Isomer-Specific Degradation of Branched and Linear 4-Nonylphenol Isomers in an Oxic Soil

摘要

Using ~(14)C- and ~(13)C-ring-labeling, degradation of five p-nonylphenol (4-NP) isomers including four branched (4-NP_(38),4-NP_(65),4-NP_(111), and 4-NP_(112)) and one linear (4-NP,) isomers in a rice paddy soil was studied under oxic conditions. Degradation followed an availability-adjusted first-order kinetics with the decreasing order of half-life 4-NP_(111) (10.3 days) > 4-NP_(112) (8.4 days) > 4-NP_(65) (5.8 days) > 4-NP_(38) (2.1 days) > 4-NP, (1.4 days), which is in agreement with the order of their reported estrogenidties. One metabolite of 4-NP_(111) with less polarity than the parent compound occurred rapidly and remained stable in the soiL At the end of incubation (58 days), bound residues of 4-NP_(111) amounted to 54% of the initially applied radioactivity and resided almost exclusively in the humin fraction of soil organic matter, in which chemically humin-bound residues increased over incubation. Our results indicate an increase of specific estrogenicity of the remaining 4-NPs in soil as a result of the isomer-specinc degradation and therefore underline the importance of understanding die individual fate (including degradation, metabolism, and bound-residue formation) of isomers for risk assessment of 4-NPs in soil. 4-NP, should not be used as a representative of 4-NPs for studies on their environmental behavior.