Hydrocarbons, C5-C7, n-alkanes, isoalkanes, < 5% n-hexane

Endpoint summary

Additional information

Hydrolysis:

Hydrolysis is a reaction in which a water molecule or hydroxide ion substitutes for another atom or group of atoms present in a chemical resulting in a structural change of that chemical. Potentially hydrolyzable groups include alkyl halides, amides, carbamates, carboxylic acid esters and lactones, epoxides, phosphate esters, and sulfonic acid esters. The lack of a suitable leaving group renders compounds resistant to hydrolysis.

This chemical substance consists entirely of carbon and hydrogen and does not contain hydrolyzable groups. As such, it has a very low potential to hydrolyze. Therefore, this degradative process will not contribute to its removal from the environment.

 

Phototransformation in air:

Standard tests for atmospheric oxidation half-lives are intended for single substances and are not appropriate for this complex substance. However, this endpoint is characterized using quantitative structure property relationships for representative hydrocarbon structures that comprise the hydrocarbon blocks used to assess the environmental risk of this substance with the PETRORISK model (see library tab in PETRORISK spreadsheet attached to Section 13).”

 

Phototransformation in water and soil:

The direct photolysis of an organic molecule occurs when it absorbs sufficient light energy to result in a structural transformation. The absorption of light in the ultra violet (UV)-visible range, 110-750 nm, can result in the electronic excitation of an organic molecule. The stratospheric ozone layer prevents UV light of less than 290 nm from reaching the earth's surface. Therefore, only light at wavelengths between 290 and 750 nm can result in photochemical transformations in the environment. A conservative approach to estimating a photochemical degradation rate is to assume that degradation will occur in proportion to the amount of light wavelengths >290 nm absorbed by the molecule. This substance contains hydrocarbon molecules that absorb UV light below 290 nm, a range of UV light that does not reach the earth's surface. Therefore, this substance does not have the potential to undergo photolysis in water and soil, and this fate process will not contribute to a measurable degradative loss of this substance from the environment.

 

Biodegradation:

There are no data available on the biodegradation of hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% n-hexane. However, there are reliable data available considered suitable for read-across using the analogue approach.

The target substance is a hydrocarbon solvent with carbon numbers in the range of C5 to C6. The main constituents of the mixed solvent consist of about 43% of C6 species and about 57% of C5 species. n-Hexane is only present in concentrations < 5% of the total volume.

Taking into account all available data, animal and human toxicity data as well as environmental fate and effects data show that source substances have a similar (eco-)toxicological and environmental fate properties as the target substance.

Therefore, read-across is performed based on an analogue approach (for details please refer to the analogue justification which is attached in section 13 of the technical dossier).

Three studies conducted with analogue substances provide experimental data:

A OECD 301F manometric respirometry test conducted with hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, < 5% n-hexane by Battersby (1997) is available. The test substance was degraded by 98% after 28 days, and degraded by 83% at the end of the 10-day window. The reference substance was degraded by 104%, therefore the test is valid. The test substance is readily biodegradable and does not inhibit degradation.

A further study is available for pentane. ExxonMobil Chemical (1997) conducted a GLP-compliant study which followed guidelines equivalent to OECD 301F manometric respirometry test. There were some minor deviations in test concentrations from the protocol but these were not considered to influence the integrity of the study, so the study was considered reliable and suitable for use as a key study for this endpoint. The study indicates that n-pentane is readily biodegradable, with 65.5% degradation reached after 13 days, thus fulfilling the 10-day criterion, and 87% degradation reached after 28 days. The test was considered valid as 97% degradation of sodium benzoate occured by Day 14.

In another study non-GLP study by ExxonMobil Chemical (1996) with isopentane, which followed guidelines equivalent to OECD guideline 301F manometric respirometry test, 71.43% degradation occurred and the isopentane was considered to be readily biodegradable.

Furthermore a QSAR calculation by Howard (2005) is available which predicts that hexane is readily biodegradable.

 

In accordance with column 2 of REACH Annex IX, the simulation testing on ultimate degradation in surface waters and soil does not need to be conducted as the chemical safety assessment according to Annex I has not indicated a need to investigate further the degradation of the substance in water. Based on an analogue approach hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% n-hexane is considered as readily biodegradable under the screening testing and further assessment is not required.

Bioaccumulation:

The substance is a hydrocarbon UVCB. Standard tests for this endpoint are intended for single substances and are not appropriate for this complex substance. However this endpoint is characterised for representative hydrocarbon substances that comprise the hydrocarbon block(s) used to assess the environmental risk of this substance with the PETRORISK model.

However, there are reliable data available considered suitable for read-across using the analogue approach and which are reported here in addition.The target substance is a hydrocarbon solvent with carbon numbers in the range of C5 to C6. The main constituents of the mixed solvent consist of about 43% of C6 species and about 57% of C5 species. n-Hexane is only present in concentrations < 5% of the total volume.

Taking into account all available data, animal and human toxicity data as well as environmental fate and effects data show that source substances have a similar (eco-)toxicological and environmental fate properties as the target substance.

Therefore, read-across is performed based on an analogue approach (for details please refer to the analogue justification which is attached in section 13 of the technical dossier).

A BCF was calculated for Hydrocarbons, C6, isoalkanes, <5% n-hexane and pentane by Veith and Broderius (1987) using a QSAR, based on a log Kow of 3.6 and 3.45, respectively. The QSAR used to calculate the BCF followed the TGD guideline and so is deemed suitable for the assessment of bioconcentration. Based on a read-across approach the calculated BCFs of 501.187 and 171 for Hydrocarbons, C6, isoalkanes, <5% n-hexane and pentane, respectively, indicate that hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% n-hexane does not greatly bioaccumulate in the lipids of ecological receptors.

Adsorption / desorption:

Substance is a hydrocarbon UVCB. Standard tests for this endpoint are intended for single substances and are not appropriate for this complex substance. However, this endpoint is characterized using quantitative structure property relationships for representative hydrocarbon structures that comprise the hydrocarbon blocks used to assess the environmental risk of this substance with the PETRORISK model (see Product Library in PETRORISK spreadsheet attached to Section 13).

However, there are reliable data available considered suitable for read-across using the analogue approach and which are reported here in addition. The target substance is a hydrocarbon solvent with carbon numbers in the range of C5 to C6. The main constituents of the mixed solvent consist of about 43% of C6 species and about 57% of C5 species. n-Hexane is only present in concentrations < 5% of the total volume.

Taking into account all available data, animal and human toxicity data as well as environmental fate and effects data show that source substances have a similar (eco-)toxicological and environmental fate properties as the target substance.

Therefore, read-across is performed based on an analogue approach (for details please refer to the analogue justification which is attached in section 13 of the technical dossier).

The log Koc of n-hexane and pentane were calculated to be 3.34 and 2.9, respectively. This has been read across to hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% hexane. These values indicate that there is amoderate adsorption potential for hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% hexane.

 

Distribution modelling:

The distribution of the substance in the environmental compartments, air, water, soil, and sediment, has been calculated using the PETRORISK Model, version 5.3. Computer modeling is an accepted method for estimating the environmental distribution of chemicals. Distribution modeling results are included in the 'Multimedia distribution modeling results' tab in the PETRORISK spreadsheet attached to IUCLID section 13.