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TOXICOKINETIC BEHAVIOUR

 

Physico-chemical properties:

Hydroquinone bis(2-hydroxyethyl)ether (HQEE) is a white solid and the molecular weight is 198.22 g/mol. The measured Log P (octanol-water) of HQEE is 0.41 at 30 degC and the mean water solubility of HQEE was 13.1 g/L at 21 degC. The substance is very soluble in water.

 

A determination of aerodynamic particle size confirmed that less than 0.151% of the substance has an aerodynamic particle size of less than 10.0 μm (thoracic fraction) and less than 0.132% of the substance has an aerodynamic particle size of less than 5.5μm (respirable fraction). The vapour pressure of HQEE is <0.45 Pa at 45 degC. As the substance is neither respirable nor volatile, inhalation is not a route of concern.

 

Absorption:

There are no specific ADME data on the extent to which HQEE absorbs across the gut, lungs or skin.

 

Oral: As HQEE is a low molecular weight chemical and highly water soluble, it should absorb readily via the oral route. There are no adverse effects seen in the acute oral study, 28 day oral repeat dose study or oral reproductive screening study (OECD 421). It is highly likely that this material is not a systemic toxicant, as oral absorption should be extensive in these studies given the physico-chemical properties of the substance, and high doses tested.

 

Inhalation: no data, as the substance is not volatile and not expected to be inhaled.

 

Dermal: There are no adverse effects seen in the acute dermal study. There are no specific skin absorption data. A significant level of absorption may take place via the skin due to small molecular weight/size of HQEE; the exact extent will depend upon the delivery vehicle in which the HMBDA is solubilised. The substance is not irritant/corrosive and therefore no damage to the skin barrier is expected upon contact. Absorption into the systemic circulation would be via passive diffusion directly into the blood stream.

 

Distribution:

There are no specific data and no indications in any of the studies as to whether the HMBDA reached particular organs or whether distribution was extensive to major organs and in blood. However, given the high degree of water solubility and low molecular weight, it is expected that distribution would be widespread.

 

Metabolism:

The results of in vitro genotoxicity assays in the presence of the S9 metabolising system have shown that metabolism does not influence the results for genotoxicity. HQEE is not genotoxic in the absence or presence of S9. HQEE is not mutagenic in an in vivo bone marrow micronucleus assay; oral absorption is expected to be significant in this assay and metabolism intrinsic, providing evidence that neither HQEE nor any metabolites are mutagenic. There is no evidence on whether the metabolism is the same or different via different routes of exposure ie oral/inhalation/dermal

 

Excretion:

There is no evidence to indicate the route of excretion. Test items that are readily absorbed across the gut will be excreted predominantly in the urine.