary could be explained by a combination of post-discharge degradation and mixing with a seawater end-member enriched in OPEO metabolites. Measured in situ Koc values of APEO metabolites were comparable to previously reported values derived from field experiments but higher than Kow and Koc values derived from laboratory experiments. Results from the present work indicate that the fate of APEO metabolites entering the estuarine environment through discharge of wastewater is directed primarily by scavenging onto particles and subsequent burial in sediments, degradation during residence in the water column, and transport out of the estuary through advective and dispersive processes.