Dietary Toxicity Reference Values for Rainbow Trout

In the Upper Clark Fork River, Montana, as well as other mining areas in the western United States, concentrations of arsenic, cadmium, copper, lead, and zinc in aquatic biota may be elevated compared to levels in background tributaries. For fish, the ingestion of aquatic invertebrates containing elevated metals concentrations may be a significant route of exposure. Although some testing previously has been conducted to evaluate dietary metals toxicity, this information has not been summarized and synthesized to establish toxicity reference values for use in ecological risk assessment. Using standardized assessment criteria, test results from the existing published literature for rainbow trout were systematically evaluated and, when possible, dietary exposure NOAEL and LOAEL values (expressed as mg/kg dry weight) were established. Specifically, NOAEL concentrations were 40 mg/kg for arsenic, 150 for cadmium, 603 mg/kg for copper, 210 mg/kg for lead, and 1900 mg/kg for zinc. LOAEL concentrations were 44 mg/kg for arsenic, 10,000 for cadmium and 664 mg/kg for copper; LOAELs could not be determined for lead and zinc since adverse effects were not demonstrated in any study not confounded by elevated exposure to multiple metals. Dietary toxicity reference values were compared to benthic invertebrate metals concentration data from the UCFR to evaluate the likelihood of adverse effects to trout via dietary exposure. During the period 1991 to 1998 no benthic tissue concentrations reported for selected species by the USGS or reported from community tissue monitoring samples collected by the USFWS and ARCO were found to exceed NOAEL or LOAEL values