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Environmental fate & pathways

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Available reliable data show that 1,1 -dichloroethene has :

- a low adsorption potential to soil and sediment : The log Koc of 1,1-dichloroethene ranges between 1.5027 and 1.8482

- a high potential of volatilization from water : The Henry's Law constant (HLC) of 1,1 -dichloroethene has been calculated to be 2572 Pa.m3/mol (corresponding to 2.5 atm.m3/mol) according to the ECHA guidance chapter R16: environmental exposure assessment (ECHA 2012). Published data from handbook and HENRYWIN calculation support this high volatility, as well as half-life of volatilisation of 27 min at 20°C (Dilling, 1977) and 1.03h from river and 93.8h from lake (calculation of Episuite).

Therefore, when released into water, 1,1 -dichloroethene is expected to be rapidly removed by volatilisation, with a very low contamination of sediment.

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 the calculation is of the steady state distribution of a 1,1 -dichloroethene 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 the level III EQC model should be used with caution.