In natural environments, organisms face anthropogenic stressors such as temperature changes, habitat alterations and pollution. Additionally, free-living organisms are often infected by parasites, which can alter their responses to pollutants. Conversely, parasites can also be affected by these pollutants. The interactions between parasites and pollutants are diverse, leading to the development of the field of environmental parasitology over the past 30 years. Today, the field has expanded to investigate a wide range of anthropogenic stressors and their interactions with parasites, including their combined effects on host health. Environmental parasitology also explores the use of parasites as indicators of pollutants and other environmental changes. This chapter focuses on pollutants as major anthropogenic stressors in aquatic ecosystems. Each pollutant has specific properties that determine its toxicity through the phases of exposure, toxicokinetics and toxicodynamics, all of which can be influenced by parasites. The chapter provides an overview of pollutant effects on parasites and their life cycles, combined effects on hosts and subsequent consequences for populations and communities. It also discusses the ecotoxicological perspective, summarising how parasites can modulate toxicity assessments and serve as indicator organisms.