Every time you wash your hands, flush a toilet, or run a washing machine, the water carries a cocktail of chemicals on a journey that often ends in the ocean. Understanding this pathway is crucial to addressing chemical pollution at its source.
The Household Source
An average household sends dozens of chemicals down the drain daily: detergents, cosmetics, cleaning products, food waste, and pharmaceuticals. A single shower can introduce microplastics from body scrubs, parabens from shampoo, and triclosan from antibacterial soap.
The Treatment Plant
Wastewater treatment plants are engineering marvels designed to remove organic matter, nutrients, and pathogens. Most use a three-stage process: primary (physical settling), secondary (biological treatment), and sometimes tertiary (advanced filtration).
However, these plants were designed in an era before CECs were understood. While they effectively remove traditional pollutants, they struggle with modern synthetic chemicals. Studies show that 30–70% of pharmaceuticals pass through treatment largely unchanged.
Into the Environment
Treated wastewater — called effluent — is discharged into rivers, estuaries, and coastal waters. In many coastal cities, it flows directly into the ocean. During heavy rainfall, combined sewer systems can overflow, releasing untreated sewage directly into waterways.
The chemicals in effluent don't stay put. Ocean currents distribute them globally. PFAS from European factories have been detected in Antarctic wildlife. Pharmaceuticals from Asian cities appear in Pacific fish populations.
Emerging Solutions
Advanced treatment technologies like activated carbon filtration, ozonation, and membrane bioreactors can remove many CECs. Switzerland has mandated that major treatment plants install such systems. The EU is developing similar requirements through its revised Urban Wastewater Treatment Directive.
Nature-based solutions like constructed wetlands and reed beds also show promise, using natural biological processes to break down certain pollutants.
What You Can Do
Reduce the chemicals entering the system in the first place. Use eco-labelled cleaning products, never flush medicines, install a washing machine microplastic filter, and support investment in wastewater infrastructure.
This article is part of the CONTRAST project, funded by the European Union under Horizon Europe. Views expressed are those of the author(s) only.