STAFF REPORT




PROPOSED IDENTlFICATlON OF METHYLENE CHLORIDE
AS A TOXIC AIR CONTAMINANT




CH2C12






State California
Air Resources Board
Stationary Source Division


May 1989






Proposed Identification of Methylene Chloride
as a Toxic Air Contaminant














Prepared by the Staffs of
the Air Resources Board and
the Department of Health Services













Stationary Source Division
Air Resources Board
May 1989







Proposed Identification of Methylene Chloride
as a Toxic Air Contaminant







Date and Address of Board Hearing:

July 13 and 14, 1989

Lincoln Plaza
Auditorium, First Floor
400 P Street
Sacramento, California  95814







Address of the Air Resources Board:

Air Resources Board
Stationary Source Division
1102 'Q' Street
Sacramento, California  95814








(This report has been reviewed by the staffs of the California Air Resources Board and the California Department of Health Services and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Air Resources Board or the Department of Health Services, nor does mention of trade names of commercial products constitute endorsement or recommendation for use.)


INTRODUCTION AND RECOMMENDATION



       Definition of a Toxic Air Contaminant. Health and Safety Coda section 39655 defines a toxic air contaminant as an air pollutant which the Air Resources Board or the Department of Food and Agriculture finds "may cause or contribute to an increase in mortality or an increase in serious illness, or which may pose a present or potential hazard to human health."

       Evaluation and Recommendation. The staffs of the Air Resources Board (ARB) and the Department of Health Services (DHS) have reviewed the available scientific evidence on the presence of methylene chloride in the atmosphere of California and its potential adverse effect on public health. Based on the finding of carcinogenicity and the results of the risk assessment, the DHS staff finds that methylene chloride meets the definition of a toxic air contaminant.

       Findings of the Scientific Review Panel. The Scientific Review Panel (SRP), which is established pursuant to Health and Safety Code section 39670, reviewed the report in accordance with Health and Safety Code section 39661, and found the report to be without serious deficiency. The findings of the SRP are attached at the end of this Report.

       Recommendation. The staff of the Air Resources Board recommends that the Board identify methylene chloride as a toxic air contaminant. In making this recommendation, the ARB and DHS staffs found that there is not sufficient available scientific evidence at this time to support the identification of an exposure level below which carcinogenic effects would not have some probability of occurring. Therefore, we recommend that methylene chloride be treated as having no identified threshold.

       Reasons for Recommendation. Methylene chloride was chosen for evaluation because: the International Agency for Research on Cancer (IARC) and the U.S. Environmental Protection Agency (U.S. EPA) have concluded that there is ample evidence that methylene chloride is carcinogenic in animals. (The IARC considers methylene chloride a possible human carcinogen and the U.S. EPA considers methylene chloride to be a probable human carcinogen.) Methylene Chloride is emitted from a variety of sources in the State, and it does not break down at a rate that would significantly reduce public exposure.

       About these Documents. In addition to making a recommendation, this report summarizes the information in the accompanied technical support document. The technical support document includes four parts which are the "Overview and Recommendation," the Part A report, the Part B report, and the Part C report. The "Overview and Recommendation" summarizes and integrates the information in Parts A and B; Part A was prepared by the ARB staff and reviews the public exposure to, environmental fate of, and sources of atmospheric methylene chloride in California; Part B was prepared by the DHS and reviews the health effects and risks associated with exposure to methylene chloride; and Part C contains the public comments that were received during the public comment periods and the ARB and the DHS staffs' responses to those comments.








































I.


SOURCES OF METHYLENE CHLORIDE


       Methylene chloride is a popular chemical, primarily because of its excellent solvent characteristics, low flammability, and low boiling point. Although methylene chloride is not produced in California, it is widely used in the state with estimated emissions of approximately 20,000 tons per year.

       Methylene chloride is a constituent in products used by industry as well as by the general population. The major use categories, representing about 90 percent of the estimated annual emissions of methylene chloride, in decreasing order are paint removers, aerosols, degreasers, and polyurethane foam manufacturing. In addition to these, several other source categories use hundreds of tons of methylene chloride each year. These categories include pharmaceuticals, electronics, chemical production and processing, and pesticide manufacturing. For some source categories such as aerosols and decreasing, the consumption of methylene chloride has or is expected to decline. This decrease has resulted from concern over health effects as well as proposed restrictions on the use of methylene chloride.

       Because emissions from many of the uses for methylene chloride are not controlled, a high percentage (about 80 percent) of the methylene chloride used in California is emitted to the atmosphere. For some categories, such as paint removers and aerosols, emissions from evaporation equal the amount used.


















II.

EXPOSURE. HEALTH EFFECTS. AND RISK


A.      EXPOSURE TO METHYLENE CHLORIDE

B.      HEALTH EFFECTS OF METHYLENE CHLORIDE

C.      RISK DUE TO METHYLENE CHLORIDE



TABLE 1

Estimate of Statewide Excess Lifetime Cancer Cases
from Exposure to Methylene Chloride

Group

Estimate of Risk

Lifetime Cancer Casesa

DHS/SRP

4 x 10-6/ppb (most plausible)b

90 to 200

DHS

1 x 10-6/ppb to 10 x 10-6/ppb

20 to 500

SRP

9 x 10-8/ppb to 10 x 10-6/ppb

2 to 500

a - Based on exposure to mean ambient concentrations (weighted by population) ranging
     from 1.1 to 2.4 ppb for a population of 20.3 million people.

b - The most plausible estimate of risk according to the DHS and the SRP.


