By Will Dunham

WASHINGTON, June 12 (Reuters) - People in a part of northern Chile suffered elevated lung and bladder cancer death rates decades after being exposed to high levels of arsenic in their drinking water, researchers said on Tuesday.

Their study detailed the enduring harm from arsenic even as millions of people in developing and developed countries continue to drink water contaminated with the naturally occurring element found in soil and minerals.

Authorities in a region of Chile around the city of Antofagasta in 1958 changed the water supply to accommodate a growing population, adding water from two rivers highly contaminated with arsenic.

U.S. and Chilean researchers compared bladder and lung cancer death rates between 1950 and 2000 in the region to rates from a similar area of Chile where water was not contaminated with arsenic.

Death rates from these cancers in the contaminated region started to increase 10 years after the arsenic levels spiked, and did not top out until between 10 and 20 years after the arsenic levels were cut in 1971, the study found.

At the peak, bladder cancer death rates were six times higher in men and 14 times higher in women in the contaminated region compared to the other region. Lung cancer death rates among both men and women were three times higher than in the uncontaminated region, the study found.

"Even when you stop (the contamination) there's going to be a long delay until finally the risks start to reduce, which makes it even more important to prevent exposure in the first place," Allan Smith, who leads an arsenic research program at the University of California Berkeley and headed the study, said in a telephone interview.

Smith worked with Guillermo Marshall of Chile's Pontificia Universidad Catolica on the study, which appears in the Journal of the National Cancer Institute.

NATURAL CONTAMINATION

Arsenic contamination of water supplies comes mainly from natural sources, but industrial activities such as mining and ore processing also may contribute in some areas, experts said.

In this case, the rivers used in the water supply originated as springs in the Andes mountains and naturally had high levels of arsenic.

From 1958 to 1970, the water for Antofagasta and another nearby city in this arid region averaged 870 micrograms per liter, nearly 90 times higher than the World Health Organization standard of 10 micrograms per liter.

A major arsenic removal plant began operating in Antofagasta in 1971, reducing the contamination but only after residents were exposed to 13 years of high concentrations.

The fact that death risk remained high long after the end of exposure to contamination demonstrated a previously unknown lengthy latency period in health damage from arsenic, the researchers said.

Studies have shown that arsenic causes lung, bladder and skin cancers and may also cause kidney and liver cancer as well as other health problems.

In the United States and many other countries, municipal water supplies are tested and treated for arsenic. But Smith said millions of Americans and far more people globally may be drinking tainted water from private wells.

"I think it's become clearer and clearer that every single well in the world should be measured and checked for arsenic periodically," Smith said.

AlertNet news is provided by