We have already discussed lead as a cause of diminished general intelligence among the population. However, there are many more substances that have an negative effect on people’s IQ. ScienceDaily has the following report:
We will quote from this article:
Overall childhood exposures cost the nation $7.5 trillion in lost economic productivity and other societal costs.
Therefore it would made sense as a public policy if governments, both here on Earth and those of future space settlements, would ban said substances, known as polybrominated diphenyl ethers (PDBEs), and organophosphate pesticides.
Raising a society’s overall level of general intelligence by combating IQ loss will be a less expensive and more morally acceptable policy than say trying to raise people’s IQ through, say, genetic engineering.
Edit: on a related not, check also the following study: