Victor has a good point. There has been a lot written of late on the potentially harmful effects from ingestion of BPA incidental to its use in many plastic objects with which we regularly come into contact. The biggest worries have to do with the health of the fetus and infants. Animal studies indicate that even low levels of BPA in the mother can result in neural and behavioral changes in the infant, especially those related to the development of normal sex-based differences between males and females. But in this case, as in so many others relating to the potentially harmful effects of trace contaminants, the evidence directly relating to humans is nonexistent or inconclusive. In response to much concern, a great many studies have been conducted. The results of all these were recently summarized in a report from the Center for the Evalution of Risks to Human Reproduction. Two things come to mind as I read through this lengthy, detailed report: First, there has been a vast amount of study of the biological effects of BPA. Secondly, it is devilishly difficult to conclude with any level of certainty the extent of the risk that BPA poses to humans. In a kind of battle of agencies, the FDA issued a report in August 2008 suggesting BPA is not something to worry about. That report was blasted by environmental and consumer groups such as the Consumers Union. It's hard to know for sure, but on the basis of the CERHR report I believe that there is little cause for adults to worry, unless they are put into extensive contact with BPA in a work environment. On the other hand, while direct evidence relating to humans is lacking, the studies with rats and mice show that BPA does pose significant dangers in the prenatal and infant stages of life.
How should we respond when faced with a state of knowledge that falls far short of certainty? First we need to assess the authority with which scientific evidence can be called into play. In this case, the evidence, though indirect, is sufficiently compelling to make a case that every effort should be made to minimize exposure of the fetus and infant to BPA. Science in this case provides no certainty, only indirect indications that BPA might cause problems. Animal responses to toxins often fail to mirror those of humans. Sometimes the animals show greater sensitivity than humans, sometimes less. Nonetheless, there is a general similarity in responses, and it is often possible, as in this case, to trace the biological pathways taken by the substance under study to achieve some degree of confidence in inferences based on animal results.
Second, in deciding what response to make to a potential risk, we should invoke the Precautionary Principle, which is embodied in such folk sayings as "look before you leap", and "better safe than sorry". In short, it has to do with the avoidance of risk. In the case of the popcorn popper Victor is applying the principle to say that if there is any chance that using the plastic popcorn popper will increase our granddaughter's body load of BPA, she should avoid using it. This is not a difficult decision for them to make. There are ways to make popcorn that avoid the contact with heated plastic. But for manufacturers who use BPA in a host of applications, the search for a substitute can be arduous and expensive. Substitutes have already come on the market to replace BPA-containing water bottles, baby bottles and infant formula cans. But for some uses, no alternative known to be safe in all respects has been identified. For example, food cans and soft drink cans are lined with a polymer formed from BPA. The amount of BPA that finds its way into the contents of the can is very small, but many environmental groups have lobbied against continued use of the liners.
Enter again the Precautionary Principle. Manufacturers of BPA-containing products are eager to point to the many virtues of plastics in our everyday lives. They stress their safety and the lack of definitive evidence that BPA produces any harmful effects in adults. And there is another side to the Precautionary Principle coin. In an effort to avoid a potentially harmful effect of some action or use, we might inadvertantly create an even greater harm. The American Chemistry Council, an association of chemical companies, makes the point that the plastic liners of cans help to prevent food poisoning. If that's true, and if lives are saved by the use of plastic liners, their removal might do more harm than the potential harm from ingestion of tiny amounts of BPA.
Cass R. Sunstein, writing in the journal Deadalus, [ Sunstein, Cass R. "Taking Precautions", Daedalus, Spring 2008, p. 49] discusses the difficulties in employing the Precautionary Principle as a source of concrete guidance. The problem is that we seldom know all the relevant risks. So we continue to struggle to find the appropriate place for science to exercise an authority consistent with what it can claim to know. Many nonscientists mistakenly expect that real science produces bulletproof answers to the questions put before it. However, the science we draw upon to address issues that affect society in the here and now more often than not can deliver only hedged bets.