chloromethane; methyl chloride

Distribution modelling

Administrative data

Endpoint:

distribution modelling

Type of information:

calculation (if not (Q)SAR)

Remarks:

Migrated phrase: estimated by calculation

Adequacy of study:

other information

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Scientifically acceptable calculation, cited in SIDS

Data source

Reference

Reference Type:

other: Mackay calculation

Title:

Mackay calculation

Author:

Mackay et al

Year:

1996

Bibliographic source:

Cited in SIDS

Materials and methods

Model:

calculation according to Mackay, Level III

Media:

air - biota - sediment(s) - soil - water

Test material

Test material information

Constituent 1

Reference substance name:

Chloromethane

EC Number:

200-817-4

EC Name:

Chloromethane

Cas Number:

74-87-3

Molecular formula:

CH3Cl

IUPAC Name:

chloromethane

Results and discussion

Any other information on results incl. tables

Level III simulations were first used to evaluate the effect
of source of entry on the distribution and persistence of
chloromethane.  Chemical specific data required for the
simulations were the same as that previously described for
the Level II simulation.  The default emission rate of 1000
kg/h was used for each simulation.  As expected on the basis
of the Level II simulation, emission of chloromethane
directly to air resulted in >99% of the total chemical mass
residing in the air compartment, with advection in air
representing the primary mechanism of removal.  Degradation
in air represented only a minor amount of the total chemical
mass (< 1%) removed from the system.  Intermedia exchange of
chloromethane between the other compartments was
insignificant.  Similar results were obtained when the
chloromethane emission was to the soil compartment.  Because
of the relatively high vapor pressure of chloromethane, only
3.6% of the total chemical mass remained in the soil
compartment whereas 96% was found in the air compartment. 
Hence, the primary removal process from soil was
volatilization and the primary removal process from the
system was advection in air.  Local persistence was about 4
days, regardless if the chloromethane emission was to the
air or soil compartment.

In contrast to that observed for emission to the air and
soil compartments, emission of chloromethane to the water
compartment resulted in only about 20% the total chemical
mass residing in the air, whereas about 80% remained in the
water.  Intermedia exchange of chloromethane with the other
compartments (e.g., soil and sediment) was insignificant. 
The dominant removal mechanism of chloromethane from the
system was advection in air, which was equal to the rate of
volatilization from the water compartment.  However,
advection and degradation in water also removed significant
amounts (28% and 2.4%, respectively) of the total chemical
mass.  Nonetheless, local persistence was about 15 days. 

The above results indicate that the environmental
compartments of concern, based on emission of chloromethane,
are air and water.  Insignificant amounts of chloromethane
are expected to be found in the soil or sediment
compartments, regardless of source of entry to the
environment.  Since chloromethane is a gas, most industrial
releases are expected to be directly to the air compartment.
 In the United States, it is estimated that about 1.346 x
10^6 kg (2.97 x 10^6 pounds) of chloromethane are annually
released to the environment (about 240 kg/h) from industrial
activities (Section 1.9).  Of this amount, about 89% is
released directly to air, 0.06% is released to water, and
about 11% is added to soil or injected underground.  These
emission rates (137 kg/hr for air, 0.09 kg/hr for water, and
16.7 kg/hr for soil) were entered into the Level III
simulation to obtain an overall assessment of the impact of
industrial releases of chloromethane to the environment. 
Results of the simulation suggest that the total, steady
state mass of chloromethane in the environment from
industrial sources is about 1.53 x 10^4 kg.  Greater than
99% of the total, steady state mass is expected to reside in
the air compartment and about 0.4% in each of the soil and
water compartments.  The local persistence is expected to be
about 4 days with advection in air accounting for >99% of
the chloromethane removed from the local system.  Less than
1% is expected to be lost through degradation processes. 


Air                        1000-1500 ng/m3
Water                              <222 ng/L
Soil or Sediment           <5,000 ng/kg

Indicating that industrial sources are insignificant with
respect to natural sources.