Relation of cumulative exposure to inorganic lead and neuropsychological test performance.

Abstract

Objectives-To determine if measures reflecting chronic occupational lead exposure are associated with performance on neuropsychological tests. Method-467 Canadian male lead smelter workers (mean (SD) age 43*4 (11.00) years, education 9-8 (3.18) years, years of employment 17'7 (7.43), and current blood lead concentration (B-Pb) 27-5 (8.4) ug dl-e) were given a neuropsychological screening battery. Time weighted average (TWA) and time integrated blood levels (IBL) were developed from B-Pb records obtained through regular medical monitoring (mean (range) TWA 40-1 (4-0-66.4) jg di-1, mean IBL 765*2 (0'6-1625-7) pg-y dl-1). 14 exposure measures may mask differences in neuropsychological functioning related to chronic, low dose exposure.'7 Measures of chronic exposure include time weighted average (TWA), a weighted average of B-Pb over the duration of exposure, and time integrated B-Pb (IBL), a measure of cumulative B-Pb concentrations over the period of exposure.Baker et al found a relation between TWA (for B-Pb) and verbal memory and motor dexterity.4 However, TWA reflected only the previous 15 months of exposure, and was not a weighted average over the entire duration of exposure. Parkinson and colleagues used current B-Pb, TWA, peak exposure, and proportion of B-Pb values greater than 60 mg/i 00 ml as exposure indices. These authors did not find a relation between exposure variables and neuropsychological measures after adjustment for the effects of age and education.5 Hogstedt et al found differences between exposed and non-exposed controls in reaction time, learning, and memory. However, when the exposed group was analysed by TWA terciles, no significant differences (dose-effect) were found.'A recent review noted that the relation of chronic exposure and neuropsychological functioning remains unexamined.8 Our study examined the effects of chronic occupational lead exposure on neuropsychological performance. Method PARTICIPANTSWe held small group informational sessions with all employees to describe the purpose and procedure of the study. The 467 Canadian men currently and previously employed in a lead smelter (370 current, 97 former; mean (SD) age 43-4 (11-00), years of education 9 8 (3.18), years employed 17-7 (7-43)) who agreed to participate, represented about 87% of current employees. No company records were available to measure the number of former employees. Participants were not paid for their involvement, and current employees completed the evaluation at the start of their shift. A consent form explaining the purpose of the study was reviewed with each participant. Because the smelter was in a bilingual area, workers chose to be tested in either French (n = 129) or English (n = 329). Nine men chose to be evaluated with a combination of French and English. PROCEDUREThe participants completed an individual two hour neuropsychological screening battery.

Cognitive effects of chronic exposure to lead and solvents

“…These findings are consistent with previous studies of chronic lead exposure where higher exposures (e.g., years of exposure; integrated blood lead (IBL); bone lead) were associated with poorer performance on motor and visuomotor tasks [Braun and Daigneault, 1991;Bolla et al, 1995;Lindgren et al, 1996;Bleecker et al, 1997;Payton et al, 1998]. However, Hanninen et al [1998] and Bleecker et al [1997] found that history of blood lead was a better predictor of performance than bone lead while Stokes et al [1998] did not find an association between bone lead and neurobehavioral performance.…”

“…This task, in both its traditional form as a part of the Wechsler Adult Intelligence Scales or its computerized form, has consistently been shown to be sensitive to the chronic effects of both lead and solvents [Grandjean et al, 1978;Valciukas et al, 1978;Bolla et al, 1990Bolla et al, , 1995Spurgeon et al, 1992;Baker, 1994;Grosch et al, 1996; Lindgren et al, 1996;Seeber et al, 1996]. However, in the present study, only those workers chronically exposed to lead performed significantly more slowly but not less accurately than controls.…”

Characterizing Golden Eagle Risk to Lead and Anticoagulant Rodenticide Exposure: A Review

“…Tasks that tested primarily visuomotor skills were significantly associated with a cumulative dose-estimate. Lindgren et al (1996) indicated that the lack of an association between current blood lead or a TWA and neuropsychological performance was not necessarily inconsistent with other studies that found such an association since in their study the current mean PbBs were lower than in other studies. Current PbB as well as a TWA may have lacked the sensitivity to detect the decrement in performance.…”

“…A subsequent study of 70 workers showed that lead impaired both the speed of making simple movements, as well as decisions, and suggested that decision slowing is due to central rather than peripheral factors (Stollery 1996). A study of 427 Canadian lead workers whose mean current PbB was 27.5 μg/dL, and mean duration of employment was 17.7 years examined the correlation between short-and long-term measures of exposure to lead and performance on neuropsychological tests (Lindgren et al 1996). Tasks that tested primarily visuomotor skills were significantly associated with a cumulative dose-estimate.…”

Cognitive deficits and magnetic resonance spectroscopy in adult monozygotic twins with lead poisoning.

“…Since that time, several other studies have assessed this association. Three studies using multiple BPb measurements to create an integrated measure of cumulative exposure among occupationally exposed populations reported cross-sectional associations of this measure with lower neurobehavioral test scores (Chia et al 1997;Lindgren et al 1996;Lucchini et al 2000), although one such study failed to find an association with their cumulative lead measure (Barth et al 2002). Several other studies used KXRF technology to assess cumulative lead exposure (the half-life of lead in bone is decades) and its association with cognitive performance.…”