Contents

[Introduction] [Physico-chemical hazards] [Acute toxicity] [Acute oral toxicity] [Acute dermal toxicity] [Acute toxicity, inhalation gas] [Acute toxicity, inhalation vapours] [Acute toxicity, inhalation dust/mist] [Skin corrosion/irritation] [Serious eye damage/irritation] [Respiratory and skin sensitisation] [Germ cell mutagenicity] [Carcinogenicity] [Reproductive toxicity] [Specific target organ toxicity – single exposure] [Specific target organ toxicity – repeated expousure] [Aspiration hazard] [Hazardous to the aquatic environment] [Hazardous to the ozone layer] [References]

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Introduction

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This resource gives the generic concentration thresholds for hazard classification of chemical mixtures.

Generic concentration limits are assigned to an ingredient indicating a threshold above which the mixture is classified for a hazardous property of the ingredient (see CLP Regulation [1], Article 10 for full definition).

The Tables below give the threshold limits according to the hazard classification of the ingredient. The data is provided in a convenient, searchable format. In some cases is over-simplified, but it can aid mixture classification and inform formulators about likely hazards of chemical products. Classifiers of hazardous product need to refer to the full legislation to ensure correct results.

Generally, if there is evidence that an ingredient can cause effects below the generic thresholds, then the classifier should take this into account and classify accordingly. In particular, generic threshold limits do not apply where specific concentration limits are available for a component of a mixture.

The thresholds pertain to the CLP Regulation, which implements the UN GHS [2], in the EU and UK. Other countries implement the GHS differently, particularly regarding ‘building blocks’ and threshold concentrations. Some details of the differences in GHS implementation in other countries are given in a previous post. Please check with local regulations.

The Tables also indicate if a hazard is additive, so that the concentrations of ingredients with the hazard should be added together, or if the threshold is per ingredient.

Additivity is used for the following hazard classes:

• acute toxicity;
• skin corrosion/irritation (except some special cases);
• serious eye damage/eye irritation (except some special cases);
• specific target organ toxicity, single exposure Category 3 (respiratory tract irritation and narcotic effects);
• aspiration hazard (plus consideration of viscosity of the final mixture);
• short-term (acute) and long-term (chronic) aquatic toxicity;
• hazardous for the ozone layer.

The concentration limits in the Tables are generally given in wt% units and apply to solids and liquids, as they are most common. They also apply to gases in vol% units, unless stated separately.

A description of the procedures for classification of mixtures is given in a previous post, and a listing of the UK and EU Hazard Classes and Categories are given here.

Physico-chemical hazards

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Physico-chemical hazards, such as oxidising properties and flammability generally do not have simple generic threshold limits. If a product contains an ingredient with a physico-chemical property, and there is doubt whether or not the product meets the criteria for classification, then the product should be tested using a method given in the Test Methods Regulation [3].

However, concentration limits are given in the CLP Regulation [3] for pyrophoric gases:

• In the absence of data on its pyrophoricity, a flammable gas mixture shall be classified as a pyrophoric gas if it contains more than 1% (by volume) of pyrophoric component(s).

Acute Toxicity

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The classification of mixtures for acute toxicity is most often based on calculations using ingredient classification and concentration. Other methods, such as using test results or bridging principles take precedence if available. A fuller discussion of methods are given in a previous blog on mixture classification.

The calculations of acute toxicity can be complex, and you should refer to the legal text if any of the following apply:

• there is more than one ingredient with an acute toxicity classification, and they are in different Categories.
• there are ingredients with no acute toxicity data
• the classifier decides to use ATEs specific to the ingredient.

In the cases where the above do not apply, the calculations can be simplified to threshold concentrations . The tables below for the oral, dermal and inhalation routes give threshold concentrations for these cases.

The acute toxicity estimate (ATE) is the acute toxicity value for a substance is usually based on animal testing, either (i) older testing that gives an LD₅₀ or LC₅₀ value, which would be the same as the ATE; (ii) more recent testing that gives a range of value (based on toxic effects, rather than mortality). The higher the ATE, the less harmful the substance or mixture.

Acute oral toxicity

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Table 1 gives the mixture classification based on the ingredient classification and its concentration in the mixture for acute toxicity by the oral route.

