A longitudinal investigation of solid-food based dietary exposure to selected elements.

As part of a longitudinal investigation of environmental exposures to selected chemical contaminants, the National Human Exposure Assessment Survey (NHEXAS), food consumption and duplicate diet samples were obtained in each of six sampling cycles from up to 80 individuals in Maryland during 1995-1996. Duplicate diet samples were weighed and analyzed for arsenic, cadmium, chromium and lead and were used to derive average daily intakes of each element. Mean log-transformed concentrations of arsenic and cadmium in duplicate diet samples and derived intakes of chromium were found to vary significantly among sampling cycles. Repeated observations of dietary exposure metrics from the same individual over time were highly variable. The results suggest that distributions of dietary exposure to arsenic and cadmium do vary for a population within a 1-year period, while those for chromium and lead do not. This may result in single measurements of exposure being sufficient to characterize population variability for these latter two elements. However, even for those elements not displaying statistically significant temporal variability for the population, a single dietary exposure measurement may still not be sufficient to characterize accurately chronic dietary exposure levels for individuals.