Zirconium (Zr)

Zirconium is relatively abundant in the lithosphere but has no known biological significance. Reported values for the zirconium levels in plant and animal tissues are highly discordant. Schroeder and Balassa found zirconium in all the organs examined from four male accident victims, and found especially high concentrations in fat (18.7 mcg/g fresh tissue), liver (6.3 mcg/g fresh tissue), and red blood cells (6.2 mcg/g). In other tissues and blood serum, the levels were reported to lie between 1 and 3 mcg/g fresh weight. These levels are questionable, because Hamilton et al. found much lower zirconium levels for human tissues than those just cited.

In addition to human and animal tissues, the food zirconium values given by Schroeder and Balassa seem high. They found that meat, dairy products, vegetables, cereal grains, and nuts generally contained 1-3 mcg zirconium per gram fresh weight. Appreciably lower levels of zirconium were found in fruits and seafoods. They estimated a daily oral zirconium intake by humans of approximately 3.5 mg. In contrast, Hamilton and Minski reported that English total diets supplied 53 +or- 34 mcg zirconium per day. This latter value seems to be more reasonable than the former, because Duke found that a limited variety of fruits, vegetables, and grains contained between 0.005 and 0.20 mcg zirconium per gram dry weight.

The metabolic movements of zirconium in the animal body apparently have not been studied directly. Its presence in the blood and tissues indicates that it is absorbed from ordinary diets, while its virtual absence from the urine suggests that it is excreted by the intestine. Bone apparently accumulates the greatest amount of intraperitoneally injected zirconium. More detailed and direct evidence of the sites of absorption, retention, and excretion of zirconium is clearly desirable.

Zirconium compounds have a low order of toxicity for rats and mice, whether injected or orally ingested. Schroeder et al. studied the lifetime effects of adding 5 ppm zirconium as zirconium sulfate to the drinking water of mice. No effects on growth were observed, but there was a small reduction in survival time. The element was neither carcinogenic nor tumorigenic, and apparently did not accumulate in the tissues of mice. However, 5 mcg zirconium per milliliter of drinking water elevated the level of copper in the liver and kidney of rats.