Metabolism and toxicity of cadmium, mercury, and lead in animals: a review.

Cadmium, mercury, and lead are toxic to humans and animals. Although cadmium and inorganic mercury toxicities occur in humans, they have not been observed in domestic livestock under practical conditions. In contrast, cattle, especially young calves, are extremely susceptible to lead toxicity. Apparently, cattle are more tolerant of cadmium than are other animal species. Due partially to higher absorption and longer retention times in the body, the alkyl mercuries, especially methyl mercury, are more toxic than inorganic mercury compounds. Inorganic forms of cadmium, mercury, and lead are poorly absorbed from the intestine. However, due to lack of effective homeostasis, after absorption retention time is long. Injected cadmium, mercury, and lead are metabolized differently from that naturally absorbed. Most cadmium and mercury are in kidney and liver (50 and 23% of total body in goats); but highest total load of methyl mercury is in muscle (72% in cows). With low to moderate body burden, most lead is retained in the skeleton. However, beyond a certain point, the kidney accumulates large quantities. Only minute amounts of cadmium and mercury are secreted into milk, but milk is only moderately well protected from dietary lead. Likewise, little cadmium and inorganic mercury pass the placental barrier whereas lead and methyl mercury pass more readily.