3.1.3.: Criteria for classification of mixtures as acutely toxic The criteria for classification of substances for acute toxicity as outlined in section 3.1.2 are based on lethal dose data (tested or derived). For mixtures, it is necessary to obtain or derive information that allows the criteria to be applied to the mixture for the purpose of classification. The approach to classification for acute toxicity is tiered, and is dependent upon the amount of information available for the mixture itself and for its ingredients. The flow chart of Figure 3.1.1 outlines the process to be followed. For acute toxicity each route of exposure shall be considered for the classification of mixtures, but only one route of exposure is needed as long as this route is followed (estimated or tested) for all components and there is no relevant evidence to suggest acute toxicity by multiple routes. When there is relevant evidence of toxicity by multiple routes of exposure, classification is to be conducted for all appropriate routes of exposure. All available information shall be considered. The pictogram and signal word used shall reflect the most severe hazard category and all relevant hazard statements shall be used. In order to make use of all available data for purposes of classifying the hazards of the mixtures, certain assumptions have been made and are applied where appropriate in the tiered approach:
(a) the ‘relevant ingredients’ of a mixture are those which are present in concentrations of 1 % (w/w for solids, liquids, dusts, mists and vapours and v/v for gases) or greater, unless there is a reason to suspect that an ingredient present at a concentration of less than 1 % is still relevant for classifying the mixture for acute toxicity (see Table 1.1).
(b) where a classified mixture is used as an ingredient of another mixture, the actual or derived acute toxicity estimate (ATE) for that mixture may be used, when calculating the classification of the new mixture using the formulas in section and paragraph
(c) If the converted acute toxicity point estimates for all components of a mixture are within the same category, then the mixture should be classified in that category.
(d) When only range data (or acute toxicity hazard category information) are available for components in a mixture, they may be converted to point estimates in accordance with Table 3.1.2 when calculating the classification of the new mixture using the formulas in sections and

Figure 3.1.1

Tiered approach to classification of mixtures for acute toxicity

image Classification of mixtures where acute toxicity data are available for the complete mixture Where the mixture itself has been tested to determine its acute toxicity, it shall be classified according to the same criteria as those used for substances, presented in Table 3.1.1. If test data for the mixture are not available, the procedures presented under sections and shall be followed. Classification of mixtures where acute toxicity data are available for the complete mixture: bridging principles Where the mixture itself has not been tested to determine its acute toxicity, but there are sufficient data on the individual ingredients and similar tested mixtures to adequately characterise the hazards of the mixture, these data shall be used in accordance with the bridging rules set out in section 1.1.3. If a tested mixture is diluted with a diluent that has an equivalent or lower toxicity classification than the least toxic original components, and which is not expected to affect the toxicity of other components, then the new diluted mixture may be classified as equivalent to the original tested mixture. Alternatively, the formula explained in section can be applied. Classification of mixtures based on ingredients of the mixture (Additivity formula) Data available for all ingredients
In order to ensure that classification of the mixture is accurate, and that the calculation need only be performed once for all systems, sectors, and categories, the acute toxicity estimate (ATE) of ingredients shall be considered as follows:
(a) ►M12  include ingredients with a known acute toxicity, which fall into any of the acute hazard categories shown in Table 3.1.1; ◄
(b) ignore ingredients that are presumed not acutely toxic (e.g., water, sugar);
(c) ignore components if the data available are from a limit dose test (at the upper threshold for Category 4 for the appropriate route of exposure as provided in Table 3.1.1) and do not show acute toxicity.
Components that fall within the scope of this section are considered to be components with a known acute toxicity estimate (ATE). See note (b) to Table 3.1.1 and section for appropriate application of available data to the equation below, and section
The ATE of the mixture is determined by calculation from the ATE values for all relevant ingredients according to the following formula for Oral, Dermal or Inhalation Toxicity:





concentration of ingredient i ( % w/w or % v/v)



the individual ingredient from 1 to n



the number of ingredients



Acute Toxicity Estimate of ingredient i. Classification of mixtures when data are not available for all components Where an ATE is not available for an individual ingredient of the mixture, but available information, such as that listed below, can provide a derived conversion value such as those laid out in Table 3.1.2, the formula in section shall be applied.

This includes evaluation of:

(a) extrapolation between oral, dermal and inhalation acute toxicity estimates ( 10 ). Such an evaluation could require appropriate pharmacodynamic and pharmacokinetic data;
(b) evidence from human exposure that indicates toxic effects but does not provide lethal dose data;
(c) evidence from any other toxicity tests/assays available on the substance that indicates toxic acute effects but does not necessarily provide lethal dose data; or
(d) data from closely analogous substances using structure/activity relationships.

This approach generally requires substantial supplemental technical information, and a highly trained and experienced expert (expert judgement, see section 1.1.1), to reliably estimate acute toxicity. If such information is not available, proceed to paragraph In the event that a component without any useable information for classification is used in a mixture at a concentration ≥ 1 %, it is concluded that the mixture cannot be attributed a definitive acute toxicity estimate. In this situation the mixture shall be classified based on the known components only, with the additional statement on the label and in the SDS that ‘x per cent of the mixture consists of component(s) of unknown acute toxicity’, taking into account the provisions set out in section If the total concentration of the relevant ingredient(s) with unknown acute toxicity is ≤ 10 % then the formula presented in section shall be used. If the total concentration of the relevant ingredient(s) with unknown toxicity is > 10 %, the formula presented in section shall be corrected to adjust for the percentage of the unknown ingredient(s) as follows:


Table 3.1.2


Conversion from experimentally obtained acute toxicity range values (or acute toxicity hazard categories) to acute toxicity point estimates for use in the formulas for the classification of mixtures


Exposure routes

Classification Category or experimentally obtained acute toxicity range estimate

Converted acute toxicity point estimate

(see Note 1)


(mg/kg bodyweight)

0 < Category 1 ≤ 5

5 < Category 2 ≤ 50

50 < Category 3 ≤ 300

300 < Category 4 ≤ 2 000






(mg/kg bodyweight)

0 < Category 1 ≤ 50

50 < Category 2 ≤ 200

200 < Category 3 ≤ 1 000

1 000 < Category 4 ≤ 2 000




1 100



0 < Category 1 ≤ 100

100 < Category 2 ≤ 500

500 < Category 3 ≤ 2 500

2 500 < Category 4 ≤ 20 000




4 500



0 < Category 1 ≤ 0,5

0,5 < Category 2 ≤ 2,0

2,0 < Category 3 ≤ 10,0

10,0 < Category 4 ≤ 20,0







0< Category 1 ≤ 0,05

0,05 < Category 2 ≤ 0,5

0,5 < Category 3 ≤ 1,0

1,0 < Category 4 ≤ 5,0





Note 1

These values are designed to be used in the calculation of the ATE for classification of a mixture based on its components and do not represent test results.