Chitosan/Tripolyphosphate Nanoparticles Encapsulating Essential Oils as a New Class of Biopesticides: Structural Properties and Ecotoxicity Evaluation

Essential oils (EO) are fragrant, hydrophobic natural products derived from aromatic and medicinal plants that can be highly sensitive to environmental conditions. Nanoencapsulation offers a promising solution to overcome environmental degradation by abiotic factors. In this work, ionic gelation was employed to synthesize formulations of EO extracted from Satureja montana, Thymus vulgaris, Anethum graveolens, and Coriandrum sativum encapsulated in chitosan/TPP (tripolyphosphate) nanoparticles. Despite their potential as biopesticides, ecotoxicological aspects have not been much explored. Herein, aquatic (Aliivibrio fisheri, Raphidocelis subcapitata, Lemna minor, and Daphnia magna) and terrestrial (Folsomia candida and soil microbial activity) non-target organisms were used to assess the environmental impact of the EO encapsulated in chitosan/TPP nanoparticles. The chitosan nanoparticles had a positive charge, high homogeneity (PDI < 0.2), an average size of about 200 nm, and showed encapsulation efficiencies between 82% and 98%. Regarding hazard assessment, EO in their free form can cause toxic effects, even though they are prone to degradation by environmental factors. Encapsulation into chitosan/TPP nanoparticles resulted in a significant reduction of the essential oils' toxic profile. Overall, the observed toxicity comes mainly from the EO activity toward the aquatic test species. By reducing the ecotoxicity of EO toward non-target species (except for collembolans), the nanoformulations proved a promising solution to be explored as biopesticides, aiming to replace the use of synthetic pesticides. Only the nanoencapsulated C. sativum EO caused an inhibitory effect on nitrogen mineralization and arylsulfatase activity. Moreover, enhancing our understanding of the ecotoxicological impact of nanobiopesticides is essential before recommending their use in crop protection.