A Critical Review of Contaminant Intrusion and Dynamics of Herbicide Intrusion in Water Distribution Systems

Public health, infrastructural resilience, and drinking water quality are all persistently threatened by contaminant intrusion into Water Distribution Systems (WDSs). There is mounting evidence that herbicides and their by-products are intruding into Water Distribution Networks (WDNs) across the world. Consequently, owing to the intricate interactions that occur during the intrusion, their prediction and modelling are challenging. The research community has created reaction-transport models and advection-dispersion equations in response to these problems. These typically try to capture part of the reaction kinetics. Furthermore, some of these mathematical models have been integrated into simulation tools, utilising the EPANET software and its EPANET-MSX extension. They have been used in scenario-based simulation studies for demonstrating various interactions between the dynamic states of the parent herbicide compounds and their transformation products. The goal of this review paper is to briefly review the occurrence, mechanism, fate, and significance of pesticide transformation products (PTPs). A review of over 2-decade-and-a-half-long (2000–2026) of journal articles, conference proceedings, technical reports, and experimental, analytical, numerical, and field-based research on contaminant intrusion is presented in this publication. Importantly, this review identifies persistent gaps in the precise fate of herbicides after incursion events into WDS, including pipe material interactions, the impact of residual disinfectants, biofilm-mediated transformations, and hydraulic mixing/dilution effects, with parent chemical transformation into more toxic and persistent metabolites. The paper provides an overview of herbicides and PTPs as contaminants of emerging concern and discusses the modes of degradation of herbicides and pesticides, their properties and associated risks.