In recent years, epidemiological evidence from Taiwan, Chile and Argentina has clearly implicated arsenic as a cause of bladder and lung cancer, but arsenic levels in these studies ran at least several hundred parts per billion. A subcommittee of the National Research Council juggled this problem in 1999. It thus estimated that a lifetime of drinking water with 50 ppb of arsenic would cause 1 to 1.5 cases of male bladder cancer per 1,000 population. This is a rather startling estimate, but clearly an iffy one, in all likelihood a worst-case one. New Mexico environmental officials report no unusual incidence of cancer attributable to arsenic, as might be expected if the 1 in 100 estimate is in the ballpark.
Some studies even suggest arsenic in low levels is an essential nutrient.
Yet in the EPA analysis, a reduction in the risks based on NRC methodology became the benefit to be weighed against the cost of implementing the new standard. These calculations have since been extensively critiqued in a paper for the AEI-Brookings Joint Center for Regulatory Studies. Since the costs would divert money from other good uses, they continue, on net the rule would actually result in a loss of life. Also, costs come now and the benefits come far in the future, and the EPA didn't discount for this. The point is that we need some way to think about risk.