Theoretical Proposals for possible Hydrolytic and Photoinitiated Degradation pathways for Cyazofamid and Cymoxanil: Implications in Food Safety

The extensive use of pesticides in intensive agricultural systems offers improved yields and reduced post-harvest losses, however, the resulting environmental contamination effects due to gas-phase migration of such noxious compounds represent a real threat to human health and safety. Hence, a thorough density functional theoretical (DFT) study of the gas-phase hydrolytic and photolytic structural evolution was conducted for two popular fungicides: cyazofamid and cymoxanil. For both compounds, the two-step hydrolytic process is limited by the addition of water to the starting structure due to steric effects and low reactivity of electrophilic sites on their chemical structures. However, their photolytic/ photo-initiated transformations are limited by the ionization step (first step) which is slowest for cymoxanil. Overall, for the first time, comprehensive kinetic models for the gas-phase transformation of both fungicides are proposed, revealing an overall slower degradation process for cymoxanil and hence, greater potential for environmental contamination.