A neurobehavioural study of long-term occupational inorganic lead exposure

A group of 38 male workers at a secondary smelter (period of employment 2-35 years; median 10 years) was divided into two subgroups depending on bone-lead concentration, arranged as 19 matched pairs according to age, education and job level. The median concentrations for finger-bone lead (Bone-Pb) were 16 vs. 32 micrograms/g; for current blood-lead (B-Pb), 1.6 vs. 1.8 mumol/1; for retrospective peak blood-lead (Peak-Pb), 2.7 vs. 3.0 mumol/1; and for a retrospective cumulative blood lead index (CBLI), 143 vs. 233 mumol/l x months. Nineteen unexposed male workers from a nearby mechanical plant served as controls, using the same matching algorithm. The triplets were examined with a standardised neuropsychological test battery, and four questionnaires for self-rating of symptoms and activity/stress level related to work environment. No sign of behavioural deterioration was observed in the exposed groups, either in objective cognitive tests or in subjective symptom/mood self-rating scales. Despite the limited sample size, the statistical power was sufficient to conclude that a concealed lead-associated effect was unlikely. Covariations between behavioural measures and lead exposure indices were generally low and non-significant, as a whole not exceeding a random level. No confounding or effect-modifying factor was detected that could explain the results as a type II error. To conclude, a current B-Pb of 1.8 mumol/l was not associated with adverse behavioural effects, and a long-term lead exposure around 2.0 mumol/l for 13 years (mean values) was not associated with permanent brain dysfunction.