Out of Sight – The Insufficiency of the Phase I Action Limit in Veterinary Early Impact Assessment

Abstract

The VICH GL 6 guideline outlines a tiered assessment scheme that is mandatory for all active substances (AS) used in veterinary medicines before they enter the market. As the first step, the predicted environmental concentration of the AS in question is compared to a so-called “action limit” of 100 μg/kg for soil. If this action limit is exceeded, an extended environmental risk assessment is required. This limit is currently based on data that were recorded between 1973 and 1997 in the USA. Since then, new active ingredients with higher efficacy (and, therefore, potential environmental impacts at lower concentrations) have been developed and put on the market. This consequently elevates the probability of environmental and organismic impact, which in turn affects biodiversity and, ultimately, the natural functioning of ecosystems. A critical evaluation of the action limit is therefore necessary. Does it still serve its purpose as a precautionary decision criterion on whether an experimental Phase II risk assessment must be conducted? To assess the protectiveness of the soil action limit of 100 µg/kg, we evaluated 82 tests (34 plant and 48 earthworm tests) for 18 parasiticides, 28 antibiotic and 5 other AS, using data from European Medicines Agencies Public Assessment Reports, supplemented by internal data of the German Environment Agency. We included parasiticides in the data evaluation, although the action limit does not apply here, as their environmental hazard is determined by their toxicity to insects. Tests between model predictions reveal no difference between models with and without parasiticides (with parasiticides n = 51, without parasiticides n = 33). For each AS, we included the lowest available NOEC/EC10 and fitted a sigmoidal non-linear least squares model in the range of [0,1]. 18±5 % of the NOECs/EC10 values are below 100 µg/kg soil. This reduces to 17±6 % if only non- parasiticides are included in the data analysis. A total of 11 substances are below or equal to the action limit, 7 antibiotics and 4 parasiticides. In order to ensure that the action limit covers approximately 95 % of AS currently on the market, a reduction from 100 to 5 µg/kg would be necessary. The analysis shows that the current action limit is insufficient to protect organisms and ecosystems. In future revisions of the guideline, it will be necessary to adapt the action limit to current scientific standards.