Key issues about the future GD on NTTPs risk assessment
Non-Target Terrestrial Plants (NTTPs), being primary producers, play a key role in the ecosystem.
In the framework of the use of plant protection products, NTTPs represent all the terrestrial plants growing outside the treated fields and all the plants, within the treated areas, not relevant to the intended use.
Concerning the toxicity as part of the risk assessment currently the species to be tested according to the OECD/EPA testing guidelines are mostly annual crop species unrepresentative of the non-crop species useful for the ecosystem as the wild plants. A critical aspect of the testing guidelines is that the trials are useful for the ecosystem as the wild plants. A critical aspect of the testing guidelines is that the trials ar performed on a limited number of life tages such as seedling and juvenile and the effects are assessed in the vegetative stage even if probably reproduction is the most sensitive one and the effects have to be measured on the whole life cycle. The visual assessment, the aboveground biomass and the height which are the endpoints measured according to the OECD/EPA guidelines, are less sensitive than the ones of the reproductive stage as flowering and seeds yield, it is very important to keep in mind that herbicides, by their nature, may adversely affect NTTPs just as other pesticides applied on soil are harmful to the roots system.
Concerning the exposure as part of the risk assessment currently the spray drift is considered to be the major route of exposure for the off-field NTTPs but also the air transport and the dust drift, under certain conditions, can contribute considerably to the deposition outside the treated area. Exposure models concerning the spray drift and the air transport events are the key tools to predict the environmental concentrations as well as the FOCUS models on surface waters for the run-off events.
While the risk assessment for the substances with non-herbicidal activity is mainly based on the Tier I tests (screening at single dose), the risk assessment for herbicides or plant grow regulators uses Tier II tests (dose-response curves), and often the mitigation measurements are sufficient to prevent an higher tier evaluation with more realistic test conditions.
Tests on NTTPs are carried out with the formulation rather than the active substances and the degradation products/metabolites, potentially more toxic than the active substance, have to be tested apart.
To date there’s an ongoing debate about the number of species to be tested (from six to ten) but an approach based on different morphological, physiological and ecological features of the species as well as a species sensitivity distribution approach, used in the risk assessment for the aquatic organisms, could be the alternatives to be followed. Certainly the standard testing guidelines have to be reviewed and a guidance document on NTTPs has to be developed.