A method for estimating dietary intake of environmental trace contaminants: Cadmium — a case study

Variations in either food content or dietary habit affect dietary intake of trace contaminants. Trace contaminants enter the human food chain through many environmental pathways, including contamination of water used for drinking or irrigation, sludge used on cropland, fertilizers and other agricultural chemicals, chemicals leached from disposal sites to water, or airborne deposition on soil, water, or crops. A flow chart (Fig. 1) summarizes these pathways.Dietary exposure to environmental trace contaminants places some segments of the U.S. population at substantially higher risk than others. A methodology to calculate population distribution curves for dietary intake of trace contaminants is presented in this report, using cadmium (Cd) as the specific example. This methodology can be applied both to calculate the distribution of daily individual intake of trace contaminants, as well as to estimate the size of the potentially at-risk population. The methodology is developed with both a stochastic approach and a matrix approach. The matrix approach is coded as program SCOPE, and the stochastic as program MONTE.The dietary habits of the U.S. population were determined by using computer codes to analyse and synthesize an array of dietary data. The 15- to 20-yr-old male population was selected for analysis because this group has the largest gram-caloric intake of any age-sex classification. Data from the U.S. Department of Agriculture and the Food and Drug Administration were analyzed to define Cd concentration distribution for 34 food categories, into which 1880 food items were classified. Food consumption frequency histograms were generated with this information, using data synthesis routines and SCOPE.A 1974 FDA survey of metal concentrations in selected foods at 71 U.S. sampling sites yielded tabular, truncated frequency histograms for Cd concentrations in 32 of the food categories studied. Histograms were then constructed by integrating consumption and Cd concentration for each food category for the total diet.The World Health Organization (WHO) recommended in 1972 a tolerable limit of Cd intake of approximately 70 μg per day. A comparison of SCOPE and MONTE total diet Cd intake frequency histograms indicates the likelihood of high Cd intake, at-rick populations. SCOPE results predict that approximately 13% of the 15- to 20-yr-old males studied ingest Cd at a rate greater than 70 μg per day. MONTE predicts that 14%, with a 12–17% range, ingest amounts greater than the WHO-recommended limit on a daily basis. This percentage represents a potential at-risk population. The actual at-risk population would be those persons who consistently ingest more than 70 μg/day.The percentage of the population projected to ingest more than 70 μg of Cd per day needs to be defined by geography, ethnicity, race, and dietary preference in order to fully evaluate Cd intake risks and to set parameters for epidemiological surveys needed for confirmation. Assuming validity for this methodology, there is justification for preventing significant increases in Cd dietary intake by way of man's activities.