Ingredient(s) classification	Converted ATE for ingredient(s) (mg/kg)	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1	0.5	≥ 10 to 100	Category 1
		≥ 1 to < 10	Category 2
		≥ 0.17 to < 1	Category 3
		≥ 0.025 to < 0.17	Category 4
		< 0.025	Not classified
Category 2	5	≥ 10 to 100	Category 2
		≥ 1.7 to < 10	Category 3
		≥ 0.25 to < 1.7	Category 4
		< 0.25	Not classified
Category 3	100	≥ 33 to 100	Category 3
		≥ 5.0 to < 33	Category 4
		< 5	Not classified
Category 4	500	≥ 25 to 100	Category 4
		< 25	Not classified

Acute dermal toxicity

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Table 2 gives the mixture classification based on the ingredient classification and its concentration in the mixture by the dermal route.

Ingredient(s) classification	Converted ATE for ingredient(s) (mg/kg)	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1	5	≥ 10 to 100	Category 1
		≥ 2.5 to < 10	Category 2
		≥ 0.5 to < 2.5	Category 3
		≥ 0.25 to < 0.5	Category 4
		< 0.25	Not classified
Category 2	50	≥ 25 to 100	Category 2
		≥ 5 to < 25	Category 3
		≥ 2.5 to < 5	Category 4
		< 2.5	Not classified
Category 3	300	≥ 30 to 100	Category 3
		≥ 15 to < 30	Category 4
		< 15	Not classified
Category 4	1100	≥ 55 to 100	Category 4
		< 55	Not classified

Acute Toxicity (inhalation, gases)

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Table 3 gives the mixture classification based on the ingredient classification and its concentration in the mixture by the inhalation route for gases.

Ingredient(s) classification	Converted ATE for ingredient(s) (ppmV)	Concentration range of ingredient(s) (wt% or vol%)	Classification of mixture
Category 1	10	≥ 10 to 100	Category 1
		≥ 2 to < 10	Category 2
		≥ 0.4 to < 2	Category 3
		≥ 0.05 to < 0.4	Category 4
		< 0.05	Not classified
Category 2	100	≥ 20 to 100	Category 2
		≥ 4 to < 20	Category 3
		≥ 0.5 to < 4	Category 4
		< 0.5	Not classified
Category 3	700	≥ 28 to 100	Category 3
		≥ 3.5 to < 28	Category 4
		< 3.5	Not classified
Category 4	4500	≥ 22.5 to 100	Category 4
		< 22.5	Not classified

Acute Toxicity (inhalation, vapours)

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Table 4 gives the mixture classification based on the ingredient classification and its concentration in the mixture by the inhalation route for vapours.

Ingredient(s) classification	Converted ATE for ingredient(s) (mg/L)	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1	0.05	≥ 10 to 100	Category 1
		≥ 2.5 to < 10	Category 2
		≥ 0.5 to < 2.5	Category 3
		≥ 0.25 to < 0.5	Category 4
		< 0.25	Not classified
Category 2	0.5	≥ 25 to 100	Category 2
		≥ 5 to < 25	Category 3
		≥ 2.5 to < 5	Category 4
		< 2.5	Not classified
Category 3	3	≥ 30 to 100	Category 3
		≥ 15 to < 30	Category 4
		< 15	Not classified
Category 4	11	≥ 55 to 100	Category 4
		< 55	Not classified

Acute Toxicity (inhalation, dust/mist)

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Table 5 gives the mixture classification based on the ingredient classification and its concentration in the mixture by the inhalation route for dust and mist particulates.

Ingredient(s) classification	Converted ATE for ingredient(s) (mg/L)	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1	0.005	≥ 10 to 100	Category 1
		≥ 1 to < 10	Category 2
		≥ 0.5 to < 1	Category 3
		≥ 0.1 to < 0.5	Category 4
		< 0.1	Not classified
Category 2	0.05	≥ 10 to 100	Category 2
		≥ 5 to < 10	Category 3
		≥ 1.0 to < 5	Category 4
		< 1.0	Not classified
Category 3	0.5	≥ 50 to 100	Category 3
		≥ 10 to < 50	Category 4
		< 10	Not classified
Category 4	1.5	≥ 30 to 100	Category 4
		< 30	Not classified

Skin corrosion/irritation

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The classification of mixtures for skin irritation/corrosion is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

If ingredient effects are additive

Skin corrosion/irritation is usually regarded as an additive property, so the concentration of ingredients are combined.

Where additivity is assumed, Table 6 gives the mixture classification based on the ingredient classification and its concentration in the mixture for skin corrosion/irritation.

