Tungsten, once thought to be an environmentally friendly metal, may not be as safe as it is thought, say researchers.

Tungsten metal is widely used in products ranging from bullets to light bulbs to jewellery.

According to C&EN Associate Editor Rachel Petkewich, scientists have long held that tungsten is relatively insoluble in water and nontoxic.

The U.S. military, had in mid-1990s developed, the so-called green bullets that contain tungsten as a more environmentally friendly alternative to lead-based ammunition.

However, new studies have now show that tungsten, which is also used in welding, metal cutting, and other applications, is not as chemically inert as thought.

It has been shown that exposure to tungsten can stunt the growth of plants, cause reproductive problems in earthworms, and trigger premature death in certain aquatic animals

Both the U.S. Department of Defence and the Environmental Protection Agency have also classified the element as an emerging contaminant of concern.

In the article, Petkewich said that although scientists think that tungsten seems much less toxic than lead or mercury, they do not know its exact health and environmental effects.

However, whether or not tungsten can cause chronic health effects in humans, and its mechanism of action, awaits further study, said Petkewich.