Mixtures classification categories and criteria

The classification system for mixtures covers the classification categories which are used for
substances, meaning categories Acute 1 and Chronic 1 and 2. In order to make use of all available
data for purposes of classifying the aquatic environmental hazards of the mixture, the following
assumption is made and is applied where appropriate:
The "relevant ingredients" of a mixture are those which are present in a concentration equal to or
greater than 0.1% (by mass) for ingredients classified as Acute and/or Chronic 1 and equal to or
greater than 1% for other ingredients, unless there is a presumption (e.g. in the case of highly toxic
ingredients) that an ingredient present at less than 0.1% can still be relevant for classifying the mixture
for aquatic environmental hazards.

The approach for classification of aquatic environmental hazards is tiered, and is dependent upon the
type of information available for the mixture itself and for its ingredients. Elements of the tiered
approach include:
(a) Classification based on tested mixtures;
(b) Classification based on bridging principles;
(c) The use of "summation of classified ingredients" and/or an "additivity formula".
Figure below outlines the process to be followed.
13 Special guidance is provided in Chapter 4.1, paragraph and Annex 9, Section A9.6 of the GHS.
Figure Tiered approach to classification of mixtures

Classification of mixtures when toxicity data are available for the complete mixture

When the mixture as a whole has been tested to determine its aquatic toxicity, this information
shall be used for classifying the mixture according to the criteria that have been agreed for
substances. The classification is normally based on the data for fish, crustacea and algae/plants
(see and When adequate acute or chronic data for the mixture as a
whole are lacking, "bridging principles" or "summation method" shall be applied (see to

The long-term hazard classification of mixtures requires additional information on degradability
and in certain cases bioaccumulation. There are no degradability and bioaccumulation data for
mixtures as a whole. Degradability and bioaccumulation tests for mixtures are not used as they are
usually difficult to interpret, and such tests may be meaningful only for single substances.

Classification for category Acute 1

(a) When there are adequate acute toxicity test data (LC50 or EC50) available for the mixture as
a whole showing L(E)C50 ≤ 1 mg/l:
Classify the mixture as Acute 1 in accordance with Table (a);
(b) When there are acute toxicity test data (LC50(s) or EC50(s) available for the mixture as a
whole showing L(E)C50(s) > 1 mg/l, or above the water solubility:
No need to classify for acute hazard under ADR.

Classification for categories Chronic 1 and 2

(a) When there are adequate chronic toxicity data (ECx or NOEC) available for the mixture as a
whole showing ECx or NOEC of the tested mixture ≤ 1mg/l:
(i) classify the mixture as Chronic 1 or 2 in accordance with Table (b) (ii)
(rapidly degradable) if the available information allows the conclusion that all
relevant ingredients of the mixture are rapidly degradable;
(ii) classify the mixture as Chronic 1 or 2 in all other cases in accordance with Table (b) (i) (non-rapidly degradable);
(b) When there are adequate chronic toxicity data (ECx or NOEC) available for the mixture as a
whole showing ECx(s) or NOEC(s) of the tested mixture > 1mg/l or above the water
No need to classify for long-term hazard under ADR.

Classification of mixtures when toxicity data are not available for the complete mixture: bridging

Where the mixture itself has not been tested to determine its aquatic environmental hazard, 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 following
agreed bridging rules. This ensures that the classification process uses the available data to the
greatest extent possible in characterising the hazards of the mixture without the necessity for
additional testing in animals.


Where a new mixture is formed by diluting a tested mixture or a substance with a diluent which
has an equivalent or lower aquatic hazard classification than the least toxic original ingredient and
which is not expected to affect the aquatic hazards of other ingredients, then the resulting mixture
shall be classified as equivalent to the original tested mixture or substance. Alternatively, the
method explained in may be applied.


The aquatic hazard classification of a tested production batch of a mixture shall be assumed to be
substantially equivalent to that of another untested production batch of the same commercial
product when produced by or under the control of the same manufacturer, unless there is reason to
believe there is significant variation such that the aquatic hazard classification of the untested
batch has changed. If the latter occurs, new classification is necessary.

Concentration of mixtures which are classified with the most severe classification categories (Chronic 1 and Acute 1)

If a tested mixture is classified as Chronic 1 and/or Acute 1, and the ingredients of the mixture
which are classified as Chronic 1 and/or Acute 1 are further concentrated, the more concentrated
untested mixture shall be classified with the same classification category as the original tested
mixture without additional testing.

Interpolation within one toxicity category

For three mixtures (A, B and C) with identical ingredients, where mixtures A and B have been
tested and are in the same toxicity category, and where untested mixture C has the same
toxicologically active ingredients as mixtures A and B but has concentrations of toxicologically
active ingredients intermediate to the concentrations in mixtures A and B, then mixture C is
assumed to be in the same category as A and B.

Substantially similar mixtures

Given the following:
(a) Two mixtures:
(i) A + B;
(ii) C + B;
(b) The concentration of ingredient B is essentially the same in both mixtures;
(c) The concentration of ingredient A in mixture (i) equals that of ingredient C in mixture (ii);
(d) Data on aquatic hazards for A and C are available and are substantially equivalent, i.e. they
are in the same hazard category and are not expected to affect the aquatic toxicity of B.
If mixture (i) or (ii) is already classified based on test data, then the other mixture can be assigned
the same hazard category.
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