Ingredient(s) classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1 (including sub-Categories 1A, 1B and 1C)	≥ 5 to 100	Category 1 (sub-Categories 1A, 1B and 1C may be assigned if ingredients have known sub-Categories)
	≥ 1 to < 5	Category 2
	< 1	Not classified
Category 2	≥ 10 to 100	Category 2
	< 10	Not classified

If ingredients are present with Category 1 (below 5%) and Category 2, then a simple equation is used to determine if mixture is classified in Category 2. If the following condition is satisfied, then the product is classified as Skin Irrit, Category 2.

10 x [Concentration Cat 1 ingredients] + [concentration of Cat 2 ingredients] ≥ 10%

If ingredient effects are not additive

In some cases additivity is not applicable to skin corrosion/irritation. The generic threshold concentration applies to each individual component, and the component concentrations are not summed. The theoretical basis for non-additivity is not stated in the CLP Regulation or guidance [4], but some examples are given (see CLP Annex I, 3.2.3.3.4.1.):

• acids and bases
• inorganic salts
• aldehydes
• phenols
• surfactants.

Where additivity is not assumed, Table 7 gives the mixture classification for skin corrosion/irritation based on the ingredient classification and its concentration in the mixture.

Ingredient classification	Concentration range of ingredient (wt%)	Classification of mixture
Category 1 (including sub-Categories 1A, 1B and 1C)	≥ 1 to 100	Category 1
	< 1	Not classified
Category 2	≥ 3 to 100	Category 2
	< 3	Not classified

For mixtures containing acids and bases, the pH should be used for classification of the mixture as corrosive, since pH is a better indicator than concentration limits (see CLP Annex I, 3.2.3.3.4.2.).

Serious eye damage/eye irritation

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The classification of mixtures for serious eye damage/eye irritation is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

Skin corrosive substance are assumed to be Eye Dam 1, which is why the threshold concentrations as indicated below include skin corrosive components. No such assumption is made for ingredients classified for skin irritation Category 2.

If ingredient effects are additive

Serious eye damage/eye irritation is usually regarded as an additive property, so the concentration of ingredients are combined.

Where additivity is assumed, Table 8 gives the mixture classification for serious eye damage/eye irritation based on the ingredient classification and its concentration in the mixture.

Ingredient(s) classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1 (either for skin corrosion, including sub-Categories 1A, 1B and 1C, or eye damage)	≥ 3 to 100	Category 1
	≥ 1 to < 3	Category 2
	< 1	Not classified
Category 2	≥ 10 to 100	Category 2
	< 10	Not classified

If ingredients are present with Category 1 (either for skin corrosion or eye damage) (below 3%) and Category 2, then a simple equation is used to determine if mixture is classified in Category 2. If the following condition is satisfied, then the product is classified as Eye Irrit, Category 2.

10 x [Concentration Cat 1 ingredients] + [concentration of Cat 2 ingredients] ≥ 10%

If ingredient effects are not additive

In some cases additivity is not applicable to serious eye damage/irritation. The generic threshold concentration applies to each individual component, and the component concentrations are not summed. The theoretical basis for non-additivity is not stated in the regulations or guidance, but some examples are given (see CLP Annex I, 3.3.3.3.4.1.):

• acids and bases
• inorganic salts
• aldehydes
• phenols
• surfactants.

Where additivity is not assumed, Table 9 gives the mixture classification for serious eye damage/irritation based on the ingredient classification and its concentration in the mixture.

Ingredient classification	Concentration range of ingredient (wt%)	Classification of mixture
Category 1 (including sub-Categories 1A, 1B and 1C)	≥ 1 to 100	Category 1
	< 1	Not classified
Category 2	≥ 3 to 100	Category 2
		Not classified

For mixtures containing acids and bases, the pH should be used for classification of the mixture as corrosive, since pH is a better indicator than concentration limits (see CLP Annex I, 3.3.3.3.4.2.).

Respiratory and skin sensitisation

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The classification of mixtures for respiratory or skin sensitisation is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

Sensitisation is considered to be substance specific, so the threshold concentrations below apply to each component individually, and the component concentrations are not summed (ie non-additive).

Skin sensitisation (causing dermatitis) and respiratory sensitisation (causing asthma) are treated as separate hazards, and generic thresholds apply separately.

Ingredients present below the generic concentration that causes classification of the mixture may require naming on the label with the EUH208 phrase: ‘Contains (name of sensitising substance). May produce an allergic reaction.’

Table 10 gives the mixture classification for respiratory or skin sensitisation based on the ingredient classification and its concentration in the mixture.

