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Category name:
HCSC Category 9 - C14-20 Aliphatics (≤ 2% aromatic) (January 2018)

Justifications and discussions

Category definition:
The C14-C20 Aliphatics (<2% Aromatics) Hydrocarbon Solvents Category is comprised of aliphatic hydrocarbon solvents with predominant carbon numbers greater than C14-C20. The constituents of these solvents could be single isomers as well as mixed solvents of which the primary constituents are straight chain (n-), branched chain (iso-), and cyclic aliphatic hydrocarbons. Aromatic constituents, if present, represent less than 2% of the total volume.

The carbon numbers, typically greater than C14-C20, and initial distillation points (IBP) characterize the substances in the C14+ Aliphatic (<2% Aromatics) Hydrocarbon Solvents Category. The distillation range is approximately 220°C to 350°C although some solvents may contain higher or lower boiling material. The benzene and sulphur contents of substances in this category are low, benzene levels for example are typically <3 ppm.

The toxicology and environmental fate and effects data show that substances in this category have a similar order of toxicological and environmental fate properties, which also supports the grouping of these substances as a category. Because the water solubility of some category members can be relatively low, some members exhibit aquatic toxicity while other members do not.

The C14-C20 aliphatics (<2% aromatics) category members are distinguished by HSPA (Hydrocarbon Solvents Producers Association) according to the following nomenclature:

Hydrocarbons, C13-C18, n-alkanes, isoalkanes, cyclics, <2% aromatics
Hydrocarbons, C14-C18, n-alkanes, isoalkanes, cyclics, <2% aromatics
Hydrocarbons, C14-C19, isoalkanes, cyclics, <2% aromatics
Hydrocarbons, C13-C16, isoalkanes, cyclics <2% aromatics
Hydrocarbons, C14-C17, n-alkanes, <2% aromatics
Hydrocarbons, C16-C20, n-alkanes, isoalkanes, cyclics, <2% aromatics
Pentadecane
Hexadecane
Heptadecane
Octadecane
Nonadecane
Icosane
Category order description:
Not specific for a UVCB category
Category rationale:
There are a number of unifying considerations, which together justify the inclusion of members within the C14-C20 Aliphatic (<2% Aromatics) Hydrocarbon Solvents Category. These include:

(1) Similarity of Use – Substances in this category are liquids at room temperature and are produced for use as solvents. The technical properties for which these solvents are intended require that the constituents have well defined rates of evaporation, related to the carbon number distribution; to limit the aromatic content; and to also have very low levels of sulphur- and nitrogen-containing constituents.

(2) Similarity of Composition – Constituents of solvents in this category can include n-alkanes, iso-alkanes, or cycloalkanes or combinations thereof with carbon numbers ranging from approximately C14-C20. However, the aromatic content of these solvents does not exceed 2%.

(3) Similarity of Functional Groups – The substances in this class are comprised almost entirely of aliphatic constituents. The only functional groups are alkyl side chains, which are found on most if not all constituents other than the n-alkanes.

(4) Similarity of Physical / Chemical Properties – The similarity of physical / chemical properties for these substances is demonstrated in Table 1a of the attached category justification document. The physical/chemical endpoints available in IUCLID 5 for the individual substances in C14C20 Aliphatic [< 2% Aromatics] Hydrocarbon Solvent Category are summarized in Table 1b of the attached category justification document.

(5) Similarity of Metabolism – Hydrocarbon molecules in this range are not well absorbed from the intestinal tract and very poorly absorbed through the skin. However, once absorbed, these molecules are relatively rapidly metabolized and excreted. They do not bioaccumulate.

(6) Similarity of Mammalian Toxicity – The constituents of this class have similar toxicological properties as shown in Table 2 of the attached category justification document. They are not acutely toxic, irritating to the eyes or skin or sensitizing. They do not produce systemic effects (other than male rat-specific kidney changes) in repeated dose studies. They are not mutagenic, and as above, do not produce carcinogenic effects other than those related to male rat-specific kidney effects. They do not produce developmental toxicity, and there is no evidence that they are toxic to the reproductive system.

(7) Similarity of Environmental Toxicity Properties – The substances in this category have similar environmental effects properties as shown in Table 4a of the attached category justification document. The environmental effects data are similar for most category members in that most members do not exhibit acute aquatic toxicity due to their low water solubility. The environmental and ecotoxicological endpoints available in IUCLID 5 for the individual substances in C14C20 Aliphatic [< 2% Aromatics] Category is demonstrated in Table 4b and Table 4c of the attached category justification document.

(8) Similarity in Health Effects and Mechanism of Toxic Action – There is a general potential health effects associated with substances in this category, acute central nervous system (CNS) depression and, if taken into the lung in a liquid state, chemical pneumonitis. Both of these are common effects shared by all hydrocarbon solvents. It should be noted, however, that the vapor pressures of hydrocarbons with more than 9 carbons are so low that acute effects on the central nervous system are not produced even at saturated vapor concentrations.

Additionally, category member constituents are neutral organic hydrocarbons that share a similar mode of action for aquatic organisms, nonpolar narcosis. The mechanism of short-term toxicity for these chemicals is disruption of biological membrane function, and the differences between their toxicities can be explained by the differences between the target tissue-partitioning behaviour of the individual hydrocarbons. There are no toxicological properties of category member constituents that are specific and distinguish them from each other or from constituents of most other hydrocarbon solvents.