Moderately raised blood lead levels in children.

There is no doubt that high blood lead levels are associated with mental subnormality and hyperactivity. Several recent studies in Britain and America have investigated the relation between moderate levels, i.e. between 20 and 40 microgram/100 ml and behavioural and cognitive phenomena. Epidemiological studies have generally failed to point to a clearcut relation between such levels and overactivity or decrements in performance on standard intelligence and educational tests. Published studies with the use of chelation techniques have suffered from methodological weaknesses. It is known that socio-economic factors are powerfully related to measured intelligence and behaviour and, on the evidence available, it is to them that attention should primarily be given if preventative measures are being considered. There remains the possibility that more refined test measures would detect impaired functioning in children with moderately raised lead levels, and that there is an interaction effect between lead and host resistance.