The strongest case is with Lead.  Lead clearly impairs intelligence at very low levels of exposure.  So we know enough now to be confident in the conclusion that certain types of contaminants are interfering with kid’s cognitive abilities as they grow up. 

The question is what can we learn from those animal experiments without people?  We all, I certainly look at what’s happening in the world today and I’m worried about the condition of families.  I’m worried about suicide rates, about dysfunctional kids, and I speculate in my mind about what we can say, what’s causing it.  I run into a problem as a scientist because I know that all sorts of things are at play.  It’s very difficult to isolate individual causes.  It’s also difficult to establish with certainty that change has taken place because our data tracking long term things changes.  Those data are credibly bad.  We don’t have good records. 

One of the areas where its clear things are going on is in terms of things like attention hyperactivity disorder, learning disabilities.  There the animal literature is very clear.  We can cause, in animals, behavioral changes that mimic as close as you come to ADHD and we can do it with low level exposures to arrange a different contaminates, all of which share the ability of altering the way the brain develops.  Now brains develop through genetic signaling and you interfere with those signals and you wind up with a brain that’s mis-wired.  So we know we can do it in animals.  We know that people are exposed to the compounds that are causing the things in animals.  We know they’re exposed at levels that are relevant.  They aren’t irrelevant.  They’re high enough so that they’re within a range where we’re worried about there having affects.  And we know in some cases there is some pretty strong epidemiological data linking altered cognitive function in children and exposure in the womb to these chemicals.  To PCB’s.  The strongest case is with Lead.  Lead clearly impairs intelligence at very low levels of exposure.  So we know enough now to be confident in the conclusion that certain types of contaminants are interfering with kids cognitive abilities as they grow up.  Now that’s one aspect of behavior.  We know that some of them are, it’s highly likely that they’re contributing to things like ADHD.  So the principal altered behavior as a result of exposure in the womb, in people, that’s been established.  How far you can go, we don’t yet know.  Exactly what range of the behavioral dysfunctions that we see in the world at large today that I as a person, not as a scientist, sense is increased.  What fraction of them might be associated?  We don’t know.  It’s now become a serious plausible scientific hypothesis that this sort of exposure could be involved.  I, as a parent, have made investments on a precautionary basis to reduce the exposure of my kids personally to some of these things.  I just don’t want to take the chance.