Comprehensive modeling of agrochemicals biodegradation in soil: A multidisciplinary approach to make informed choices to protect human health and the environment

Abstract

Numerical models are used to predict the dynamics of potentially hazardous pesticides in soil. Those models may account for fundamental processes affecting pesticide dynamics, such as environmental and edaphic conditions, water flow, degradation, and sorption. However, those models lack the ability to account for complex biogeochemical and ecological feedbacks, and thus create challenges in achieving robust predictions. In particular, no attention has been paid on the coupled mechanistic description of microbial dynamics and soil organic matter cycling and the implications on agrochemicals biodegradation and soil and groundwater quality. This thesis aims to provide this description by developing a comprehensive framework through a multidisciplinary approach. Microbiological regulation of pesticide dynamics was investigated by coupling theoretical and numerical approaches with experiments carried out in our environmental laboratory or sourced from the literature. We propose the use of reaction networks to highlight the possibly multiple pesticide degradation pathways and the feedbacks with macronutrient cycles. Biochemically-similar pathways are mediated by a specific microbial functional group, which represents the microbial community carrying out particular functions; these functions are biodegradation of pesticides and metabolism of carbon-, nitrogen-, and phosphorus-containing molecules. We describe biochemical reactions by means of Michaelis-Menten-Monod (MMM) kinetics. Indeed, MMM parameters fully encompass the microbial life strategies including rapid growth, high affinity for substrates, or high substrate consumption efficiency. Michaelis-Menten terms allow us to include microbial competition for substrates, growth inhibition, and the memory-associated catabolite repression herein presented. Finally, the relevance of the described processes was quantified by means of sensitivity analyses. The latter are crucial to explore the range of likely outcomes under a suite of scenarios, thus allowing one to make informed choices. Agrochemicals are accumulating in soil and water resources worldwide. The proposed high-level process coupling approach is urged to develop sustainable plans in accordance with Nature-based strategies to cope with environmental changes.