Renewable hydrocarbons (naphtha type fraction)

Endpoint summary

Description of key information

Absorption: Occurs via oral and dermal routes. Absorption by the lung is also expected.
Distribution: Expected to distribute mainly to fat tissue.
Metabolism: Based on the available data aliphatic hydrocarbons and aromatic hydrocarbons are oxidised to various alcohol and carboxylic acid derivatives.
Excretion: Based on the available data aliphatic and aromatic hydrocarbons and their metabolites are rapidly excreted, either exhaled from the lungs or excreted in the urine.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

There are no experimental studies of the toxicokinetic of renewable hydrocarbons of wood origin (naphtha type fraction), but there are several studies available of the substance constituents. The first part of the discussion on toxicokinetics is based on physical and chemical properties of the substance. The second part concentrates on toxicokinetics of the most critical and main constituents of the substance.

Absorption

Based on physicochemical considerations uptake of substances across the gastrointestinal tract may occur when the log Pow is greater than 4 and water solubility is equal to or less than 1 mg/l. In addition, direct uptake of substances across the respiratory epithelium by passive diffusion is favoured when the log Pow is greater than 4 and water solubility is equal to or less than 1 mg/l. On the other hand, dermal uptake of substances with a log Pow of 6 or above and water solubility less than 1mg/ml will be low.

The experimentally determined log Pow for renewable hydrocarbons (naphtha type fraction) is 4.7 and its experimentally determined water solubility is 18.0 mg/l. However, since this substance is a complex mixture of hydrocarbons, the testing of the above properties is not technically feasible as the methods are intended to single substances. The physicochemical and toxicological properties are also dependent on the properties of the hydrocarbon blocks in the substance. Therefore, the estimated log Pow and water solubility of the representative hydrocarbon blocks were taken into account for assessment of toxicokinetics of the substance.

For purpose of hazard assessment and environmental risk assessment the log Kow values were estimated with the PETRORISK tool that was used for the environmental risk assessment. The estimation is based on log Kow values of individual compound structures, which are included in the CONCAWE Library. The overall range for the estimated log Kow values was from 2 to 6.43. The log Kow values of the representative individual structures that form the major part of the substance based on mass fraction (sum 0.7) were in the range 3.65 - 4.77. In addition to PETRORISK, the octanol-water partition coefficients were estimated with the EPISUITE model. The calculated log Kow values for the ten most abundant individual structures (based on mass-%) of the substance ranged from 3.21 to 5.65. These log Kow values were used as a basis for the bioaccumulation estimation with the EPISUITE model.

The water solubility was also estimated with the PETRORISK tool that was used for the environmental risk assessment. The estimation is based on water solubility values of individual compound structures, which are included in the CONCAWE Library. The overall range for the estimated water solubility values was from 0.02 mg/L to 1600 mg/L. The water solubility values of the representative individual structures that form the major part of the substance based on mass fraction (sum 0.7) were in the range 1.3 mg/L - 19 mg/L.

As conclusion based on the water solubility value and the octanol-water partition coefficients the uptake of renewable hydrocarbons of wood origin (naphtha type fraction) from the gastrointestinal tract may occur. Uptake of the substance (especially volatile short chain hydrocarbons) by the lung is evident following exposure to vapour or respirable aerosol. Also, the dermal absorption is expected.

Distribution

Based on physicochemical considerations, the molecule is highly lipophilic, if log P > 4 and it is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration particularly in fatty tissues. Renewable hydrocarbons (naphtha type fraction) is a lipophilic substance (log Pow = 4.7) with moderate water solubility (18 mg/L). Based on this data the substance is likely to distribute into cells, especially in adipose tissue.

Metabolism

There is no experimental data available on the fuel oils to estimate the route of metabolism and possible metabolites. It is very difficult to predict the metabolic changes a substance may undergo on the basis of physico-chemical information, because this substance is a complex mixture of hydrocarbons with different physico-chemical properties.

Excretion

There is no quantitative information on the excretion of surrogate substances, such as fossil gasoline, following inhalation, oral, or dermal exposure in humans or animals. This renewable gasoline is composed mainly of C4-C12 non-aromatic hydrocarbons (ca. 94 % w/w) and of C6-C12 aromatic hydrocarbons (ca. 6 % w/w). Absorption, distribution, metabolism and excretion of these compounds are discussed below. This summary is based on the OECD existing Chemicals database (OECD 2013).

Absorption

C7-C9Alkanes are readily absorbed. Majority of C9-C14 hydrocarbon solvents (70 %) would be absorbed when ingested. When inhaled, especially short chain hydrocarbons are readily absorbed. Based on the data from a human volunteer study, percutaneous absorption of C9-C14 aliphatic constituents would be in the range of 0.01 %/hr to 0.1 %/hr and that of aromatic constituents would be approximately 0.2 %/hr.

Distribution

C7-C9 Alkanes are readily absorbed and distributed through the body. C9 -C14 Aliphatic hydrocarbons are widely distributed throughout the body of both humans and animals and preferentially accumulate in the adipose tissues due to the lipophilic nature of the solvents. A toxicokinetic study on the distributions of C9 to C10 alkanes, aromatics and cycloalkanes in blood, brain, liver, kidney and perirenal fat demonstrated that aromatics generally showed higher blood concentrations than alkanes and cycloalkanes. C9 cycloalkanes showed higher brain concentrations than the corresponding aromatics and alkanes, while brain concentrations of C10 alkanes were slightly greater than C10 cycloalkane concentrations, which in turn were greater than C10 aromatic concentrations. Fat contained the highest concentrations of each of the hydrocarbons examined; concentrations of aromatics and cycloalkanes in fat were higher than concentrations of alkanes.

Metabolism

C7-C9 Normal alkanes are readily metabolized and excreted in urine and expired as CO2. C7-C9 Iso-alkanes are less readily metabolized to a range of metabolites that are excreted in the urine. Aliphatic hydrocarbons are typically metabolized by side chain oxidation to alcohol and carboxylic acid derivatives by cytochrome P-450 dependent monooxygenases. These metabolites can be glucuronidated and excreted in the urine or further metabolized before being excreted. C10 -C13 aromatic hydrocarbons are typically metabolized by side chain oxidation to alcohol and carboxylic acid derivatives.

Excretion

Generally speaking, it is expected that components or metabolites of C9-C14 hydrocarbons that have low solubility in the blood, would be rapidly exhaled from the lungs. The metabolites of C10-C13 aromatics are expected to be excreted in the urine and to a lower extent, in the feces. Excretion is expected to be rapid with the majority of the elimination occurring within the first 24 hours of exposure.