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Arsenic-laced water ups TB risk: report
NEW YORK |
NEW YORK (Reuters Health) - New evidence from a region in Chile with a history of arsenic contamination in drinking water suggests the chemical may have a surprising effect: tuberculosis (TB).
Ten years after arsenic leached into the water, rates of the lung infection shot up, peaking at twice the level found in a neighboring region with uncontaminated drinking water. Following the construction of an arsenic removal plant, the disease then began to wane.
"Arsenic-contaminated water looks good, does not smell, and you cannot taste it," study author Dr. Allan Smith at the University of California, Berkeley, told Reuters Health. "It is therefore hard to believe that it could have terrible effects."
That arsenic may increase the risk of lung infections isn't as strange as it sounds, Smith explained, because the chemical suppresses the immune system and has already been tied to lung cancer.
It's not clear yet whether arsenic makes pre-existing TB more deadly, or makes people more susceptible to developing it in the first place, Smith noted.
"We are planning studies to try to work this out," he said.
Arsenic is an element found naturally in rock, soil and water, as well as in the air and the food supply, and it is also released into the environment through industrial activities. For instance, arsenic is used as a wood preservative and in some paints, dyes and fertilizers.
Worldwide, millions of people are being exposed to potentially dangerous levels of arsenic in drinking water. High arsenic exposure can lead to cancer, and chronic exposure to even moderately elevated levels has been linked to high blood pressure and type 2 diabetes.
The U.S. Environmental Protection Agency (EPA) has set the maximum allowable level of arsenic in drinking water at 10 parts per billion (or 10 micrograms per liter), and is currently considering lowering that limit.
According to the Centers for Disease Control and Prevention, about 80 percent of U.S. drinking-water supplies have an arsenic level below 2 parts per billion (ppb), but two percent exceed 20 ppb.
Researchers are trying to understand the health effects of arsenic and how to mitigate them. Last month, a report out of Bangladesh showed that people drinking water naturally contaminated with high levels of arsenic may benefit from eating more "roots" and gourds -- specifically radishes, sweet potatoes and similar plants.
The current study, published in the American Journal of Epidemiology, focused on a region in northern Chile that in 1958 began piping in water from two rivers contaminated by arsenic, causing concentrations to increase from 90 micrograms per liter to 870. In 1971, an arsenic removal plant brought levels down dramatically, and they are now less than 10 micrograms per liter.
Looking at residents' health in this region and comparing it to another region in Chile with relatively little exposure, Smith and his colleagues found that between 1968 and 1995, an extra 359 men and 95 women died of TB in the region with contaminated water. The total population in the region was roughly 300,000 people at that time, Smith said.
It's not surprising that more men died than women, he explained in an e-mail, since men are typically at higher risk of problems from arsenic than women, perhaps due to gender differences in how arsenic is processed in the body.
Many countries are struggling to remove arsenic from drinking water, and these findings suggest that officials should take extra care to protect residents with TB, Smith noted.
"Arsenic in water results in higher risks of disease and death than any other environmental exposure we know of," he said. "Nobody should be drinking arsenic-contaminated water."
SOURCE: bit.ly/i2Ju8J American Journal of Epidemiology, online December 29, 2010.
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