This compound was previously evaluated for an ADI for man by the
    Joint FAO/WHO Expert Committee on Food Additives in 1980 (see Annex I,
    Ref. 51). A toxicological monograph was published in 1980 (see Annex
    I, Ref. 52). Since then the following data have been published, and
    are summarized in the following monograph.




         Dichloromethane and other dihalomethanes are metabolized to
    carbon monoxide catalysed by the hepatic mixed function oxidase
    system. This pathway has been proposed to proceed through an oxygen
    insertion reaction yielding a formyl halide intermediate which
    decomposes to yield carbon monoxide. Another pathway, possibly
    involving a glutathione transferase located in the liver cytosol
    fraction, yields formaldehyde or formic acid (Ahmed et al., 1980;
    Ahmed & Anders, 1976),

         Label from 14C-dichloromethane is covalently bound in vitro
    when added to rat liver microsomal systems. Binding was increased if
    the animal had been pre-treated with phenobarbital (Ahmed et al.,

         Male Sprague-Dawley rats (body weight approximately 250 g) given
    a single 1 mg dose of 14C-methylene chloride by gavage metabolized a
    greater percentage of the dose than animals given 50 mg. Over 48
    hours, only about 12% of the 1 mg dose was exhaled as unchanged
    methylene chloride as compared to 72% of the 50 mg dose.
    Proportionately greater amounts of the 1 mg dose were found as expired
    CO2 or CO or were present as metabolites in urine or faeces. At the
    1 mg dose the major metabolites were CO2 (35% of the administered
    dose) and CO (31%). After 48 hours relatively little activity from
    either dose, less than 10% total, was present in organs, skin or
    carcass. The authors indicated a dose-dependent metabolism for
    methylene chloride with saturation of the metabolic pathways at the
    50 mg dose (McKenna & Zempel, 1981).

         A total of 11 male and three female human volunteers were exposed
    to 50, 100, 150, or 200 ppm (0.005, 0.01, 0.015 or 0.02%) of methylene
    chloride in air for 7.5 hours per day for five consecutive days. About
    70% of the unchanged methylene chloride was absorbed and about 25-34%

    of the absorbed compound was ultimately excreted in expired air as CO,
    less than 5% was expired as methylene chloride after exposure had
    ceased (DiVincenzo & Kaplan, 1981).

         Suspensions of hepatocytes prepared from the livers of male
    Sprague-Dawley rats were incubated with 42 micromoles of 14C-labelled
    dichloromethane over a 30 minute incubation period, alkylation of
    lipid and protein by labelled metabolites of dichloromethane was
    observed, however, no alkylation of DNA or RNA could be detected
    (Cunningham et al., 1981). A theoretical pharmacokinetic computer
    model was constructed to compare simulated methylene levels and
    metabolite production in mice administered methylene chloride at
    1000 mg/kg, five days per week in corn oil by gavage or at 250 mg/kg
    in the drinking-water. For maximum peak height and total area under
    the liver concentration curve (AUC), higher levels were obtained by
    gavage administration. Corn oil gavage also gave higher values for the
    AUC above the apparent Michaelis constants (KM) for CO2 and CO
    production, but the drinking-water route gave a longer time interval
    so that AUC values were greater than the apparent KM. According to the
    model, more metabolites may have been produced on a daily basis in
    drinking-water than by the gavage route (National Coffee Association,


    Special studies on carcinogenicity

         The doses selected for the following NTP gavage studies were
    based on the conventional guidelines used by the NTP for estimating an
    MTD, namely no more than 10% weight decrement as compared to the
    appropriate control group and do not produce mortality, clinical signs
    of toxicity or life-shortening pathological lesions other than those
    which may be related to a neoplastic lesion. Details of the studies
    are provided in the section on short-term studies (NTP, 1982).

