DICHLOROMETHANE Dichloromethane was reviewed previously by the Working Group in 1987 and 1998 (IARC, 1987, 1999). New data have since become available, and these have been incorporated, and taken into consideration in the present evaluation. 1. Exposure Data 1.1.3 Chemical and physical properties of the pure substance 1.1 Identification of the agent Description: Colourless liquid with pene- 1.1.1 Nomenclature trating ether-like odour (O’Neil et al., 2006; Haynes, 2010) Chem. Abstr. Serv. Reg. No.: 75-09-2 Boiling point: 40 °C Chem. Abstr. Serv. Name: Dichloromethane Melting point: –97.1 °C 20 IUPAC Systematic Name: Dichloromethane Density: d4 1.327 g/mL Synonyms: Methane dichloride; methylene Solubility: Slightly soluble (1.38 g/100 mL) in bichloride; methylene chloride; methylene water at 20 °C; soluble in carbon tetrachlo- dichloride ride; miscible in ethanol, diethyl ether, and dimethylformamide 1.1.2 Structural and molecular formulae, and Volatility: Vapour pressure, 58.2 kPa at relative molecular mass 25 °C; relative vapour density (air = 1), 2.93 (Verschueren, 1996) H Stability: Vapour is nonflammable and is not explosive when mixed with air, but may Cl C Cl form explosive mixtures in atmospheres with higher oxygen content (Sax, 1984) H Reactivity: Reacts vigorously with active metals (lithium, sodium, potassium) and Molecular formula: CH Cl 2 2 with strong bases (potassium tert-butoxide) Relative molecular mass: 84.93 (Sax, 1984) Octanol/water partition coefficient (P): log P, 1.25 (Hansch et al., 1995) 177 IARC MONOGRAPHS – 110 Table 1.1 Methods for the analysis of dichloromethane Sample Sample preparation Assay Limit of detection Reference matrix procedurea Air Adsorb on charcoal; desorb with carbon disulfide GC/FID 0.4 μg/sample NIOSH (1998) Adsorb on charcoal; desorb with toluene GC/ECD 0.002 μg/sample Adsorb on charcoal; desorb with carbon disulfide GC/FID 94 μg/m3 OSHA (1990) Adsorb on carbon-based molecular sieve; desorb with GC/FID 697 μg/m3 99:1 mixture of carbon disulfide/dimethylformamide in anhydrous sodium sulfate Air collected in specially prepared canister; desorb on cold GC/MS 0.84–1.38 ppm EPA (1999a) trap [2.97–4.87 μg/m3] GC/ECD NR GC/FID NR GC/PID NR Analyte collected on sorbent tube; thermally desorb to GC GC/MS NR EPA (1999b) GC/ECD NR GC/FID NR GC/PID NR Water Purge with inert gas and trap; desorb to GC GC/PID NR EPA (1995a) GC/ECD 0.02 μg/L EPA (2013) GC/MS 0.18 μg/L EPA (2009) GC/MS 0.14 μg/L Purge with inert gas and trap; desorb to GC GC/MS 0.03 μg/L EPA (1988) Add internal standard (isotope labelled dichloromethane); GC/ MS 10 μg/L EPA (1996c) purge with inert gas and trap; desorb to GC Liquid Purge with inert gas and trap GC/PID NR EPA (1996b) and solid GC/HECD 0.02 μg/L wastes Purge with inert gas and trap; and various other methods GC/MS 5 μg/kg (soil/ EPA (1996a) sediment) 500 μg/kg (wastes) 5 μg/L (groundwater) ECD, electron capture detection; FID, flame ionization detection; GC, gas chromatography; HECD, Hall electrolytic conductivity detection; MS, mass spectrometry; NR, not reported; PID, photoionization detection Conversion factor: Assuming normal applications). Purity, when reported, ranges temperature (25 °C) and pressure (101 kPa), from 99% to 99.99%. Acidity (as hydrochloric 1 mg/m3 = 3.53 ppm; calculated from: mg/m3 acid) may be up to 5 mg/kg. The maximum = (relative molecular mass/24.47) × ppm. concentration of water in these grades of dichlo- romethane is 100 mg/kg (Rossberg et al., 1986; 1.1.4 Technical products and impurities Holbrook, 1993; Dow Chemical Co, 1995; Vulcan Chemicals, 1995, 1996a, b, c, d). Dichloromethane is available in several Small amounts of stabilizers are often added grades according to intended end use: tech- to dichloromethane at the time of manufac- nical grade; aerosol; vapour degreasing; ture to protect against degradation by air and special; urethane; and Food Chemicals Codex/ moisture. The following substances in the listed National Formulary (food and pharmaceutical concentration ranges are the preferred additives 178 Dichloromethane (wt%): ethanol, 0.1–0.2; methanol, 0.1–0.2; 1.2 Production and use cyclohexane, 0.01–0.03; and amylene (2-methyl- 2-butene), 0.001–0.01. Other substances have 1.2.1 Production also been described as being effective stabilizers, Dichloromethane was first prepared in 1840 including phenols (phenol, hydroquinone, para- by the chlorination of methyl chloride in sunlight. cresol, resorcinol, thymol, 1-naphthol), amines, It became an industrial chemical of importance nitroalkanes (nitromethane), aliphatic and cyclic during the Second World War (Rossberg et al., ethers, epoxides, esters, and nitriles (Rossberg 1986). Two commercial processes are currently et al., 1986; Holbrook, 1993). used for the production of dichloromethane: hydrochlorination of methanol and direct 1.1.5 Analysis chlorination of methane (Rossberg et al., 1986; Methods for the analysis of dichloromethane Holbrook, 1993; ATSDR, 2000). in air, solids, liquids, water, and