Vibration perception thresholds in workers with long term exposure to lead

Objectives-To evaluate the impact of long term occupational exposure to lea d on function of the peripheral nervous system as reflected by vibration pe rception threshold (VPT), measured with a portable vibrameter. Methods-217 Workers in a lead battery factory were required to have an annu al blood lead measurement during each of the 5 years preceding this study. All were invited to take the VPT test. A total of 206 workers were studied. The associations were analysed between VPTs and current blood lead concent ration, mean concentration of blood lead over the past 5 years, maximum blo od lead concentration during the past 5 years, index of cumulative blood le ad (ICL), time weighted index of cumulative blood lead (TWICL), and percent age of lifespan spent at work in the plant, as well as the other potential confounders. Ordinary multiple regressions, generalised additive models, an d hockey stick regression analyses were used to explore the potential exist ence of a threshold effect of blood lead variables on VPT. Results-VPT at a frequency of 220 Hz ranged from 6 to 100 (10(-2) g, or 0.0 98 m/s(2)) with a mean (SD) of 19.8 (14.2) for the feet and from 4 to 43 wi th a mean (SD) of 10.2 (6.1) for the hands. The five variables of exposure to lead were all significantly correlated with VPT of the feet but not the hands. In multiple linear regression analyses, the mean of the blood lead c oncentrations and the TWICL were significantly associated with VPT of the f eet. The relation between VPT of the feet and mean blood lead was shown to be a J shaped curve with a generalised additive model and local smoothing t echnique. In the hockey stick regression, evidence was found of a threshold effect at a mean blood lead concentration of 31 mu g/dl. Above this thresh old it was estimated that each increase of 1 mu g/dl mean blood lead over 5 years would increase VPT of the feet by 0.29 (10(-2) g) or 0.028 m/s(2) (a t a frequency of 220 Hz) with other potential confounders held constant. Conclusion-This study suggests that measurement of vibration sensory thresh old is a relatively effective tool for detecting lead neuropathy in field s tudies, and that lead might cause sensory neuropathy with an effect thresho ld corresponding to a 5 year mean blood lead concentration of 31 mu g/dl.