         Groups of 50 male and 50 female Fischer-344/N rats were
    administered 0, 500 or 1000 mg/kg bw of "Food Grade"* dichloromethane
    by gavage in a corn oil vehicle five days per week for 103 weeks
    (volume of corn oil was 5 ml/kg bw). Two batches of dichloromethane
    were used during the course of the study. The animals were housed five
    per cage. In addition there was an untreated control group consisting
    of 50 male and 50 females. After the 103 week dosing period, animals
    were maintained until terminal sacrifice at 106 or 107 weeks. Complete
    gross and histopathological examinations were performed on animals
    found dead and on those sacrificed at the end of the study. Mean body
    weights of dosed rats were slightly lower than those of vehicle


    *    A detailed analysis is given in Appendix E of NTP, 1982.

    controls throughout most of the study. The effect was most pronounced
    in the high-dose females. The survival of the high-dose males was
    significantly less than that of the vehicle controls. In females, the
    survival of the high dose was significantly less than that of the
    vehicle controls and the low dose. In males, survival to the end of
    the study was 40/50 in the vehicle control, 33/50 in the low dose and
    24/50 in the high dose. The corresponding values in the females were
    35/50, 25/50 and 12/50. A large number of animals died from gavage
    errors. A total of three vehicle control, nine low-dose and 10
    high-dose males died from this cause. In females the corresponding
    values were 1, 17 and 18. The report suggested that the deaths from
    gavage errors may not have all been due to gavage error per se, but
    that a local or systemic action of the solvent may increase the
    animals susceptibility to gavage accident. In the liver, neoplastic
    nodules occurred in male and female rats with a significant positive
    trend and significantly increased incidence as compared to the vehicle
    treated animals. The incidence in males was 5/49 untreated controls,
    2/48 vehicle control, 8/50 low dose and 9/47 high dose. In females the
    corresponding incidences were: 6/50, 3/50, 13/50 and 10/49,
    Hepatocellular carcinomas were found in one vehicle control and one
    low-dose male and one high-dose female. No significant treatment-
    related non-neoplastic lesions were noted in the livers of treated
    rats. There was a significant increase in the incidence of adrenal
    cortical adenomas in both males and females. The incidence was 1/49,
    3/50 and 7/47 in vehicle control, low- and high-dose males. The
    corresponding incidence in females was 3/50, 8/50 and 5/49. The
    incidence of pancreatic acinar cell adenomas in dosed male rats
    occurred with a significant positive trend. The incidence in males was
    1/48 in untreated controls, 10/48 in vehicle controls, 17/50 at the
    low dose and 9/47 at the high dose. The incidence in the vehicle
    controls was significantly higher than in the untreated controls.
    There was a significant positive trend and a significant increase in
    the incidence of C-cell carcinoma in high-dose male rats as compared
    to the vehicle control. However, the incidence of C-adenoma alone or
    the combined incidence of C-cell adenomas and carcinomas was not
    significantly increased as compared to male vehicle controls. These
    rumours were not significantly increased in dosed female rats,
    although the incidence of C-cell hyperplasia was significantly
    increased over the vehicle controls; but not the untreated control,
    which had a higher incidence (13/50) than the high dose (12/50)
    (National Toxicology Program, 1982).

         Groups of 50 male and 50 female B6C3F1 mice were administered 0,
    500 or 1000 mg/kg bw of "Food Grade" dichloromethane by gavage in corn
    oil vehicle five days per week for 103 weeks. Two batches of
    dichloromethane were used during the course of the study. (The volume

    of corn oil was 10 ml/kg bw.) In addition, there was an untreated
    control group consisting of 50 males and 50 females. Animals were
    housed five per cage. After the 103 weeks dosing period, animals were
    maintained for several weeks prior to terminal sacrifice at 106 or 107
    weeks. Complete gross and histopathological examinations were
    performed on all animals found dead and those sacrificed at the end of
    the study. Mean body weights of high-dose male mice were lower than
    those of vehicle control females had comparable body weights
    throughout the study. In male mice, survival was not affected by
    treatment; in females, survival in the high dose was significantly
    decreased compared to vehicle controls or the low dose. Although the
    incidence of hepatocellular adenoma was not influenced by dosing,
    there was a significant positive trend in hepatocellular carcinomas in
    both males and females and the incidence of this lesion was
    significantly increased compared to vehicle controls in high dose
    males and at both doses in females. The incidence in males was 13/48
    in untreated controls, 8/48 in vehicle controls, 13/48 in low-dose and
    18/49 in high-dose males. In females the corresponding incidence was
    2/48, 0/49, 6/48 and 9/49. Hepatocellular carcinomas metastasized to
    the lung in two low-dose and five high-dose male mice. Fatty
    metamorphosis was found in the livers of nine high-dose female mice
    but not in any vehicle control or low-dose females. Alveolar/
    bronchiolar carcinomas occurred with a significant positive trend in
    female but not male mice, but the incidence of males and females with
    alveolar/bronchiolar carcinomas was not influenced by treatment
    (National Toxicology Program, 1982).

