International Ring Test on the Effects of Chemicals on the Symbiotic and Pre-symbiotic Phases of Arbuscular Mycorrhizal Fungi - Potential for Risk Assessment of Plant Protection Products

Ecological relevance of arbuscular mycorrhizal fungi (AMF) led the European Food Safety Authority (EFSA) to identify AMF as a potential group of non-target in-soil organisms to be included in environmental risk assessment (ERA) of plant protection products (PPPs). Currently, no OECD test guidelines including AMF exist, and technical specification standard documents are limited to ISO/TS 10832:2009 for pre-symbiotic phase testing and AFNOR FDX31-205-2 for symbiotic phase testing. A new methodology was developed to assess the effects of contaminants on the AMF-plant symbiosis and the method described in the ISO/TS document was updated with new methodologies and test conditions. A ring test involving nine laboratories for symbiotic-phase experiments and six laboratories for pre-symbiotic-phase experiments was performed to assess the validity of these methods using Rhizophagus irregularis, artificial soil and two fungicides (Azoxystrobin and Fluazinam). Allium ampeloprasum was the host plant used in the symbiotic phase tests. Endpoints estimated during the ring test were variable: 8-week EC10 for total colonization in the symbiotic phase varied from 0.1 to 5 mg/kg of soil for Azoxystrobin (coefficient of variation (CV)=123.5%) and 0.03 to 7.8 mg/kg for Fluazinam (CV = 185.9%); in the pre-symbiotic phase, 14-day EC10 for spore germination with Fluazinam was 0.6 mg/kg of soil and for Azoxystrobin 0.4 and 1.4 mg/kg of soil (CV = 78.6%). The outcome of the ring test suggests a potential sensitivity of AMF but the high data variability and the fact that the validity criteria are frequently not met indicate that further development of the test system is needed. Nevertheless, comparisons between these data and data from published studies suggest that AMF may be more sensitive than other non-target soil organisms currently considered in EU ERA, particularly for Azoxystrobin. Consequently, current ERA procedures may not provide sufficient protection for AMF communities, but additional data are needed to confirm this assumption.