Elsevier

Neurotoxicology and Teratology

Volume 20, Issue 5, September–October 1998, Pages 511-521
Neurotoxicology and Teratology

Article
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

https://doi.org/10.1016/S0892-0362(98)00010-5Get rights and content

Abstract

Within a larger environmental health screening program neurobehavioral measures were taken in 384 6-year-old children (mean age 74 months) in the cities of Leipzig, Gardelegen, and Duisburg. Lead concentrations in venous blood samples (PbB) and urinary mercury excretion in 24-h samples (HgU) were measured as markers of environmental exposure by electrothermal AAS. Dependent variables included two subtests from the WISC [vocabulary (V) and block design (BD)] as well as five tests from the NES2 [pattern comparison, pattern memory, tapping, simple reaction time, and the continuous performance test (CPT; child version)]. In addition, visual functions [visual acuity (TITMUS-test) and contrast sensitivity (FACT)] were tested as covariates. The overall average PbB (geometric mean) was 42.5 μg/l (upper 95% value = 89 μg/l). The overall average mercury excretion (HgU) was 0.16 μg/24 h. Whereas no significant or borderline associations between HgU and any of the target variables was found, significant negative associations were observed between 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 sensitivity and computer familiarity also proved predictive for performance in several computer-based NES subtests. It is concluded that non-IQ measures, namely measures of sustained attention, are negatively affected in children with 95% of blood-lead levels below 90 μg/l, even after adjustment for intelligence and contrast sensitivity, whereas the causative role of lead in altering IQ functions remains somewhat equivocal, because important covariates could not be controlled for.

Section snippets

Study Areas

As in 1991, the study was conducted in the cities of Leipzig, Gardelegen, and Duisburg. Leipzig is one of the largest cities (about 500,000 inhabitants) in East Germany (Saxonia) formerly characterized by high dust and SO2 levels that keep declining since the year of reunification (1989), but without specific sources of exposure to heavy metals. The specific study area (South-West Leipzig) is characterized by old dilapidated housing close to small-scale industry. Lead pipes in domestic water

Check for selection bias

Three hundred and eighty-four children, namely 60.3% of the eligible children, participated according to their mother’s prior agreement. The samples of participating and nonparticipating children and their families were compared for relevant biosocial and exposure variables, and the results of this comparison are given in Table 1. Except for PbB, HgU, and education as a relevant proxy for social status, no further significant differences between participating and nonparticipating

Discussion

In the present study neurobehavioral functions in 6-year-old children, assessed by means of conventional vs. computerized testing, were examined for associations with background levels of lead in blood (PbB) and urinary mercury excretion (HgU).

With regard to the latter, the observed associations were small, throughout, and statistically not significant, even if two-tailed probabilities were replaced by one-tailed probabilities. This observation supports the opinion that current background

Acknowledgements

We would like to thank Drs. M. Mangold, S. Teichmann, F. J. Gutsmuths, and R. Behler from the local Health Offices for their support in organizing the studies within the regular medical examinations prior to school entrance, as well as Birgit Dziersan, Ulrike Hennekes, Thekla Petursdottir, and Ursula Zovkic for their help in testing the children.

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