Distribution of Added Lead and Cadmium in Human and Bovine Milk

Distribution of added lead and cadmium to bovine and human milk and whey has been studied. In bovine milk, about 97 and 89% of lead and cadmium, respectively, were recovered in the casein fraction obtained by enzymatic coagulation. However, only 6% of lead and 41% of cadmium were found in the same fraction separated by acid precipitation, indicating that the distribution of both metals is very different depending on the method used for milk fractionation. Moreover, gel filtration of bovine and human skimmed milk and whey after addition of lead and cadmium was carried out. Most of the lead was associated to the casein fraction after gel filtration of skimmed milk, whereas in the chromatography of whey, lead was eluted with the low molecular weight fraction in both species. However, a different pattern in the distribution of cadmium has been observed in the two species studied. In contrast to the binding of cadmium to the low molecular weight fraction in human skimmed milk and whey, it was mainly associated to a component of a molecular weight around 70,000 in bovine skimmed milk. This component was not present in bovine whey indicating that it is separated with casein during fractionation.