Radical formation by copper application in agriculturally relevant clay-rich soils and its ecotoxicological consequences

• Applicant: Dr. Jonas Fischer
• Subject Area: Soil Sciences ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553620826

Sustainable agriculture operates in a field of tension between productivity and preserving soil health. Copper is widely applied as fungicide and fertilizer, but has negative impact on soil biota. Copper toxicity usually is explained by soil adsorption and uptake by organisms, but the possibility of other toxic pathways, e.g. radical formation is not yet considered. The relevance of radicals was previously shown in our studies, where copper-based nanoparticles were harmful to soil organisms at very low, field-realistic concentrations, including reactions in the antioxidative system. Surprisingly, this was only the case for highly-adsorbing clay-rich soils, which are very relevant for agriculture. Copper and clay combined in soils have the ability to form reactive oxygen species (ROS) or to transform widespread polyaromatic pollutants into environmental persistent free radicals (EPFRs), which can have negative consequences for soil biota, but also human health. The formation of these radicals is based on electron transfer processes in which transition metals such as copper or iron (especially nano-sized), clay minerals and organic matter serve as a source and/or transporter of excess electrons. All of these substance groups are naturally occurring in the soil, but also introduced by agricultural activities. In this project, I will combine multiple representative substance groups simulating an agricultural soil system and being relevant for radical formation. The radical-forming potential of both natural and anthropogenic substances alone and in combination will be identified, i.e. different types of clay and iron minerals, organic matter and anthropogenic copper. Radical formation will be investigated chemically, measuring ROS and EPFR formation in artificial soil solutions and soils, but also biochemically and ecologically by the antioxidative and fitness response of springtails (Folsomia candida). To transfer the lab results to the field, the factors that were identified being most striking in the lab will be used to identify potential radical forming hotspots in the field; hereby, podsols will be compared with fluvisols (more fluctuating redox conditions due to their proximity to rivers) with respect to the correlation between their soil properties and ROS and EPFR occurrence. Identifying the soil factors for radical formation in the lab and in the field will have implications for soil protection, risk assessment of nanopesticides and agricultural management and will enable direct recommendations for soil sustainability.

• DFG Programme: Research Grants