Accumulation and depletion of cadmium and lead in tissues and milk of lactating cows fed small amounts of these metals.

Groups of lactating cows were fed 0, 40, and 200 mg of added cadmium (as chloride) and 0, 100, and 500 mg of added lead (as acetate) per animal per day in separate experiments. Milk and blood were sampled periodically and analyzed for concentrations of metal ions. Metal feeding was discontinued after 3 mo, and selected animals were necropsied for tissue residue studies. Remaining animals were continued on control ration for another 3 mo and then killed and tissues obtained. Cadmium feeding did not produce a dose-related increase of this metal in blood, milk, or skeletal muscle. Liver and kidneys were the primary organs of cadmium accumulation, and concentration of cadmium in these organs continued to rise during 3 mo of feeding the control diet after the initial exposure period. Lead did not accumulate in skeletal muscle but showed a dose-related increase in blood, milk, bone, liver, and kidney. In most tissues there was a rapid decline of lead concentrations after cessation of treatment, except in bone. Low dietary intake of cadmium and lead do not produce an appreciable rise of these metals in edible products, e.g., milk or meat. Of the tissues analyzed, liver and kidney accumulate both cadmium and lead, and cadmium especially persists in these organs for long periods. Bone is the primary site of deposition for lead but not cadmium.