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Environmental fate & pathways

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When a complex petroleum substance is 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 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 (Redman, A. et al., 2010c) based on the principles of the hydrocarbon block method and using fate factors derived from EUSES v2.

References

 

CONCAWE (1996). Environmental risk assessment of petroleum substances: the hydrocarbon block method. Report no. 96/52, CONCAWE, Brussels, Belgium.

 

CONCAWE (1999). Exposure profile: Kerosines/jet fuels. Report no. 99/52, CONCAWE, Brussels, Belgium

 

EU (2003). European Commission Technical Guidance on Risk Assessment. In support of Commission Directive 03/67/EEC on Risk Assessment for new notified substance, Commission Regulation (EC) No 1488/94 on Risk Assessment for existing substances and Directive 98/8/EC of the European Parliament and of the Council concerning the placing of biocidal products on the market. European Commission Joint Research Centre, Ispra. Eur 20418 EN/1

 

ECHA 2008,Guidance on information requirements and chemical safety assessment Chapter R.7c, Appendix R.7.13-1 Technical Guidance for Environmental Risk Assessment of Petroleum Substances, pp 221-

 

Mackay, D. (1991). Multimedia Environmental Models. The Fugacity Approach, Lewis Publishers, Boca Raton, USA.

Redman, A. (2010). PETRORISK v.5.4 Users Guide, HydroQual, Inc., for Conservation of Clean Air and Water in Europe (CONCAWE)