Campus researchers find unparalleled health effects from in utero and childhood arsenic exposure
| 05 April 2006
Children exposed to high levels of arsenic in their drinking water are 7 to 12 times more likely to die of lung cancer and other lung diseases in young adulthood, a new study by Berkeley and Chilean researchers suggests.
The risk of dying due to bronchiectasis, usually a rare lung disease, is 46 times higher than normal if the child's mother also drank the contaminated water while pregnant, according to the study. These findings provide some of the first human evidence that fetal or early-childhood exposure to any toxic substance can result in markedly increased disease rates in adults.
"The extraordinary risk we found for in utero and early-childhood exposure [to arsenic] is a new scientific finding," says the study's lead author, Allan Smith, professor of epidemiology at the School of Public Health. "I sometimes ponder the improbability that drinking water with concentrations of arsenic less than one-thousandth of a gram per liter could do this, and think that I've got to be wrong. But our years of working with arsenic exposure in India and Chile tie in with this study perfectly."
Arsenic is one of the most potent cancer-causing agents known. Rates of skin, bladder, and lung cancer are substantially higher in regions where the tasteless, colorless substance occurs in drinking water.
Arsenic is particularly prevalent in Region II, a province in the north of Chile that is one of the driest places on earth. There, in 1958, the cities of Antofagasta and neighboring Mejillones tapped into arsenic-laden rivers to supply their growing populations with water. For the next 13 years, until an expensive arsenic-removal plant was installed, the water supply was laced with an average of 860 micrograms per liter of arsenic. (A microgram is a millionth of a gram.) In contrast, the standard for arsenic in drinking water in the United States was recently dropped from 50 micrograms per liter to 10, with compliance required in 2006.
From earlier work he and others conducted in India, Smith knew that arsenic is associated with bronchiectasis, a rare lung disease that causes distortion and dilation of the bronchi, eventually leading to chronic infections. A study involving death certificates for young adults in Mejillones and Antofagasta, Smith realized, would reveal whether lung cancer and bronchiectasis could also occur as a result of childhood exposure to arsenic.
Working with colleagues from the Pontificia Universidad Catolica de Chile in Santiago, Smith compared the death rates from 1989 to 2000 of young adults in the two cities with the rates in the rest of Chile, outside of Region II. The team focused on two groups: those born between 1951 and 1958, when the water supply to the cities had relatively low arsenic concentrations, and those born during the high-exposure period of 1958 to 1971.
Both groups, they reasoned, would have been exposed to high levels of arsenic throughout some or most of their childhoods, but the second group would also have been exposed in the womb. Exposure for both groups would have abruptly declined in 1971, when the arsenic-removal plant went online.
The researchers' findings were dramatic. For people exposed to arsenic only as children, the death rate from lung cancer was 7 times greater than in the rest of Chile, while the death rate from bronchiectasis was 12 times greater. For those with both early-childhood and in utero exposure, the death rate from lung cancer was 6 times greater than that in the rest of Chile, and the death rate from bronchiectasis was an astonishing 46 times greater.
In absolute numbers, there were 9 deaths from bronchiectasis, 16 from lung cancer, and 7 from other lung diseases in adults aged 30 to 49 who were born during the period of high exposure. In the year 2000 there were about 300,000 people living in the two cities studied.
"These are the most amazing findings I've confronted so far in my career," Smith says. "Their magnitude is unparalleled. Not only are these the highest death rates for lung cancer and bronchiectasis ever discovered among young adults, but they are also the strongest evidence I know of to date that implicates not just arsenic, but any environmental exposure in utero or in early childhood, to any adverse health effect in adults."
Putting these results in perspective, studies have found that the rates of early-adult lung cancer among survivors of the atomic bombings at Hiroshima and Nagasaki who were exposed to high levels of radiation before birth or as children are many times lower than those in Antofagasta and Mejillones, as are the rates among young adults exposed to second-hand tobacco smoke as children. Only active smoking itself results in lung-cancer rates higher than the seven-fold increase found in his study, Smith says.
The study, which will appear in the July print issue of Environmental Health Perspectives, is online at www.ehponline.org/docs/2006/8832/abstract.html. The work was conducted by the Arsenic Health Effects Research Program at the School of Public Health and funded by the National Institute of Environmental Health Sciences, one of the National Institutes of Health.