         The doses selected for the following drinking-water study (in
    which the maximum exposure was a quarter of that used in the gavage
    study) were based on pharmacokinetic and histopathology data.
    Comparison of the pharmacokinetic curves of methylene chloride
    administered by inhalation, and by gavage either in corn oil or water
    showed that a significant change in slope occurs around 250 ppm
    (0.02%) and 100 mg/kg/day, respectively. At this level there was a
    significant change in the rate of formation of metabolites, as
    measured by CO and CO2 in expired air. In addition the dose was
    given seven days a week, rather than give in the gavage study, and
    provides for a continuous rather than a discontinuous challenge.

         "Food Grade" dichloromethane was administered in the drinking-
    water for 24 months to groups of 85 male and 85 female Fischer-344
    rats at levels of 5, 50, 125, and 250 mg/kg bw per day. There was an
    additional control group (2) of 50 animals of each sex as well as an
    additional high-dose/recovery group that received deionized water only
    after week 78 of the study. Interim sacrifices were carried out at
    weeks 26 (five animals per sex per group), 52 (10 per sex per group)
    and 78 (20 per sex per group) in all groups except for the second
    control group (2) and the high-dose/recovery group (2). There was no
    treatment-related effect on survival, food consumption or on body
    weight gain except for a slight (less than 10%) depression in weight

    gain in the high-dose group. Significantly lower water consumption was
    noted in all of the dosed males and in the two highest doses in the
    females. Clinical chemistry and haematology studies were carried out
    at weeks 52 and 78 on 10 animals per sex per dose. Slightly increased
    haematocrit and haemoglobin levels were noted in the two highest doses
    in males at weeks 52 and 78. At one or both time intervals, there were
    apparent compound related decreases in serum alkaline phosphatase in
    males and creatine, BUN, serum protein and serum cholesterol in both
    sexes. There were no reported compound related changes in absolute or
    relative organ weight or in gross pathological lesions. The report
    stated that treatment-related histomorphological alterations of the
    liver were observed and consisted of an increased incidence of
    foci/areas of cell alteration in the groups given 50, 125 and
    250 mg/kg of methylene chloride in both sexes. In the females, no
    neoplastic nodules were observed in either of the control groups; in
    the dosed groups a total of 1, 2, 1 and 4 neoplastic nodules were
    observed in the animals given 5, 50, 125, 250 mg/kg respectively, of
    dichloromethane for 104 weeks. While two nodules were found in the
    group given 250 mg/kg for 78 weeks and then deionized water until
    terminal sacrifice. There was also a treatment related increase in
    fatty liver in the groups given 125 and 250 mg/kg of the test
    compound. Although there was no decrease in the incidence of
    foci/alteration of the liver in the high-dose/recovery group, the
    incidence of fatty liver did decrease in this group suggesting a
    possible regression of this effect. The report also stated that a
    no-effect level of 5 mg/kg bw per day was observed (National Coffee
    Association, 1982).

