Examining the Presence of Microplastic in Wastewater-Derived Soil Amendment

Abstract

There is growing research on the impact of microplastics in terms of uptake in consumer products (e.g., sea salt, bottled/tap water, beer, mussels, fish, and soil amendments). Studies have shown that wastewater effluent and biosolids are potential pathways for microplastics to enter marine, freshwater, and terrestrial environments. Some soil amendments derive from the bacterial mats associated with wastewater processing and are potential pathways of microplastics via soil runoff into surrounding waterbodies. The presence of microplastics in these ecosystems impacts food webs at varying trophic levels and contributes to the persistence of microplastics in the environment. We examined a wastewater-derived soil amendment for microplastics using standard characterization methods. Quantification of microplastics following distilled water hydration of 82g of soil amendment yielded 69 particles. These particulate were primarily fibers (69%) and foams (19%), with lesser films (4%), beads (4%), and fragments (3%). The majority were smaller (125-355um) fiber particles. A standard bag of this soil amendment is 14515g with coverage of 232m2. The average-sized lawn in the United States is approximately 911m2, resulting in the potential to contribute 330,240 particles into soil and ultimately adjacent waterways. Next steps have begun to streamline this process by adopting the wet peroxide oxidation digestion method in an attempt to reduce organic matter. Nile red staining is a recently introduced method that effectively binds to plastic and is visualized using ultraviolet light. Microplastic researchers have developed automated (MP-VAT) software to streamline microplastic quantification and characterization in conjunction with Nile red staining procedures. We aim to incorporate this new approach and evaluate best practices in microplastic quantification and characterization of wastewater-derived soil amendments, as their potential ecosystem consequences are broad. It is important to continue elucidating pathways of these emerging persistent pollutants.