There are always multiple chemicals simultaneously present in the environment. It is therefore of importance to assess the combined effects of co-occurring chemicals. Current risk assessment practices under the European chemicals regulation (REACH) however insufficiently consider these effects. REACH stipulates that companies that produce, process or pass on substances to customers have to draw up an inventory of the risks and must recommend measures for controlling those risks.

Mixture Assessment Factor

RIVM suggests a data-driven Mixture Assessment Factor (MAF) as one approach to address combined effects of chemicals at European level. This factor explicates the number of chemicals one should take into account to assess the safety of a single substance. How this may work is illustrated for the assessment of risks of substances in water. Introduction of the MAF aims to ensure that, after emission to water, the substance together with all other chemicals present causes no combined environmental risk. This is in line with the existing national approach in the Netherlands.

In addition to this generic EU European Union (European Union )-wide approach, it is possible to consider further protective and curative measures on a site-specific basis. Such a local or national approach can sometimes be more efficient.

The current thought starter does not address combined effects in soil and air, nor the assessment of effects on humans. This may be topic of further work.