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

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, thesedata 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 mixtureshall be assumed to be substantially equivalent to that of another untestedproduction batch of the same commercial product when producedby 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 untestedbatch has changed. If the latter occurs, new classification is necessary.

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

If a tested mixtureis classified as Chronic 1and/or Acute 1, and the ingredients of the mixture which are classified as Chronic 1and/or Acute 1are further concentrated, the more concentrated untestedmixture shall be classified with the same classification category as the original testedmixture 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 hazardsfor A and C are available and are substantially equivalent, i.e. theyare 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.

Classification of mixtures when toxicitydata are available for all ingredients or only for some ingredients of the mixture

The classification of a mixture shall be based on summation of the concentrations of its classified ingredients. The percentage of ingredients classified as "Acute" or "Chronic" will feed straight into the summation method. Details of the summation method are described in2. to

Mixtures may be made of a combination of both ingredients that are classified (as Acute 1 and/or Chronic 1, 2) and those for which adequate toxicity test data are available. When adequate toxicity data are available for more than one ingredient in the mixture, the combined toxicity of those ingredients shall be calculated using the following additivity formulas (a) or (b), depending on the nature of the toxicity data:

(a)Based on acute aquatic toxicity:


Ci=concentration of ingredient i(mass percentage);

L(E)C50i=LC50or EC50for ingredient i (mg/l);

n=number of ingredients, and i is running from 1ton;

L(E)C50m=L(E)C50of the part of the mixture with test data;

The calculated toxicity shall be used to assign that portionof the mixture an acute hazard category which is then subsequently used in applying the summation method;

(b)Based on chronic aquatic toxicity:


Ci=concentration of ingredient i (mass percentage) covering the rapidly degradable ingredients;

Cj=concentration of ingredient j (mass percentage) covering the non rapidly degradable ingredients;

NOECi=NOEC (or other recognized measures for chronic toxicity) for ingredient i covering the rapidly degradable ingredients, in mg/l;

NOECj=NOEC (or other recognized measures for chronic toxicity) for ingredient j covering the non-rapidly degradable ingredients, in mg/l;

n=number of ingredients, and i and j are running from 1 to n;

EqNOECm=equivalent NOEC of the part of the mixture with test data;

The equivalent toxicity thus reflects the fact that non-rapidly degradingsubstances are classified one hazard category level more "severe" than rapidly degrading substances.

The calculated equivalent toxicity shall be used to assign that portion of the mixture a long-term hazard category, in accordance with the criteria for rapidly degradable substances (Table (b) (ii)), which is then subsequently used in applying the summation method.


When applying the additivity formula for part of the mixture, it is preferable to calculate the toxicity of this part of the mixture using for each ingredienttoxicity values that relate to the same taxonomic group(i.e. fish, crustaceaor algae) and then to use the highest toxicity (lowest value) obtained (i.e. use the most sensitive of the three groups). However, when toxicity data for each ingredient are not available in the same taxonomic group, the toxicity value of each ingredient shall be selected inthe same manner that toxicity values are selected for the classification of substances, i.e. the higher toxicity (from the most sensitive test organism) is used. The calculated acuteand chronictoxicity shall then be used to classify this part of the mixture as Acute 1and/or Chronic 1 or 2using the same criteria described for substances.

If a mixture is classified in more than one way, the method yielding the more conservative result shall be used.

Summation method

Classification procedure

In general a more severe classification for mixtures overrides a less severe classification, e.g. a classification with Chronic 1overrides a classification with Chronic 2. As a consequence the classification procedure is already completed if the results of the classification is Chronic1. A more severe classification than Chronic 1is not possible; therefore, it is not necessary to pursue the classification procedure further.

Classification for category Acute 1

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