If anyone remakes "Erin Brockovich," this is a scene I want to see. A scientist launches a study to determine the toxicity of hexavalent chromium, the drinking-water contaminant at the center of the lawsuits Brockovich spearheaded. The study will be a meta-analysis, combining existing individual studies to, he says, produce more-authoritative conclusions. Some of the earlier studies measured rates of lung cancer among pigment-factory workers exposed to airborne chromium, so it makes sense to include them. But the scientist is working for industry, so he chooses his other studies carefully: he includes those that assessed all forms of cancer among residents who drank chromium-laced water. Only the workers, not the residents, had increased rates of lung cancer. No surprise there: only inhaled