Ingredient classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1 (and sub-Category 1B) (solid and liquid) (skin and respiratory sensitisation)	≥ 1 to 100	Category 1
	≥ 0.1 to < 1	EUH208
	< 0.1	Not classified
Category 1 (and sub-Category 1B) (gases for respiratory sensitisation)	≥ 0.2 to 100	Category 1
	≥ 0.02 to < 0.2	EUH208
	< 0.02	Not classified
Sub-Category 1A (all physical states) (skin and respiratory sensitisation)	≥ 0.1 to 100	Category 1
	≥ 0.01 to 0.1	EUH208
	< 0.01	Not classified

Germ cell mutagenicity

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The classification of mixtures for mutagenicity is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

Mutagenicity is considered to be substance specific, so the threshold concentrations below apply to each component individually, and the component concentrations are not summed (ie non-additive).

The Hazard Class sub-Categories and generic threshold concentrations are the same for mutagenicity and carcinogenicity.

Table 11 gives the mixture classification for mutagenicity based on the ingredient classification and its concentration in the mixture.

The concentration limits in Table 11 apply to solids and liquids (wt% units) as well as gases (vol% units).

Ingredient classification	Concentration range of ingredient (wt%)	Classification of mixture
Sub-Category 1A	≥ 0.1 to 100	Sub-Category 1A
	< 0.1	Not classified
Sub-Category 1B	≥ 0.1 to 100	Sub-Category 1B
	< 0.1	Not classified
Category 2	≥ 1.0 to 100	Category 2
	< 1.0	Not classified

Carcinogenicity

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The classification of mixtures for mutagenicity is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

Carcinogenicity is considered to be substance specific, so the threshold concentrations below apply to each component individually, and the component concentrations are not summed (ie non-additive).

The Hazard Class sub-Categories and generic threshold concentrations are the same for mutagenicity and carcinogenicity.

Table 12 gives the mixture classification for carcinogenicity based on the ingredient classification and its concentration in the mixture.

The concentration limits in Table 12 apply to solids and liquids (wt% units) as well as gases (vol% units).

Ingredient classification	Concentration range of ingredient (wt%)	Classification of mixture
Sub-Category 1A	≥ 0.1 to 100	Sub-Category 1A
	< 0.1	Not classified
Sub-Category 1B	≥ 0.1 to 100	Sub-Category 1B
	< 0.1	Not classified
Category 2	≥ 1.0 to 100	Category 2
	< 1.0	Not classified

Reproductive toxicity

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The classification of mixtures for reproductive toxicity is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

Reproductive toxicity is considered to be substance specific, so the threshold concentrations below apply to each component individually, and the component concentrations are not summed (ie non-additive).

Table 13 gives the mixture classification for reproductive toxicity based on the ingredient classification and its concentration in the mixture.

The concentration limits in Table 13 apply to solids and liquids (wt% units) as well as gases (vol% units).

Ingredient classification	Concentration range of ingredient (wt%)	Classification of mixture
Sub-Category 1A	≥ 0.3 to 100	Sub-Category 1A
	< 0.3	Not classified
Sub-Category 1B	≥ 0.3 to 100	Sub-Category 1B
	< 0.3	Not classified
Sub-Category 2	≥ 3.0 to 100	Category 2
	< 3.0	Not classified
Effects on or via lactation	≥ 0.3 to 100	Effects on or via lactation
	< 0.3	Not classified

Specific organ toxicity – single exposure (STOT-SE)

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The classification of mixtures for STOT-SE is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

STOT-SE components in Categories 1 and 2 are considered to be substance specific, so the threshold concentrations below apply to each component individually. However, for Category 3 respiratory irritants (H335: May cause respiratory irritation) and narcotics (H336: May cause drowsiness or dizziness) additivity is assumed and the component concentrations are summed.

Table 14 gives the mixture classification for STOT-SE based on the ingredient classification and its concentration in the mixture.

The concentration limits in Table 14 apply to solids and liquids (wt% units) as well as gases (vol% units).

Ingredient(s) classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1	≥ 10 to 100	Category 1
	≥ 1.0 to < 10	Category 2
	< 1	Not classified
Category 2	≥ 10 to 100	Category 2
	< 10	Not classified
Category 3 (H335 or H336)	≥ 20 to 100	Category 3 (H335 or H336)
	< 20	Not classified

Specific organ toxicity – repeated exposure (STOT-RE)

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The classification of mixtures for STOT-RE is most often based on thresholds using ingredient classification and concentration. Other methods for classification, such as using test results or bridging principles take precedence if available.

STOT-RE components are considered to be substance specific, so the threshold concentrations below apply to each component individually, and the component concentrations are not summed (ie non-additive).

