A holistic approach for the evaluation of iron nanoparticles on maize plants and earthworms in natural soil

There is a debate about the implications of the effect of nanoparticles or nanomaterials on edible plants and soil organisms. Earthworms have been used to evaluate soil quality, reproduction, survival, and other biochemical parameters when organisms are exposed to nanomaterials. Most studies have been performed in laboratory settings, and little has been studied under realistic conditions, especially when earthworms and corn plants share the same natural soil and organic matter space. The objective of this research was to evaluate concentrations of 10, 100, 200, 400, and 800 mg kg^-1 of iron nanoparticles (Fe NPs, combination of magnetite [Fe₃O₄] and hematite [α-Fe₂O₃]) on the growth and development of maize plants (Zea mays L.), and of the reproduction parameters of Eisenia fetida during 110 days of exposure. The results demonstrated that concentrations of 100 and 400 mg kg^-1 of Fe NPs positively changed some morphological, photosynthetic, and yield parameters in maize crops. Unexpectedly, concentrations of 400 and 800 mg kg^-1 decreased earthworm population but, at the same time, increased the number of juveniles. With this holistic approach experiment, it was demonstrated that the use of Fe nanoparticles as a biostimulant can promote corn yield parameters, but at the same time it impacts the reproductive capacity of the earthworms. However, it is necessary to explore the long-term effect of the proposed nanomaterials in agriculture to rule out risks or ecological implications in agricultural systems.