Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information


Phototransformation in air

In the presence of moisture, 1,2,3,6-tetrahydro-3-methylphthalic anhydride is rapidly hydrolysed to the correspondent 3-methylcyclohex-4-ene-1,2-dicarboxylic acid, that is more relevant to various environmental compartments than the submission substance.

The stability of the substances in the atmosphere was calculated using the software AOPWIN (v1.92). It is predicted that both anhydride and acid forms will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals, with a half-life of 5.9 hours, and overall degradation rate constants with OH radicals of 5.66E-6 cm3/(molecule-day).


Hydrolysis of a structural analogue of the substance, tetrahydromethylphthalic anhydride (MTHPA), has been investigated. The substance was found to hydrolyse rapidly, resulting in formation of the respective di-acid. The calculated half-lives at 20 deg C are, for all three pH values (4, 7 and 9) below 3.5 minutes (about 0.06 hours).



The ready biodegradability of tetrahydromethylphthalic anhydride (MTHPA), of which 1,2,3,6-tetrahydro-3-methylphthalic anhydride (3-MTHPA D4) is an isomer, was studied in a Modified MITI Test according to OECD guideline 301C test methods.

Modelling of possible biodegradation pathways estimated by enviPath, according to the biotransformation rules, indicates that aerobic degradation of 1,2,3,6-tetrahydro-3-methylphthalic anhydride is likely; the degradation products were identified until two transformation levels.

All these substances were subjected to a Biodegradation screening assessment, according to the EPA BIOWIN 4.10 model.

According to the evaluation criteria set in the ECHA Guidances Chapters R.7b and R.11, 1,2,3,6-tetrahydro-3-methylphthalic anhydride was estimated as being inherently biodegradable and not  potentially P or vP to the environment.



Under environmental conditions, the log Kow of both 1,2,3,6-tetrahydro-3-methylphthalic anhydride (3-MTHPA D4) and the corresponding dicarboxylic acid 3-methylcyclohex-4-ene-1,2-dicarboxylic acid (3-MTHPAc D4) is below 3.

It is therefore concluded that the potential for bioaccumulation of 3-MTHPA D4 and 3-MTHPAc D4 is very low.



Henry's Law Constant

The Henry's Law constant of 3-methylcyclohex-4-ene-1,2-dicarboxylic acid (3-MTHPAc D4), as hydrolysis product of 1,2,3,6-tetrahydro-3-methylphthalic anhydride (3-MTHPA D4) was estimated to be 2.73E-4 Pa m³/mol at 25°C and is taken into account for further assessments.

The value of 2.73E-4 Pa m³/mol indicates that 3-MTHPAc D4 is essentially non volatile from surface water.