Potential considerations & concerns in the risk characterization for the interaction profiles of metals

The contaminants of concern for smelting and mining sites include arsenic (As), cadmium (Cd), lead (Pb) and zinc (Zn). Risk assessments for such sites need to consider whether toxicity values can be developed for this mixture, and if not, whether interactions among the individual components are significant and can be incorporated quantitatively into the assessment. No information is available for the risk characterization of the toxic interactions of AsCdPbZn mixtures. Studies of the AsCdPb and CdPbZn mixtures supported the assumption that a reasonable approximation to the toxicity of a mixture can be achieved by considering the binary submixtures. Data relevant to long-term simultaneous exposure to binary submixtures were not conclusive. For example, data from animal and human studies of Zn and Pb suggested that moderately elevated Zn intakes may slightly inhibit Pb absorption and haematological effects in children who have deficient or marginal Zn intakes, but were not adequate for adjusting absorption parameters in the Integrated Exposure Uptake Biokinetic (IEUBK) model for Pb. Thus the existing database calls for plausible approaches for risk characterization and considerations in the data usage for such characterization. This article is an attempt to identify such data gaps and the scientific considerations for such efforts.