Polluting potential of microplastic and heavy metals in landfill leachate of an urban municipal solid waste disposal site

Abstract

Landfill leachate has emerged as a least explored pathway of microplastic release to the environment and a potential reservoir of toxic contaminants such as heavy metals. The study investigates the polluting potential of microplastics and heavy metals in landfill leachate from Njeliyanparamba, an urban municipal solid waste disposal site in northern Kerala that processes approximately 100 tons of municipal solid waste daily and contains legacy waste accumulated over 15 years, using an integrated analytical approach. The results showed that the abundance of microplastic in the leachate ranges between 110 ± 23 and 465 ± 22 particles/L and mainly composed of small (100-1000 μm), transparent and blue colored microplastics. The dominance of fragments and fibrous (>70%) shape of the microplastic indicate its origin from secondary source. Nine polymers were identified by Confocal Raman Spectroscopic analysis, among which Polyethylene(PE), Polystyrene(PS), and Polypropylene(PP) (67 to 82%) were the dominant microplastic polymers. The risk assessment studies indicated that the landfill area falls within hazard categories II to V, representing hazard levels ranging from moderate to extreme danger. The heavy metal analysis of leachate indicates high metal concentration in particulate fractions compared to dissolved fractions. The SEM-EDS analysis clearly indicates the presence of heavy-metals on the surface of dominant microplastic polymers i.e, PE and PS which includes Cr, Mn, Fe, Co, Hg and Cr, Mn, Fe, Co, Hg, Ni, Zn respectively. The present study reported that the heavy-metals (Cr, Mn, Ni, Zn, Cd and Pb) associated with particulate fractions were positively correlated with PE which may indicate the microplastic in the landfill act as a carrier for the toxic heavy metals to the surrounding environment. The study will help to improve the landfill management, leachate treatment strategies and risk-informed policy development. Moreover, the study will impetus the necessity for further research on the role of microplastic in the co-contaminant transport, its interaction and to develop treatment, removal strategies for emerging contaminants in landfills.