NEW YORK (Reuters Health) - People exposed to very high levels of arsenic in Chilean drinking water back in the 1950s and 60s are still showing a higher-than-normal risk of bladder cancer -- years after the arsenic problem was brought under control, a new study shows.
The findings are not surprising, researchers say, since the cancer would take decades to emerge.
But the results underscore the importance of continuing to screen high-risk people for bladder cancer, according to lead researcher Dr. Fernando Coz, a professor of urology at the Universidad de Los Andes in Santiago de Chile.
The study, reported in the Journal of Urology, focused on people in the Antofagasta region of Chile. In the 1950s and 60s, drinking water in the region became contaminated with high levels of arsenic.
Arsenic is semi-metallic element found in rock, soil, water and air. It is also released into the environment through industrial activities, and can be found in products like paints, dyes and fertilizers. High exposure has been linked to several cancers, including tumors of the bladder, liver and lungs.
In Antofagasta, a combination of factors led to a huge increase in drinking-water arsenic by the late-1950s: naturally high arsenic levels in the environment, heavy mining and a move to make two rivers the area's main drinking-water sources.
Arsenic concentrations reached 800 to 900 micrograms per liter (mcg/L) -- far above the current allowable limit of 10 micrograms per liter recommended by the World Health Organization (WHO) and the U.S. Environmental Protection Agency EPA).
The arsenic problem was first reported in 1971, which prompted the first water treatment plants to be set up in the area. Arsenic levels dropped sharply, though it took until about 1990 for levels to fall in line with WHO standards (which at the time allowed for more arsenic than the current standard).
But even two decades after the arsenic problem came under control, people in Antofagasta are showing high bladder cancer rates, Coz and his colleagues found.
Among the region's men in 2009, the rate was about 16 cases per 100,000. That compared with just under six per 100,000 for the rest of Chile.
There was a similar gap seen among women. In Antofagasta, the bladder cancer rate was 13.5 cases for every 100,000 women -- versus just 2.5 per 100,000 in the rest of Chile.
"Our observation shows that bladder cancer appears in high rates in the population that was exposed to arsenic during childhood" in the 50s and 60s, Coz told Reuters Health in an email.
On top of that, he said, they are developing bladder cancer earlier -- in their 50s and 60s, on average, rather than the typical age range of 60s and 70s.
None of that is surprising, according to Coz. High arsenic exposure in childhood or in the womb would lead to cancer decades down the road -- though possibly, as seen in Antofagasta, at an earlier-than-average age.
It's possible to screen for bladder cancer through urine tests, though routine screening is not recommended for the general public -- since there's not enough evidence that the possible benefits would outweigh the risks (like false-positive results).
But Coz said that people from Antofagasta known to have had high arsenic exposures as children should be screened.
He added, however, that the current findings apply only to that Chilean region. "We have no data regarding the risk of cancer if exposed to lower levels of arsenic," Coz said.
Potentially dangerous arsenic levels in drinking water are major problem globally.
Researchers have estimated that about 140 million people worldwide drink water with arsenic levels above 10 micrograms per liter. Bangladesh has been among the hardest hit, with millions exposed to high levels of naturally occurring arsenic in well water.
But no one is sure if arsenic levels below the 10-microgram threshold are completely "safe." And researchers are still studying whether there could be health effects at those concentrations.
In the U.S., most public drinking-water supplies are well below the 10-microgram level.
Still, it's estimated that 13 million Americans live in areas where the public water supply exceeds that threshold. And unregulated private wells might also contain too much arsenic -- particularly in certain areas of the West, Midwest and New England where the groundwater contains high concentrations of the toxic metal.
Experts suggest that people have private well water tested for arsenic. If the level exceeds 10 micrograms per liter, it can be treated with special filtration systems.
SOURCE: bit.ly/x9wGvy Journal of Urology, online January 16, 2012.