Are micro-/mesocosm studies really not suitable for the risk assessment of plant protection products? A comment on Reiber et al. (2022)

Abstract Background A recently published article, by Reiber et al., on the representativity of macroinvertebrate communities in outdoor micro- or mesocosm studies, used as a higher tier tool in the environmental risk assessment of plant protection products (PPPs) in the EU, concluded that ‘micro-/mesocosm studies do not represent natural macroinvertebrate communities’. Fundamentally, the article based its conclusion on the analysis of data from 26 streams used in a monitoring project in Germany (2018–2019), in comparison to taxa found in seven lentic micro- and mesocosm studies, conducted at four test sites (2013 – 2018), and submitted to the UBA, Germany. Results There are multiple reasons why this conclusion is incorrect, e.g. the number of taxa, for which the Minimum Detectable Differences (MDDs) were low enough to allow a detection of direct effects in the seven lentic mesocosm studies, cannot be compared to the number of taxa just present in at least five of 26 streams. We have further investigated the data from five of the seven studies which were analysed in detail by Reiber et al. and determined that the MDDs of 12 to 18 invertebrate taxa per study fulfilled the current recommendation to allow a detection of medium effects (MDD up to 70%). However, which taxa can be considered potentially sensitive depends on the specific test item. While lentic test systems may not be suitable to test effects on typical stream taxa, taxa occurring in lentic systems such as ponds and ditches are not by definition less sensitive, or vulnerable, to pesticides than taxa living in streams, and their relative sensitivity can be checked in laboratory tests, or artificial streams, if needed. Conclusions In our view, well conducted micro- and mesocosm studies do provide reliable and useful data for the environmental risk assessment of plant protection products covering long-term, as well as indirect, effects under semi-natural conditions.