Manganese is dangerous to humans at high levels. Although we are all exposed to small amounts every day, at higher levels manganese is toxic to the nervous system and can lead to a Parkinson's-like disorder. It's already regulated in our drinking water. A new study reveals that we are at risk not just by drinking it but also by inhaling it... in our bath water: A new analysis based on animal studies suggests that showering in manganese-contaminated water for a decade or more could have permanent effects on the nervous system. The damage may occur even at levels of manganese considered safe by the Environmental Protection Agency, according to researchers from Wake Forest University School of Medicine. "If our results are confirmed, they could have profound implications for the nation and the world," said John Spangler, M.D., an associate professor of family medicine. "Nearly 9 million people in the United States are exposed to manganese levels that our study shows may cause toxic effects." Manganese is regulated in the water supply, but the standard is set based on the risk from drinking the water, not from inhaling the steam: The Environmental Protection Agency (EPA) has set 0.5 milligrams/liter as the upper limit of manganese advisable in water supplies. The limit, however, is based on odor and taste of the water. The potential risk of manganese accumulating in the brain through showering has not been considered by the EPA in setting this limit. In their analysis, Spangler and Elsner found that concentrations well below 0.5 milligrams might lead to brain injury. "Inhaling manganese, rather than eating or drinking it, is far more efficient at delivering manganese to the brain," said Spangler. "The nerve cells involved in smell are a direct pathway for toxins to enter the brain. Once inside these small nerves, manganese can travel throughout the brain. ... Regulatory agencies may one day need to rethink existing drinking water standards for manganese." Reminiscent of the historical problem of leaded gasoline, we may also be at risk from manganese in gasoline: The addition of manganese to gasoline as an anti-knock agent may also be a threat, the researchers said. "The manganese, as it settles from car exhaust onto streets and highways, may enter the water supply, increasing manganese levels in the water we drink and bathe in," said Spangler.