Metabolism and Toxicity of Cadmium, Mercury, and Lead in Animals: A Review

Abstract

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.

A Comparison of Cadmium Concentrations in Tissues of Different Categories of Cattle

“…Comparable values were reported by Drapal et al (1997) who found values of 2 to 10 Jlg-kg ol , 11 to 50 Jlg-kg-I , and 100 to 300 Jlg-kg-I in 85.7%, 13.6%, and 0.7% of adult cattle, respectively. Our results have confirmed the finding of Neathery and Miller (1975) that muscular tissue, representing a major part of body mass, is well protected against cumulation of cadmium and that its concentration is not age-dependent unless the intake is markedly increased. Underwood (1977) observed a marked increase in the concentration of cadmium in muscles only when the diet contained 450 ppm Cd.…”

Cadmium toxicokinetics and bioaccumulation in turtles: trophic exposure of Trachemys scripta elegans

“…Our results on levels of gastrointestinal absorption are consistent with levels reported in various vertebrate experiments ranging from 0.5 to 16% (Neathery and Miller 1975;Xu andWang 2002, Hispard et al 2008;Mann et al 2006;Zalups and Ahmad 2003) according to the Cd-concentration in diet that individuals were fed. In our study, the proportional accumulation in liver and kidney depended on the amount of Cd ingested with decreasing assimilation efficiency when ingestion increased, suggesting that as the dose of Cd increases, assimilation decreases.…”

Relationship between Renal Dysfunction and Bone Metabolism Disorder in Male Rats after Long-Term Oral Quantitative Cadmium Administration.

“…In the limited observations in humans and in animal experiments, the average absorption of Cd from the gastrointestinal tract has been estimated as 1%-8% of the Cd that enters the mucosa from the lumen and actually passes into the body [7][8][9][10][11][12][13] . Factors affecting the absorption and tissue distribution of ingested Cd include the animal species, the chemical form of Cd, the dose, the duration, the age of the animal, and interactions of Cd with various nutrients 1-6, 14, 15) .…”