Tuesday, May 18, 2010

Chemicals and comparison groups

Current legislation is trying to ban a plastic that has been used for 50 years to line cans, so I decided to look into how much evidence there is that this plastic is dangerous, and whether the potential substitutes for this plastic are safe. The American Council on Science and Health finds little evidence that this plastic is dangerous; they find no proposals for what plastics might substitute, much less any evidence on the alternatives' safety profiles. Their analysis raises very good points and is worth reading.

Just as in statistics, the important question for any risk analysis is "compared to what?" Nothing is dangerous on an absolute level: risks always have to be weighed against their alternatives. When we banned DDT decades ago, it may or may not have had beneficial effects for the eagle population, but malaria has rebounded: going from millions of cases in Sri Lanka to a couple dozen, and then back up to a million cases after the DDT ban. Malaria still affects hundreds of millions of people around the world, many cases that might be prevented if DDT spraying were allowed. The developed world has not had malaria since the 1940s --- perhaps if malaria had rebounded, perhaps we would see pesticides as the life-saving tools that they are --- but we do have the resurgence of bed bugs, even on the Upper East Side, after they had been almost completely eliminated 50 years ago. Maybe the good effects of the DDT ban are worth hundreds of millions of cases of malaria in the developing world and bedbugs in the developed world, but alternatives always need to be considered. The WHO has backed bringing back DDT because it was so useful.

With the current talk of banning BPA, the comparison group is completely missing. By banning a plastic without discussing alternatives and their risks, we risk having worse alternatives or no alternatives.

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