         Groups of 129 male and 129 female Sprague-Dawley rats were
    exposed to 0, 500, 1500 or 3500 ppm (0, 0.05, 0.15 or 0.35%) of
    technical grade methylene chloride in the air for six hours per day,
    five days per week for two years. Animals were housed not more than
    three per cage. About 95 animals per sex per dose were part of the
    chronic toxicity/carcinogenicity part of the study, the remainder of
    the animals were utilized at interim sacrifices after six, 12, 15 or
    18 months of exposure or were sacrificed for cytogenetic analysis.
    There were no compound related changes in body weight gain. A
    significant increase in mortality occurred in female high-dose rats
    during the 18-24 month exposure period. A slight CNS depression was
    noted in dosed animals during the first week of the study. There was a
    significant increase in relative and absolute liver weight in males
    and in absolute liver weight in females at the 18 month interim
    sacrifice. No treatment-related haematological changes were noted
    except that the red cell MCD and MCH indices in both males and females
    tended to be increased as compared to controls. The report stated this
    increase could have been a physiological adaptation to increased
    carboxyhaemoglobin levels. No compound-related effects on clinical
    chemistry were reported. Carboxyhaemoglobin levels were elevated as
    compared to controls in males and females at all dose levels. There
    were no treatment-related effects on the incidence of cytogenetic

    aberrations. There appeared to be a compound-related effect on gross
    pathological hepatic lesions, especially in high-dose females. There
    was an increased incidence of multiple light or dark foci in the liver
    and mottled livers or livers with an accentuated lobular pattern in
    high dose females.

         On histopathologic examination, dosed male and female rats had an
    increased incidence of hepatic vacuolization, multinucleated
    hepatocytes and hepatic foci/areas of cellular alterations. There was
    no reported increase in malignant liver tumours, however, two of 10
    females sacrificed at 18 months had hyperplastic liver nodules. There
    was an increased incidence of malignant mesenchymal tumours (sarcomas)
    in or around the salivary glands in high- and mid-dose males. One of
    these tumours was found in a control male, five in the mid-dose males
    and 11 in the high-dose males. The increased incidence was
    statistically significant in the high-dose animals. In the report it
    stated that the effects may have been related to viral salivary gland
    infection, however, these tumours were not detected in females with
    the viral infection. As compared to controls, there was an increased
    number of benign mammary tumours in male and female rats; the effect
    was more prominent in females. There was no apparent increase in
    malignant mammary tumours in either sex (Burek et al., 1980).

         Groups of 107 to 109 male and 107 to 109 female Syrian Golden
    hamsters were exposed to 0, 500, 1500 or 3500 ppm (0. 0.05, 0.15 or
    0.35%) of methylene chloride in air for 24 months. Interim sacrifices
    were carried out at six, 12 and 19 months. There were no significant
    compound-related effects on body weight gain or absolute or relative
    organ weight. During the latter part of the study, mortality was
    decreased in mid and high dose hamsters. Haematology parameters were
    unchanged except for a compound-related increase in haemoglobin and
    haematocrit in both sexes. No treatment-related effects on clinical
    chemistry or urinalysis were reported. Carboxyhaemoglobin values were
    in treated animals of both sexes. No compound-related increases in
    gross or microscopic pathological lesions were reported in males or
    females. The incidence of amyloid lesions was reported to decrease in
    the treated hamsters (Burek et al., 1980).

         Groups of 90 male and 90 female Sprague-Dawley rats were exposed
    six hours per day, five days per week for 20 (male) or 24 (female)
    months to air containing 0, 50, 200 or 500 ppm (0, 0.005, 0.02 or
    0.05%) of technical grade (99.5 pure) methylene chloride. Two
    additional groups of 30 females each were exposed to 500 ppm (0.05%)
    of methylene chloride for 12 months and then maintained without
    exposure to the test compound for 12 months (group 500/0) or were
    maintained with no exposure for 12 months and then 500 ppm (0.05%) for
    12 months (0/500 group). Interim sacrifice of five animals per sex per
    dose groups were conducted at six, 12, 15, and 18 months. Satellite
    groups of 18 females per dose level were utilized for assays of the
    rate of hepatic DNA synthesis. There was no reported effect of
    treatment on mortality; because of high mortality in all groups of

    males they were sacrificed at 20 months. No treatment-related effects
    were observed on body weight gain or absolute or relative organ
    weights. In animals sacrificed at the end of the experiment, there was
    a significant increase in incidence of foci of altered hepatocytes at
    500 ppm (0.05%) in females and in males at 200 and 500 ppm (0.02 and
    0.05%). The incidence of foci of altered cells at terminal sacrifice
    was 9/25, 5/17, 10/22 and 17/27 in control, low-, mid- and high-dose
    females, respectively. The corresponding incidence in males was 1/18,
    3/19, 5/13 and 7/19. The incidence of this lesion is not significantly
    increased, however, in either males or females if lesions observed at
    the terminal sacrifice and in animals dying prior to the terminal
    sacrifice are combined. There were small increases in hepatocellular
    vacuolization in high-dose males and females and in multinucleated
    hepatocytes in high-dose females. The incidence of rats with benign
    mammary tumours was increased in dosed females (Nitschke et al.,

