Lithium hydride – inhalable fraction
Journal Title: Podstawy i Metody Oceny Środowiska Pracy - Year 2016, Vol 32, Issue 3
Abstract
Lithium hydride (CAS 7580-67-8) at room temperature is a solid, odorless substance, which reacts violently with water and forms lithium hydroxide. Lithium hydride is an inorganic compound created during chemical synthesis. Lithium hydride is used mainly as an intermediate in organic synthesis, the source of hydrogen and a desiccant. In Poland, the existing norm for lithium hydride in workplace air is MAC-TWA (NDS) – 0.025 mg/m3 (documentation from 1994). Short-term exposure limit (STEL, NDSCh) has not been established. According to GUS, in 2007, 2010 and 2013 there were no cases of exceeded norms for lithium hydride. SCOEL proposed for inhalable fraction of lithium hydride only short-term exposure limit (STEL 15 min) of 0.02 mg/m3. The basis of this value was no airway irritation when exposed to lithium aluminum hydride at a concentration exceeding 0.025 mg/m3. The value of an 8-hour (OEL) has not been established. The documentation and the recommendation from SCOEL were consulted in 2007. Interdepartmental Commission for MAC and MAI reported the remark to the proposals SCOEL on determining only the short-term exposure limit of the lithium hydride (NC/NDS/18/1907/2008) without setting values for 8-hour exposure. In conclusion, SCOEL stated that lithium hydride has no systemic action and is only irritant, so determined only short-term exposure limit. The Commission's comments were as follows: The basis of the value STEL proposed in the SCOEL are unpublished results obtained from the studies of workers occupationally exposed to the compound, with not given them the relevant data (number of workers exposed, exposure time). Lithium hydride may be irritating an even corrosive to the mucous membranes of the eyes and respiratory tract and skin. These results from the reaction of an alkali compound, but also the lithium ion has an adverse effect on the nervous system. We therefore believe that there is no basis to determine only the STEL for lithium hydride. In response to the notice, SCOEL reported that therapeutic concentrations of lithium in the blood plasma is far above the value that can be achieved by a professional exposure to lithium aluminum hydride. Inhalation the lithium at a concentration of 0.1 mg/m3 for 8-hour, which at this concentration is strongly irritant, corresponds with the calculated daily dose of 10 mg of lithium (assuming 10 m3 of air inhaled and absorption of 100%). This dose is substantially lower than the dose of lithium estimated during ingestion of food and water and much lower than the daily dose of 167 mg lithium Li/day (specified in Sweden for the treatment of affective disorders). Without data on concentration-effect relationships of long-term exposure, OEL values for lithium hydride has not been established. Due to its irritating property short-term exposure limit (STEL) was proposed. Value STEL of 0.02 mg/m3 for lithium hydride without OEL values for an 8-hour exposure was proposed in a draft directive establishing 4th list of indicative occupational exposure limit values. Therefore, the Group of Experts on Chemical Agents prepared new documentation for the compound. In the available literature, lithium hydride is described as a strongly irritant substance. A high chemical reactivity, especially in a humid environment, causes a risk of irritation and/or corrosion of tissues. Lithium hydride is a potential health risk with acute effects. The consequence of food poisoning can be permanent damage to the cornea, narrowed esophagus and pulmonary edema. Lithium hydride is not mutagenic and carcinogenic. The basis for the proposed MAC values are irritating properties of lithium aluminum hydride in people occupationally exposed to this compound. It is therefore proposed for lithium hydride exposure limit value of 0.01 mg/m3 as TWA-MAC and of 0.02 mg/m3 as short-term exposure limit (STEL). There is no basis to determine the biological exposure index (BEI). Due to strong corrosive effects of lithium hydride it was recommended to label the compound with the letter C – a corrosive substance.
Authors and Affiliations
Jadwiga Szymańska, Barbara Frydrych, Elżbieta Bruchajzer
Keywords
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