Review of regulatory reference values and background levels for heavy metals in the human diet.

The U.S. Food and Drug Administration (US FDA) has identified dietary exposure to heavy metals as a public health concern, focusing particularly on arsenic, cadmium, lead, and mercury. One way to determine current risk is to compare established safe exposure limits (reference values) with current population-based dietary background levels. Information on reference values and dietary background exposures for these metals and chromium were critically evaluated in support of an interactive risk assessment screening tool (Heavy Meals Screening Tool [HMST]). Cadmium, arsenic, and mercury background exposures from food and water were found to be below current safe US regulatory limits based on non-cancer effects, while lead background exposures were nearly equivalent to the US FDA's newest interim reference level for children. Because detections of chromium in foods are infrequent and data on speciation (trivalent versus hexavalent) are limited, chromium was excluded from the HMST. The focus of this work was to present U.S. based reference and background exposure values, although the tool can use inputs that may be more appropriate for other countries, cultures, and situations. With emerging science, new health endpoints, and changes in food consumption trends, both reference values and background exposure levels are likely to evolve.