Update of the RCP methodology to assess hydrocarbon solvent mixtures at the workplace

Status:

completed 10/2014

Aims:

Objectives of this project:

• revisioning of an existing methodology (RCP-method) to derive occupational limit values for hydrocarbon solvent mixtures,
• covering the inclusion of recent toxicological data and the integration of an updated systematic approach to classify hydrocarbon fractions for solvents within REACH,
• eliminating of some contradictions between the current approach and single substances’ toxicity data,
• calculation of occupational limit values for an infinite multitude of mixtures of similar substances by using this updated methodology.

Activities/Methods:

Therefore, existing regulatory values for single substances in the range of C5-C15 aliphatic and C6-C15 aromatic hydrocarbons and additional recent data were documented and the original background information was retrieved. Toxicological profiles from similar substances were clustered to groups with segmentation according to carbon-chain length to derive group guidance values (GGV). Single substances with identified distinct mode of action or with clearly deviating toxic potency were exempted from the more homogeneous groups. Toxicological findings on defined mixtures or UVCB (substances of unknown or variable composition, complex reaction products or biological materials) were used for comparison.

Results:

As result, two options (option A, B) for grouping and GGVs are proposed:

• Option A:
  Single group: C6-C15 aliphatics with GGV of 300 mg/m³
  Single group: C9-C15 aromatics with GGV of 50 mg/m³
• Option B:
  Single group: C6-C8 aliphatics with GGV of 700 mg/m³
  Single group: C9-C15 aliphatics with GGV of 300 mg/m³
  Single group: C9-C15 aromatics with GGV of 50 mg/m³

The following single substances should be exempted from the respective groups and GGV:

pentanes (all isomers, including cyclopentane), n-hexane, decalin, benzene, toluene, xylenes (all isomers), ethylbenzene, naphthalene, tetralin, diethylbenzenes (all isomers), n-butylbenzenes, methylnaphthalene (all isomers), acenaphthene, acenaphthylene, biphenyl, 1,2,4-triethylbenzene, fluorene.

Single substance OELs (SSVs) and/or maximum tolerable amounts (cut offs for irrelevance) for these exempted single substances were not determined within this project.

With the given experimental data it caused considerable uncertainty, that in many cases the highest concentration tested had to be assumed to be equal to the "no observed adverse effect concentration" (NOAEC), though the "real" NOAEC could have been higher. Also, the use of default assessment factors may be regarded as an uncertain screening procedure. However, not always the lowest resulting OEL was used for GGV. It should be noted that sometimes very deviating study results between the various single substance’s or mixture’s NOAECs also may reflect a significant heterogeneity in mode of action and potency, which does not support a highly homogeneous toxicity profile within the respective hydrocarbon solvent groupings. This makes it necessary to apply default factors and take conservative starting points for the assessments.

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