Lead, exposure standards

However, if air sampling estabHshes that the lead exposure concentration is excessive, engineering controls (such as improved ventilation), adrninistrative controls (such as job rotation), and work practices (such as improved personal hygiene of workers) have to be appHed to comply with the permissible exposure limit (PEL) of the OSHA standard. 

EPA. 1989g. Review of the national ambient air quality standard for lead Exposure analysis, methodology and validation. OAQPS staff report. Research Triangle Park, NC U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards. EPA-450/2-89-011. 

Landrigan et al. (1982) conducted an epidemiologic survey to evaluate occupational exposure to arsine in a lead-acid battery manufacturing plant. Arsine concentrations ranged from nondetectable to 49 /breathing zone samples. A high correlation was found between urinary arsenic concentration and arsine exposure (r=0.84 p=0.0001 for an n of 47). Additionally, arsine levels above 15.6 /ig/m3 (=0.005 ppm) were associated with urinary arsenic concentrations in excess of 50 //g/L. The investigators concluded that exposure to a 200 /ig/m3 arsine exposure standard would not prevent chronic increased absorption of trivalent arsenic. 

While there are standards for lead exposure, at this time there is no level that is considered safe, so the best policy is to avoid lead exposure. This is difficult because as a contaminant in food, water, or dust, lead cannot be seen, tasted, or smelled. 

Sweeney et al. (1986) studied mortality among 2510 male chemical workers in the United States, followed from 1952 to 1977. Potential exposures included tetraethyl lead (lARC, 1987b), ethylene dibromide (see this volume), 1,2-dichloroethane, inorganic lead (lARC, 1987b) and vinyl chloride monomer (lARC, 1987c). There were 156 deaths (SMR, 0.7) and 38 cancer deaths (SMR, 1.0) observed. There were excesses of cancer of the larynx (SMR, 3.6 90% CI, 0.7-11.5, based on 2 cases) and brain (SMR, 2.1 90% CI, 0.7-4.9, based on 4 cases). The SMR for all lymphatic and haematopoietic cancers w as 0.9 (90% CI, 0.3-1.9, based on 4 cases). Levels of exposure were not reported, but a NIOSH surv ey in 1980 found levels of exposure to 1,2-dichloroethane to be below the recommended NIOSH standard, while lead exposures were elevated. It was not possible to link mortality to any particular chemical exposure. 

About 90% of blood lead is associated with red blood cells. Measurement of the concentration of lead in the blood is the standard test for recent or ongoing exposure to lead. This test is used routinely to monitor industrial exposure to lead and in screening children for lead exposure. 

Another important issue relates to the reliability of the test. That is, how reproducible or consistent are the test results across multiple administrations Inadequate reliability almost guarantees that a subtle toxicant effect will not be detected against a background of scores of broad individual variability that will be present in any normal population. An issue that has not received adequate attention is the sensitivity of these tests to detect toxicant effects, a factor that is of particular importance if the test results are used in the context of setting exposure standards. If a particular test indicates effects of lead, for example, at a blood lead concentration of 40 pg dl one may wonder whether this represents the bottom limits of sensitivity of the test or the actual blood lead value at which such effects occur. In other words, could the test have detected effects at even lower levels of exposure if it had been more sensitive A deficiency in test sensitivity could mean that exposure standards will be set at levels that are too high and will not protect the exposed populations. 

In any case, it s estimated that the human fetus is ten to a hundred times more sensitive to ambient lead than children or adults, such that the so-called national averages are almost certainly dangerous for the fetus. In 2006, researchers reported a study of 146 pregnant women in Mexico City.13 It s one of the few studies to measure maternal lead values during each trimester of pregnancy. The researchers examined the impact of prenatal lead exposure on fetal neurodevelopment by measuring whole blood and plasma levels of lead in the pregnant mothers at each trimester and then in umbilical cord blood at delivery. When the infants were at 12 and 24 months of age, the researchers measured their BLL and also evaluated their neural development with a standard method (the Spanish version of the Bayley Scales of Infant Development). From the evidence,... 

Vi. Dosage and method of administration for lead poisoning (adults and children). Note Administration of EDTA should never be a substitute for removal from lead exposure. In adults, the federal OSHA lead standard requires removal from occupational lead exposure of any worker with a single blood lead concentration in excess of 60 mcg/dL or an average of three successive values in excess of 50 mog/dL. (However, recent declines in background lead levels and concern over adverse health effects of lower-level exposure support removal at even lower levels). Prophylactic chelation, defined as the routine use of chelation to prevent elevated blood lead concentrations or to lower blood lead levels below the standard In asymptomatic workers, is not permitted. Consult the local or state health department or OSHA (see Table IV-3, p 525) for more detailed information. 

This paper therefore reviews briefly the adverse health effects associated with a number of metals encountered in the lead and zinc industries. It then reviews the hygiene precautions which have been evolved to protect the workforce - principally from the effects of lead exposures - but are generally effective against other metals as well since the exposure routes are similar. Finally it examines the evolution of standards for the protection of workers and the changes in these standards which might be encountered in the short to medium term. 

Since lead and several of the other metals routinely encountered in the workplace are widely acknowledged to be potentially harmful, there is universal acceptance of the need to employ control measures to limit the exposure of individuals involved in the production and use of lead and zinc. However, there is less agreement over the degree of protection which is required, and so, exposure standards vary from country to country. In lead and zinc plants, the greatest concern is invariably related to lead and an extensive body of legislation has been developed to ensure adequate protection of workers. Generally speaking, the techniques employed to limit lead exposure are effective also for other metals and so the discussion in this section of the paper focuses on lead. 

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