The influence of drinking water constituents on the level of microplastic release from plastic kettles

Microplastic (MP) release from household plastic products has become a global concern due to the high recorded levels of microplastic and the direct risk of human exposure. However, the most widely used MP measurement protocol, which involves the use of deionized (DI) water, fails to account for the ions and particles present in real drinking water. In this paper, the influence of typical ions (Ca2+/HCO3-, Fe3+, Cu2+) and particles (Fe2O3 particles) on MP release was systematically investigated by conducting a 100-day study using plastic kettles. Surprisingly, after 40 days, all ions resulted in a greater than 89.0% reduction in MP release while Fe2O3 particles showed no significant effect compared to the DI water control. The MP reduction efficiency ranking is Fe3+ ≈ Cu2+ > Ca2+/HCO3- > > Fe2O3 particles ≈ DI water. Physical and chemical characterization using SEM-EDX, AFM, XPS and Raman spectroscopy confirmed Ca2+/HCO3-, Cu2+ and Fe3+ ions are transformed into passivating films of CaCO3, CuO, and Fe2O3, respectively, which are barriers to MP release. In contrast, there was no film formed when the plastic was exposed to Fe2O3 particles. Studies also confirmed that films with different chemical compositions form naturally in kettles during real life due to the different ions present in local regional water supplies. All films identified in this study can substantially reduce the levels of MP release while withstanding the repeated adverse conditions associated with daily use. This study underscores the potential for regional variations in human MP exposure due to the substantial impact water constituents have on the formation of passivating film formation and the subsequent release of MPs.