Transition-state rate theory sheds light on ‘black-box’ biodegradation algorithms

Abstract

Biodegradation is a predominant removal mechanism for organic pollutants in the aquatic and terrestrial environment and needs to be determined to design ‘green chemicals’ amongst an increasingly large set of industrial chemicals. Decades of research have been dedicated to producing biodegradation models, though improving those models has become problematic due to ‘black box’ models driven by incomparable or conflicting experimental results. In this study, we tested the plausibility and applicability of an intuitive algebraic formula stemming from transition-state rate theory. The formula is overarching, describing the pseudo first-order biodegradation rate constant in terms of computationally easily obtainable electronic, steric/geometrical, energetic and thermodynamic properties. Surprisingly, statistical evaluation using experimental data shows that the formula performs equal to or better than established ‘black-box’ models. We interpret the properties used, highlight the precise (inter)dependencies and discuss reaction- and diffusion-limiting mechanisms. Altogether, the work shows the potential to improve our understanding of biodegradation via ‘first principles’: it helps to unravel the causal mechanisms of the chemical fate in complex matrices. Amongst potential ramifications, this will enable a more precise and comprehensive environmental risk assessment.