Open Access

Glyphosate-based herbicides were used as plant protection product globally for several decades. However, glyphosate is discussed as showing genotoxicity and many other side-effects such as inhibiting the mitochondrial succinate dehydrogenase, leading to a decreased ATP production. Therefore, finding alternative active substances is necessary. Pelargonic acid (nonanoic acid) and its ammonium salt (saponified form), which are used as alternatives to glyphosate-based herbicides, are biological derived substances considered as environmentally friendly herbicides. To test the effects of pelargonic acid in its acidic form (active substance in TopGun) and its saponified form (in Finalsan Plus) on the aquatic ecosystem, students of the master study program “environmental management and ecotoxicology” compared the toxicity levels of these substances using zebrafish embryos within the scope of a student research course. The project was developed by applying the 7-step problem-based learning method which allowed the students to design their experiments independently with the guidance and feedback of the lecturers. Acute toxicity was determined according to OECD test guideline 236 in D. rerio which revealed a LC50 of 1.55 mg/L of pelargonic acid, a LC50 value of 0.93 mg/L pelargonic acid in TopGun and a LC50 of 36.37 mg/L of Finalsan Plus. Neutral Red Uptake assays were performed on the rainbow trout-derived gill cell-line RTgill-W1 to determine the acute toxicity according to the OECD test guideline 129 which revealed the IC50 value of 12.4 mg/L pelargonic acid in TG. Due to solubility limits, no reliable IC50 could be obtained. The results of the tests indicate differences in the acute toxicity of the pelargonic acid-based formulations TopGun and Finalsan Plus. However, more investigations have to be done in order to analyse if the acidic form is more toxic than the saponified form. Furthermore, detailed ecotoxicological risk assessments and an evaluation of the genotoxicity of both herbicides has to be performed before any conclusion can be drawn. Financial support from the City of Vienna project PBL in Molecular Life Science (21-06) is gratefully acknowledged.