Lead excretion in milk of accidentally exposed dairy cattle.

Lead (Pb) exposure in dairy cattle is associated with economic losses due to mortality and treatment costs, but with production animals there is also risk to the human food chain. The first objective of this study was to quantify the Pb concentration in milk from Pb-exposed cattle. The second objective was to correlate blood and milk Pb concentrations from individual cows. The third objective was long-term monitoring to determine the duration of milk contamination after exposure ceased. A dairy herd of more than 100 cows was accidentally exposed to Pb-contaminated feed. Milk and blood were collected for Pb analysis. Serial collection of milk samples continued for 2.5 years. The initial concentration of Pb in bulk tank milk was 0.0999 mg l⁻¹. The highest milk Pb concentration from an individual cow was 0.4657 mg l⁻¹ and the highest blood Pb concentration was 1.216 mg l⁻¹. One milk sample collected at the end of the study (day 922) contained 0.0117 mg Pb l⁻¹ of Pb. The calculated relationship between milk (y) and blood (x) Pb concentration was ln(y) = 3.4(x) - 2.21 (R² = 0.98).