Abstract
The aerobic biodegradation of nonylphenol polyethoxylates (NPnEOs) and nonylphenol pentaethoxylates (NP5EO) was investigated by a river die-away test in the dark at 25°C for 10-14 days, spiked at a concentration of 0.5 mg/l.The concentration of NPnEOs or NP5EO and their intermediate degradation products were monitored at 2-4 day intervals. Direct analysis of the samples applying high performance liquid chromatography revealed a relatively fast degradation of starting material of NP5EO with >95 % degradation observed after 10-14 days in slightly organic polluted river waters with some exceptions. But degradation in clean river waters was slow. There are a very large number of bacteria degrading NP5EO in slightly polluted rivers, but small in clean water. Contrary to the generally proposed degradation pathway of the initial formation of nonylphenol diethoxylate (NP2EO), the initiating step of the degradation is ω-carboxylation of the individual ethoxylate chains and metabolites with long carboxylated EO chains (NP5EC) are identified. Further degradation proceeds gradually into short-chain carboxylated EO. NPnECs were dominant metabolites of the NP5EO biotransformation and were still present in the test water after 14 days. On a molar basis, residual NP5EC accounted for 13-66 % (av.34 %) of degradation products at 14 days of the experiment. Much smaller amounts of NP2EO and nonylphenol monoethoxylate (NP1EO) were detected.
