Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

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 IUCLID 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.

 

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 (Neely, 1985). The lack of a suitable leaving group renders compounds resistant to hydrolysis. Hydrocarbons, C7 -C9, isoalkanes as other constituent chemicals of the C7-C9 aliphatic hydrocarbon solvents, are composed of carbon and hydrogen and are not amenable to hydrolysis because of their molecular structure and the chemical reaction required for this type of transformation to occur. Therefore, this degradative process will not contribute to their removal from the environment.

 

Biodegradation

 

Two studies using a standardized OECD 301F test guideline are available for hydrocarbons, C7-C9, isoalkanes (ExxonMobil Chemical 1998a, 1998b). Results from this manometric respirometry test procedure demonstrated 60% biodegradation of hydrocarbons after 60 days with an unadapted inoculum and 64% degradation after 75 days with an adapted inoculum. These results demonstrate that the substance, hydrocarbons, C7-C9, isoalkanes, is inherently biodegradable and not expected to persist in the environment under aerobic conditions.

 

Bioaccumulation

 

Standard bioaccumulation studies are not applicable to petroleum UVCB substances, therefore in accordance with Annex XI Section 1.3 testing is not scientifically necessary and the endpoint has been fulfilled using QSAR calculations for relevant constituents based on BCFBAF v3.01.

BCF for Hydrocarbons, C7-C9, isoalkanes is 105 L/kg wet-wt.

 

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 IUCLID section 13).

Adsorption calculated in PETRORISK for Hydrocarbons, C7-C9, isoalknes is ca. 2.95.

 

Distribution modelling

 

The distribution of the substance in the environmental compartments, air, water, soil, and sediment, has been calculated using the PETRORISK Model, version 5.0. 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.

Based on the regional scale exposure assessment, the multimedia distribution of the substance is 100% to air.

Additional information