Scientific criteria used for the development of occupational exposure limits for metals and other mining-related chemicals.

The scientific approaches employed by selected internationally recognized organizations in developing occupational exposure limits (OELs) for metals and other mining-related chemicals were surveyed, and differences and commonalities were identified. The analysis identified an overriding need to increase transparency in current OEL documentation. OEL documentation should adhere to good risk characterization principles and should identify (1) the methodology used and scientific judgments made; (2) the data used as the basis for the OEL calculation; and (3) the uncertainties and overall confidence in the OEL derivation. At least within a single organization, a consistent approach should be used to derive OELs. Opportunities for harmonization of scientific criteria were noted, including (1) consideration of severity in identification of the point of departure; (2) definition of the minimum data set; (3) approaches for interspecies extrapolation; (4) identification of default uncertainty factors for developing OELs; and (5) approaches for consideration of speciation and essentiality of metals. Potential research approaches to provide the fundamental data needed to address each individual scientific criterion are described. Increased harmonization of scientific criteria will ultimately lead to OEL derivation approaches rooted in the best science and will facilitate greater pooling of resources among organizations that establish OELs and improved protection of worker health.