Contaminant Classes, Sources, and Pathways in Freshwater Environments

Freshwater environments are increasingly impacted by a diverse array of chemical contaminants, many of which pose significant ecological and human health risks. This chapter categorizes major contaminant classes – including persistent organic pollutants, heavy metals, nutrients, pesticides, pharmaceuticals and personal care products, microplastics, and emerging contaminants – highlighting their physicochemical properties, environmental persistence, and modes of toxicity. It explores both point and non-point sources of pollution, such as industrial effluents, agricultural runoff, municipal wastewater, atmospheric deposition, and urban stormwater. Central to the discussion are the environmental pathways, through which contaminants are transported, transformed, and bioavailable within aquatic systems, including surface runoff, groundwater infiltration, atmospheric deposition, sediment resuspension, and trophic transfer. Special attention is given to interactions between contaminants and environmental matrices, as well as to the role of hydrological and climatic factors in modulating their fate and behavior. The chapter underscores the complexity of contaminant dynamics and the need for integrated monitoring and management strategies aligned with the One Health framework.