Impact of Polyethylene Microplastic, Electrical Conductivity and E. coli of Composts on Seed Germination

This study evaluated the influence of polyethylene (PE) microplastic, electrical conductivity (EC), and the presence of E.coli in different composts on the seed germination of mung bean seeds. Four types of composts were examined: T1 and T2, originating from dining food waste and kitchen waste, respectively; T3, a vermicompost produced by earthworms; and T4, a chemical organic fertiliser derived from human hair. The composts were prepared and diluted with deionised water, and PE microplastic particles were added at various concentrations. Mung bean seeds were soaked in these solutions for 8 hours, then placed on tissue paper in closed containers and kept moist by spraying with the solutions every 2 days. Germination tests were conducted over five days, and the germination index (GI), relative seed germination (RSG), and relative radicle growth (RRG) were calculated. EC and pH of the solutions were measured, and E.coli presence was assessed using the US EPA method 1603. PE microplastics at concentrations below 0.8% w/w stimulated seed germination, with the highest GI observed at these levels, suggesting low concentrations may not be as harmful as previously thought. High EC levels significantly inhibited seed germination, with the chemical organic fertiliser (T4) exhibiting the highest EC values and severe phytotoxicity even at high dilutions, highlighting the need to manage salt content in composts. Only the food waste compost (T1) contained E. coli, likely due to post-contamination, but E.coli did not significantly inhibit germination after dilution and filtration, indicating proper treatment can mitigate microbiological risks. The combined effects of microplastics and EC on germination were complex, underscoring the need for balanced management of both factors. These findings provide insights into the interactions between microplastics, EC, and E.coli in composts, informing better compost management practices and contributing to sustainable agricultural productivity.