Effect of fluctuating lead exposures on lead accumulation by rainbow trout (Salmo gairdneri)

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Abstract
Contaminant concentrations in aquatic ecosystems vary spatially and temporally, so that surveillance data exhibit a log‐normal distribution; i.e., the majority of measurements are low but a few are quite high. These data are best characterized by geometric means. Contaminants that are taken up quickly but excreted slowly should accumlate in fish at concentrations that reflect the highest exposure rather than the geometric mean exposure. To confirm this prediction, blood lead concentrations of rainbow trout were measured after 20‐d exposures to concentrations of waterborne lead that fluctuated about a fixed geometric mean. Four levels of exposure variability were used. A lead exposure characterized by wide fluctuations was expected to cause greater lead uptake by trout than the equivalent exposure with less variability. Lead accumulation was best described by the following equation: log10 blood lead concentration (μg/L) = 0.814 + 0.999 log10 waterborne lead (μg/L) + 1.335 × standard deviation of log10 waterborne lead. Increasing lead concentrations and increasing variability of waterborne concentrations increased lead accumulation by trout. These results were accurately predicted by a simple one‐compartment model of contaminant kinetics in fish. Applying this model to other contaminants and to hypothetical exposure regimes demonstrated that high depuration rate constants increase the importance of exposures over the previous 24 h. This anaylsis also demonstrated that arithmetic mean exposures were a better way of describing contaminant accumulation by fish than were geometric mean exposures. Therefore, brief (24 h) violations of water quality criteria may cause a greater toxicity to fish than would be expected from simple estimates of the geometric mean concentrations in water. Water quality surveillance programs must be designed to accurately describe both contaminant variance and the arithmetic mean concentration.