COGNITIVE AND SENSORIMOTOR FUNCTIONS IN 6-YEAR-OLD CHILDREN IN RELATION TO LEAD AND MERCURY LEVELS - ADJUSTMENT FOR INTELLIGENCE AND CONTRAST SENSITIVITY IN COMPUTERIZED TESTING

Within a larger environmental health screening program neurobehavioral measures were taken in 384 6-year-old children (mean age 74 months) i n the cities of Leipzig, Gardeiegen, and Duisburg. Lead concentrations in venous blood samples (PbB) and urinary mercury excretion in 24-h s amples (HgU) were measured as markers of environmental exposure by ele ctrothermal AAS. Dependent variables included two subtests from the WI SC [vocabulary (V) and block design (BD)] as well as five tests from t he NES2 [pattern comparison, pattern memory, tapping, simple reaction time, and the continuous performance test (CPT; child version)]. In ad dition, visual functions [visual acuity (TITMUS-test) and contrast sen sitivity (FACT)] were tested as covariates. The overall average PbB (g eometric mean) was 42.5 mu g/l (upper 95% value = 89 mu g/l). The over all average mercury excretion (HgU) was 0.16 mu g/24 h. Whereas no sig nificant or borderline associations between HgU and any of the target variables was found, significant negative associations were observed b etween PbB and verbal intelligence (WISC vocabulary but not WISC Block Design) and false-positive responses (false alarms), as well as false -negative responses (miss) in the CPT. Whereas parental education was the most important confounder for WISC performance, visual contrast se nsitivity and computer familiarity also proved predictive for performa nce in several computer-based NES subtests. It is concluded that non-I Q measures, namely measures of sustained attention, are negatively aff ected in children with 95% of blood-lead levels below 90 mu g/l, even after adjustment for intelligence and contrast sensitivity, whereas th e causative role of lead in altering IQ functions remains somewhat equ ivocal, because important covariates could not be controlled for. (C) 1998 Elsevier Science Inc.