Occupational lead exposures dose-response relationships

Effect of Dose and Duration of Exposure on Toxicity. No studies were located where -hexane concentration was measured in workplace air before workers became ill, so no dose-response relationship can be defined for human neurotoxicity as the result of -hexane exposure. Information on duration of exposure leading to toxicity is available from some case series reports. An occupational exposure caused sensory disturbances in the lower extremities after approximately 2 months (Herskowitz et al. 1971). A case of peripheral neuropathy after 7 months of exposure was reported among press-proofing workers in Taipei (Wang et al. 1986) a serious case resulting in quadriplegia after 8 months of exposure was reported among sandal workers in Japan (Yamamura 1969). Based on case reports, it can be estimated... 

Several other studies published in the last 5 years have reported adverse associations between occupational lead exposure and impaired renal function. A study in Nigeria described impaired creatinine clearance in 190 lead workers (mean BLL 50 pg/dL) compared with 80 controls but did not adjust for aity covariates (Alasia et al. 2010). A study of 87 industrial workers (mean BLL 29 pg/dL) and 61 controls in Pakistan reported statistically significant correlations between BLL and seram creatinine, uric acid, and several early biologic markers of renal dysfunction (Khan et al. 2008). Early biologic markers of tubular and glomeralar function were explored in 155 battery workers (mean BLL 20 pg/dL) and 36 controls in China (Sun et al. 2008). The study reported a dose-response relationship between BLL and renal function, biomarkers of bone metabolism, and the prevalence of osteoporosis. Those and many other studies summarized by EPA (2012) have been rather consistent in making the link between occupational lead exposure and impaired renal function. 

First, reproductive and developmental lead toxicity in both men and women remains a significant human health issue on several grounds, whether adequately characterized in terms of dose—response relationships or not. Occupational lead exposures remain as sources of toxicity in both industrialized and developing countries. These exposures of both male and female workers potentially persist at levels not greatly different from those reported in past decades. 

Other forms of immunotoxic expression with occupational Pb exposures have been described. Brazilian Pb workers (Queiroz et al., 1993) had significantly reduced peripheral blood neutrophil populations versus controls, using both chemotaxis and nitroblue tetrazolium reduction. These impairments were seen in workers with PbB <60pg/dl. Mishra et al. (2003) examined immunotoxic effects of Pb in three groups of workers versus controls lead battery plant workers, jewelry makers, and three-wheeler drivers. Phytohemagglutinin-induced lymphocyte proliferation was inhibited versus controls, but no dose—response relationship was seen. T-cell mitogen-stimulated monocytes also showed an increase in IFN- but NK-cell level was unaffected. There was a positive correlation of IFN- with PbB. 

Blood lead concentration (PbB) and erythrocytic protoporphyrin concentration (EP) are both used as indices of lead exposure in children and in occupationally exposed adults. In a previous study we reported dose-effect and dose-response relationships, in EP vs. PbB (Hammond et al, 1955). In the present study we report the influence of age on the threshold for an EP response to PbB, as well as on the slope of the dose-effect interaction. In the age range 12-30 months the threshold for effect of PbB on EP falls progressively, while the magnitude of the dose-effect increases with age. The rate of decline in the threshold for In EP and the rate of increase for In EP PbB are linearly related to age. 

Hammond, P.B., Lemer, S.J., Gartside, P.S., Hanenson, J.B., Roda, S.B., Foulkes, E.C., Johnson, D.R. and Pesce, A.J. (1980). The relationship of biological indices of lead exposure to the health status of workers in a secondary lead smelter. ]. Occup. Med., 22, 475-484 Hammond, P.B., Bomschein, R.L. and Succop, P. (1985) Dose-effect and dose-response relationships of blood lead to erythrocytic protoporphyrin in young children. Environ. Res., 38, 187-196... 

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