Effects of chronic lead ingestion on social development in infant rhesus monkeys

The social behavior of infant rhesus monkeys during the first year of life was examined under a variety of lead (Pb) exposure conditions in four separate experiments. Daily ingestion of PB acetate in milk for one year elevated blood Pb levels to 30-100 microgram/dl, suppressed play, increased social clinging, and exacerbated the disruption of social behavior caused by changing the play environment midway through the year of observation. The presence of control monkeys in social test-groups reduced the magnitude of Pb-induced social behavior changes. In contrast to daily postnatal Pb exposure, chronic exposure to Pb during gestation had no measurable effect on postnatal social development, and acute, transient postnatal Pb exposure (producing blood Pb levels > 200 microgram/dl during month 2 of life) affected only the monkeys' response to the change in the plan environment. These data suggest that daily ingestion of Pb, and not a previously-acquired tissue burden, was responsible for the long-term changes in social development observed. The results are discussed in the general context of primate social development, which is thought to require adequate interactive play for appropriate social integration and reproductive behavior at maturity.