Characterization and source apportionment of microplastics in Indian composts

Area of Science:

• Environmental Science
• Pollution Control
• Materials Science

Background:

• Microplastics (MP) are plastic particles <5 mm, recognized as vectors for heavy metals in ecosystems.
• Composts derived from municipal solid waste (MSW) represent a substantial pathway for soil microplastic contamination.
• The accumulation of heavy metals on microplastics within composts raises ecological concerns.

Purpose of the Study:

• To quantify microplastic concentrations and analyze heavy metal accumulation on microplastics in MSW composts from Kochi and Kozhikode, India.
• To identify the types of plastic resins present and determine the primary sources of microplastic pollution in the composts.
• To assess the ecological risk associated with microplastic and heavy metal contamination in the composts.

Main Methods:

• Microplastic isolation using zinc chloride density separation and Fenton's reagent for organic matter oxidation.
• Fourier-transform infrared (FTIR) spectroscopy for resin identification (PE, PP, PS, nylon, PET, allyl alcohol copolymer).
• Heavy metal analysis on microplastics and composts, alongside source apportionment and ecological risk index calculations (PLI, PHI).

Main Results:

• Microplastic concentrations were 840 ± 30 items/kg in Kozhikode and 1600 ± 111 items/kg in Kochi, predominantly polyethylene (PE) films.
• PE constituted 58.3% (Kozhikode) and 73.37% (Kochi) of identified resins.
• Heavy metals (Pb, Cd, Zn, Cu, Mn) were significantly adsorbed onto microplastics, with concentrations 1.02–2.85 times higher than in the compost.
• Single-use plastics accounted for 64% (Kozhikode) and 77% (Kochi) of microplastic sources.
• Ecological risk indices indicated a hazard level V for composts from both locations.

Conclusions:

• Composts from unsegregated MSW are a major source of soil microplastic and heavy metal contamination.
• Single-use plastics are the predominant contributors to microplastic pollution in these composts.
• The findings highlight the urgent need for better waste management strategies to mitigate ecological risks.