Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Phototransformation in air

According to a generally accepted calculation method (AopWin v1.92), the half-life of hydroquinone in the atmosphere due to OH radical degradation is 16.58 hour (24-hr day; 0.5E6 OH/cm3).


According to REACH regulation (Annex VIII), the study on hydrolysis does not need to be done if the test substance is readily biodegradable or is poorly soluble in water. Hydroquinone is classified as readily biodegradable, in addition no hydrolyzable groups are present in the molecule.

Phototransformation in water

Hydroquinone is photo-oxidized in aqueous solution forming p-benzoquinone, hydroxy-p-benzoquinone and trihydroxybenzene as products. In natural waters radicals like OH and RO2 are present and can react with organic compounds. Based on an oxidation rate constant for the reaction of hydroquinones with alkylperoxy radicals (RO2•) of 1*10^6 (M*sec)^(-1) and an average environmental concentration of RO2• near surface of 1*10^(-9) M, the half-life of hydroquinone in sunlight exposed natural waters is calculated to be 12 minutes. Considering turbidity and decreasing light intensities in deeper water layers, a 100-times lower concentration of [RO2•] is assumed, leading to a worst-case estimate for the half-life of hydroquinone in surface waters of 20 hours based on photooxidation with RO2• alone (leaving behind other oxidative degradation events as well as biodegradation).

This value is confirmed by the OECD SIDS document (2002) on hydroquinone, which states a half-life in surface water of 20 hours.

Phototransformation in soil

Phototransformation in soil is expected to be of no or minor relevance for the fate of hydroquinone in the terrestrial environment. The test substance is regarded as readily biodegradable and hydroquinone is expected to biodegrade in soil. Therefore, a study on phototransformation in soil is scientifically unjustified.