TRANSFORMATION OF PARASUBSTITUTED BENZONITRILES IN SEDIMENT AND IN SEDIMENT EXTRACT

Degradation mechanisms of chemicals in sediment must be known in order to permit more accurate assessment of aquatic pollutants. One possibl e degradation mechanism -- abiotic transformation -- has received litt le attention, however. In this study, the abiotic transformation of pa rasubstituted benzonitriles in an extract prepared by protein extracti on from sediment was compared with that in raw sediment and in water. In water, the benzonitriles were hydrolyzed to benzoic acid through be nzamides at elevated temperature. In anaerobic river sediment, the ben zonitriles were transformed to the corresponding benzoic acids, except for iodo- and methoxy-derivatives. In the sediment extract, the benzo nitriles, including iodo- and methoxy-derivatives, were transformed to benzoic acids. Benzonitrile transformation did not produce benzamides as intermediates in the latter two media. Transformation in sediment and in sediment extract must have been mediated by an enzyme whose act ivity is similar to that of nitrilase. Analyses using quantitative str ucture activity relationships (QSAR) were carried out with the three s ets of rate constants measured in the three media. The rate constants in sediment and sediment extract were correlated mainly with the hydro phobicity substituent parameter pi. Rate constants for purely chemical hydrolysis in water were correlated with the electronic substituent p arameter Hammett sigma(p). These results showed that the reaction mech anisms in sediment and sediment extract resembled each other and indic ate that the abiotic reaction mediated by the extracted sediment prote in fraction was responsible for at least part of the reaction occurrin g in raw sediment.