The spore germination test (ISO 10832) with <i>Funneliformis mosseae</i> for use in an environmental risk assessment for chemicals—necessary adaptations and exemplary testing

Mycorrhizal fungi play a fundamental role in terrestrial ecosystems. Through the root symbiosis they form with about 80% of all terrestrial plants, they contribute to multiple ecosystem services like e.g. nutrient exchange or pest control. However, ecotoxicological studies have shown that arbuscular mycorrhizal fungi (AMF) are sensitive to chemicals. It is therefore crucial to consider these key organisms in an environmental risk assessment (ERA), especially as the European Food Safety Authority (EFSA) has proposed the inclusion of AMF as test organisms for future ERA. Our aim was to determine the effect of various pesticides, a veterinary pharmaceutical and a biocide using the spore germination test (ISO 10832) with Funneliformis mosseae, to compare the results with the currently in ERA used Nitrogen(N)-transformation test (OECD 216), and to evaluate the potential use of the spore germination test for future ERA. Furthermore, recommendations for a revision of the ISO 10832 were elaborated, aiming to use natural soils as an alternative to artificial soil. Evaluation of the spore germination test revealed a significant and higher sensitivity, compared to the results of the N-transformation test for the three tested substances ethofumesate, pyraclostrobin and tiamulin hydrogen fumarate. A reduced maximum water holding capacity (WHCmax) to 50%, compared to the recommended WHCmax of 90% according to ISO 10832, led to a sufficient germination rate of F. mosseae in natural soil. Additionally, pH plays an important role for germination; when using natural soils with a pH below 5.5, a sufficient spore germination of 75% could not be reached. If WHC is reduced and a pH of above 5.5 is tested, the established germination test with F. mosseae is suitable for testing different substances in natural soils and could be a valuable addition to the current ERA for chemicals like pesticides, veterinary pharmaceuticals or biocides.