    Special studies on mutagenicity

         When 0.5 ml of dichloromethane was added to an open glass dish
    within a desiccator also containing Salmonella plates (rather than
    added directly to the plates) mutagenicity was observed; there was a
    sixfold increase in the number of revertants in Salmonella strain
    TA-100 and a twofold increase in strain TA-1535. An S-9 activation
    system was not present. No mutagenic response was detected with or
    without S-9 in a standard assay system where dichloromethane was added
    directly to plates containing Salmonella strains TA-1535, TA-1537,
    TA-1538, TA-98 or TA-100 (Nestman et al., 1980).

         Dichloromethane was reported to be mutagenic to Salmonella
    typhimurium strain TA-100 when aliquots of 50, 100, 200, 400 and 800
    microlitres of the compound were placed in a glass dish in a
    desiccator along with plates containing the bacteria. A linear
    response of histidine revertants/plate occurred over the entire tested
    dose range; the maximum response obtained at 800 microlitres, was
    about 10 times background levels (Simmon, 1977).

         Dichloromethane was reported to induce mitotic gene convertants,
    revertants and recombinants in Saccharomyces cerevisiae strain D-7
    grown in log plase and exposed to 157 mm of the test compound for one
    hour (Callen et al., 1980). Earlier it was reported that
    dichloromethane did not affect the frequency of mitotic recombination
    in S. cerevisiae strain D-3 exposed to dichloromethane for four
    hours (dose not stated) (Simmon et al., 1977).

         No increase in sex-linked recessive lethal mutations was reported
    in male offspring of Drosophila melanogaster exposed to ingested or
    injected dichloromethane (Abrahamson & Valencia, 1980 as cited in
    Science Applications, Inc., 1982).

         Dichloromethane was found to cause a weak positive effect on
    sister chromatid exchange in V79 Chinese hamster epithelial cells. A
    negative effect was found on forward mutation at the HGPRT locus on
    V79 and Chinese hamster ovary (CHO) cells. No effect of
    dichloromethane on unscheduled DNA synthesis in V79 and human
    fibroblasts (AH cells was found. The compound caused an aspecific,
    non-persistent inhibition of DNA synthesis in V79 and AH cells, unlike
    the persistent effect seen with the positive control, 4-nitroquinoline
    oxide (Jongen et al., 1981).

         Analytical grade dichloromethane was found to be mutagenic
    without S-9 when it was added to exposure chambers containing
    S. typhimurium TA-100. Addition of S-9 mixtures, S-100 mixture or
    the microsomal fraction from phenobarbitol induced rats increased the
    mutagenic response to the compound. The addition of glutathione (GSH)
    alone also enhanced the mutagenicity of dichloromethane (Jongen et
    al., 1982).

         Dichloromethane was reported to increase the frequency at which
    primary hamster embryo cells in culture were transformed by SA7 virus
    when the cells were incubated in a treatment chamber with an
    atmosphere containing 22-72 micrograms/cm3 of dichloromethane (Jongen
    et al., 1981).

    Special studies on occupational exposure

         A group of male workers exposed to work place air containing
    methylene chloride for up to 30 years were studied for mortalities as
    compared to several control groups. A total of 334 deaths occurred in
    the study group. Mortality of the exposed group was consistent with
    other industrial workers and there was no significant increase in
    deaths from any special causes including the different categories of
    malignant neoplasm (Friedlander et al., 1978).

