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As toxicants move into aquatic systems, the concentration at any point in space or time is heavily influenced by the flow dynamics. The dispersion of these chemicals creates a toxicant concentration that fluctuates widely in time and is highly dependent on the spatial heterogeneity of turbulence. Despite this knowledge on the movement of toxicants in natural systems, most ecotoxicological studies use static exposure paradigms that ignore the spatio-temporal dynamics of toxicants in aquatic systems. Although recent studies have begun to use pulsed paradigms in an attempt to mimic natural conditions, the heterogeneity of real concentrations in natural systems rarely is considered for use in these tests. Thus, understanding how organisms are impaired by naturally distributed toxicants is relatively unknown. The purpose of this experiment was to determine how turbulent dispersion of a toxicant negatively impacts a behavioral task and if altering the nature of turbulence will change the negative impact of the toxicant. Crayfish were exposed to a turbulent plume of carbaryl, an insecticide, under two different turbulent conditions and two different spatial conditions. Turbulence was altered by placing an obstruction within the flow which mimics a natural obstruction in lentic systems. Crayfish were exposed to sublethal concentrations of carbaryl for 48 h under these different dynamic conditions. After toxicant exposure, crayfish foraging ability was measured in a flow-through Y maze. We hypothesized that crayfish exposed to the toxicant under more turbulent conditions would exhibit more detrimental responses due to the increased variation in chemical fluctuations. The fine-scale chemical distribution of the toxicant and the three-dimensional velocity profile were characterized for each of the turbulent conditions and each of the spatial locations. Analyses of these data showed that changes in turbulence or spatial location created a unique exposure condition. Particularly, significant variations in the rise time, intermittency, and slope of toxicant pulses were quantified, whereas average concentration of the peaks remained constant across locations. Deficits in the foraging ability of crayfish exposed under these dynamic conditions paralleled the differences quantified in parameters of the turbulent toxicant plume. Given these results, the concept of toxicant exposure needs revision and needs to incorporate the more temporally based measures of toxicant dispersion. In addition, static and pulsed exposure models do not duplicate natural exposure and may not reflect behavioral or physiological impairments that occur under more realistic exposure conditions.

The Degree of Impairment of Foraging in Crayfish (Orconectes virilis) due to Insecticide Exposure is Dependent upon Turbulence Dispersion