Death rates from lung and bladder cancer remained high decades after residents in northern Chile were exposed to high levels of arsenic in their drinking water, according to a new study by researchers from the University of California, Berkeley, and the Pontificia Universidad Cat'lica de Chile in Santiago.
That the mortality risks remained elevated long after exposure to high levels of arsenic ended indicates a clear pattern of latency in health effects that had not been known before, said the authors of the study, which will appear in the June 12 issue of the Journal of the National Cancer Institute.
"The impact of this environmental health risk on cancer mortality in a human population is without precedent," said Allan Smith, professor of epidemiology at UC Berkeley's School of Public Health and principal investigator of the study. "This study adds to the overall body of evidence of the harmful effects of arsenic."
Smith, head of UC Berkeley's Arsenic Health Effects Research Program, worked with Guillermo Marshall, professor and dean of the Faculty of Mathematics at Chile's Pontificia Universidad Cat'lica and lead author of this publication.
Arsenic, a known carcinogen, is a semi-metal element that occurs naturally, with some regions containing higher levels than others. Until recently, the maximum level of arsenic allowed in community water systems in much of the world, including the United States, was 50 micrograms per liter.
Studies - including some by Smith - have shown that arsenic causes lung, bladder and skin cancers. Additional evidence has also linked arsenic with other cancers, including those of the kidney and liver. As a result, the U.S. Environmental Protection Agency lowered the maximum contaminant level for municipal water supplies to 10 micrograms per liter, effective January 2006, the same standard recommended by the World Health Organization.
For 15 years, Smith has been studying Region II of Chile, a northern province that gets its water from arsenic-contaminated rivers originating from the Andes mountains. The municipal water supply of Antofagasta, the region's largest city, and neighboring communities contained about 90 micrograms per liter of inorganic arsenic up until 1958, when government officials sought out additional sources of water to supply the region's growing population. Because there is so little rainfall in the region, considered one of the driest in the world, residents rely almost exclusively on municipal water supplies.
Unfortunately, the supplemental water came from the Toconce and Holajar rivers, which contained even higher levels of arsenic. From 1958 to 1970, water to Antofagasta and the nearby city of Mejillones averaged 870 micrograms per liter, nearly 90 times higher than today's WHO standard. In 1971, the first large-scale arsenic removal plant in the world was installed in Antofagasta, but by then, residents had been exposed to high levels of arsenic for 13 years.
With further improvements to the water treatment system, the arsenic concentration steadily dropped over the years, reaching levels below 50 micrograms per liter after 1990. The recent addition of treated seawater has further reduced arsenic levels to around 10 micrograms per liter in the city water supply.
The well-defined arsenic exposures in Region II in Chile provided researchers with a uniquely large population in which to base their studies.
Prior research led by Smith has confirmed higher rates of lung and bladder cancer deaths for Region II compared with the rest of Chile. What was not known until this study was the latency period between the onset and reductions in exposure, and the subsequent rise and fall in cancer rates.