    Special studies on renal toxicity

         Single i.p. injections of 1330 mg/kg bw to adult male Fischer-334
    rats were reported to result in renal proximal tubular degeneration in
    both the cortex and outer medula (Kluwe et al., 1982).

    Special studies on teratology

         Groups of 18-21 female Long Evans rats were exposed to 0 or
    4500 ppm (0 or 0.45%) of dichloromethane in air for six hours a day,
    seven days a week. Four different treatment regimens were used with
    the longest regimen consisting of exposure for three weeks prior to
    pregnancy through day 17 of gestation. One group was exposed only
    during gestation (up to day 21) a third group was exposed for three
    weeks prior to, but not during gestation, while the controls were not

    exposed to the test substance for any time period. Dams were
    sacrificed on day 21 and foetuses delivered by Caesarian section.
    Maternal absolute and relative liver weights were significantly
    increased in dosed animals. Foetal body weights were significantly
    depressed (by a small amount) in the offspring of animals exposed
    during gestation. No effects on embryo toxicity or gross skeletal or
    soft tissue anomalies were reported except for a possible increase in
    the incidence of rudimentary fourteenth ribs in offspring whose
    mothers were exposed to dichloromethane prior to breeding or prior to
    breeding and through gestation. However, the report stated that the
    effect was not significant if the litter, rather than the foetus was
    considered as the experimental unit (Hardin & Manson, 1980).
    Behavioural teratology studies were conducted on the offspring of
    female rats dosed with dichloromethane according to the protocol of
    the preceding study of Hardin & Mansen. No effects on offspring were
    noted with regard to growth rate, long-term food or water consumption,
    wheel running or avoidance activity. However, offspring of females
    exposed to dichloromethane during pregnancy habituated to novel test
    environments more slowly than controls (Bornschein et al., 1980).

         Groups of at least three pregnant Sprague-Dawley rats were
    exposed to 507 ppm (0.0507%) of dichloromethane for one hour on the
    twenty-first day of gestation. After exposure the animals were
    sacrificed and maternal and foetal blood levels of dichloromethane and
    carbon monoxide were measured. Maternal and foetal blood levels of
    carbon monoxide did not differ significantly (Anders & Sunram, 1982).

    Short-term studies

         Groups of 10 male and 10 female Fischer-334 rats were given 0,
    125, 250, 500, 750, 1000, 1500 or 2000 mg/kg bw of dichloromethane
    five days a week for 13 weeks by gavage in a corn oil vehicle. There
    were no compound-related deaths except in high dose females where two
    animals died. High-dose males and females exhibited about a 17-20%
    reduction in weight gain. These animals also exhibited severe CNS
    depression lasting about two hours after receiving each dose. No gross
    or microscopic lesion related to the administration of dichloromethane
    was reported. A complete set of tissues was evaluated (NTP, 1982).

         Groups of five male and five female Fischer-344 rats were
    administered 0, 250, 500, 1000, 1500 or 2000 mg/kg of dichloromethane
    in a corn oil vehicle by gavage daily for 14 days (continuous dosing
    group). Other groups received the same doses five days per week for 12
    weeks, and four doses on the third week (intermediate dosing). Severe
    depression lasting for one to three hours was noted after dosing at
    the 1500 and 2000 mg/kg doses. Mortality was only noted in the
    high-dose animals and was most severe (three out of five) in the
    continuously dosed females. No deaths were noted in continuously dosed
    males and one out of five on the intermittent high-dosed males.
    Changes in mean body weight gain were not dose-related, but compared

    to controls the most severe decrements occurred at the two highest
    doses. No compound related gross pathological changes were noted, nor
    were there any microscopic changes noted in the liver, the only organ
    so examined (NTP, 1982).

         Groups of 10 male and 10 female C57B1/6 mice were administered 0,
    500, 1000, 1500, 2000, 2500, 3000 or 3500 mg/kg by gavage in corn oil
    vehicle five days per week for 13 weeks, compound related mortality
    occurred at doses of 1500 mg/kg or greater in females and 2000 mg/kg
    or greater in males, being most severe in the high-dose females where
    only two out of 10 females survived. Changes in body weight gain were
    difficult to interpret due to lack of a dose response effect. No
    compound related gross or microscopic lesions were noted. A complete
    set of tissues was evaluated (NTP, 1982).

