Review of the persistence of nonylphenol and nonylphenol ethoxylates in aquatic environments

Alkylphenol ethoxylates, in particular nonylphenol ethoxylates, are widely used nonionic surfactants that are discharged in high quantities to sewage treatment plants and directly to the environment in areas where there is no sewage or industrial waste treatment. This article reviews the treatabilit y of nonylphenol ethoxylates and nonylphenol in sewage treatment plants and their persistence in aquatic environments. Nonylphenol ethoxylates can be biologically degraded in sewage treatment plants and in natural environment s. Some of the degradation products, including nonylphenol, are more persis tent than the parent surfactants and they are found in receiving waters of sewage treatment plants. Nonylphenol in particular is found at high concent rations in some sewage sludges that may be spread on agricultural lands. Wh ile some sewage treatment plants discharge significant amounts of nonylphen ol ethoxylate degradation products in their final effluents and digested sl udges compared to what enters the plant, others degrade nonylphenol ethoxyl ates more or less completely. The differences in treatment efficiency of su ch compounds and their degradation products among different sewage treatmen t plants have been attributed to the load of the surfactants in influent st reams, plant design and operating conditions, and other factors such as tem perature of treatment. The highest nonylphenol ethoxylate elimination rates were achieved in plants characterized by low sludge-loading rates and nitr ifying conditions. In natural waters, it appears that parent nonylphenol et hoxylates are not persistent, but some degradation products may have modera te persistence, especially under anaerobic conditions. Recent results from mesocosm experiments indicate moderate persistence of nonylphenol in sedime nts, with half-lives of 28 to 104 days. Microbial acclimation to the chemic als is an important determinant of persistence vis-a-vis biodegradation. Su nlight photodegradation of such products is also likely important. Further research on the persistence in natural environments of the lower ethoxylate and carboxylate degradation products, as well as nonylphenol, is necessary . Based on the limited data available, nonylphenol and the lower ethoxylate s and carboxylates are persistent in groundwater. They are also persistent in landfills under anaerobic conditions, but they do not appear to be persi stent in soil under aerobic conditions. Recommendations are made for furthe r research in order to more fully characterize the treatability of nonylphe nol ethoxylates and their degradation products in sewage treatment plants a nd their persistence in the natural environment.