Accumulation of thallium in rainbow trout (Oncorhynchus mykiss) following acute and sub-chronic waterborne exposure.

The accumulation and tissue distribution of toxicants in aquatic biota can be determinative of their toxic impact to both the exposed organism, and their potential human consumers. In the current study the accumulation of the trace metal thallium (Tl) in gill, muscle, plasma and otoliths of rainbow trout (Oncorhynchus mykiss) following acute (96-h) and sub-chronic (28-d) waterborne exposures was investigated. Owing to known interactions between Tl and potassium ions (K + ), plasma and muscle K + concentrations were also determined. Branchial Tl accumulated in a dose-dependent manner in both acute and sub-chronic exposures, while plasma Tl was rapidly mobilized to tissues, and accumulated only at exposure concentrations of 141 µg L -1 or higher. For muscle tissue, Tl concentrations at 28-d were markedly lower than those at 96-h at comparable exposure concentrations (0.9 µg L -1 ), indicating the presence of mechanisms that act to reduce Tl accumulation over time. However, after acute exposure muscle Tl reached concentrations that, if consumed, would exceed acceptable daily intake values for this element, indicating some risk to human health from the consumption of fish from waters heavily contaminated with Tl. Otoliths showed Tl concentrations that reflected exposure concentration and length, confirming their capacity to provide insight into fish exposure history. No changes in tissue K + concentrations were observed, suggesting that the accumulation of Tl in rainbow trout plasma and muscle does not occur at the expense of K + homeostasis. In addition to highlighting the capacity of rainbow trout to accumulate Tl to levels that exceed recommended dietary doses to human consumers, this study provides the first data of tissue-specific Tl accumulation in an important regulatory species.