Environmental fate and ecotoxicological impact of leptospermone a natural β-triketone herbicide in soils

Most agricultural production relies on the use of chemicals to maintain high crop yields. The use of these chemicals in farming practices is viewed as an integral part of the success of the intensive farming. However, most of the pesticides applied to agricultural lands may affect non-target organisms and contaminate soil and water media. Increasing public concern about the impact of pesticides on the environment, and European legislation has led to develop some strategies to evaluate and to prevent the potential impacts of different land management practices. In this context, new generations of less environmentally dangerous molecules, such as lower impact pesticides, biopesticides and natural product-based pesticides have been introduced. Despite this, a lot of work has to be carried out to evaluate the possible risks and adverse effects of such compounds on environment and humans. In the frame of the TRICETOX project, we study the β-triketone herbicide family, a post-emergence maize selective herbicides belonging to this new generation of molecules. Inside this family, we focus on leptospermone, an allelopathic compound isolated from the bottlebrush plant Callistemon citrinus. Since few data are available for this molecule, we want to gain new insights by addressing its soil behaviour, by studying its impact on soil microbial communities with microcosm studies, by studying its biodegradation pathways and by testing its toxicity. Then, multidisciplinary approaches were applied to assess the fate and impact of leptospermone to know if this natural product could be a good alternative as synthetic herbicides in weed treatment.[br/] Our results showed that leptospermone has a similar behaviour in soil compared to the synthetic β-triketone herbicides. Interestingly, this natural compound exhibits a 10 fold lower toxicity, determined with Microtoxâ than the synthetic counterparts. Although leptospermone was rapidly dissipated from soil, mainly controlled by biotic degradation, this natural product has a significant ecotoxicological impact on the abundance and diversity of soil bacterial community. This ecotoxicological impact was transient and when leptospermone was fully dissipated, the bacterial community recovered its composition and diversity. However, the recovery cannot be reached in soil microcosms where leptospermone remained. Identification of a bacterial isolate with leptospermone degrading capacities is in progress