Risk assessment of fungicides on symbiotic phase of arbuscular mycorrhizal fungi

The widespread use of plant protection products (PPPs) may lead to soil contamination, potentially compromising the symbiotic integrity of arbuscular mycorrhizal fungi (AMF) in agricultural systems. However, the effects of PPPs on AMF are underexplored due to the absence of standardized methodology for ecotoxicological assessments. The objective of this study was to introduce an in vivo method for assessing the effects of PPP pollutants on the AMF symbiotic phase and to evaluate the suitability of this method as an intermediate-tier protocol in risk assessment frameworks. Four tests were conducted using combinations of: (1) Gigaspora albida + Glycine max; (2) G. albida + Urochloa brizantha; (3) Rhizophagus clarus + G. max; (4) R. clarus + U. brizantha). All assays were performed in tropical artificial soil (TAS) under a gradient of chlorothalonil concentrations (0, 12, 18, 24, 36, 48, and 72 mg a.i. kg⁻1). The evaluated endpoints included total root colonization, percentage of arbuscules colonization, total extraradical mycelial length (ERM), and spore number. All endpoints were sensitive to the presence of PPPs in TAS, with mycorrhizal colonization and ERM being the most sensitive, meeting the validity criteria (CV < 30%). The Inhibitory concentration (IC50) values for all endpoints were higher than the predicted environmental concentrations (PECs). Therefore, this method can be considered suitable as an intermediate-tier protocol, as it exhibits key characteristics of a standardized approach and can be applied to ecotoxicological studies involving other potentially contaminating PPPs, as well as additional classes of environmental contaminants.