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What Is M-factor and How It Is Used for GHS Classification

Little Pro on 2017-02-02

M-factor stands for multiplying factor for substances that are highly toxic to aquatic environment (i.e, LC50 or EC50<1mg/L). When classifying a substance as acute aquatic toxicity category 1 or chronic aquatic toxicity category 1 under GHS, it is usually necessary to indicate an appropriate M-factor (Note: This is mandatory under EU CLP regulation) . The purpose of applying M-factor is to give an increased weight to highly toxic components when classifying a mixture. In this article, we will show you how to use M-factor for mixture environmental hazard classification and how to assign M-factor.

GHS Classification Criteria for Aquatic Environment

The picture below shows you the aquatic environmental hazard classification criteria for a substance. Lower LC50/EC50/NOEC indicates higher toxicity. Please note that degradation and bio-concentration shall also be taken into account.

GHS classification criteria environmental hazard

When classifying a mixture containing multiple components, we will need to start using M-factor. M-factor is also important for determining whether a mixture belongs to marine pollutant or not.

How to Use M-factor for Environmental Hazard Classification

The picture below shows you how to classify a mixture for its environmental hazard by using M-factor. For any component classified as ‘Acute Category 1’ or ‘Chronic Category 1’, its presence has to be taken into account if its concentration >= (0.1/M-factor) %.

GHS mixture classification enviromental hazard

How to Assign M-factor

The value of multiplying factor (M-factor) for a substance can be assigned according to the table below:

GHS M-factor

2 M-factors for 1 Substance?

In the annex VI to CLP regulation (EU's harmonised substance classification list), you may find 1 or 2 M-factors for some substances (see example below). This is because M-factors can be assigned to Aquatic Acute 1 or Aquatic Chronic 1 or both. The M-factors for Aquatic Acute 1 and Aquatic Chronic 1 do not have to be the same.

2 M-factors 1 substance

Where no M-factor is listed in the Annex VI to CLP regulation, M-factor(s) based on available data for the substance shall be set by the manufacturer, importer or downstream user. 

Reference and More Reading

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