Hydroquinone

Endpoint summary

Additional information

Stability in the environment

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).

Hydrolysis: 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. The half-life for hydroquinone oxidation with RO₂ radicals was estimated based on an experimental oxidation rate constant and experimentally determined radical concentration to be 12 minutes. With worst-case assumptions considering lower light intensities in deep water layers a half-life of 20 hours was estimated for environmental exposure assessment.

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.

Biodegradation

Biodegradation in water: For assessing the biodegradation of hydroquinone in water under aerobic or anaerobic conditions five valid screening tests are available.In studies conducted according to OECD Guideline 301C (MITI I), hydroquinone proved to be readily biodegradable, fulfilling the 14 d window criterion (70% biodegradation after 14 d). Under aerobic conditions,1,4-benzoquinone, 2-hydroxy-1,4-benzoquinone, and β-ketoadipic acid were identified as metabolic intermediates, however at low concentrations.

Proposed metabolism pathway under anaerobic conditions: degradation via phenol, cyclohexanol, cyclohexanone to caproic and adipic acid which are further degraded to acetate, propionate, butyrate, CO₂, H₂and CH₄.

Biodegradation in water and sediment: simulation tests: In a laboratory activated sludge unit (equivalent to the set-up of OECD 303 A: Simulation Test – Aerobic Sewage Treatment) using adapted sludge hydroquinone was removed by >=99.9% at influent concentrations between 55 and 275 mg/L. The extent of TOC removal was between 70% and 92% for hydroquinone containing experiments, while it was lower (69%) in the control experiment without hydroquinone and synthetic domestic sewage, only.

Biodegradation in soil: Hydroquinone was degraded in soil within 1 day under laboratory conditions. However, only primary degradation was determined. The detection of a transformation product (which was not identified) indicates that within 1 day mainly primary degradation occurs. Due to the ready biodegradability observed in the screening and simulation tests hydroquinone is expected to be rapidly biodegraded in soils.

Bioaccumulation

Based on the low octanol water partition coefficient (log Kow 0.59) a low bioaccumulation of hydroquinone is expected. A bioaccumulation factor BCF of 3.162 L/kg is calculated from EPISUITE 4.00 (BCFBAF v3.00). The low potential for bioaccumulation is confirmed by the study using of 14C-labelled Hydroquinone and the fresh water fish Leuciscus idus melanotus. After 3 days, a BCF of 40 L/kg was determined. Radioactivity determination of the BCF includes possibly formed metabolites.

Due to low bioaccumulation potential and the fast biodegradability in soil, the bioaccumulation in terrestrial species does not need to be investigated.

Transport and Distribution

Adsorption and distribution: The estimated Koc values were in the range of 9 to 50. These values indicate a very low to low sorption to organic matter in soil and sediment (according the scheme of Litz 1990). Therefore hydroquinone is expected to show high to very high mobility in soil and sediment (without taking into account potential ion-ion interactions).

Henry's Law constant: In the EPA database EPI Suite Version 4.00 (HENRYWIN v3.10 Results, Data available in EPIWIN: Experimental Database Structure Match) an experimental value for the Henry Law Constant at 25°C of 4.73E-11 atm-m³/mole is given, equivalent to 4.7927 E-06 Pa-m³/mol.

Distribution modelling: Due to its physicochemical properties (e.g. water solubility, vapor pressure), hydroquinone is expected to be found predominantly in the aquatic compartment.

Environmental data

There are no monitoring data and data on field studies available.

Additional information on environmental fate and behaviour

Hydroquinone was shown to be rapidly oxidized in aqueous solution. The reaction rate is dependent on pH. The DT50 increased from 111 days at pH 7 to 0.84 at ph 9.