A novel herbicide formulation to reduce the environmental impact of agrochemicals

The use of pesticides is essential for yield optimization in agriculture. However, uncontrolled use can cause serious damage to the environment, as well as drawbacks on human health. The consequences of many pesticides on bees and butterflies due to its high volatilization and on microorganisms of the soil are also known. These adverse consequences are more pronounced in the case of herbicides because of their broad use. The aim of this thesis is to develop a novel formulation of a broadly used herbicide, namely Dicamba, with reduced environmental impact compared to formulations nowadays available on market and evaluate its potential spreading in the subsurface environment. Dicamba is an auxin herbicide and can be used to treat several crops against broadleaf weeds. The high selectivity to many varieties and the great efficacy in weeds’ control are the advantages of using this herbicide compared to others. The novel formulation wants to overcome the problems of Dicamba’s volatility, high mobility in soil and solubility in water with risk of runoff and leaching. A reduced volatility and mobility in soil and water is expected. The thesis was performed in the framework of the Nanograss project, co-funded by Compagnia di Sanpaolo, and a patent application will be submitted in the next months. The developed herbicide formulation is based on the use of four different nano-sized carriers, constituted by low-cost and harmless components naturally present in the subsoil. The use of a protective coating of the herbicide-loaded carriers with biodegradable polymers has been tested to reduce the release of the incorporated active substance, avoiding its runoff and volatilization. Firstly, the candidate carriers were characterized in size and surface charge (zeta potential); sedimentation tests were carried out to evaluate their propensity to form a stable colloidal dispersion, suitable for the dispersion in field using conventional systems. Loading tests were performed to identify those carriers and loading conditions that guarantee the higher amount of herbicide incorporated. FTIR analysis was used to understand the nature of the Dicamba incorporation in the carrier. Release tests were then performed on all suspensions to evaluate the herbicide’s release as a function of time, mimicking dilution of the formulation in field application. The best formulation in terms of adsorption and release was used in column transport tests to evaluate its mobility in groundwater. The results were compared to similar tests carried out with the pure active ingredient and a commercial product. The new nano-herbicide presented a low mobility in column tests compared both to pure Dicamba and its commercial formulation: for the nano-herbicide, a maximum outlet concentration equal to 8.2% of the injected one was obtained, compared to almost 100% from both the commercial product and the pure herbicide. The nano-herbicide turned out to be the more environmental-friendly formulation, that could allow a strong reduction in groundwater contamination. In conclusion, the experimental results indicate that for the novel formulation the amount of free herbicide in water and its mobility in porous media are both significantly reduced, compared to classical Dicamba’s based products. These promising findings suggest that, in field-scale applications, it can help reducing volatilization and leaching in groundwater, overcoming the principal environmental drawbacks of Dicamba.