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Overzicht van recente literatuur over mengseltoxiciteit van bestrijdingsmiddelen voor waterorganismen

Review of recent literature concerning mixture toxicity of pesticides to aquatic organisms

Synopsis

The simplest way to assess the effects of mixtures of pesticides is to add the effects of the individual substances to each other (concentration addition). In general, experiments show that substances do not enhance each other's action (no synergism). If there is still an enhanced effect, this will usually be small. Therefore, the concept of concentration addition is useful to estimate the adverse effects of mixtures of pesticides. This was concluded on the basis of a review of recent literature concerning the toxicity of mixtures of pesticides that was carried out by RIVM, together with the research institute Alterra. This inventory is an update from an analysis from 2000 and it confirms its conclusions. As a client, the ministry of VROM wanted to map out which new developments in the field of assessing the effects of pesticide mixtures are of importance. Therefore, the study also describes the methodological improvements that can refine the risk assessment of mixtures. It is now possible to determine the effects of substances when they are used consecutively instead of simultaneously. This concept is relevant for pesticides because these substances are often used in succession. Further, the so-called species sensitivity distributions are now also applicable to mixtures of substances. These species sensitivity distributions describe the variation to which a group of different organisms is sensitive to the effects of substances. On the basis of these distributions, it is determined what concentrations are safe for the environment. For this method, however, a lot of data are required about the adverse effects of substances on organisms, which are usually not available. So-called mesocosm studies, in which ecosystems are simulated in laboratories, show that synergetic effects are not to be expected if pesticides are used for the same biological groups, such as plants or insects. If several pesticides are applied for different biological groups, indirect effects that enhance each other are often noted, that is in the next level of the food web. When the practical application of pesticides for a particular crop is mimicked, the effects are mostly no larger than those of the most toxic substance. In that situation, enhanced effects are also not observed.
 

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