There is nothing like the suggestion of a cancer risk to scare a parent, especially one of the over-educated, eco-conscious type. So you can imagine the reaction when a recent USA Today investigation of air quality around the nation ’ s schools singled out those in the smugly(自鸣得意的) green village of Berkeley, Calif., as being among the worst in the country. The city ’ s public high school, as well as a number of daycare centers, preschools, elementary and middle schools, fell in the lowest 10%. Industrial pollution in our town had supposedly turned students into living science experiments breathing in a laboratory ’ s worth of heavy metals like manganese, chromium and nickel each day. This in a city that requires school cafeterias to serve organic meals. Great, I thought, organic lunch, toxic campus. Since December, when the report came out, the mayor, neighborhood activists (活跃分子) and various parent-teacher associations have engaged in a fierce battle over its validity: over the guilt of the steel-casting factory on the western edge of town, over union jobs versus children ’ s health and over what, if anything, ought to be done. With all sides presenting their own experts armed with conflicting scientific studies, whom should parents believe? Is there truly a threat here, we asked one another as we dropp ed off our kids, and if so, how great is it? And how does it compare with the other, seemingly perpetual health scares we confront, like panic over lead in synthetic athletic fields? Rather than just another weird episode in the town that brought you prote sting environmentalists, this latest drama is a trial for how today ’ s parents perceive risk, how we try to keep our kids safe — whether it ’ s possible to keep them safe — in what feels like an increasingly threatening world. It raises the question of what, in o ur time, “safe” could even mean. “ There ’ s no way around the uncertainty, ” says Kimberly Thompson, president of Kid Risk, a nonprofit group that studies children ’ s health. “ That means your choices can matter, but it also means you aren ’ t going to know if they do. ” A 2004 report in the journal Pediatrics explained that nervous parents have more to fear from fire, car accidents and drowning than from toxic chemical exposure. To which I say: Well, obviously. But such concrete hazards are beside the point. It ’ s the dangers parents can ’ t — and may never — quantify that occur all of sudden. That ’ s why I ’ ve rid my cupboard of microwave food packed in bags coated with a potential cancer-causing substance, but although I ’ ve lived blocks from a major fault line( 地质断层 ) for more than 12 years, I still haven ’ t bolted our bookcases to the living room wall.