Effect of zinc supplementation on the distribution of lead in tissues of rats intoxicated by lead compounds

The permissible threshold level of lead in blood (Pb-B) is currently established at 5mg dL-1, but evidence suggests that it is impossible to determine the safety threshold for lead (Pb) and any exposure, especially in children, must be considered as potentially harmful. Methods used to reduce the concentration of Pb in blood (e.g. EDTA, penicillamine) are not always effective and are associated with serious side effects. One of the proposed dietary supplements in the case of exposure to Pb and low blood Pb concentrations is zinc (Zn), but the published literature on its effectiveness is limited. Therefore, the aim of this study was to clarify whether Zn supplementation may help reduce the concentration of Pb in the blood and tissues of rats, at the Pb-B level previously recognized as safe. Tests were performed on 6-8 week old male Wistar rats. Rats were divided into control and experimental groups: Group C - rats receiving drinking water ad libitum for 4 weeks; Group Pb - rats receiving Pb acetate 0.1% (PbAc) in drinking water ad libitum for 4 weeks; Group Zn - rats receiving ZnCO3 300 mg kg-1 diet for 4 weeks; Group Pb+Zn - rats receiving PbAc in drinking water ad libitum plus 300 mg ZnCO3 kg-1 diet for 4 weeks. The applied dose of 300 mg of ZnCO3 kg-1 diet results in a high but non-toxic Zn level. The concentrations of Pb and Zn in  blood, plasma, liver and bone were determined by emission spectrometry in inductively coupled argon plasma (ICP OES). Incidental exposure of adult rats to Pb at doses resulting in the level of Pb in blood below the previously recognized as safe one caused: (i) increased Pb concentration in the bones and plasma and its reduction in the whole blood and liver (ii) simultaneous supplementation of rats exposed to Pb with a high but non-toxic dose of zinc did not result in the reduction of the Pb concentration in the blood and tissues of rats, nor did it induce any changes in the distribution of Pb in the examined tissues (iii) supplementation of diets with a high but non-toxic dose of Zn is not an effective method of reducing the concentration of Pb in blood at Pb-B previously recognized as safe. However, the therapy consisting of zinc supplementation to support the action of chelators could be crucial for the elimination of Pb from the body.