The Gas Oils Category includes 28 substances comprised of 4 finished products (distillate fuels) and 25 refinery streams with similar carbon ranges. Gas oil streams are produced either by atmospheric distillation or by secondary processing of the materials derived from the vacuum distillation of the residuum from the atmospheric distillation of crude oil. Materials from this secondary processing may have higher aromatic and olefin contents than straight run gas oils. The distillate fuels may be straight run or a blend of various gas oil streams (both straight run and streams from secondary processing). In comparison to gas oil refinery streams that do not have product specifications, no. 2 diesel fuel and fuel oil must meet stringent American Society for Testing Materials (ASTM) and the United States Environmental Protection Agency (EPA) specifications for commercialization. The boiling point specifications for these fuels essentially limit the aromatics to 1, 2 and 3-ring compounds with minimal 4-ring or higher polycyclic aromatic compounds (PAC). Physical properties, process history and product use specifications rather than composition define gas oils streams and provide the rationale for the composition of this category.
To meet the HPV Challenge, the Testing Group has thoroughly evaluated the substances within the Gas Oils category and has made all of the reliable human health and ecological hazard data available to the public. Key parameters when analyzing this category for environmental hazards are the distribution of aromatic and saturated hydrocarbons, and for some mammalian endpoints (repeated-dose, developmental, reproduction, and mutagenicity) the content and distribution of polycyclic aromatic compounds (PACs) are important.