Declining blood lead levels and changes in cognitive function during childhood: the Port Pirie Cohort Study.
BACKGROUND
Many studies have found a significant inverse association between early exposure to environmental lead and cognitive function in childhood. Whether these effects are reversible when exposure is reduced is not clear.


OBJECTIVE
To assess the reversibility of the apparent effects of lead on cognitive abilities in early childhood by testing whether declines in blood lead concentrations beyond the age of 2 years are associated with improvements in cognition.


METHODS
Urban and rural communities surrounding a large lead smelter in Port Pirie, South Australia.


METHODS
A total of 375 children followed up from birth to the age of 11 to 13 years.


METHODS
Long-term prospective cohort study.


METHODS
The Bayley Mental Development Index at age 2 years, the McCarthy General Cognitive Index at age 4 years, and IQs from the Wechsler Intelligence Scale (revised version) at ages 7 and 11 to 13 years.


RESULTS
Mean blood lead concentrations in the children decreased from 1.02 pmol/L (21 .2 microg/dL) at age 2 years to 0.38 micromol/L (7.9 microg/dL) at age 1 1 to 13 years, but cognitive scores in children whose blood lead concentration declined most were generally not improved relative to the scores of children whose blood lead levels declined least. Changes in IQ and declines in blood lead levels that occurred between the ages of 7 and 11 to 13 years (r= 0.12, P= .09) suggested slightly better cognition among children whose blood lead levels declined most.


CONCLUSIONS
The cognitive deficits associated with exposure to environmental lead in early childhood appear to be only partially reversed by a subsequent decline in blood lead level.
Tong
S
S
Centre for Public Health Research, Queensland University of Technology, Brisbane, Australia. s.tong@qut.edu.au
Baghurst
P A
PA
Sawyer
M G
MG
Burns
J
J
McMichael
A J
AJ
D002648:Child; D002675:Child, Preschool; D003071:Cognition; D003072:Cognition Disorders / Q000209:etiology; D015331:Cohort Studies; D004781:Environmental Exposure; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007361:Intelligence Tests; D007854:Lead / Q000097:blood*; D007855:Lead Poisoning / Q000150:complications; D008137:Longitudinal Studies; D011446:Prospective Studies; D012044:Regression Analysis; D013021:South Australia
D007854:Lead