Sources, Occurrence, and Removal of Microplastic/Nanoplastic in landfill leachate: A Comprehensive Review

Due to a massive amount of plastic waste from municipal and industrial sources accumulates in landfills, landfill leachate is becoming a significant reservoir of microplastic (MPs)/ Nanoplastics (NPs), and MPs/NPs in landfill leachate released to the environment can pose detrimental effects on humans and biota. This study critically reviewed most available up-to-date scientific literature on MPs/NPs in landfill leachate and provides the state-of-the-science regarding their detection and quantification, occurrence and characteristics, and remediation. MPs/NPs in landfill leachate can be classified into primary source that is in micro- or nano- scale when manufactured, and secondary source that is made as regular sized plastic but fragmented in to micro- or nano- scale in landfills. In the global scale, the concentration of MPs/NPs in raw and treated landfill leachate varied between 0-382 item/L and 0-2.7 item/L, respectively. Occurrence of MPs/NPs in raw landfill leachate is largely related to the local plastic waste production and solid waste management practice. Among all types of polymers, low-density and high-density polyethylene (PE), polystyrene (PS), polypropylene (PP), are the four most abundant MPs/NPs polymers in landfill leachate worldwide. Though the color of MPs/NPs primarily depends on their parent plastic waste, the dominance of light color in MPs/NPs in leachate is a sign of long-term degradation in landfills. The identified morphologies of MPs/NPs in leachate from all literatures have the highest abundance of fiber and fragments. Depending on the treatment technique, leachate treatment processes can achieve removal rate from 3 to 100% for MPs/NPs. Also, the critical review provides unique perspectives for MPs/NPs in landfill leachate regarding remediation, ultimate disposal, fate and transport among engineering systems, standardized detection methods, source reduction, etc. The landfill-WWTP loop and bioreactor landfills create unique challenges and opportunities for the management of landfill leachate induced MPs/NPs.