POLAROGRAPHIC-DETERMINATION OF SOME PESTICIDES - APPLICATION TO A STUDY OF THEIR ADSORPTION ON LIGNIN

Polarographic reduction of the nitro group in acifluorfen and of the disulfidic bond in thiram as well as the anodic waves of mercury salt formation of dazomet can be used to follow adsorption of pesticides on lignin. Within this group, thiram was adsorbed most strongly, then dazomet, and weakest was the adsorption of acifluorfen. The adsorption depends on the pH of the medium, because of both the acid-base equilibria involving the pesticide and the equilibria involving acidic groups on lignin. The effect of variations in spatial arrangement (tertiary structure) of lignin with pH, indicated in previous studies, cannot be excluded. In all cases, the adsorption on kraft lignin used in this study was weaker than that on natural lignins. The greater part of the sulfur-containing pesticides (dazomet, thiram) was bound to lignin irreversibly. This decreases the bioavailability of the pesticide in forest litter and forest soil.