Organic amendments as vectors of micro and macro plastic pollution of terrestrial ecosystems

Microplastics (MPs) are a growing concern as they are increasingly detected in various environmental compartments. An important pathway for MPs to enter terrestrial ecosystems is the application of organic amendments for soil improvement. This study aims to investigate the size, morphology, and composition of MPs in different types of treated organic waste commonly used in agricultural soils and soil restoration. A total of seven organic amendments, including sewage sludge, horse manure, two composts and two digestates from agri-food industries and selectively collected municipal organic waste, respectively, and a biostabilized product from non-selectively collected municipal organic waste, were analyzed. The samples underwent pretreatment steps including advanced Fenton oxidation, alkaline and enzymatic digestion, and density separation, followed by spectroscopic confirmation. The results revealed high plastic concentrations ranging from 6774 to 551,696 items/kg of dry weight, depending on its origin and treatment. Sewage sludge samples exhibited the highest MPs concentrations, while horse manure showed the lowest. The most prevalent MPs morphologies were fragments, followed by fibers and films. Among the particles, the most prevalent polymers observed were PE, PP, PET, PVC, and PS, whereas PES constituted the primary composition of the fibers. The present study underscores the substantial presence of MPs in organic waste amendments and when they are applied to soil can be ingested by terrestrial organisms, entering the food chain and posing risks to human health.