ACCUMULATION DYNAMICS OF TRICLOPYR ESTER IN AQUATIC LEAF PACKS AND EFFECTS ON DETRITIVOROUS INSECTS

Previous field studies have demonstrated that residues of the herbicid e, triclopyr butoxyethyl eater (3,5,6-trichloro-2-pyridinyloxyacetic a cid, butoxyethyl ester) (TBEE), can accumulate in submerged leaf mater ial of aquatic systems at concentrations up to 20 times the maximum aq ueous concentrations. Accumulated TBEE residues may pose a risk of adv erse effects to detritivorous invertebrates inhabiting and using natur al leaf packs. We examined the dynamics of TBEE accumulation and persi stence in leaf materials of laboratory and outdoor aquatic systems, an d determined the ecological significance of this in terms of effects o n detritivorous insects and organic matter processing. Accumulations o f TBEE in leaf packs of semi-static laboratory microcosms; were up to 80 times aqueous concentrations, and residues persisted for 4 to 5 d. Leaf material of flow-through laboratory microcosms accumulated TBEE a t much higher rates (up to 1000 times aqueous concentrations), but res idues were cleared by 48 to 72 h. Accumulation and persistence in flow -through units were dependent on water depth, velocity, and exposure d uration. Accumulated TBEE residues were less in outdoor stream channel s than in laboratory flow-through units, probably because of losses th rough sorption to natural benthic material in the stream channels. Des pite accumulations of TBEE in leaf packs at up to 90 mg kg(-1) in syst ems treated at or near expected environmental concentrations, there wa s no significant mortality of detritivorous insects and no significant reductions in leaf consumption. Significant mortality and reduced fee ding occurred only in systems treated at concentrations well above (up to 10 times) expected environmental concentrations.