1,1-dichloroethylene

Distribution modelling

Administrative data

Endpoint:

distribution modelling

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The EQC model is a generally accepted model to assess the distribution of substance between the environmental compartments.

Justification for type of information:

QSAR prediction

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

other: (Q)SAR

Title:

EQC Model: Fugacity-Based EQC-Equilibrium Criterion Model (Version 2.02 - May 2003)

Author:

The Canadian Centre for Environmental Modelling and Chemistry

Year:

2003

Bibliographic source:

Canadian Environmental Modelling Centre, Trent University, Peterborough, Ontario, K9J 7B8, CANADA

Materials and methods

Model:

calculation according to Mackay, Level III

Calculation programme:

EQC Model

Release year:

2 003

Media:

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

Test material

Test material information

Constituent 1

Reference substance name:

1,1-dichloroethylene

EC Number:

200-864-0

EC Name:

1,1-dichloroethylene

Cas Number:

75-35-4

Molecular formula:

C2H2Cl2

IUPAC Name:

1,1-dichloroethene

Details on test material:

Not applicable (calculation model)

Study design

Test substance input data:

Data entered into the model for the estimation:
- Molar mass: 97 g/mol
- Data temperature: 20°C
- Water solubility: 2500 g/m3
- Vapour pressure: 66340 Pa
- log Pow: 2 (the value of "2.17" has been entered, but the model indicated "2" in its report)
- Melting point: -122°C

Reaction half-life :
- Air: 57 hours (this is the highest half time selected which has been calculated by AOPWIN)

- Water: 37.5 days * 24 = 900 hours (justification below)
The half-life should cover the biotic and abiotic degradation. The substance is not readily biodegradable, but shows a rapid primary biodegradation with 45-78% of removal in 7 days and 100% of removal in 14 days in the study of Tabak et al. (1981). In a conservative approach, the result of BIOWIN 3 is used to assess the half-life in water as described in Episuite as follows:
The mean value within the estimated time range returned by Biowin3 is converted to a half-life using a set of conversion factors.  These conversion factors consider that 6 half-lives constitute "complete" degradation of a chemical substance, assuming first-order kinetics. The resulting conversion factors for water are provided below:

BIOWIN Output          Converted Assigned Half-Life (days)
Hours                            0.17
Hours to Days                  1.25
Days                           2.33
Days to Weeks                   8.67
Weeks                             15
Weeks to Months           37.5
Months                           60
Recalcitrant                     180                

- Soil: 1800 hours
According to EPI Suite, it is generally believed that the biodegradation rate for a chemical in soil is, on average, one-half (1/2) that in water.

- Sediment: 20 weeks * 7 * 24 = 3360 hours
To take into account the slower rate of ultimate biodegradation in sediment, EPI Suite uses a conversion factor developed in EPA's P2 framework.  It assumes that sediments are anaerobic and that the rate of ultimate biodegradation in sediment is on average one-ninth (1/9) of that in the water column (which is assumed to be aerobic).  However, the study of Wilson et al. (1986) shows a disappearance of 1,1-dichloroethene in anaerobic conditions of around 50% in 16 weeks and 60-100% in 40 weeks.

Environmental properties:

No modification of the default parameters has been performed.

Results and discussion

Percent distribution in media

Air (%):

23.2

Water (%):

76.5

Soil (%):

0.006

Sediment (%):

0.27

Any other information on results incl. tables

It should be noted that this estimation is based on a default assumption that the substance is initially released into the 2 compartments air and water. Based on the data from the CSR, the initial release into the water compartment is much lower than in the air compartment, therefore the % in water compartment may be overestimated by the model level III.

 

Additionally, it seems that in the level III, the half-life in the compartment is more important than the advection intermedia transport processes (e.g. evaporation). However, the volatilization process from water is of great importance for this substance. Indeed, Episuite estimates a volatilization from river with a half-life of 1 hour and the study of Dilling (1977) shows that the half-life for evaporation of 1,1-dichloroethene (1 g/litre) from a stirred aqueous solution with a depth of 6.5 cm was 27.2 min at 20 °C.

 

Based on the above two elements, the fugacity model level III seems to overestimate the distribution in water compartment. To illustrate this conclusion, the model has been used with the same rate of release in water and air but at two subsequent steps. The results are as follows and show that when release into air, the substance will remain in this compartment where it is degraded, and when released into water solely, around 10% of the substance is transported into the atmospheric compartment:

With a release of 1000 kg/h in air, the level III model estimates the following repartition:

air: 99.9%

water: 0.11%

soil: 0.02%

sediment: < 0.01%

With a release of 1000 kg/h in water, the level III model estimates the following repartition:

air: 10%

water: 89.7%

soil: <0.01%

sediment: 0.32%

Applicant's summary and conclusion

Conclusions:

If released equally between air and water, 1,1-dichloroethene will primarely go to the air and water compartments. Sediment and soil compartments are of very low concern. If released in air, the substance will remain in this compartment. If released into water, 10 % will volatilise into air, the rest will remain in water.

Executive summary:

The EQC model uses chemical-physical properties to quantify a chemical's behaviour in an evaluative environment. Levels I and II assume thermodynamic equilibrium is achieved; Level II includes advective and reaction processes. Level III is a non-equilibrium, steady state assessment.

 

The Level III has been applied for 1,1-dichloroethene. This calculation is of the steady state distribution of a chemical, in an environment not at equilibrium. For the calculation, it has been considered that the chemical is continuously discharged at a default constant rate of 1000 kg/h into the air and water compartments, and achieves a steady-state condition at which input and output rates are equal. This involves calculating the rates of degradation and advection, from half-lives or rate constants, and advective flow rates and considering the emission. Intermedia transport processes (e.g. wet deposition, evaporation, or sedimentation) are included.

 

The media receiving the emissions are very important and have a controlling influence on the overall fate of the chemical. The default release value of 1000 kg/h is very conservative compared with the data of the CSR. Additionally, based on the data from the CSR, the initial release into the water compartment is much lower than in the air compartment, therefore the % in water compartment may be overestimated by the model level III.

   

Based on the physico-chemical properties of the substance, the fugacity model level III seems to overestimate the distribution in water compartment. To illustrate this conclusion, the model has been used with the same rate of release in water and air but at two subsequent steps. The results show that when release into air, the substance will remain in this compartment where it is degraded, and when released into water solely, around 10% of the substance is transported into the atmospheric compartment. However, the volatilization process from water is expected to be of greater importance for this substance. Indeed, Episuite estimates a volatilization from river with a half-life of 1 hour and the study of Dilling (1977) shows that the half-life for evaporation of 1,1-dichloroethene (1 g/litre) from a stirred aqueous solution with a depth of 6.5 cm was 27.2 min at 20 °C. Therefore, the assessment made by this model should be used with caution.