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Environmental fate & pathways

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Hydrolysis

Since trimellitic anhydride has been shown to be readily biodegradable (Point 5.2.1), a study of its hydrolysis under a range of is not strictly necessary.

However, a study of the hydrolysis of the closely related substance, trimellitic anhydride acid chloride, has been performed in the context of the requirements for substances that may come into contact with food via packaging material. This study examined the behaviour of trimellitic anhydride acid chloride in unbuffered distilled water as a simple food simulant. Trimellitic anhydride acid chloride was found to hydrolyse completely at 40 °C in less than ½ hour to trimellitic acid and hydrogen chloride gas. Hydrolysis of the monomer was virtually instantaneous. Based on its close structural similarity, rapid hydrolysis is anticipated for trimellitic anhydride, which would also be expected to undergo almost instantaneous conversion to trimellitic acid on contact with aqueous matrices in the environment and in vivo in exposed humans and other organisms.

This behaviour defines trimellitic acid (and its salts) rather than the anhydride as the entity relevant to exposure in the environment and also justifies the consideration of toxicology data provided by studies in which animals or test systems were administered trimellitic acid (bypassing the in vivo hydrolysis step) rather than the parent trimellitic anhydride polyester monomer.

Phototransformation in air

The stability of TMA in the atmosphere was calculated using the software AOPWIN (v1.92). It is predicted that the substance will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals, with a half-life ranged from 161.0 hours to 482.9 hours, at different test conditions.The most conservative value was selected.

The overall degradation rate constant with OH radicals is estimated to be equal to 6.89E-08 cm3/(molecule-day).

The stability of TMLA in the atmosphere was calculated using the software AOPWIN (v1.92). It is predicted that the substance will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals, with a half-life ranged from 78.6 hours to 235.8 hours, at different test conditions.The most conservative value was selected.

The overall degradation rate constant with OH radicals is estimated to be equal to 1.41E-07 cm3/(molecule-day).

In the presence of moisture, trimellitic anhydride (TMA) is rapidly hydrolysed to trimellitic acid (TMLA) and this entity is therefore more relevant to various environmental compartments than the submission substance.