JOURNAL OF APPLIED TOXICOLOGY, zyxwvu VOL. zyxwv 10(2), 7%81 (1990) Further Evidence that Dichloromethane does not Induce Chromosome Damage* Barbara Westbrook-Collins? and James W. Allen Gcnctic Toxicology Division, Health Effect?. Research Laboratory, U.S. Environmental Protcction Agcncy. Rcscarch l'rianglc Park. NC 2771 I. USA Yousuf Sharief and James Campbell Environmental Health Research and Tcsting. Inc.. P.O. Box 121W. Research Triangle Park, NC 27709. USA Key words: dichloromcthane; chrornosomc aberrations; sister chromatid exchange. Dichloromethane (DCM) is a widely used industrial solvent that has been determined to be a carcinogen in rats and mice. In vitm and in vivo analyses of chromosome damage induced by this agent have provided conflicting results. In order to further investigate the clastogenic potential of DCM in vivo, we analyzed sister chromatid exchanges (SCES) and chromosome aberrations (CAs) in mouse bone marrow cells following intraperitoneal exposures of 1MMOOO mg kg-' DCM. Dichloromethane failed to increase the frequencies of either SCEs or CAs. INTRODUCTION zyxwvutsrq Dichloromethane (DCM) or methylene chloride is an aliphatic hydrocarbon that is commonly used as an industrial solvent. I There is increasing concern regard- ing potential carcinogenic and mutagenic hazards associated with exposure to this substance. Several studics of DCM carcinogenesis in rodents have pre- sentcd equivocal or mildly positive results.' A recent investigation by the National Toxicology Program (NTP) found clear evidence of DCM's carcinogenicity in zyxwvutsrqp lilts and mice.' 'I'csts for mutagenic activities of DCM have provided mixcd results. For example, it induces gene mutations in lxicteria.'-4 but not mammalian c e k S In mammalian cell cultures (tS9 activation), DCM induces chromo- sonic aberrations" and minimal increases in SCE t'rcqucncies.s-" Although DCM appears to be direct- acting for clastogenic activity in cultured mammalian cclls. reactive intermediates such as formyl chloride and S-chloromethyl glutathione are thought to be derivcd from mammalian metabolism of DCM.-' Exposure of rodents to DCM reportedly docs not lead to cithcr increased micronuclei in bone marrow' or unscheduled DNA synthesis (UDS) in liver.x In view of the widespread human exposurc to DCM. evidence for its carcinogenicity in rodents, and current zyxwvu * hlthough the rewiirch dcscrihcd in this article has hccn supported hy tlic United States Environmental Protcction Agency. it has not hccii \uhjectcd to A rcncy rcvicw and therefore docs not necessarily rcllcct the views of %c Agcncy tind no official cndorscment should he iiilcrrcd. Mention of trade niimcs or commercial products docs not constitute endorsement or recommendation for use. i. Aui hor to whom cJrrcspondcncc should he addrcsscd. theory recognizing a role of chromosome damage in cancer induction, a clear appreciation for the potential clastogenic properties of this agent is important. Because of the paucity of zyxw it? vivo cytogenetic studies on DCM and the positive it? vifro results, additional in vivo studies to confirm that DCM is indeed negative under a variety of experimental conditions should be useful. In the present work, we have exposed mice by intraperitoneal (i.p.) injection to DCM and evaluated chromosome aberrations (CAs) and sister chromatid exchange (SCE) induction in bone marrow cells. EXPERIMENTAL Mice Male 3-5-month-old C57B1/6J mice (The Jackson Laboratory, Bar Harbor. ME) were housed in laminar flow rooms maintained at 15 cycles h - ' of biocleaned air, 6040% relative humidity, 68-70°F and with a 12-h light cycle. They were fed Purina rodent chow and water ad libitum. Chemicals Spectrophotometric-grade dichloromethane (>99'20) (Aldrich Chemical Co., Milwaukee, WI) was dissolved in corn oil (Fisher Scientific Co.. Raleigh, NC) immedi- ately before use. 5-Bromodeoxyuridine (BrdUrd) (Sigma Chemical Co., St. Louis. MO) was used to prepare 50-mg BrdUrd pellets, which were then coated with paraffin (Fisher Scientific Co.. Raleigh. NC). Cyclophosphamide (CP) and colchicine were obtained from Sigma Chemical Co. and dissolved in physiological saline. Thih ;irticlc was authored by a US Government employcc and is thcrclorc not subject to copyright protection. Received 14 April 1989 Accepied 9 Jiira 1989