W – Tungsten is found in igneous rocks at 1.5 ppm; shale at 1.8 ppm; sandstone at 1.6 ppm; limestone at 0.6 ppm; sea water at 0.0001; soils at I ppm; marine plants at 0.035 ppm; marine animals at 0.0005 to 0.05 ppm; land animals at 0.005 ppm (accumulates in heart muscle and teeth at 0.00025 ppm).
Tungsten apparently is a component of formate dehydrogenase from Clostridium thermoaceticum. However, although an interaction between tungsten and molybdenum metabolism has been established, no known essential role for tungsten has been found for animals. In a life-term study with mice and rats, Schroeder and Mitchener found a slight enhancement in growth of rats when the drinking water was supplemented with tungsten at 5 mcg/ml On the other hand, tungsten slightly shortened the longevity of mice and rats. Tungsten was virtually innocuous as judged by incidence of tumors and levels of serum cholesterol, glucose, and uric acid. In six experiments with growing, gravid, and lactating goats fed either 0.06 or 1.0 mcg tungsten per gram of semisynthetic diet, dietary tungsten did not affect growth, hematocrits, hemoglobin, insemination, conception, or abortion rate, sex or number of kids per goat, or mortality of kids. However, the tungsten-low mothers tended to show higher mortality and an elevated reticulocyte count. Nonetheless, Anke and co-workers concluded from their studies that either tungsten is not essential, or that tungsten at a dietary level of 60 ng/g meets the requirement for growth and reproduction in goats. Whanger and Weswig found that 500 mcg tungsten per gram of diet increased the life span of selenium-vitamin E deficient rats. However, they attributed this finding to decreased food intake caused by unpalatability of the tungsten-containing diet.
The suggestion that any requirement for tungsten would be small is supported by the apparent relatively low dietary intake of tungsten by humans and animals. Hamilton and Minski reported that English total diets supplied < 1 mcg tungsten per day. Furr et al. found that maple syrup and a variety of nuts contained only 0.02-0.10 mcg tungsten per gram dry weight. Anke and coworkers stated that normal ruminant feedstuffs of Middle Europe contained only between 0.15 and 0. 50 mcg/g dry weight. Nonetheless, any tungsten ingested probably is well absorbed. Bell and Sneed found that an oral dose of a tracer level of (NH4)2 185WO4 was eliminated principally in the urine. Kaye (reported that 40% of a single oral tracer dose of K2 185WO4, or K2 187WO4, was excreted within 24 hr, with approximately equal amounts appearing in the urine and feces. By 72 hr, 97% of the tungsten dose was excreted. Bone apparently was a retention site for tungsten.