Which method do many pharmaceuticals enter freshwater ecosystems?
Many pharmaceuticals are consumed, incompletely metabolised, and excreted in urine or faeces. Sewer systems carry the parent compounds and active metabolites to treatment plants, where conventional processes may not remove them completely; treated effluent or untreated sewage then reaches rivers and lakes. Improper disposal can add to this route. Aerosols, fertilisers, and forest runoff are not the dominant general pathway. Because conventional polymers persist, fragmentation redistributes plastic into smaller pieces rather than removing its mass from the ecosystem. Trophic transfer can occur
Ref: Campbell Biology, Urry et al., 12th Ed., Unit 8 Ecology