Lead and its inorganic compounds, other than lead arsenate and lead chromate as Pb, inhalable fraction. Documentation of suggested occupational exposure limits (OELs)
Journal Title: Podstawy i Metody Oceny Środowiska Pracy - Year 2014, Vol 30, Issue 2
Abstract
Lead (Pb, atomic weight 207.19) in inorganic compounds usually has the oxidation state II, but state IV also occurs. Lead is a soft, silvery grey metal. In the Earth’s crust it is present in various minerals such as sulfide, carbonate and sulfate. The metallurgy of lead consists of three separate operations: concentrating ,smelting and refining. Occupational lead exposure occurs in the wide variety of settings during primary and secondary lead smelting, working in non-ferrous foundries, production of electric storage batteries, as well as scraping and sanding lead paint. Exposure to lead, both in the occupational and environmental settings decreased significantly during last 20 years. In 2004-2005, in Poland, 3297 persons were exposed to lead in occupational settings in concentrations higher than the Polish OEL amounting to 0.050 μg/m[sup]3[/sup]. In the occupational setting, inhalation is then most significant route of exposure to lead. However, improvements in industry resulted in a reduction of lead concentrations in the air, making the gastrointestinal absorption increasingly important. Deposition and absorption of inhaled lead-containing particles are influenced by their size and solubility in water. About 30 – 50% of lead containing parti-cles is deposited in the lungs. That which is not deposited in alveoli is cleared by the mucociliary escalator and ingested. Only small fraction of ingested lead (about 10 %) in absorbed in adults. Under steady-state conditions, lead in blood is found primarily in the red blood cells (99%). In human adults, approximately 90% of the total body burden is found in the bones. This compartment contains two different pools of lead with different turnover rates, trabecular bone (23%) and cortical bone (69%). At the steady state conditions T1/2 of elimination of lead from blood amounts to about one month and from bones to 5 – 10 years. Most of the information on human exposure to lead , and the health effects resulting from it, is based on the lead in blood (B-Pb) levels. At steady state B-Pb reflects a combination of recent lead exposure to that which occurred several years ago. The relationship of B-Pb to air lead (A-Pb) exposure concentrations is as the bridge between A-Pb and possible damage to health of workers. The relationship varied from 0.3 to 1.9 μg/L blood per μg Pb/m3 air. In adults, the health effects of exposure to lead may include inhibi-tion of several enzymes involved in heme syn-thesis, influence on the functions of the kidney, peripheral and central nervous system, and an increase of blood pressure, which is a significant risk factor for cardiovascular diseases. The threshold for these effects in adults amounts to about 300 μg/L B-Pb. The central nervous system is the main target organ for lead toxicity in children. There is no evidence of a threshold below which lead does not cause neurodevelopmental toxicity in children. Lead is carcinogenic in animal experiments, but there is only limited evidence for carcinogenicity in humans (IARC category 2A). Identifying of a blood lead level in workers that would be protective during a working lifetime was necessary for recommending a TLV, because B-Pb values, rather than A-Pb concentrations, were most strongly related to health effects. The recommended BEI of 300 μgL is designed to minimize the possible effects on the mentioned above organs and systems in adults. Certain studies have reported effects at B-Pb below the proposed BEI value. However, the observed effects were transient, did not constitute a decrement in the worker’s functional capacity, or was contradicted by other adequately conducted studied. If the steepest slope representing the relationship between B-Pb and A-Pb concentration in the workplace (1.9 μg/L of lead in blood per μg/m[sup]3[/sup] air) is used for judging the contribution of airborne concentrations to B-Pb the proposed TLV-TWA of 0.050 mg/m[sup]3[/sup] would contribute an airborne, work- related fraction of B-Pb concentration of 95 μg/L. Therefore contributions from community sources and nonairborne workplace contamination should be controllable such that the total B-Pb concentrations could be kept below the BEI of 300 μg/L. For example in Germany geometric mean concentration of B-Pb in the general population amounted to 31 μg/L and 95% percentyles to 70 μg/L in women and 90 μg/L in men Thus, the persons responsible for occupational hygiene must keep in mind that B-Pb, rather than A-Pb is the principal means for moniotoring lead exposure control. <br/><br/>
Authors and Affiliations
Marek JAKUBOWSKI
Keywords
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- DOI 10.5604/1231868X.1111932
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