Award: OCE-2033860

Since 1950, global production of plastic has grown exponentially. An estimated 5 to 13 million metric tons of plastic flows from the land and enters the ocean each year. However, model assessment indicates that 99% or more of the plastic entering the ocean is currently unaccounted for. Presumably this missing plastics resides in the ocean interior, seafloor, has been ingested and fragmented by biota, or has been degraded to nano-sized fragments, but to date few studies validate either of these scenarios. Little is known about the processes that affect plastics and itste fate once it enters the deep ocean environment. This project focused on evaluating if the deep ocean conditions support plastics degradation, if the microbial communities in the deep ocean can colonize plastics, and if they are able to degrade and/or utilize plastics as a carbon and/or energy source, thus contributing to plastics removal. For this project, the investigators deployed custom-built deep-sea plastics incubators at 750 meters and 3600 meters water depth at the NSF-funded Oceanic Flux Program (OFP) mooring site, located in the northern Sargasso Sea about 75 km SE of Bermuda. The deployed plastic incubators included both weathered and un-weathered materials and included plastic sheets of high- and low-density polyethylene (PE), polypropylene (PP), polystyrene (PS), and Polycarbonate, but also textile materials (polyethylene terephthalate (PET), polyacrylonitrile (PAN) and polyvinyl alcohol (PVA)). These polymers represent the diversity of plastics found in the marine environment and have different stability against microbial degradation. We also deployed ceramic plates as controls for biofilm formation. Additionally, the incubators included 13C-carbon labelled high- and low-density PE, and as control materials non-labelled high- and low-density PE, to evaluate if the polymeric carbon can used as energy source by the microbial communities. This project combined state-of-the-art polymer chemistry, microscopy, gas chromatography, Raman spectroscopy, isotope mass spectrometry and nucleic acid sequence analyses, to evaluate the plastics before and after being incubated in the deep ocean. Laboratory-simulated weathering of the plastics prior to the deep-sea incubation to mirror natural weathering in the environment (UV, mechanical abrasion, etc.), revealed the strong resistance of plastics to weathering, emphasizing the need for a broader range of plastics with varying properties and sizes to accurately estimate plastic degradation in the marine environment. So far the project revealed that deep ocean microbes can colonize plastics, and that the microbial colonization depends on the plastic type, weathered status, and the environmental conditions (mid-depth vs deep ocean). Microbial lineages that were previously shown to be associated to plastics- and/or hydrocarbon degradation were enriched and often dominant in the biofilms growing on plastics tabs at both incubated depths. The results of this project are helping to determine if microbial communities living within the ocean interior can utilize the synthetic carbon polymers that make up plastics, and thus play an important role in the removal of global plastics. The custom-built deep-sea incubator deployed inline on the OFP mooring represents a new method to study plastic polymer degradation processes in situ, contributing to the technology development for oceanographic research. Undergraduate and graduate students, technicians, and a postdoc were trained in state-of the art techniques, sampling, analyses and approaches through participation in this project. The skills they gained will help advance their research goals and careers. The project research goals, background and experimental design was incorporated in several undergraduate lectures, stimulating the students to think about ocean plastic pollution, and cutting-edge techniques that can be used to evaluate plastic polymer chemistry and biofilm formation. Additionally, the outreach and education activities involved in this project informed the community at large, increasing general awareness to plastic pollution. Last Modified: 07/31/2024 Submitted by: RutPedrosa Pamies