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Environmental fate & pathways

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Methylcyclohexane is not readily biodegradable in the aquatic environment. The assessment of biodegradation of Methylcyclohexane is however entirely “theoretical” as triggered by the high volatility, the substance will even if released to a sewage treatment plant, quickly vanish into the air. As an approximation, if the Henry´s Law constant is greater than 100 Pa m3/mol, more than 50% of the substance could be lost from the water phase in 3-4 hours (Mackay, 1992). Considering the Henry´s Law Constant of Methylcyclohexane (> 34000 Pa m3/mol) the evaporation should occur even more rapidly. Consequently, abiotic degradation processes in air may represent a more important and relevant environmental sink for this substance. As indicated, due to the high volatilization potential of Methylcyclohexane the target compartment for environmental distribution will be air, where it is subject to atmospheric oxidation (AOPWIN v1.92, half time for the reaction with OH-radicals is 37.9 hours; 24 h day; OH-concentration: 0.5E+06 OH/cm3). The Guidance on information requirements and chemical safety assessment Chapter R.11: PBT Assessment (ECHA, 2014) states that: “If the substance has a half-life in air < 2 days it is not expected to stay in the atmosphere for long as it will degrade rapidly. Thus there will be a limited potential for long range atmospheric transport“. Based on this Methylcyclohexane is regarded as rapidly degradable in air as the half-life for indirect photodegradation is predicted as below < 2 days.

Due to its chemical composition, Methylcyclohexane is no subject to hydrolysis. Bioaccumulation in fish is low (BCF = 95 - 321 L/kg, METI 1986). No studies on adsorption are available for Methylcyclohexane. However, the substance is not expected to sorb significantly to organic matter in soil, sediment, and wastewater solids based on calculated log Koc values of 2.37 and 3.37 (molecular conductivity index and log Kow method, respectively).