Abiotic behaviour of organic micropollutants in soils and the aquatic environment. A review: II. Transformation

The abiotic processes contributing to the transformation of pesticides in s oils and natural waters are reviewed for pyrethroid, carbamate and organoph osphorus (OP) insecticides; and the urea, chlorophenoxy and 5-triazine herb icides. The review aims to highlight the known abiotic thermochemical and p hotochemical reactions that may contribute to the overall degradation of pe sticides, and to identify the environmental factors influencing degradation pathways and rates of transformation. Studies indicate that transformation by hydrolysis is restricted to alkaline pH for pyrethroids, OPs, carbamate s and benzoylphenylureas, and limited to acid pH for sulphonylureas OPs are also susceptible to catalysed hydrolysis by certain cations and mineral-bo und +III and +IV metal ions. Little or no hydrolysis of triazines occurs in the water column or groundwaters, although triazines may be subject to hyd rolysis in certain soils at acid pH. Tests indicate that alkaline hydrolysi s is the most significant abiotic process for mono-substituted carbamates, and that photosensitised degradation is the most important abiotic pathway many OPs. Certain pyrethroids, triazines and urea pesticides are susceptibl e to photodegradation. However, the potential for phorosensitised transform ation for the majority of pesticide classes is uncertain (e.g. ureas, carba mates, triazines and CPHs). Tests for sensitised photodegradation need to b e extended and undertaken in mixtures of natural sensitisers because of the variable effects of dissolved organic matter (DOM). There appears to be in sufficient information regarding the significance of hydrolysis, photochemi cal degradation, and metal/mineral-catalysed transformation in the environm ent for the majority of these extensively used pesticide classes.