Transport in porous media of sulfur micro- and nanoparticles used as fungicide in organic agriculture

The continuous increase in food demand brings with it several questions, such as how to cope with food production in an ever-shrinking space, what technologies to use and in which way. Humans have not always addressed these questions with the best of techniques or with the appropriate foresight in considering the consequences for the environment. At a time when natural resources are not enough to satisfy an ever-growing population, it is therefore necessary to find solutions by acting on several fronts such as agriculture, climate, and geopolitical relations, which are inescapably interconnected. The need to find new technological solutions for a more sustainable and productive agriculture leads to the application of micro-nanotechnologies in the food production sector. Research affirms that nanoparticles have better potential than conventional pesticides for both the efficacy in yield and crop protection and the environmental protection. In this context, micro- and nanosulfur pesticides are collocated. This thesis aims to evaluate different S-based commercial and non-commercial colloidal suspensions currently applied or candidate to the application in crop protection as fungicides, particularly in organic farming. Among the open questions associated to their use ¿ including interactions with plants and pests, potential accumulation in plant tissues and in fruits, and environmental fate ¿ this thesis aims at gather a better understanding of how such particles may be transported in soils and ultimately in groundwater. After their application to crops, rain events or intense irrigation may flush particles away from leaves and in general the aerial part of the plants, and vehiculate them through soil and in the subsurface environment. This thesis analyzes five micro/nanosulphur commercial or near-to-market products. As a first step the particles were characterized in size, morphology, surface charge and optical properties using SEM, DLS, disk centrifuge and UV-vis spectrophotometry. Then, column transport tests were performed in saturated porous media to investigate the main transport mechanisms and identify the condition that may promote their mobility in the subsurface, with specific reference to aquifer systems. The results show in general an average good mobility of the particles through the saturated porous media, even though their transport is significantly affected by their peculiar characteristics (size and surface charge in particular). As a perspective, more insight analysis should be carried on particle transport in unsaturated soils, exploring the entire path from the plant to the aquifer, thus understanding the potential environmental fate of these new nanomaterials before their extensive release in the market. This thesis was carried out in collaboration with Aukland University.