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."
Elsner and Spangler extrapolated data from rodents to estimate human exposure to manganese during showering. They found that after 10 years of showering in manganese contaminated water, children would be exposed to doses of manganese three times higher than doses that resulted in manganese deposits in the brains of rats. Adults would be exposed to doses 50 percent higher than the rodents.
The researchers said that while limitations to their calculations do exist, regulatory agencies have not considered this potential pathway when setting drinking water standards.
"Studies should be carried out among populations that have experienced high levels of manganese in their water supplies over long periods of time," Spangler said. "Regulatory agencies may one day need to rethink existing drinking water standards for manganese."
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 man
Source:Wake Forest University Baptist Medical Center