Fortification variability in rat diets fortified with arsenic, cadmium, and lead.

Eleven rat diets fortified with 200 ppm Pb as lead acetate, and/or 50 ppm Cd as cadmium chloride, and/or 50 ppm As as sodium arsenate or p-arsanilic acid for use in a feeding study to determine the interactive effects of the three elements in rats were analyzed to confirm the fortification levels. Gross inhomogeneity was found. After remixing, variability within and among diets was improved but was still unacceptable. Fortification levels of Pb and of As as sodium arsenate could be accurately determined only by taking a very large sample and homogenizing the diet subsamples with a Polytron homogenizer. A review of the recent literature indicates that no standard procedures exist for fortification, mixing, or analysis of animal feeding study diets. Such procedures should be developed and analysis of the diets before and at intervals during a feeding study should be adopted as standard procedure.