Scientists this week urged further research on tungsten— the metal used to make lightbulb filaments, shotgun shells, electrical wires and even wedding bands—to rule out possible health risks to humans and the environment in the wake of studies showing that it may cause reproductive problems in earthworms and stunted growth in sunflowers.
In an article published this week in Chemical & Engineering News, researchers suggest that not enough is known to determine whether tungsten is safe, and that studies need to be conducted to assess how much is in drinking water and the soil – and whether it poses dangers for humans, animals and plants.
Experts say that tungsten is safe when used in its pure form in lightbulb filaments, jewelry, and electrical devices. But researchers quoted in the article and interviewed by ScientificAmerican.com say that when tungsten gets into the soil (through, say, lightbulbs in landfills), it reacts with substances such as oxygen, forming new chemicals such as polytungstates that may cause growth and reproduction problems in plants and animals. Studies show that sunflowers grown in soil spiked with tungsten powder grow shorter roots, stalks, and leaves and “start looking sickly,” says David Johnson, a toxicologist with the Environmental Laboratory of the U.S. Army Engineer Research & Development Center (ERDC) in Vicksburg, Miss.
He adds that it's also "a pretty potent reproductive toxin" in earthworms, noting that worms exposed to even minute levels of tungsten (700 milligrams of tungsten per one kilogram of soil) become infertile. Johnson says that the effects of tungsten on earthworm reproduction are “comparable” to that of lead in humans, which has been linked to neurological problems in fetuses and children.
So how much tungsten are people in the U.S. exposed to daily in their drinking water? No clue, says the U.S. Environmental Protection Agency (EPA). "We wouldn't know how much is in the drinking water system," says EPA spokesperson Enesta Jones, because it's not among chemicals on its list of known contaminants or regulated under the Safe Drinking Water Act.
ERDC geochemist Anthony Bednar told ScientificAmerican.com that scientists are trying to get a handle on the various chemical forms of tungsten in the environment, how they move through the soil – and whether any of them pose risks for people and the environment. Lab toxicologist Johnson, meanwhile, is trying to figure out how tungsten moves up the food chain—from its absorption by the plants (including agricultural varieties) to the animals and humans that eat them.
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