Specific Concentration Limits
Specific Concentration Limits (SCLs) are used within CLP where a substance behaves differently in a mixture to that predicted by the normal mixture classification rules. This can be where the effects of the mixture are more severe than calculations would predict, or sometimes where they are less severe. The concept is used in GHS and was also part of CHIP. SCLs are only applicable to health hazards, and not to physical or environmental hazards.
A Specific Concentration Limit is expressed for an individual hazard as a concentration limit, either % w/w or % v/v. If the substance is contained in a mixture at or above that limit, the mixture attracts the classification listed in the Specific Concentration Limit information. Note that an SCL only applies to that individual published hazard, and you should not “read across” to any other hazards.
SCLs are published in the Harmonised Classifications, and also in REACH dossiers, and very occasionally in the Classification and Labelling Inventory. They are intended to be derived by people classifying substances, and not by end-users classifying mixtures. If there is no published SCL for a hazardous property of a substance, you should use the generic classification limits to classify it in a mixture.
Example – Cadmium Sulphate
Cadmium Sulphate has a Harmonised Classification with three SCLs under CLP:
Carc. 1B; H350: C ≥ 0,01 %
STOT RE 1; H372: C ≥ 7 %
STOT RE 2; H373: 0,1 % ≤ C < 7 %
These apply to two hazard types (or “end-points” in toxicologist jargon), carcinogenicity, and specific target organ toxicity (repeated exposure), which has two classifications available depending on the concentration of Cadmium Sulphate in a mixture.
The overall classifications available to a mixture containing non-classified components and Cadmium Sulphate are:
- < 0.01% w/w Cadmium Sulphate – not classified for CLP
- 0.01 – 0.09 % w/w Cadmium Sulphate, Carc. 1B; H350
- 0.1 – 6.99% w/w Cadmium Sulphate, Carc. 1B; H350, STOT RE 2, H373
- 7% w/w or above Cadmium Sulphate, Carc. 1B; H350, STOT RE 1, H372
Specific concentration limits scope
Specific concentration limits are not applicable to:
- physical hazards
- environmental hazards, where the concept of M-factors is used as an alternative, see https://ttenvironmenta.wpengine.com/clp-knowledgebase/m-factors/ )
- acute toxicity hazards, as these are classified in CLP on the basis of their individual toxicity test results (some substances used to have acute toxic SCLs under CHIP, and these are identified with an asterisk in the SCL column of their Harmonised Classification)
- respiratory sensitisers, as these cannot be tested on animals so data for SCLs cannot be derived
- STOT SE3 H336, may cause drowsiness or dizziness, as these cannot be tested on animals, so data for SCLs cannot be derived (and there are no Harmonised Classifications at the time of writing, August 2017)
- aspiration hazard
- Specific target organ toxicity (single exposure) Cat 2 (a more severe classification would be Cat 1)
- Specific target organ toxicity (repeated exposure) Cat 2 (a more severe classification would be Cat 1)
This means that specific concentration limits only apply to these hazards:
- Skin corrosion / irritation
- Skin sensitisation
- Eye damage/ irritation
- Toxic for reproduction
- Specific target organ toxicity (single exposure) Cat 1
- Specific target organ toxicity (single exposure) Cat 3, H335, May cause respiratory irritation
- Specific target organ toxicity (repeated exposure) Cat 1
Most of the hazards where SCLs apply involve comparing individual component substances with a threshold, and where this is the case, the specific concentration limit should be used as a comparison rather than the generic threshold.
However, skin corrosion/ irritation and eye damage/ irritation (and some other hazards) can use an additive method for calculating overall classification, and in this case the SCL needs to be included as part of the addition. This involves dividing each component by its SCL (or by the general classification limit, where there is no SCL), and adding them together. If the result is 1 or greater, then the mixture is classified.