RIVM has derived surface water risk limits for 18 active substances in pesticides. The Ministry of Infrastructure and Water Management can use these risk limits as a basis to establish water quality standards. Evidence suggests that existing standards for some of these substances do not sufficiently protect the ecosystem. For others, no standards exist yet or the existing standards are outdated. If these pesticide residues end up in surface water, they can have harmful effects on nature.

Pesticides contain hazardous substances

RIVM derives environmental risk limits for a large number of chemical substances. This study looked at 18 active substances in pesticides, which are used to protect crops against weeds, disease and pests (plant protection products). Residues of these substances can reach surface water directly or percolate through the soil. In this way, they can contaminate water in the vicinity of farmland. If concentrations of these substances in surface water exceed the risk limits, harmful effects on nature may occur.

Some substances are difficult to measure

In six cases, the new risk limits are lower than the existing water quality standards. These risk limits have been revised because the methodology for risk limit derivation has improved. In addition, more data about these substances have become available. For seven substances, risk limits have been derived for the first time. More than half of the 18 substances cannot be adequately measured in surface water using common analytical methods. This makes it impossible to check compliance with the risk limits, although they can be harmful even in small quantities. However, additional or more extensive analysis – for instance by analysing larger volumes of water – may result in lower detection limits.

Some substances may need to be substituted

The European Union has designated a number of these 18 active substances as ‘candidates for substitution’. These are substances with undesirable properties, namely that they are persistent (do not break down in the environment), bioaccumulative (are present in ever greater concentrations) and toxic – PBT for short. The use of PBT substances as active substances in pesticides is forbidden in the EU. Substances having a combination of two such properties should be substituted with safe alternatives, if possible.

Exposure limits are recommended levels

The risk limits defined in this study are advisory values. The Ministry of Infrastructure and Water Management can use them as a basis to establish surface water quality standards. Based on these standards, water managers can make an initial assessment of whether substances detected in their area are cause for concern.