Risk assessment of the threat of secondary poisoning by metals to predators of earthworms in the vicinity of a primary smelting works

An assessment was performed of the risk to predators of cadmium, copper, lead and zinc in the food chain soil earthworm - vertebrate. To estimate risk, the scheme proposed by Romijn et al. (1993, 1994) was used. The procedure compares mean bioconcentration factors (BCFs) (concentration in earthworms divided by concentration in soil) for the pollutants in prey with a predator sensitivity value. This allows maximum permissible concentrations (MPCs) to be determined for each metal. For the study, BCFs of the four metals were recorded in the tissues of earthworms collected from a number of sites located around a primary smelting works where soils are heavily contaminated with cadmium, copper, lead and zinc. Predator sensitivity was estimated using literature toxicity data as a hazardous concentration for 5% of species (HC5) by the technique of Aldenberg and Slob (1993). Comparison of field BCFs and literature HC5(predator) values gave MPCs for metals in soil of 0.017 mu g Cd g(-1), 18.9 mu g Cu g(-1), 30.4 mu g Pb g(-1) and 36.1 mu g Zn g(-1) which would theoretically protect 95% of predators from poisoning. A comparison of the calculated MPCs for cadmium, copper, lead and zinc with the concentrations of these metal found in a range of field soils indicates that the MPCs are almost always exceeded, even in uncontaminated agricultural soils. Possible causes for the overassessment of the risk of secondary poisoning are discussed and an alternative strategy based on the use of critical target organ levels is outlined.