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Environmental fate & pathways

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Chloroethane is a gaseous substance and thus is assumed to be mainly present in air. The available Mackay Level I distribution modelling predicts a distribution of 99.7% to the air and 0.33% to water (Mackay Level I v3.00). Level III modelling using loading rates for air, soil and water of 1000 kg/h predicted the following distribution: air (52.1%), water (43.2%), soil (4.54%) and sediment (0.12%) (Level III Fugacity Model). Thus, if the substance is released to the environment a distribution to the atmospheric compartment can be assumed. The dominant elimination process in the atmosphere will be the removal by reaction with photochemically-generated hydroxyl radicals in the air. A half-life of 39.7 days for this reaction has been estimated based on a reaction rate constant of 4.04×10-13cm3/molecule-second. The estimation assumes a temperature of 25 °C and a typical hydroxyl radical concentration of 5.0×105molecules/m3at a 24 hour day (AOP v1.92).

Though chloroethane is characterised by a relatively high water solubility (WS: 5.74 g/L at 20°C) an accumulation in aqueous compartments is not likely. The high vapour pressure indicates a rapid evaporation from the water phase (VP 134200 Pa). A fast evaporation from the water phase is also predicted by the available estimated Henry´s Law Constant of 1124.70 Pa m³/mol at 25 °C (Gossett, 1987). Thus the major process by which chloroethane is removed from aquatic compartment is volatilization. The estimated half-life is 51.72 min in rivers and 3.2 d in lakes (EPIWIN summary, v4.10).

Degradation processes like hydrolysis or biodegradation are of minor importance regarding the environmental fate of the substance. The abiotic degradation of chloroethane by hydrolysis is a slow process. Half-lives of 38 days and 2.6 years were estimated for the hydrolysis at pH 4, 7 and 9 and 25°C respectively (Mabey and Mill, 1978, Jeffers and Wolfe, 1996). Biotic degradation is considered to be of no relevance for chloroethane as indicated by the available data on aerobic and anaerobic biodegradation in water. A study on the ready biodegradability of chloroethane determined no biodegradation under the tested conditions (Schöberl, 1993).

Based on the physico-chemical properties and the consequent environmental fate of the substance an accumulation in biota is not likely. The bioavailability of chloroethane is assumed to be very low due to the low expected concentrations in water, sediment or soil. Furthermore, the low BCF determined for the substance indicates a low potential to bioaccumulate.