Understanding the Impacts of UV-Weathering and Plastic Additives on Microplastic Toxicity to Ammonia-Oxidizing Bacteria

Nitrification is a key nitrogen cycle pathway, essential for nutrient bioavailability and denitrification in various environments. Recent studies have shown that some microplastics can affect the nitrification activities of sedimentary and wastewater-associated microbial communities. However, it remains unclear which nitrifying taxa are negatively impacted by exposure to microplastics and to what degree variable chemical factors of microplastics in the environment, including plastic additive composition and degree of UV photooxidation, drive these effects. To investigate these questions, we conducted a four-day exposure experiment using cultures of the ammonia-oxidizing bacterium Nitrosospira sp. AV. Untreated or UV-weathered microplastics composed of polyethylene (PE), polylactic acid (PLA), polyurethane foam (PUF), or polyvinyl chloride (PVC) were added to cultures at a concentration of 1 mg/mL. Changes in nitrite and nitrate concentrations were measured to determine impacts on nitrification rates. Among polymer types, only unweathered PVC inhibited the nitrification activity of Nitrosospira sp. AV after four days. Interestingly, no inhibition was observed with UV-weathered PVC. To identify possible chemical differences driving these effects, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) as well as solvent extraction of microplastics followed by gas chromatography coupled to quadrupole time-of-flight mass spectrometry (GC-QTOF-MS) were utilized to characterize the additive composition of the microplastics before and after UV-weathering. Both mass spectrometry analyses revealed changes in the composition of several plastic additive chemicals. Furthermore, we conducted an exposure experiment to investigate the toxicity of one additive of interest, which was detected in the toxic unweathered PVC microplastics but absent from the non-toxic UV-weathered microplastics. Our results indicated that this additive may have driven the observed effects. Overall, this work provides additional insight into the influence that microplastics and their additives may have on microbes involved in the nitrogen cycle. Furthermore, this study provides an example of how strategic analyses can pinpoint drivers of effect—a success story towards identifying practical mitigation strategies for impacts of plastics on the environment.

Presentation Preference: Oral

Primary Presenter: Mara Walters, Virginia Institute of Marine Science/William & Mary (mfwalters@vims.edu)

Authors:

Mara Walters, Virginia Institute of Marine Science  (mfwalters@vims.edu)

Bongkeun Song, Virginia Institute of Marine Science  (songb@vims.edu)

Meredith Seeley, Virginia Institute of Marine Science  (meredith.seeley@vims.edu)

Hyo-Bang Moon, Hanyang University  (hbmoon@hanyang.ac.kr)

Sori Mok, Hanyang University  (healsori@gmail.com)