A 5 point loss in IQ might not affect the ability of an individual to live a productive life. But if that loss is experienced by an entire population, the implications for that society could be profound.



Bernard Weiss, a behavioral toxicologist at the University of Rochester, examined the societal impact of seemingly small losses of intelligence.


Imagine an unaffected population numbering 260 million people (like the US) with an average IQ of 100 and a standard deviation of 15 (right, above). In that population there would be 6 million people with IQs above 130 and 6 million below 70.

A decrease in average IQ of 5 points would shift the distribution to the left (right, below). The number of people scoring above 130 would decline by 3.6 million while the number below 70 would increase by 3.4 million.




No actual data are available that would allow a test of this "Weiss Effect" at a population level. At least two pervasive contaminants known to impair intelligence, lead and certain PCBs, are sufficiently widespread to raise concerns.

Recent data, for example, reveal that over 60% of inner city children in Philadelphia carry lead levels above criteria established by the US CDC for lead poisoning. Lead contamination in many major cities in developing countries is much worse, with millions of children affected (see discussion in Williams 1997). Other research documents significant declines in IQ in children exposed in utero to levels of PCBs experienced by many people in the United States.

These are just two of many neurotoxic chemicals. Vast quantities are released by accident or design from industrial facilities, or released purposively (e.g., pesticides) each year. Given what is already known about the exposures these releases create, especially given emerging science on interactions among diverse chemicals in mixtures, (e.g., Porter et al. 1997), it is scientifically indefensible to assume there are no effects.