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Category name:
HCSC Category 3 - C9-14 Aliphatics (2-25% aromatics) (September 2017)

Justifications and discussions

Category definition:
The C9-C14 Aliphatic [2-25% Aromatics] Hydrocarbon Solvents Category is comprised of multi-constituent aliphatic hydrocarbons with predominant carbon numbers in the range of C9 to C14. The primary constituents are straight chain (n-), branched chain (iso-), and cyclic aliphatic hydrocarbons with 2% to 25% aromatics.

The carbon numbers, typically C9-C14, and initial distillation points (IBP) characterize the substances in the C9-C14 Aliphatic [2-25% Aromatics] Hydrocarbon Solvents Category. The distillation range is approximately 132°C to 270°C although some Category 3 solvents may contain higher boiling material. The benzene and sulphur contents of category members are low.

Category members are distinguished by HSPA (Hydrocarbon Solvents Producers Association) according to the following nomenclature:
Hydrocarbons, C8-C12, n-alkanes, isoalkanes, cyclics, aromatics (2-25%)
Hydrocarbons, C9-C10 n-alkanes, isoalkanes, cyclics, aromatics (2-25%)
Hydrocarbons, C9-C12, n-alkanes, isoalkanes, cyclics, aromatics (2-25%)
Hydrocarbons, C10-C13, n-alkanes, isoalkanes, cyclics, aromatics (2-25%)
Hydrocarbons, C11-C14, n-alkanes, isoalkanes, cyclics, aromatics (2-25%)
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 C9-C14 Aliphatics [2-25% Aromatics] Hydrocarbon Solvents Category. These include:

(1) Similarity of Production Methods – Hydrocarbon solvents in this category are separated from wide boiling hydrocarbon streams by a refining process known as atmospheric distillation. The resulting hydrocarbon streams are fractionated by boiling range and further refined, usually by hydrogenation, to reduce levels of sulphur- and nitrogen-containing
constituents.

(2) Similarity of Use – Substances in this category are liquids at room temperature and produced for use as solvents. The technical properties for which these solvents are intended require that the constituents have relatively low volatility (high carbon number/molecular weight) and very low levels of sulphur- and nitrogen-containing substances. The total
content of aromatic constituents is also limited by technical specifications.

(3) Similarity of Composition – Constituents of solvents in this category are hydrocarbons of the 4 structural types: n-alkanes, iso-alkanes, cycloalkanes, and aromatics with carbon numbers ranging from approximately C9-C14.

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

(5) 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 (CJD). The physical/chemical endpoints available in IUCLID 6 for the individual substances in C9-C14 Aliphatic [2-25% Aromatics] Hydrocarbon Solvents Category are
summarized in Table 1b of the CJD.

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

(7) Similarity of Mammalian Toxicity – Category members have similar toxicological properties (table 2 of the CJD). Additionally, data is available for most of the toxicological endpoint for each substance in the category (Table 3 of the CJD). Where there is a lack of data for an endpoint, data from another category member can be used to interpolate the likely
result. The full results, as compiled in IUCLID 6, of the data are attached to the substance dossier (labeled as “Matrix Report, Category 3, C9-C14 Aliphatics, 2-25pt aromatics.html”).

(8) Similarity of Environmental Toxicity and Fate Properties – Category members have similar environmental effects and fate properties as shown in Table fa of the CJD. The environmental and ecotoxicological endpoints available in IUCLID 6 for the individual substances in C9-C14 Aliphatic [2-25% Aromatics] Hydrocarbon Solvents Category is demonstrated in Table 4b of the CJD.

(9) Similarity in Health Effects and Mechanism of Toxic Action – There are two 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 of hydrocarbon solvents. It should be noted, however,
that the vapor pressures of some of the substances in this category are so low that it is unlikely that they would be present in the vapor state at concentrations high enough to cause acute CNS effects by inhalation.

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 interference with biological membrane function, and the differences between their toxicities can be explained by the differences between the target tissue-partitioning behavior of the individual hydrocarbons. There are no toxicological properties of category member constituents that are specific and distinguish them from each other or from other constituents of these hydrocarbon solvents.