Investigation of heavy metals adsorbed on microplastics in drinking water and water resources of Zabol

This study investigates the presence and adsorption of heavy metals (HMs) on microplastics (MPs) in the drinking water and water resources of Zabol, Iran. Sampling was conducted at five stations in Zabol and two Chah-Nimeh reservoirs (CHWRs), the primary drinking water sources, using glass samplers and polyvinylidene fluoride membrane filters. Fourier-transform infrared spectroscopy, scanning electron microscopy, and optical microscopy identified MPs, while inductively coupled plasma optical emission spectrometry quantified heavy metals. Results revealed that polyethylene, polystyrene, polyamide, and polypropylene were the predominant polymers, with Fe, Mn, Zn, Cu, and Ni adsorbed on their surfaces. Iron (Fe) exhibited the highest concentration, reaching 84 µg.L⁻¹ in CHWRs and 85 µg.L⁻¹ in the distribution network. In CHWRs the highest percentage (61%) of size of MPs were between 500 and 1000 μm, while in water distribution network maximum range of obtained MPs were between 50 and 100 μm. The average concentration of the other detected heavy metals were as: zinc (Zn) 43.9 µg.L^{- 1} and 7.75 µg.L^{- 1}, manganese (Mn) 11.48 µg.L^{- 1} and 6.5 µg.L^{- 1}, arsenic (As) 20.22 µg.L^{- 1} and 0.26 µg.L^{- 1}, cadmium (Cd) 3.16 µg.L^{- 1} and 2.8 µg.L^{- 1}, copper (Cu) 15.18 µg.L^{- 1} and 0.03 µg.L^{- 1}, and nickel (Ni) 0.10 µg.L^{- 1} and 2.25 µg.L^{- 1} in distribution network and CHWRs, respectively. World Health Organization recommended the permissible limit of these cations in drinking water as 10 µg.L^{- 1} for As, 5 µg.L^{- 1} for Cd, 50 µg.L^{- 1} for Cr, 20 µg.L^{- 1} for Ni, 10 µg.L^{- 1} for Mn, 500 µg.L^{- 1} for Zn, 300 µg.L^{- 1}, 2000 µg.L^{- 1} for Cu and 300 µg.L^{- 1} for Fe. The study highlights MPs as carriers of toxic heavy metals, presenting significant health and environmental risks. This novel research emphasizes the impact of secondary pollution and water treatment processes on MP fragmentation and HM contamination. Recommendations include adopting enhanced water treatment protocols to mitigate MP and HM risks, implementing stricter quality monitoring at all stages of water distribution, and promoting public awareness of plastic pollution. Future studies should explore the health effects of MPs and HMs, optimize sampling methods, and focus on long-term monitoring under diverse environmental conditions to address this emerging issue comprehensively.