Effect of different levels and periods of lead exposure on tissue levels and excretion of lead, zinc, and calcium in the rat.

Influence of lead on tissue content and urinary excretion of lead, zinc, and calcium in rats was studied following various exposure periods. Weanling male rats were fed a trace mineral-sufficient diet with either 0, 200, 500, or 1000 ppm lead (as acetate) in drinking water for 4, 8, or 12 weeks. Blood lead ranged from 40 to over 100 micrograms/dl; kidney lead was highest at 4 weeks. Urinary lead excretion was highest at 4 weeks and declined with longer exposure. Urinary zinc excretion correlated positively with lead excretion at the lower excretion rates but plateaued at higher lead excretion rates. After 12 weeks exposure at each lead dose employed, decrease zinc concentration was observed in testes, bone, and brain. Plasma, erythrocyte, and kidney zinc were not affected, while pancreas and liver zinc were slightly elevated. Urine calcium was increased significantly only in rats exposed to 1000 ppm, possibly reflecting renal cell damage as determined by elevated renal calcium levels. These results indicate that lead dose is more important than exposure period for determining kidney lead levels, while urinary lead excretion rate is both dose and time dependent. Blood lead clearance values are relatively independent of dose and fall as exposure continues. Essential trace metal balance for zinc, especially, and to a lesser extent for calcium, is affected by the dose and length of chronic lead exposure.