Curious classification: acute toxicity

How is the “acute toxicity” classification determined?

The reason for this blog entry was a question from a user of the SDBcheck® online tool on the topic of acute toxicity: “How does the classification Acute Tox. 2 with H330 result, even though none of the individual components is also classified as “Acute Tox.”?

A quick overview

In accordance with the CLP Regulation, the acute toxicity can be calculated based on the toxicity of the components. If toxicity data are available for a component (e.g. LD50 or LC50), they must be used in the calculation. Only if none of those values are present, “replacement values” are used if the component is classed as “Acute Tox.” (conversion values of Table 3.1.2 in the CLP Regulation). It is important to know that acute toxicity always has “three parts”. This means that information may exist for oral, dermal or inhalative toxicity, and sometimes for all three of these routes of exposure.

Special case: inhalative toxicity

Let’s take a closer look at inhalative toxicity:

  • If the mixture is a gas, things are relatively simple: the toxicity of the component as a gas is relevant for the calculation of the toxicity.
  • If the mixture is solid or liquid, a distinction must be made if a toxicity specification is present for vapour or dust/mist. This is often the relevant difference.
  • Vapour: Best viewed as a liquid which evaporates over time. The droplets of the liquid are then suspended in the air and can (could) be inhaled.
  • Dust/mist: If the mixture is a powder, inhalative dust can be created, for example when pouring the product. If the product is sprayed, for example spray paint particles, this is called a mist.

The answer

I’m sure you have spotted the first part of the answer already: if tox. values exist (provided in Section 11 of the safety data sheet), the classification is made using this information. This means that a classification of the component(s) as toxic is not necessary for this purpose. But the second part is more difficult. The safety data sheet often simply states “LC50 inhalative”. What does information such as 6.82 mg/L refer to in this context? “Gas” can be excluded as an answer straight away, because the unit would be “ppmV”. Deciding whether the component is a “vapour” or “dust/mist” is best determined via the aggregate state of the product: “liquid” indicates “vapour”, “solid” or “powdered” indicates “dust/mist”.


The component with “LC50 inhalative” of 6.82 mg/L is included in the product with (up to) 45%. We will assume that the remaining 55% are “unknown”. The calculation then results in an “ATEmix” of 6.82 mg/L (=[100% – 55%] * 6,82 mg/L : 45%).

  • In accordance with Table 3.1.1 of the CLP Regulation, for “vapour”, this means Acute Tox. 3, H331.
  • For “dust/mist” however, no classification is established in accordance with Table 3.1.1 of the CLP Regulation.

Incidentally, if the remaining 55% were “non-hazardous” instead of “unknown”, our example for “vapour” would have resulted in the classification “Acute Tox. 4, H332”.


When calculating the classification for acute toxicity, it follows that the correct application of the toxicological information is very important. As a result, when carrying out the classification calculation you should only use toxicological information which is as secure as possible, e.g. provided by ECHA or GESTIS. See this blog entry as well. If you know that a certain route of exposure for a substance does not have acute toxicity, explicitly set this route of exposure to “non-hazardous”. When using SDBcheck®, pay attention to the precise route of exposure involved. This applies in particular to “surprising” deviations.

Sources: Regulation (EC) No 1907/2006 (REACH Regulation), consolidated version dated 24/08/2020

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