Buta-1,3-diene. Documentation of proposed values of occupational exposure limits (OELs)

Abstract

Buta-1,3-diene is a gas used in the production of thermoplastic resins, elastomers and synthetic rubber. Buta-1,3-diene is absorbed mainly in the respiratory tract and then metabolized to monoepoxide – 1,2-epoxybut-3-ene and diepoxide – 1.2:3,4 diepoxybutane, and after their conjugation with glutathione is excreted with urine. According to data from the Central Registry on Exposure to Substances, Mixtures, Agents or Carcinogenic or Mutagenic Technological Processes, in 2015 the number of people exposed to buta-1,3-diene in Poland was 958 and additionally about 200 were exposed to petroleum substances which carcinogenic effect is depending on the buta-1,3-diene. According to data from sanitary-epidemiological stations, in Poland in 2013 and 2016, there were no workers exposed to buta-1,3-diene at levels exceeding maximum allowable concentration (MAC) of 4.4 mg/m3. Buta-1,3-diene in small concentrations is a mild narcotic agent for humans, while for occupationally exposed workers it has irritating properties to the mucous membranes of the eyes and airways. Buta-1,3-diene is a substance with low acute toxicity to animals (LC50 value for rats is 270 000 mg/m3). This substance is mutagenic and genotoxic, it can cause damage to the genetic material of somatic and germ cells. It has been proved that buta-1,3-diene is carcinogenic for B6C3F1 mice and rats. There is also epidemiological evidence that occupational exposure to buta-1,3-diene is associated with the risk of a cancer of a lymphohematopoietic system. According to the IARC classification, buta-1,3-diene is included in group 1, i.e., carcinogenic substances for humans, and according to ACGIH classification to group A2, i.e., substances suspected to be carcinogenic for humans. In Europe, buta-1,3-diene is classified in Cat. 1A. carcinogens and Cat. 1B. mutagenic compounds. Buta-1,3-diene does not cause fertility disturbances, and its teratogenic effects appeared when doses were toxic to mothers only. In Directive 2017/2398 of the European Parliament and of Council (EU) 2017/2398 of 12 December 2017 amending Directive 2004/37/EC on the protection of workers from the risks related to exposure to carcinogens or mutagens at work for buta-1,3-diene, binding occupational exposure limit value (BOELV ) was at the level of 2.2 mg/m3 (Official Journal of the EU L 345 of 27/12/2017, p. 87). The directive will be in force in the EU Member States on January 17, 2020. It was proposed to adopt the value of the maximum allowable concentration (MAC) of the buta-1,3-diene at the level of 2.2 mg/m3 and the following values of the biological exposure indices (BEI): • 1.6 mg/g creatinine of 1,2-dihydroxy-4-(N-acetyl-cystein-S-yl)butane in urine measured at the end of working shift • 2.1 pmol/g Hb - hemoglobin adducts: mixture of N-[1-(hydroxymethyl)prop-2-enyl]valine and N (2-hydroxybut-3-enyl)valine in blood showing exposure for the last 120 days. This standard is additionally marked Carc. 1A – a substance with proven carcinogenic effect for humans and Muta. 1B – a substance that is considered mutagenic for humans. There is no evidence for establishing STEL value for buta-1,3-diene. The estimated additional risk of leukemia during the 40-year exposure to buta-1,3-diene at a concentration of 2.2 mg/m3 is 8×10-7, it is lower than the risk for the general population in Poland, which is 7.15×10-5.