You probably associate arsenic more with health problems than with health benefits, but it seems the chemical could actually help in the fight against breast cancer. The news comes from a study of a city in Chile.

Between 1958 and 1970, Antofagasta had way too much arsenic in its water: some 80 times the maximum amount recommended by the World Health Organization. Some forms of cancer, including those of the lung, bladder, and kidney, soared among locals, Ozy reports.

But breast cancer mortality rates among women actually sank by 50%, UC Berkeley reveals in a press release; among women under 60, the figure was 70%.

The findings were "completely unexpected," researcher Allan Smith tells Ozy. Researchers were able to use arsenic to kill lab-grown breast cancer cells, and they found that healthy breast cells showed arsenic resistance.

"Based on what we’ve found, it’s not a stretch at all to say arsenic could treat breast cancer," says another expert. The next step: "Carefully designed clinical trials should take place as soon as possible based on this new evidence," Smith notes.

Forms of arsenic have previously been used in the treatment of other cancers; the chemical has been called a "double-edged sword," Medical Daily reports. As for that other edge, another recent study linked arsenic intake to lower IQs.

This article originally appeared on Newser: Arsenic: A New Weapon Against Breast Cancer?

More From Newser