Occupational lead exposures thresholds

Heavy metal content of ayurvedic herbal medicine products. JAMA 292 2868-2873 Saryan, L.A. and C. Zenz. (1994) Ixad and its compounds. In Occupational Medicine (third edition). L.A. Saryan and C. Zenz (editors), Mosby, St. Louis, pp. 506—541 Schwartz, J. (1994) Low-level lead exposure and children s IQ A meta-analysis and semch for a threshold. Environ. Res. 65 42-55... 

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. 

Magnesium vanadates, as vanadium compounds in general, are known irritants of the respiratory tract and conjunctiva. The threshold limit value (TLV) for vanadium compounds in air recommended by the National Institute of Occupational Safety and Health is 0.05 mg/m based on a typical 8-h workday and 40-h workweek (7,147). Chronic inhalation can lead to lung diseases such as bronchitis, bronchopneumonia, and lobar pneumonia. These dust-related effects can be avoided by use of individual respirators in areas where exposure is likely. 

A dose-related elevation of EP or ZPP in lead workers has been documented extensively (Herber 1980 Matte et al. 1989). Correlations between PbB levels and log EP or ZPP indicate an apparent threshold for EP elevation in male workers at 25-35 pg/dL (Grandjean and Lintrup 1978 Roels et al. 1975) for FEP and a threshold of 30-40 pg/dL for EP (Roels and Lauwerys 1987 Roels et al. 1979). The threshold for EP elevation appears to be somewhat lower (20-30 pg/dL) in women than in men (Roels and Lauwerys 1987 Roels etal. 1975, 1976, 1979 Stuik 1974), regardless of whether exposure is primarily by inhalation (occupational) or oral (nonoccupational). These studies were controlled for possible confounding factors such as iron deficiency or age, both of which increase erythrocyte ZPP. 

ALAD, an enzyme occurring early in the heme pathway, is also considered a sensitive indicator of lead effect (Hemberg et al. 1970 Morris et al. 1988 Somashekaraiah et al. 1990 Tola et al. 1973). Because there is no well-defined blood lead threshold at which inhibition of ALAD does not occur, it allows measurement of the effect on the general population at environmental lead levels and does not require high exposure levels as with occupational workers (Hemberg et al. 1970). However, ALAD activity may also be decreased with other diseases or conditions such as porphyria, liver cirrhosis, and alcoholism (Somashekaraiah et al. 1990). 

Toluene (methylbenzene) does not possess the myelotoxic properties of benzene, nor has it been associated with leukemia. It is, however, a central nervous system depressant. See Table 57-1 for the threshold limit values. Exposure to 800 ppm can lead to severe fatigue and ataxia 10,000 ppm can produce rapid loss of consciousness. Chronic effects of long-term toluene exposure are unclear because human studies indicating behavioral effects usually concern exposures to several solvents, not toluene alone. In limited occupational studies, however, metabolic interactions and modification of toluene s effects have not been observed in workers also exposed to other solvents. 

Most adult exposure is occupational. The Immediately Dangerous to Life or Health value for lead is lOOmgm . The recommended exposure limit is O.lmgm and the permissible exposure limit/ threshold limit value for lead is 0.05 mg m. ... 

Due to experimental data, an indirect rather than direct genotoxic carcinogenic effect of lead has been indicated (Silbergeld et al. 2000). Thus, there may be a threshold for the carcinogenic effects in man that would argue in favor of setting health-based occupational exposure limits for lead. 

Other critical endpoints of lead toxicity include toxicity to the nervous system and the kidneys. Based on experimental findings, it seems plausible that lead has no direct genotoxic effects, which argues for establishing a practical threshold limit value for lead toxicity. Thus, an occupational exposure limit (OEL) based on avoiding functional CNS alterations is expected also to protect versus toxicity to the peripheral nervous system and the kidney, including possibly the development of renal cancer. 

Chuang, H.Y., J. Schwartz, S.Y. Tsai, M.L. Lee, J.D. Wang, and H. Hu. 2000. Vibration perception thresholds in workers with long term exposure to lead. Occup. Environ. Med. 57(9) 588-594. 

Defining the Science of Occupational and Environmental Health, the ACGIH is a member-based organization that advances occupational and environmental health. The ACGIH is one of the industry s leading publications resources, with approximately 400 titles relative to occupational and environmental health and safety, including the renowned Threshold Limit Values (TLVs ) and Biological Exposure Indices... 

The very low mean PbBs in these women and those men and women in the Muntner et al. (2003) U.S. NHANES III provided good evidence that the relative threshold for Pb nephrotoxic effects with environmental exposures in the general population is an order of magnitude less than was observed in the older occupational Pb literature, 60 pg/dl. Low body lead burdens indexed as chelatable Pb amounts of <80 pg/dl were also found to be a predictor of decreased kidney function (Lin et al., 2006). Taiwanese chronic kidney disease patients (N = 108) without diabetes were assigned to chelation and nonchelation groups. Those patients who were not periodically chelated over a 24-month testing period sustained a mean reduction in GFR of 4.6 ml/min/1.732 m and showed increased serum creatinine. 

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