Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

General discussion of environmental fate and pathways:

When complex petroleum substances are released into the environment, the hydrocarbon constituents distribute to the different environmental compartments according to individual physico-chemical properties (e.g. volatility, water solubility, partition coefficients). Exposure concentrations are further modulated by differential degradation rates between constituents and compartments. This makes it difficult to assess environmental exposure of petroleum substances from field monitoring studies because measured concentrations of constituents or total hydrocarbons detected in the environment can no longer be directly related to the original petroleum substance. A further complication is multiple hydrocarbon sources, both man-made and natural, which may contribute to concentrations observed in each environmental compartment (CONCAWE, 1999). Therefore, it is not possible to directly apply current risk assessment guidance, originally developed for simple substances, to complex petroleum substances.

To quantify environmental exposure resulting from multimedia distribution and degradation of hydrocarbon components that comprise a complex petroleum substance the ‘Hydrocarbon Block Method’, has been proposed by CONCAWE (1996) and EC (2003) and subsequently implemented in REACH (ECHA, 2008). In this approach, individual hydrocarbons with different partitioning and degradation properties are used to simulate petroleum substance fate in the environment.

Degradation in the environment is a result of abiotic processes and biodegradation. The relative importance of these processes will depend upon the environmental compartment to which the individual components of the petroleum product partition. In general, abiotic processes are important in the atmosphere, whilst biodegradation is the principle mechanism of the breakdown of lower carbon chain length products in water and soil. Direct photolysis is not expected to be a major degradation pathway for many of the hydrocarbon components in petroleum substances and neither is hydrolysis, as the components of petroleum products lack hydrolysable functional groups.

The combined role of partitioning and degradation properties of constituent hydrocarbons on environmental fate and resulting exposure of complex petroleum substances at both local and regional scales has been predicted using the PETRORISK model (https://www.concawe.eu/reach/petrotox) based on the principles of the hydrocarbon block method.

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 and Blau, 1985). The lack of a suitable leaving group renders compounds resistant to hydrolysis.

The chemical constituents of diesel/gas oil fractions consist entirely of carbon and hydrogen and do not contain hydrolyzable groups. As such, they have a very low potential to hydrolyze. Therefore, this degradation process will not contribute to their removal from the environment.

Further testing is not required under Annex XI, section 1.2.

Biodegradation:

Diesel / gas oil fractions are not readily biodegradable but are considered inherently biodegradable. In a report on environmental classification (Concawe 2001), it was concluded that, based on the known properties of hydrocarbons in the range C9 to C26,diesel/gas oil fractions are not readily biodegradable, but are regarded as being inherently biodegradable, since they can be degraded by micro-organisms.

In a further investigation (Concawe 2012) on PBT evaluation of petroleum substances CONCAWE developed QSAR estimates (BioHCwin) and reviewed existing data for individual hydrocarbons representative of the various ‘hydrocarbon blocks’ covering a range of petroleum substances. Using the Hydrocarbon Block method and data on biodegradation of representative hydrocarbons in the range C9 to C26, it is concluded that diesel / gas oil fractions do not meet the persistence criteria and can be regarded as being inherently biodegradable.

Biodegradation in water, screening test:

Substance is a hydrocarbon UVCB. Test results for biodegradation in water are used for classification. For the purpose of risk assessment, this endpoint is characterized using quantitative structure property relationships for representative hydrocarbon structures that comprise the hydrocarbon blocks. The environmental risk of this substance is assessed using the PETRORISK model (see Product Library in PETRORISK spreadsheet attached to IUCLID Section 13).

Biodegradation in water and sediment, simulation test:

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 tab in PETRORISK spreadsheet attached in IUCLID section 13).

Biodegradation in soil:

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).

Aquatic/sediment bioaccumulation:

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 has been calculated for representative hydrocarbon structures using the BCFWIN v2.16 model within EPISuite 3.12 as input to the hydrocarbon block method incorporated into the PETRORISK model. The predicted BCFs for hydrocarbons are generally overly conservative since biotransformation is not quantitatively taken into account. Therefore, indirect exposure and resulting risk estimates predicted by PETRORISK are likely to be overestimated. For the purposes of PBT assessment, measured bioaccumulation data for representative hydrocarbon constituents have been used as detailed in section 8 of the CSR.

Terrestrial bioaccumulation:

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 has been calculated for representative hydrocarbon structures using default algorithms in the EUSES model as input to the hydrocarbon block method incorporated into the PETRORISK model. The predicted BCFs for hydrocarbons are generally overly conservative since biotransformation is not quantitatively taken into account. Therefore, indirect exposure and resulting risk estimates predicted by PETRORISK are likely to be overestimated.

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 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 in IUCLID section 13).

Distribution modelling:

The distribution of the substance in the environmental compartments, air, water, soil, and sediment, has been calculated using the PETRORISK Model. Based on the regional scale exposure assessment, the multimedia distribution of the substance is 91.14% to air, 1.09% to water, 5% to sediment and 2.77% to soil. Distribution modelling results are included in the ‘Multimedia distribution modelling results’ tab in the PETRORISK spreadsheet attached to IUCLID Section 13 (Penman Consulting 2015a).