Evaluating the ecotoxicity of nitrification inhibitors using terrestrial and aquatic test organisms

Abstract Background The increasing demand for food and animal fodder worldwide has led to an intensified agriculture with an increasing use of nitrogen fertilizers. More recently, nitrate leaching and gaseous nitrogen emissions have become the focus of environmental discussions and climate politics. One approach to reduce such negative impacts is the use of nitrification inhibitors (NIs) that have shown to effectively reduce nitrogen losses to the groundwater and the air. However, ecotoxic effects of NIs have been studied to a limited extent only. Therefore, two commercial NIs (Piadin and Vizura) and an active ingredient of another NI, dicyandiamide (DCD), were assayed using various ecotoxicological biotests and test species: the Lemna Growth Inhibition Test (Lemna gibba), the Seed Germination/Root Elongation Toxicity Test (Agrostemma githago, Fagopyrum esculentum, Glycine max, Hordeum vulgare, Lunaria annua, Zea mays), the Seedling Emergence and Seedling Growth Test (A. githago, F. esculentum, Z. mays) and the marine Luminescent Bacteria Test (Aliivibrio fischeri). The fresh water L. gibba and the bacterium A. fischeri were exposed to different test concentrations in liquid growth media, whereas the terrestrial plants were exposed to the test substances diluted/dissolved in deionized water and added to the solid growth medium. Results Dicyandiamide did not show ecotoxic effects in any test conducted. Piadin and Vizura showed ecotoxic effects throughout all experiments. Frond number and frond area of L. gibba were inhibited with increasing concentrations of both substances with Piadin leading to an earlier inhibition and therefore lower EC50 values. In the Seed Germination Test, Vizura generally inhibited seed germination and root development more effectively than Piadin. Regarding both substances, the endpoint root length was much more sensitive than the endpoint germination. In the Seedling Emergence Test, Z. mays was the least sensitive and the rare weed species A. githago the most sensitive species with regard to the tested endpoints and both substances. A. fischeri was strongly inhibited by Vizura, whereas Piadin had barely effects on the bacteria. Conclusion All findings indicate ecotoxic effects of Piadin and Vizura, especially on the aquatic species L. gibba and on the root development of several terrestrial plant species. However, the origins of the ecotoxic properties remain unclear as both substances contain a mixture of—to some extent unknown—chemical compounds.