PHOTOCHEMICAL DEGRADATION OF NONYLPHENOL AND NONYLPHENOL POLYETHOXYLATES IN NATURAL-WATERS

The rates of photochemical transformation of nonylphenol (NP) and nonylphenol polyethoxylates (NPnEO) in natural waters were assessed by exposing their solutions in filtered lake water (DOC=4 mg/L) to sunlight. The first-order rate constant of sunlight photolysis (k(p)) for NP was estimated at 0.09 m2/(kWh). This corresponds to a half-life of 10-15 hours under continous clear sky, noon, summer sunlight in the surface layer of natural waters. The photolysis rate in the deeper layers is strongly attenuated, being approximately 1.5 times slower at depths of 20-25 cm than at the surface. The photochemical oxidation of NPnEO was shown to be significantly slower than that of NP. Additional laboratory experiments using a merry-go-round reactor (MGRR) have shown that the photochemical degradation of both NP and NPnEO was due mainly to sensitized photolysis whilst direct photolysis was comparatively slow. Moreover, experiments with D2O revealed that singlet oxygen was not an important photooxidant of NP at pH values usually found in natural waters.