Static die-away of a nonylphenol ethoxylate surfactant in estuarine water samples

The static die-away of the nonylphenol ethoxylate (NPE) surfactant used to stabilize the bitumen-water emulsion in the fuel Orimulsion was studied usi ng estuarine water samples collected at four stations in Tampa Bay, FL. Inc ubations were in the dark at 28 degrees C for 183 days. Primary degradation was complete in 4-24 days with lag periods between 0 and 12 days. The conc entration of five NPE intermediate degradation products and total surfactan t were monitored at 4-8-day intervals for the first 89 days and at 30-day i ntervals thereafter. The intermediates detected included nonylphenol dietho xylate (NP2EO) and nonylphenoxy ethoxy acetic acid (NP2EC). Much smaller am ounts of nonylphenoxy acetic acid (NP1EC) and nonylphenol monoethoxylate (N P1E0) were detected. The completely deethoxylated metabolite nonylphenol (N P) was not detected. On a molar basis, NP2EC accounted for 66.6-93.3% of de gradation products and for 22.7-75.6% of the starting material at the termi nation of the experiment. The sequence of degradation and intermediate accu mulation and decay indicated the initial formation of NP2EO from higher NPE homologues followed by oxidation to NP2EC. A second phase of the experimen t was initiated on day 296. The remaining water in two sample incubation co ntainers was combined with equal volumes of freshly collected Tampa Bay wat er. In three of five replicates from one sample, die-away of the residual N P2EC began at day 20 and declined to approximately 50% of the initial conce ntration on day 32. In other replicates of this sample and in a second samp le, no change in NP2EC or NP1EC concentrations was observed. The data have confirmed relatively rapid primary degradation of the parent NPE and the fo rmation 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 were present in the Bay that are ca pable of transformation and degradation of the compound.