Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/1998
Publication Date: N/A
Citation: Potter, T.L., Simmons, K., Wu, J., Sanchez-Olvera, M., Kostecki, P., Calabrese, E.J. 1999. Static die-away of a nonylphenol ethoxylate surfactant in estuarine water. Journal of Environmental Science and Technology. 33:113-118. DOI: 10.1021/es9804464. Interpretive Summary: Surfactants are compounds used to emulsify and solubilize oils, greases and other substances. In agriculture, their primary use is in pesticide spray formulation. This facilitates application and increases efficacy. In general, use of surfactants lowers the potential for adverse environmental impacts from pesticides by reducing application rates. However, recent studies with one common class of surfactants, the nonylphenol ethoxylates (NPE), have indicated that when these compounds are degraded by bacteria in freshwater environments, products may form which are more toxic to aquatic organisms than many pesticides. This study was conducted to determine whether the same types of compounds form in seawater and to evaluate potential impacts on coastal ecosystems. Using water samples collected in Tampa Bay, Florida, it was found that the main degradation products of NPE were not these which have been reported to be most toxic. This indicates that NPE surfactants can be used safely in pesticide sprays in coastal areas. The study has contributed data to industry scientists and action agencies which can be used to evaluate potential impacts to water quality and ecosystem health.
Technical Abstract: Static die-away of the NPE surfactant used in the fuel Orimulsion was studied using water samples collected in Tampa Bay, FL. The concentration of the surfactant and five intermediate products was monitored by HPLC and GC/MS for 183 days. Surfactant primary degradation was complete in 4 to 24 days with lag-periods between 0 and 12 days. The principal intermediates detected included nonylphenol diethoxylate (NP2EO) and nonylphenoxy ethoxy acetic acid (NP2EC) with the sequence of appearance indicating NP2EC formation by oxidation of NP2EO. On a molar basis, NP2EC accounted for 66.0-93.3% of the degradation products and 22.7 to 75.6% of the starting materials at the termination of the experiment. A second phase of the experiment was initiated on day 296. The remaining water in two sample incubation containers was combined with equal volumes of freshly collected Tampa Bay water. In one sample, die-away of the residual NPE2C began at day 20 and declined to approximately 50% of the initial concentration on day 32. In a second sample, no change in NP2EC or NP1EC concentration was observed. These data have confirmed relatively rapid primary degradation of the parent NPE surfactant and the formation in sequence of two degradation products, NP2EO and NP2EC. The later compound appears to be relatively resistant to further degradation. However, data did indicate that microorganisms are present in the Bay, which are capable of transformation and degradation of the compound.