         Groups of five male and five female B6C3F1 mice were given doses
    of 0, 500, 1000, 1500, 2000 or 2500 mg/kg of dichloromethane by gavage
    as 14 consecutive daily doses (continuous dosing). Other groups of
    five male and five female B6C3Fa mice were given the same doses on a
    regimen of five administrations per week for two weeks and then four
    doses in the third week. No mortality occurred among the females. In
    the high dose males two out of five of the continuously and three out
    of five of the intermittently dosed males died before the end of the
    study. Body weight gain data are very difficult to interpret; between
    group variations are large and there is no dose-related trend. No
    compound-related histopathology hepatic lesions were noted. The liver
    was the only organ examined histopathologically (National Toxicology
    Program, 1982).


         In a recent lifetime study in rats, in which methylene chloride
    was administered in olive oil, by gavage, numerous deaths occurred,
    particularly in the high-dose groups. Although these deaths may have
    been caused by gavage errors, it may also have been due to systemic
    toxicity of test compound. In this study, neoplastic nodules occurred
    in male and female rats with a significant positive trend. Although,
    these lesions may progress to carcinomas, the pathological carcinomas
    were found only in one vehicle control and one low-dose male and one
    high-dose female. There was a significant increase in the incidence of
    pancreatic-acinar cell tumours in male rats. However, there are
    numerous reports of an increase in pancreatic-acinar cell tumours in
    lifetime studies with rats, and this problem is undergoing active
    review. The significance of this observation cannot be established at
    this time. It is also noted that two batches of methylene chloride
    were used in this study, each containing different impurities. In a
    similar study in mice, the major lesion reported was hepatocellular
    carcinomas. Because of the known wide fluctuations in the background
    level of this tumour in mice, no firm conclusions can be drawn on the
    significance of this lesion.

         In a rat study in which methylene chloride was administered in
    the drinking-water at lower doses than those used in the gavage study,
    no hepatocellular carcinomas were reported, although there were minor
    changes in the livers of test animals, including a dose-related
    increased incidence of foci/areas of cell alteration, fatty livers in
    the high-dose groups, and a very low incidence of neoplastic nodules
    that was not dose-related.

         Two inhalation studies in rats, using, technical grade methylene
    chloride indicated a compound-related increase in liver lesions
    including foci/areas of cellular alterations. One study indicated an
    increased incidence of mesenchymal tumours in or around the salivary
    glands. In another inhalation study in Golden hamsters, at equivalent
    levels of exposure, no effects on salivary glands were observed.

         The available data are inadequate for a complete evaluation of
    the carcinogenicity of methylene chloride. The mutagenicity data are
    inconsistent, and no conclusion can be made on the possible
    mutagenicity of methylene chloride.

         A study with B6C3F1 mice exposed to methylene chloride in
    drinking-water will be completed in 1983. This will permit a more
    complete evaluation of the possible carcinogenicity of methylene
    chloride by this route. In addition, an inhalation study in rats and
    mice is under way, and the results of this study will assist in
    resolving questions raised in the previous inhalation study.


    Estimate of acceptable daily intake for man

         The previously allocated ADI has been withdrawn.


    (1) Results of a lifetime study with B6C3F1 mice exposed to methylene
    chloride in drinking-water.

    (2) Results of lifetime inhalation studies with rats and mice.


    Ahmed, A. & Anders, M. (1976) Metabolism of dichloromethanes to
         formaldehyde and inorganic halide. In vitro studies, Drug
         Metab. Disposition, 4, 357

    Ahmed, A. et al. (1980) Halogenated methanes: metabolism and toxicity,
         Fed. Proc., 39, 3150

    Anders, M. & Sunram, J. (1982) Transplacental passage of
         dichloromethane and carbon monoxide, Toxicol. Letters, 12,

    Bornschein, R. et al. (1980) Behavioral toxicity in the offspring of
         rats following maternal exposure to dichloromethane, Toxicol.
         Appl. Pharmacol., 52, 29

    Burek et al. (1980) Methylene chloride: A two-year inhalation toxicity
         and oncogenicity study in rats and hamsters, report submitted to
         the U.S. Food and Drug Administration by Toxicology Research
         Laboratory, Health and Environmental Sciences, USA, Dow Chemical,
         USA, Midland, MI 48640, 846 pp.

