A new analysis based on animal research shows that bathing in manganese contaminated water for 10 years or more may have permanent effects on the nervous system. Researchers from Wake Forest University School of Medicine said that even at the level of manganese content considered safe by the Environmental Protection Agency, damage may occur.

John Spangler, MD, associate professor of family medicine, said: "If our research results are confirmed, they will have a profound impact on the United States and the world." "There are nearly 9 million people in the United States who are exposed to manganese. Our research shows that this may lead to poisoning."

This study shows for the first time that inhalation of vaporized manganese during bathing may cause permanent damage to the brain. The researchers consulted the medical literature and calculated the amount of manganese that people can absorb by bathing for 10 minutes every day according to animal experiments.

As manganese is monitored in public water supply, this naturally occurring metal is particularly high in wells and private water supply.

Dr. Spangler and Robert Elsner published their findings on the latest issue of medical hypothesis, which is a forum of views on medicine and related biomedical science.

The magazine published "interesting and important theoretical papers to promote the diversity and debate of the vigorous development of the scientific process."

Everyone will be exposed to a small amount of manganese, which exists in food and many types of rocks and enters the air, soil and water. However, high content of manganese is toxic to the central nervous system, which can lead to learning and coordination disorders, behavioral changes and symptoms similar to Parkinson's disease.

Children, pregnant women, the elderly and patients with liver diseases have the highest risk of manganese poisoning. Spangler said that some people in these groups would suffer from manganese poisoning even if they used relatively low doses of manganese in their water supply.

The United States Environmental Protection Agency (EPA) has set the upper limit of manganese content in water supply at 0.5 mg/L. However, the limitation is based on the smell and taste of water. When setting this limit, the Environmental Protection Agency did not take into account the potential risk of manganese accumulation in the brain during bathing. In their analysis, Spangler and Elsner found that the concentration far below 0.5 mg may cause brain damage.

"Inhaling manganese is more effective than eating or drinking manganese to transport manganese to the brain," Spangler said

Elsner and Spangler deduced the data of rodents to estimate the manganese exposure of human beings in bathing. They found that after 10 years of bathing in manganese-contaminated water, children were exposed to three times more manganese than the dose that caused manganese deposition in the brain of rats. Adults are exposed to 50% higher doses than rodents.

The researchers said that although their calculations did have limitations, regulators did not take this potential approach into account when formulating drinking water standards.

Spangler said: "People who drink high manganese water for a long time should be studied." "The regulatory authority may need to reconsider the existing manganese standard for drinking water one day."

Researchers said that adding manganese to gasoline as an antiknock agent could also be a threat.

Spangler said: "Manganese is deposited into the streets and highways from automobile exhaust, which may enter the water supply system and increase the manganese content in our drinking and bathing water."