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Environmental fate & pathways

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Phototransformation in air (4-MHHPAc): Half-life for reaction with photochemically-produced hydroxyl radicals estimated to be 30.1 hours.


Hydrolysis: Half life - at ph 4: 1.43 minutes at 20 deg C; 2.04 minutes at 30 deg C and 0.692 minutes at 50 deg C. at ph 7: 1.90 minutes at 20 deg C; 1.26 minutes at 30 deg C and 0.327 minutes at 50 deg C. at ph 9: 1.27 minutes at 20 deg C; 1.18 minutes at 30 deg C and 0.233 minutes at 50 deg C. As a result of this rapid hydrolysis, in the water compartment, the environmental fate of the acid degradation product (4 -MHHPAc) should be considered.



Ready biodegradability in water: 2% in 28 days



The potential for bioaccumulation of 4-MHHPAc (the hydrolysis produc of 4-MHHPA) is low, less than 2.4 L/Kg, as expected from low values of log Kow for both substances.


Henry's Law Constant

The Henry's Law constants of 1,2-Cyclohexanedicarboxylic acid, 4-methyl- (4-MHHPAc), as hydrolysis product of hexahydro-4-methylphthalic anhydride, was considered for the environmental assessment. The value of 2.75E-4 Pa m³/mol shows that 4-MHHPAc is essentially non volatile from surface water.

Distribution modelling

Distribution in environmental compartments has been calculated using a Fugacity model according to Mackay, Level III. Distribution in various environmental compartments is estimated as:Air= 0.236%; Water= 4.89%; Soil= 94.8% and Sediment= 0.028%.

.However, the substance is known to be unstable, rapidly hydrolysing to the corresponding di-carboxylic acid in aqueous media and this process is expected to occur in the environment should release occur. As a result the calculated distribution may not be a reasonable estimate. Similar modelling of the degradation product of the substance, 4 -methyl-1,2 -cyclohexanedicarboxylic acid, estimated distribution in the various environmental compartments as:Air= 0.08%; Water= 20.4%; Soil= 79.4% and Sediment= 0.109%.

Refinement of the modelling, undertaken as part of the CSA, and taking account of the uses of the substance, does not support these estimates.