Extrapolation across plant species and endpoints in tiered risk assessment frameworks: are lower tier species and endpoints always protective?

Ecological effect assessment for pesticides typically relies on the testing of standard test species in the 1st Tier of the risk assessment. Other species and endpoints, different from the standard ones, are protected by the application of assessment factors. In the EU, pesticide effect assessment follows a tiered approach. Ideally, higher tiers are more realistic and less conservative than higher tiers. For a few, data-rich herbicides, enough data are available to test the protectiveness of the lower tiers for the higher tiers in current regulatory frameworks. The available data indicate that the Tier 1 effect values and Regulatory Acceptable Concentrations are not always protective for Hazard Concentrations deduced from a range of species and endpoints as assessed by means of the Species Sensitivity Distribution (SSD) method. This is especially the case when Tier 1 is not based upon the most sensitive species, e.g. when a sediment-rooted macrophyte is more sensitive than the standard floating test species Lemna spp. This is the case for specific Modes of Action. If in that case the effect value for the sediment-rooted Myriophyllum spicatum is considered with a safety factor, this value is protective for effects on other submerged macrophytes. Also in the case of photosynthesis inhibitors, while plants exhibit a comparable range in sensitivity based on inhibition of photosynthesis, the standard Tier 1 species are not always protective for other species and endpoints. In general, hazardous concentrations from species distributions were below population and community NOEC values from mesocosm studies, although differences were sometimes small. Laboratory toxicity tests with rooted macrophytes, as well as SSDs based on these toxicity data, are sensitive tools in the risk assessment.