Zahnarztpraxen vergiften das
Wasser
ScienceDaily
(Mar. 27, 2008)
— Mercury is a large component of dental fillings, but it is not believed to
pose immediate health risks in that form. When exposed to sulfate-reducing
bacteria, however, mercury undergoes a chemical change and becomes methylated,
making it a potent, ingestible neurotoxin.
While the major source of
neurotoxic mercury comes from coal-fired electric power plants, researchers at
the University of Illinois at Chicago and at Urbana-Champaign say mercury
entering drain water from dental clinics and offices is also a source.
"We found the highest
levels of methyl mercury ever reported in any environmental water sample,"
said Karl Rockne, associate professor of environmental engineering at UIC and
corresponding author of the study that appeared online March 12 in the journal
Environmental Science and Technology.
Working with James
Drummond, UIC professor of restorative dentistry, Rockne gathered waste water
samples in collection tanks generated from both a single-chair dentist's office
and a 12-chair dental clinic to check for methyl mercury.
Water collected was allowed
to settle. Clear layers above the settled particles were then analyzed for
presence of methyl mercury. Fine, slow-settling particles of mercury get into
the waste water mostly after dentists use high-speed drills to remove old
amalgam fillings. The numerous fine particles the drilling produces provide an
ample source of exposed mercury surfaces, making them prime targets for
sulfur-reducing bacteria that commonly live in anaerobic conditions and are
known to methylate mercury.
"It appears to be
produced partially, if not fully in the waste water, and it's being produced
very rapidly," said Rockne, adding that it was significant this was
happening before the particles were getting into sewers, where sulfur-reducing
bacteria thrive.
The finding raised the
question whether the culprit bacteria were living in the mouths of dental
patients. "We don't have the answer," Rockne said.
Based on their sample
studies, the researchers estimate that 2-5 kilograms, or up to 11 pounds, of
methyl mercury could be entering the public water supply of the United States
each year from dental waste water. While this may not seem like much, methyl
mercury is highly toxic in minute amounts.
When in waterways, methyl
mercury tends to get biomagnified up the food chain, moving from algae and
phytoplankton to fish and, ultimately, to humans.
While surprised by the
level of contaminants found in the study, Rockne says follow-up research is
necessary -- then, possibly, some basic engineering.
"Amalgam separators
are a good first step, but maybe something else is necessary downstream to
prevent further methylation and prevent further soluble mercury from getting
through the system," he said.
"We have to take more
steps to prevent the problem from occurring in the first place," he said. "We're
dealing with a pipe -- a control point. As an engineer, I see this as a problem
that is tractable -- something we can definitely do something about."
Other researchers in the
study include UIC environmental engineering Ph.D. student Xiuhong Zhao and
orthodontics resident Ryan Hurley. Measurements of methyl mercury were
performed using a technique developed at UIUC's department of natural resources
and environmental sciences. Contributing department members were Robert Hudson,
associate professor, and graduate student Christopher Shade.
Funds were provided by the
National Science Foundation and the National Institutes of Health.
Adapted from materials
provided by University of Illinois at
Chicago.
http://www.sciencedaily.com/releases/2008/03/080326161639.htm