    Callen, D. et al. (1980) Cytochrome P-450 mediated genetic activity
         and cytoxicity of seven halogenated aliphatic hydrocarbons in
         Saccharomyces cerevisiae, Mutat. Res., 77, 55

    Cunningham, M. et al. (1981) Covalent binding of halogenated volatile
         solvents to subcellular macromolecules in hepatocytes, Life
         Sci., 29, 1207

    DiVencenzo, G. & Kaplan, C. (1981) Uptake metabolism and elimination
         of methylene chloride vapors by humans, Toxicol. Appl.
         Pharmacol., 59, 130

    Friedlander, B. et al. (1978) Epidemiologic investigation of employees
         chronically exposed to methylene chloride, J. Occupat. Med.,
         20, 657

    Hatch, G. et al. (1981) In vitro transformation of hamster cell
         embryo cells exposed to gaseous or volatile chlorinated
         hydrocarbons, Proc. Amer. Assoc. Cancer Res., 22, 119

    Hardin, B. & Manson, J. (1980) Absence of dichloromethane
         teratogenicity with inhalation exposure in rats, Toxicol. Appl.
         Pharmacol., 52, 22

    Jongen, W. et al. (1978) Mutagenic effect of dichloromethane on
         Salmonella typhimurium, Mutat. Res., 56, 245

    Jongen, W. et al. (1981) Mutagenicity testing of dichloromethane in
         short-term mammalian test systems, Mutat. Res., 81, 203

    Jongen, W. et al. (1982) The effect of glutathione conjugation and
         microsomal oxidation on the mutagenicity of dichloromethane in
         S. typhimurium, Mutat. Res., 95, 183

    Kluwe, W., Harrington, F. W. & Cooper, S. (1982) Toxic effects of
         organohalide compounds on renal tubular cells in vivo and
         in vitro, J. Pharmacol. Exp, Theraput., 220, 597-603

    McKenna, M. & Zempel, J. (1981) The dose dependent metabolism of
         [14C] methylene chloride following oral administration to rats,
         Food Cosmet. Toxicol., 19, 73

    National Coffee Association (1982) Methylene chloride, Health
         assessment for carcinogenicity potential. Report submitted to the
         U.S. Food and Drug Administration, 1982

    National Toxicology Program (1982) NTP report on the carcinogenesis
         bioassay of dichloromethane (methylene chloride) (CAS No.
         75-09-02) in F-344 rats and B6C3F1 mice (gavage study), draft

    Nestman, E. et al. (1980) Mutagenicity of constituents identified
         in pulp and paper mill effluents using the Salmonella/mammalian
         microsome assay, Mutat. Res., 79, 203

    Nestman, E. et al. (1981) Mutagenicity of paint removers containing
         dichloromethane, Cancer Letters, 11, 295

    Nitschke et al. (1982) Methylene chloride: A two year inhalation
         toxicity and oncogenicity study, Report submitted to the U.S.
         Food and Drug Administration by Toxicology Research Laboratory,
         Health and Environmental Sciences, USA, Dow Chemical, USA,
         Midland, MI 48640, 326 pp.

    Simmon, V., Kawhanen, K. & Tardiff, R. G. (1977) Mutagenicity activity
         of chemicals identified in drinking water. In: Scott, D. et al.,
         eds, Progress in Genetic Toxicology, Elsevier/North Holland
         Biomedical Press, pp. 249-258

    Simmon, V. (1977) Structural correlations of carcinogenic and
         mutagenic alkylhalides, in Structural Correlates of
         Carcinogenesis and Mutagenesis. In: Asher, I. & Zervos, C. eds,
         Proceedings of the Second FDA office of Science Summer
         Symposium, HEW Publ. No. (FDA) 78-1046, pp. 163-171

    See Also:
       Toxicological Abbreviations