food have been Global production of dichloromethane reviewed by ATSDR (2000) and HSDB (2012). increased from 93 000 tonnes in 1960 to an Selected methods for the analysis of dichloro- estimated 570 000 tonnes in 1980 (IARC, 1986), methane in various matrices are presented in and is estimated to range from 764 000 to 814 000 Table 1.1. Exposures to dichloromethane can tonnes per year from 2005 to 2010 (OECD/SIDS, also be monitored in air using a direct-reading 2011). In 2009, dichloromethane was produced infrared analyser, with a minimum detectable by 26 manufacturers worldwide and was avail- concentration of 0.7 mg/m3 (0.2 ppm) (Goelzer able from 133 suppliers (NTP, 2011). Production & O’Neill, 1985). and imports of dichloromethane in the USA Exposure to dichloromethane can be moni- totalled 45 000–227 000 tonnes between 1996 and tored in samples of blood, breath, or urine 2006 (NTP, 2011). In the European Union, the total (ATSDR, 2000; WHO, 2000; SCOEL, 2009). tonnage band for dichloromethane was reported Urinary concentrations of dichloromethane to be 100 000 to 1 000 000 tonnes per year (ECHA, in humans are reported to correlate well with 2016). The production and import of dichloro- exposure concentrations in air (Di Vincenzo methane reported in Japan was 58 000 tonnes in et al., 1972; SCOEL, 2009). The concentration 2011 (METI, 2013). of dichloromethane or carboxyhaemoglobin (COHb) levels are measured in blood (SCOEL, 1.2.2 Use 2009). Since the relationship between alveolar Most of the applications of dichloromethane carbon monoxide (CO) and COHb has not been are based on its solvent properties (IARC, 1999). well established for workers exposed to dichloro- The principal uses worldwide comprise paint methane, breath analysis for CO cannot be stripper (23–50%), aerosol solvents and propel- considered as providing definitive quantitative lants (10–25%), process solvent in the chem- information regarding exposure to dichloro- ical and pharmaceutical industry (10–20%), methane (WHO, 2000). and metal degreasing (8–13%) (WHO, 1996; IARC, 1999). The distribution of uses varies considerably among countries (OECD, 1994). Dichloromethane has also been used in the prod- uction of cellulose fibre, in the manufacture of photographic film, in textile manufacturing, for extraction of food flavourings and decaffeination 179 IARC MONOGRAPHS – 110 of coffee, as a blowing agent for polymer foams, and, to a lesser extent, as a solvent in the coating in production of hydrofluorocarbon refrigerants, of tablets. Other uses include oil de-waxing, in and in pesticides (OECD, 1994; IARC, 1999; inks and adhesives, and in plastics manufacture NTP, 2011; EPA, 2012). Use of dichloromethane (Rossberg et al., 1986; Holbrook, 1993; IARC, in Europe and the USA has been declining since 1999). the 1970s (Holbrook, 1993; WHO, 1996; EPA, 2012). (d) Metal cleaning In the metalworking industries, dichloro- (a) Paint stripper methane is used as a vapour degreasing solvent, For use in paint strippers, dichloromethane or blended with petroleum and other hydro- is typically blended with other chemical carbons as a dip-type cleaner (IARC, 1999). In components (Holbrook, 1993; WHO, 1996). the manufacture of metal products, cleaning is Dichloromethane has been the major component needed before painting, plating, plastic coating, of nearly all solvent-based paint stripper formu- etc. Degreasing in the engineering industry is lations for industrial, professional, and consumer normally carried out with special equipment use; the aircraft industry and military are impor- in which dichloromethane is used either in the tant users (OECD, 1994). Alternative paint strip- liquid or vapour phase. Dichloromethane is also pers have come onto the market (Joe et al., 2013), used in the electronics industry in the production and paint-strippers containing dichloromethane of circuit boards and as a stripper for photoresists are no longer permitted for professional or (OECD, 1994). In Japan and elsewhere, dichloro- consumer use in Europe, although they remain methane has widely been used for metal cleaning available elsewhere (European Commission, as an alternative solvent to 1,1,1-trichloroethane 2009; Joe et al., 2013). after the implementation of the Montreal Protocol on Substances that Deplete the Ozone (b) Aerosols Layer (OECD, 1994). Dichloromethane is used as propellant and (e) Printing industry solvent in aerosol products including paints, automotive products, adhesives, and hair sprays Dichloromethane is a major ingredient of (WHO, 1996; ATSDR, 2000; NTP, 2011). The use cleaning solvent used to remove printer ink of dichloromethane in consumer aerosol prod- during the offset printing process. For efficient ucts has declined in the USA (ATSDR, 2000), manual wiping with a cloth, dichloromethane is and dichloromethane is no longer permitted for often blended with other halogenated hydrocar- use in cosmetic products in the USA since 1989 bons or kerosene to adjust its evaporation rate.