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Veel douchen kan leiden tot
hersenbeschadiging*
Regelmatig een douche nemen kan tot
hersenbeschadiging leiden. Dat heeft een studie van de Wake Forest
University School of Medicine in New Carolina uitgewezen. Volgens de
wetenschappers kan het inademen van kleine hoeveelheden mangaan opgelost in
water het zenuwstelsel beschadigen.
John Spangler, die de studie leidde, zegt dat het onderzoek grote gevolgen kan
hebben voor de wereld als de resultaten bevestigd worden. Door
milieuvervuiling komt steeds meer mangaan in het grondwater en andere wateren en
uiteindelijk ook in het drinkwater. Bij het inademen van mangaan wordt er meer van
de stof naar de hersenen gestuurd dan bij het eten of drinken ervan. De
zenuwcellen die gebruikt worden bij het ruiken vormen een rechtstreekse
toegangsdeur voor gifstoffen naar de hersenen. Eens de stof zich in deze kleine
zenuwcellen bevindt, kan het mangaan trillingen veroorzaken vergelijkbaar bij de
ziekte van Parkinson.
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."
The study is the
first to show the potential for permanent brain damage from breathing vaporized
manganese during a shower. It was conducted by reviewing the medical literature
and calculating, based on animal studies, the amount of manganese people would
absorb by showering 10 minutes a day.
Because
manganese is monitored in public water supplies, high levels of this naturally
occurring metal are especially found in wells and private water supplies.
Spangler and
Robert Elsner, Ph.D., published their findings in the current issue of Medical
Hypotheses, a forum for ideas in medicine and related biomedical sciences.
The journal
publishes "interesting and important theoretical papers that foster the
diversity and debate upon which the scientific process thrives."
Everyone is
exposed to small levels of manganese, which is found in food and many types of
rocks and enters the air, soil and water. But, at higher levels, manganese is
toxic to the central nervous system and can cause learning and coordination
disabilities, behavioral changes and a condition that is similar to Parkinson's
disease.
Children,
pregnant women, the elderly, and patients with liver disease are at highest risk
from manganese toxicity. Some of these groups have developed manganese poisoning
even at fairly low doses in their water supplies, Spangler said.
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 manganese levels in the water we drink and bathe
in," said Spangler.