Low Dose, Low Disturbance: PET and PLA Microplastics Show Limited Effects on Soil Microbes via PLFA Analysis
Observations of microplastics in terrestrial soils are increasing and their potential effects on soil microbial communities (and/or their diversity) are poorly understood. To understand how microplastics may affect soil communities, we performed a microcosm study using soil collected from a forest located in northeastern United States (U.S.). The soil was characterized for pH, soil organic matter (SOM), soil organic carbon (SOC), and other parameters. Polylactic acid (PLA) or polyethylene terephthalate (PET) powders were added to the soil to achieve a mass concentration of 0.7% and 0.6% w/w plastic to soil, respectively. This concentration was selected to be representative of pristine or natural environments rather than heavily polluted environments and to serve as a baseline for future work or similar studies. The experiment occurred over 49 days and while most soil variables (i.e., moisture and temperature) were held constant, we specifically exposed a set of microcosms to a diurnal light/dark cycle while another set was held under continuous dark conditions. Phospholipid fatty acid (PLFAs) biomarkers were used to identify and evaluate soil microbial biomass and community composition in the presence and absence of plastics. In general, our observations show that fungal biomarkers continuously decreased irrespective of treatments. Gram-negative and gram-positive bacterial markers, however, oscillated around the initial values. This may be due to resource availability or competitive disadvantages that are not related to microplastic treatments. Stress indicators exhibited a gradual increase over time; however, no significant differences were detected between soil treatments. These findings imply that polylactic acid and polyethylene terephthalate microplastics did not significantly alter the microbial community at the chosen amendment level.
Microplastic, PLFA, Soil, GCMS, Microbial Communities, Analytical Chemistry, Environmental Sciences, Soil Science
City University of New York - City College
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