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1. Isolating Microplastics from Biofilm Communities

   https://doi.org/10.1525/abt.2022.84.9.555  

   Meiller, Jesse; Sosa, Ana; May, Eva; Frederick, J. Adam (November 2022, The American Biology Teacher)

   Plastic debris in aquatic and marine environments often breaks up into fragments that are smaller than 5 millimeters, which are then classified as microplastics. While there is not yet a standardized and validated methodology for characterizing microplastics, the protocol developed in this study uses methods for isolating and observing microplastics and for the investigation of how they interact with organisms present in biofilms from urban waterways. Project-based learning (PBL) has been proven to be a successful strategy in K–12 science education; the implementation of PBL provides opportunities for student-driven inquiry and provides teachers with a means to integrate curriculum with current research and to consider the effects of human impacts on the environment. This paper describes the protocol developed for high school teachers to educate students about microplastics and how to successfully isolate and observe them. Teachers and students in Maryland successfully isolated microplastics from biofilm samples from the Inner Harbor, Baltimore, Maryland, and shared their results. International teachers and students in Barcelona, Spain, involved in a related project, had similar results and shared experiences through images, video, and online meetings. These collaborations provide important opportunities for student-driven inquiry and for them to engage in methods of current scientific research. 

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2. Environmental impacts of biodegradable microplastics

   https://doi.org/10.1038/s44286-024-00127-0  

   Piao, Zhengyin; Agyei_Boakye, Amma_Asantewaa; Yao, Yuan (September 2024, Nature Chemical Engineering)

   Abstract Biodegradable plastics, perceived as ‘environmentally friendly’ materials, may end up in natural environments. This impact is often overlooked in the literature due to a lack of assessment methods. This study develops an integrated life cycle impact assessment methodology to assess the climate-change and aquatic-ecotoxicity impacts of biodegradable microplastics in freshwater ecosystems. Our results reveal that highly biodegradable microplastics have lower aquatic ecotoxicity but higher greenhouse gas (GHG) emissions. The extent of burden shifting depends on microplastic size and density. Plastic biodegradation in natural environments can result in higher GHG emissions than biodegradation in engineered end of life (for example, anaerobic digestion), contributing substantially to the life cycle GHG emissions of biodegradable plastics (excluding the use phase). A sensitivity analysis identified critical biodegradation rates for different plastic sizes that result in maximum GHG emissions. This work advances understanding of the environmental impacts of biodegradable plastics, providing an approach for the assessment and design of future plastics. 

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3. Optimizing density separation methods for microplastics extraction from marine sediments Session: GC068: Microplastics and the biosphere

   Arbaugh, H.; Gray, S.C. (December 2023, Transactions American Geophysical Union)

   no editor (Ed.)

   Many different techniques are used to extract microplastics (MPs) from sediment samples of variable composition and grain size. The lack of uniform methodology makes it challenging to compare results across studies and to select methods appropriate to local sedimentary conditions. This study (a) evaluates the separation efficiency, yield, and contamination (blank) of settling compared centrifugation density separation, and (b) examines the distribution of MP across successive separation phases (interstitial water, organic matter, sediment). Two different density-separation dependent extraction methods were tested with tropical marine sediments from the US Virgin Islands with variable grain size and composition: (1) suspension within a settling column, and (2): centrifugation. The samples were processed under a laminar flow hood using published best practices to minimize contamination. The two separation techniques produced similar MP yields (85-100%), which were calculated by tracing polyethylene microspheres. However, processing in the settling column sometimes produced incomplete settling of fine organic matter and took a significantly longer time (week vs. minutes) than did separation via centrifugation. Analytical blanks (contamination) were also slightly greater using a settling column (avg: 5.3±1.1) vs the centrifuge (avg: 3.6±0.9). However, the most important reason why the centrifugation is preferable is that it allows for the complete removal of separatory solutions via compaction of the sediment. This allows phased separation of MPs through sequential interstitial water removal, hydrogen peroxide treatment and removal (to target organic matter bound MP), and density separation phases. Our experiments showed that a significant portion of the total MP in the samples were potentially located in the interstitial water phase (16±12%) and the following hydrogen peroxide phase (25±20%). In the literature, intermediate treatment solutions are often discarded, resulting in an underestimation of total MP in the sediments. In summary, we found that the most effective method of MP extraction from organic rich or fine-grained sediments is a phased centrifugation process which includes counting MP from all phases. 

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4. Microplastics and their interactions with microbiota

   https://doi.org/10.1016/j.heliyon.2023.e15104  

   Parsaeimehr, Ali; Miller, Cassandra M.; Ozbay, Gulnihal (April 2023, Heliyon)
5. Wastewater treatment alters microbial colonization of microplastics

   https://doi.org/10.1371/journal.pone.0244443  

   Kelly, John J.; London, Maxwell G.; McCormick, Amanda R.; Rojas, Miguel; Scott, John W.; Hoellein, Timothy J. (January 2021, PLOS ONE)

   Nerenberg, Robert (Ed.)

   Microplastics are ubiquitous contaminants in aquatic habitats globally, and wastewater treatment plants (WWTPs) are point sources of microplastics. Within aquatic habitats microplastics are colonized by microbial biofilms, which can include pathogenic taxa and taxa associated with plastic breakdown. Microplastics enter WWTPs in sewage and exit in sludge or effluent, but the role that WWTPs play in establishing or modifying microplastic bacterial assemblages is unknown. We analyzed microplastics and associated biofilms in raw sewage, effluent water, and sludge from two WWTPs. Both plants retained >99% of influent microplastics in sludge, and sludge microplastics showed higher bacterial species richness and higher abundance of taxa associated with bioflocculation (e.g. Xanthomonas ) than influent microplastics, suggesting that colonization of microplastics within the WWTP may play a role in retention. Microplastics in WWTP effluent included significantly lower abundances of some potentially pathogenic bacterial taxa (e.g. Campylobacteraceae ) compared to influent microplastics; however, other potentially pathogenic taxa (e.g. Acinetobacter ) remained abundant on effluent microplastics, and several taxa linked to plastic breakdown (e.g. Klebsiella , Pseudomonas , and Sphingomonas ) were significantly more abundant on effluent compared to influent microplastics. These results indicate that diverse bacterial assemblages colonize microplastics within sewage and that WWTPs can play a significant role in modifying the microplastic-associated assemblages, which may affect the fate of microplastics within the WWTPs and the environment. 

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