Distribution and impact of trifluralin, atrazine, and fonofos residues in microcosms simulating a Northern Prairie Wetland

Results are presented from microcosm tests simulating inputs of pesticides in runoff into a semi-permanent wetland in South Dakota. The microcosms contained composited sediment and associated biota collected from the wetland, and were also seeded with small populations of Daphnia magna and Chironomus riparius. A single application of a mixture of sediment, water, and radioactively-labelled pesticide, simulating edge-of-field runoff, was added to each microcosm, and the constituents of the microcosm were monitored over a 6-week period. The results are discussed in detail, and the concentrations of the pesticides in the various components of the microcosm are illustrated graphically. Pesticide residues disappeared rapidly from the water column, mainly as a result of adsorption on the organic phase of the sediment. There was also some loss due to volatilization (in the case of trifluralin and fonofos) and photolysis (in the case of trifluralin). The regeneration of parent pesticide compounds from sediment-bound residues appeared to be unlikely. For the pesticides tested, the probability of chronic effects on aquatic organisms or of biomagnification of toxic residues through food chains appeared to be low. There are 62 references.