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No experimental data were located on the toxicokinetics of gas oils in vivo, hence other information sources must be used to assess the toxicokinetics of these substances in vivo.


Results of experimental studies in animals provide qualitative evidence of absorption by the lung, as indicated by a modest increase in startle reflex in rats inhaling respirable aerosols of diesel fuel. Physico-chemical considerations also suggest that highly respirable aerosols of poorly water soluble substances with a log Pow greater than zero will be absorbed to some extent from the respiratory tract. In the absence of further guidance, it will be assumed that 50% of an inhaled dose of aerosolised gas oil will be absorbed by animals and humans.


No measured data are available on the dermal absorption of gas oils, however the occurrence of systemic tissue changes in repeated dose toxicity studies (in the absence of dermal irritation, and after controlling for incidental ingestion during grooming) indicates that some absorption across the skin is possible. Results from the SKINPERM model indicate that uptake of gas oil across the skin is likely to be low, with an estimated dermal flux of 0.0001058 mg cm-2.hour for human skin. However the reliability of this value is not known, and therefore complete absorption of gas oil by human skin has been assumed (conservative default) as recommended by the TGD (ECB, 2003). This is probably highly conservative given that the log Pow of the majority (>98.5%) of gas oil components falls outside the 1-4 range that favours dermal uptake (ECB, 2003). Since experimental studies demonstrate greater absorption of lipophilic substances by animal skin compared to human skin, it will be therefore be assumed during risk characterisation that animal skin is 2-fold more permeable to topically applied gas oils than is human skin.


Substances in Vacuum Gas Oils/Hydrocracked Gas Oils/ Distillate Fuels are UVCBs; hence it is not possible to apply standard methodology for assessing absorption, distribution, and metabolism. Relevant data for use in risk assessment are available for key constituents.