Table 15 gives the mixture classification for STOT-RE based on the ingredient classification and its concentration in the mixture.

The concentration limits in Table 15 above apply to solids and liquids (wt% units) as well as gases (vol% units).

Ingredient classification	Concentration range of ingredient (wt%)	Classification of mixture
Category 1	≥ 10 to 100	Category 1
	≥ 1.0 to < 10	Category 2
	< 1	Not classified
Category 2	≥ 10 to 100	Category 2
	< 10	Not classified

Aspiration hazard

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Aspiration means the entry of a liquid into the trachea and lower respiratory system, eg from swallowing or indirectly following vomiting.

The classification of mixtures for aspiration hazard is most often based on measurement of the kinematic viscosity (≤ 20.5 mm²/s indicates Category 1). Other evidence for classification, such as using test results or bridging principles should considered, if available.

In the absence of such data, the generic thresholds apply. Table 16 gives the mixture classification for aspiration hazard based on the ingredient classification and its concentration in the mixture.

Additivity is assumed and the component concentrations are summed.

Ingredient(s) classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1	≥ 10 to 100	Category 1
	< 10	Not classified

Hazardous to the aquatic environment

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The classification of mixtures for Hazardous to the aquatic environment is most often based on calculations using ingredient classification and concentration. Other methods, such as using test results or bridging principles take precedence if available.

Full equations using additivity formulae are given in the CLP Regulation, Annex I, 4.1.3.5.2. Simpler summation calculations are given in Section 4.1.3.5.5.

Hazardous to the aquatic environment classification may require calculation if:

• there is more than one ingredient with a hazardous to the aquatic environment classification, and they are in different Categories.
• there are ingredients with no acute toxicity data
• there is acute and chronic data.
• the classifier uses data specific to the ingredient.

The calculation can be simplified to threshold concentrations only in the cases where the above do not apply.

A multiplying factor (M-factor) may be applied to the concentration of a component that is very toxic, ie classified as acute Category 1 or chronic Category 1. The concentration ranges causing classification of the mixture are divided by the M-factor. Classification thresholds are given in the Tables below for M = 1 and 10, but the same principles apply to higher M-factors (100, etc).

Hazardous to the aquatic environment is an additive property, so the concentration of ingredients with the same classification and Category can be combined.

Short-term (acute) hazards

Table 17 gives the mixture classification for aquatic acute toxicity based on the ingredient classification and its concentration in the mixture.

Ingredient(s) classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1 (M = 1, or not available)	≥ 25 to 100	Category 1
	< 25	Not classified
Category 1 (M = 10)	≥ 2.5 to 100	Category 1
	< 2.5	Not classified

Long-term (chronic) hazards

Table 18 gives the mixture classification for aquatic chronic toxicity based on the ingredient classification and its concentration in the mixture.

Ingredient(s) classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1 (M = 1, or not available)	≥ 25 to 100	Category 1
	≥ 2.5 to < 25	Category 2
	≥ 0.25 to < 2.5	Category 3
	< 0.25	Not classified
Category 1 (M = 10)	≥ 2.5 to < 25	Category 1
	≥ 0.25 to < 2.5	Category 2
	≥ 0.025 to < 0.25	Category 3
	< 0.025	Not classified
Category 2	≥ 25 to 100	Category 2
	≥ 2.5 to < 25	Category 3
	< 2.5	Not classified
Category 3	≥ 25 to 100	Category 3
	< 25	Not classified
Sum of Categories 1,2, 3 and 4	≥ 25 to 100	Category 4
	< 25	Not classified

Hazardous to the ozone layer

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The classification of mixtures for hazardous to the ozone layer is based only on ingredient concentration thresholds.

Hazards to the ozone layer is an additive property, so the concentration of ingredients with the same classification should be combined.

Table 19 gives the mixture classification for hazardous to the ozone layer based on the ingredient classification and its concentration in the mixture.

Ingredient(s) classification	Concentration range of ingredient(s) (wt%)	Classification of mixture
Category 1	≥ 0.1 to 100	Category 1
	< 0.1	Not classified

References

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[1] Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures (as amended).

[2] Globally Harmonized System of Classification and Labelling (GHS); Ninth Revised Edition; United Nations; 2021.

[3] Regulation (EC) No 440/2008 laying down test methods pursuant to Regulation (EC) No 1907/2006 (REACH) (as amended).

[4] Guidance on the Application of the CLP Criteria; Guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures; ECHA; Version 5.0, July 2017.