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Cognitive and sensorimotor functions in 6-year-old children in relation to lead and mercury levels: adjustment for
J Walkowiak1, L Altmann, U Krämer
1Division of Biological Psychology, Medical Institute of Environmental Hygiene at the Heinrich-Heine-University Düsseldorf, Germany.
Insights
Environmental lead exposure in children negatively impacts sustained attention, even at low levels. While blood lead levels showed associations with cognitive deficits, the impact on IQ remained unclear due to confounding factors.
Area of Science:
- Environmental Health
- Neurotoxicology
- Pediatric Neurobehavioral Assessment
Background:
- Children's neurobehavioral development is susceptible to environmental toxins.
- Lead and mercury are common environmental pollutants with known neurotoxic effects.
- Assessing low-level exposure impacts is crucial for public health.
Purpose of the Study:
- To investigate the association between blood lead levels (PbB) and urinary mercury excretion (HgU) and neurobehavioral outcomes in 6-year-old children.
- To examine the influence of lead and mercury exposure on cognitive functions and attention.
- To identify potential confounding factors affecting neurobehavioral performance.
Main Methods:
- Neurobehavioral tests (WISC, NES2) and visual function tests were administered to 384 children.
- Blood lead concentrations (PbB) and urinary mercury excretion (HgU) were measured using electrothermal AAS.
- Statistical analyses were performed to assess associations, controlling for covariates like parental education and visual contrast sensitivity.
Main Results:
- Significant negative associations were found between PbB and verbal intelligence (WISC vocabulary) and performance on the Continuous Performance Test (CPT).
- No significant associations were observed between HgU and neurobehavioral variables.
- Sustained attention measures (CPT false alarms and misses) were negatively affected by PbB, even at levels below 90 microg/l.
Conclusions:
- Environmental lead exposure, even at relatively low levels, negatively impacts children's sustained attention.
- The causative role of lead in altering IQ functions requires further investigation with better control for covariates.
- Non-IQ neurobehavioral measures may be more sensitive indicators of low-level lead toxicity in children.
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 microg/l (upper 95% value = 89 microg/l). The overall average mercury excretion (HgU) was 0.16 microg/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 microg/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.