ALTERNATIVES AND ENVIRONMENTAL IMPACTS


A.      ALTERNATIVES

B.      ENVIRONMENTAL IMPACTS





STATE OF CALIFORNIA                            ATTACHMENT                             George Deukmejian Governor


AIR RESOURCES BOARD
1102 Q STREET P.O. BOX 2815
SACRAMENTO, CA  95812




Mr. William C. Lockett, Chief
Office of External Affairs
California Air Resources Board
1102 Q Street
Sacramento, California  95814

Dear Bill:

         The Scientific Review Panel on Toxic Air Contaminants has reviewed the Report on Methylene Chloride, which includes Tables 8-5 and 8-7 from Part B of the report by the Department of Health Services, and has formulated its findings regarding the report. I am formally submitting the Scientific Review Panel's findings to the Air Resources Board.


Enclosure

cc:  Scientific Review Panel




Findings of the Scientific Review Panel on
THE REPORT ON METHYLENE CHLORIDE
As Adopted at the Panel's April 18, 1989 Meeting


       In accordance with the provisions of Health and Safety Code section 39661, the Scientific Review Panel (SRP) has reviewed the reports of the staffs of the ARB and DHS on the public exposure and biologic and health effects of methylene chloride, and the public comments on these reports. Based on this review, the SRP finds that the reports are without serious deficiencies and further finds that:

1.       Methylene chloride has been identified as an animal carcinogen and should be
          regarded as a potential human carcinogen.

2.       Methylene chloride is emitted into the air by a variety of stationary sources in
          California.

3.       Based on its gas-phase reactivity with hydroxyl radicals, methylene chloride has
          an atmospheric lifetime estimated to range from 80 to 250 days.

4.       Approximately 20.3 million people in California are estimated to be exposed to a
          population-weighted mean methylene chloride concentration of 1.1 to 2.4 parts
          per billion.

5.       Adverse health effects other than cancer are not known to occur at predicted
          concentrations of methylene chloride in ambient outdoor air.

6.       Based on available scientific information, a methylene chloride exposure level
          below which carcinogenic effects are not expected to occur cannot be identified.

7.       Based on an interpretation of available scientific evidence, DHS staff estimated
          risks using both the applied dose and a physiologically based pharmacokinetic
          model (PBPK) (see attached table). The range of lifetime excess cancer risk
          from exposure to 1 ppb (3.5 g/m3) of atmospheric methylene chloride based on
          the upper 95% confidence limit is from 9 x 10-8/ppb (PBPK model without
          surface area correction)(a) to 10 x 10-6/ppb (applied dose). This includes EPA's
          application of the PBPK model which would estimate a risk of 1 x 10-6/ppb with
          a surface area correction). DHS uses a PBPK model with a high to low dose
          adjustment which generates a risk of 4 x 10-6/ ppb. Based on available data it is
          the most plausible estimate of the upper limit of risk. These upper bound excess
          lifetime risks are health protective estimates; the actual risk may be below these
          values.

8.       Exposure to the range of mean ambient concentrations (weighted by population)
          of 1.1 to 2.4 ppb for a population of 20.3 million people, could result in up to 2 to
          500 excess lifetime cancers, based on the upper-bound of the 95% confidence
          interval of the models.

       For these reasons, we agree with the ARB staff recommendation to its Board that methylene chloride be listed by the ARB as a toxic air contaminant.

(a) NOTE:  The DHS staff chose only to report a range using a surface area correction.


Attachments























CONDENSATION OF DHS TABLES 8-5 AND 8-7


COMPARISON OF HUMAN CANCER RISK ESTIMATES FROM A CH2Cl2
EXPOSURE, BASED ON LUNG TUMORS IN FEMALE MICE,
USING VARIOUS MODELS AND ASSUMPTIONSa

Approach

Mathematical Model

Lifetime Risk

Applied Dose

Linearized Multistage

ppb-1

(ug/m3)-1

Applied Dose

Time-Dependent Multistage

9 x 10-6

3 x 10-6

High-to-Low Doseb

Linearized Multistage

10 x 10-6

3 x 10-6

High to Low Dose

Time Dependent Multistage

4 x 10-6

1 x 10-6

Total PBPKc

Linearized Multistage

5 x 10-6

1 x 10-6

Total PBPKd

Linearized Multistage

1 x 10-6

3 x 10-7

a   All values were adjusted for continuous exposure. That is, the mouse exposure in ppm
     was multiplied by (6 hours/day)/(24 hours/day) x (5 days/week)/(7 days/week). The
     concentrations are calculated from the female mouse lung tumor data (NTP 1986). The
     extrapolation was also corrected for surface area (a factor of 12.7) unless indicated
     otherwise. The risks are based on the linearized multistage model. Surface area
     conversion for rodent to human risks, and risk estimates are reported at 95% upper
     bound values.

b   High-to-low adjustment for saturation of MFO pathway based on the HRAC report
     (EPA 1987a).

c   High-to-low adjustment for saturation of MFO pathway and the species to-species
     adjustment based on the HRAC report which includes a 12.7 surface area correction
     (EPA 1987a).

d   High-to-low adjustment for saturation of MFO pathway and the species adjustment
     based on the HRAC report (EPA 1987a), except without use of a surface area
     correction.