FACTORS DETERMINING THE BIOACCUMULATION POTENTIAL OF PESTICIDES IN THE INDIVIDUAL COMPARTMENTS OF AQUATIC FOOD CHAINS

Abstract

Abstract Representative members of aquatic food chains, i.e., algae (Scenedesmus acutus), daphnids (Daphnia magna), and catfish (Ictalurus melas), have been used to evaluate the bioaccumulation potential of 10 pesticides. The objectives of the studies were to determine the kinetics of bioacumulation and depuration of pesticides and to estimate the contribution of food chain transfer of pesticide residues to the total magnitude of bioaccumulation. Furthermore, the influence of physicochemical properties and the stability of pesticides in the aquatic environment on their final concentration in aquatic organisms and on their possible availability in the aquatic environment was investigated. In standardized experiments it was shown that bioaccumulation of nonionic organic chemicals from water can essentially be described as sorption or, as a simplification, as a distribution phenomenon which was correlated with the n-octanol/water partition coefficient of the compounds. Increasing the biomass at a given pesticide concentration caused a decrease in the bioaccumulation factor. Depuration of pesticides from aquatic organisms followed second-order reaction kinetics. The half-lives as well as the reciprocal of the rate constants of depuration were found to be highly correlated with the lipophilicity of the pesticides. Transfer of pesticide residues via food chains was found to be of lesser importance compared with direct uptake from water. It did not result in a buildup of residues so that higher residues would have been obtained in higher trophic levels of the aquatic food chains (biomagnification). Even for the highly lipophilic p, p′-DDT only 23 and 44% of the residue of the respective lower food chain organisms (algae, daphnids) were retained by the respective higher food chain organisms (daphnids, catfish). Also the transfer of residues can be estimated by means of the partition coefficient of the pesticide. The possible appearance of a soil-applied pesticide in water systems depends on its soil mobility which was found to be inversely correlated with the partition coefficient and also with the sorption constants of aquatic organisms. Consequently, a high bioaccumulation potential of a lipophilic compound is significantly reduced due to its limited transfer to the aquatic environment.