Sampling, identification, and characterization of microplastics and their associated emerging contaminants in wastewater effluents

Abstract

Microplastics are emerging pollutants of growing concern due to their persistence, widespread distribution, and capacity to act as vectors for hazardous chemicals. This study examines the presence, composition, and contaminant load of microplastics in the effluent of a wastewater treatment plant with a processing capacity of 7,500 liters per second in Nuevo León, Mexico. Samples were collected from final effluents and treated using the ASTM D8333-20 oxidation method to eliminate organic matter prior to analysis. Characterization via Raman spectroscopy revealed that the predominant polymers were polyethylene, polypropylene, and polystyrene, mainly present as fragments with a mean size of 198.3 μm. Color analysis indicated a predominance of white particles, suggesting a likely origin from disposable packaging materials. To detect sorbed organic contaminants, analytical techniques including Gas Chromatograph coupled with Mass Spectrometry and Gas Chromatography with an Electron Capture Detector were employed. Four volatile organic compounds were reliably identified: dimethyl disulfide, 2-butyl-1,1,3-trimethylcyclohexane, trichloromethane, and 1,1'-oxybis decane. Although polycyclic aromatic hydrocarbons were not detected, organochlorine pesticides such as γ-BHC (lindane), Endosulfan I, and Endosulfan sulfate were present, while polychlorinated biphenyls were not detected. Interference from linear hydrocarbons, fatty acids, and plasticizers was consistently observed, emphasizing the need for improved sample cleanup protocols. Based on effluent flow rates and particle concentrations, it is estimated that the wastewater treatment plant discharges over 4.97 × 10¹¹ microplastic particles annually. These findings highlight the urgent need for standardized monitoring approaches and advanced treatment strategies to mitigate the environmental and chemical risks associated with microplastic pollution in aquatic ecosystems.