MAGNITUDE AND DISTRIBUTION OF CONTAMINANTS IN SALT-MARSH SEDIMENTS OF THE ESSEX COAST, UK .3. CHLOROPHENOXY ACID AND S-TRIAZINE HERBICIDES

Concentrations of chlorophenoxy acid (CPH) and s-triazine herbicides were determined in the sediments of five salt marsh sites on the Essex coast (UK). The degree of contamination, in the ng g-1 range, was related to herbicide usage in the adjacent catchment, the duration between herbicide application and sampling and the mobility and persistence of individual herbicides. Contamination of the salt marshes by herbicides was due to both agricultural and urban sources. In general, the herbicides were found to concentrate at the surface of the sediment profile and decrease in concentration with depth. Vegetated marsh areas exhibited a greater degree of s-triazine contamination than mud flat/creek sediments, while the CPH were more evenly distributed between these two morphologically different regions. The detection of the s-triazine herbicide metabolites indicated both the active degradation of these herbicides within salt marsh sediments and that detected sediment herbicide concentrations were residual rather than maximum values.