Critical dose of lead affecting postural balance in workers.
BACKGROUND
The threshold blood lead (BPb) level for nervous system dysfunction in adults has been estimated to be 30-40 microg/dl. This study was carried out to estimate the critical dose of lead affecting the neuromotor function in workers by introducing the benchmark dose (BMD) approach, as well as to identify the specific postural sway to lead exposure.


METHODS
Postural sway parameters with spectral analysis were compared between 121 lead workers with BPb levels of 6-89 (mean 40) microg/dl and 60 unexposed controls.


RESULTS
All sway parameters, except for sagittal sways with eyes open, were significantly larger in the lead workers than in the controls; also, the Romberg quotient for sagittal sway was significantly higher in the lead workers. The BPb level in the lead workers was significantly related to sagittal sways at 1-2 Hz and 2-4 Hz with eyes open, and sagittal and transversal sways at 1-2 Hz and 2-4 Hz with eyes closed. The BMD levels of BPb (i.e., lower 95% confidence limits of BMD) were estimated to be 12.1-17.3 (mean 14.4) microg/dl for postural sway.


CONCLUSIONS
Neuromotor dysfunction in lead workers may be initiated at BPbs below the level previously accepted as effectless, and be characterized mainly by an increased sway of high frequency (1-4 Hz) in the sagittal direction with eyes closed (high Romberg quotient).
Iwata
Toyoto
T
Department of Environmental Health Sciences, Akita University School of Medicine, Akita, Japan.
Yano
Eiji
E
Karita
Kanae
K
Dakeishi
Miwako
M
Murata
Katsuyuki
K
D016022:Case-Control Studies; D006801:Humans; D007854:Lead / Q000009:adverse effects*; D007855:Lead Poisoning / Q000150:complications*; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000209:etiology*; D016272:Occupational Health; D004856:Postural Balance; D018570:Risk Assessment; D012307:Risk Factors; D015837:Vestibular Diseases / Q000209:etiology*
D007854:Lead