Collaborative Research: CBET: The role of sunlight in determining the fate and microbial impact of microplastics in surface waters

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Microplastics are plastic particles smaller than 5 mm in size. Microplastics mostly originate from fragmentation of larger plastic objects and are now found globally from drinking water to rivers, lakes and streams, and the oceans. An estimated 8 million tonnes of plastic waste enter the oceans from land each year, yet only a fraction of this material is accounted for by floating microplastics. One hypothesis for the missing microplastic is that exposure to sunlight degrades them to dissolved carbon. This project will assess whether sunlight-driven photochemical reactions release dissolved organic carbon from plastics, resulting in removal of the plastics from the water. A second objective of this project will test whether the chemicals released affect bacterial growth and survivability in natural waters. Results will improve our understanding of the fate of floating plastics in natural waters. This project will have significant broader impacts in the fields of environmental microbiology and photochemistry. Results will be incorporated into high school classroom learning geared towards middle and high school students, to increase the Nation's scientific literacy and educate the next generation of environmental engineers and scientists. In addition, the results will inform society on how to prioritize plastic waste management to protect human and ecological health. Microplastics are plastic particles smaller than 5 mm in size and originate from fragmentation of larger plastic objects released to the environment. Microplastics are found globally from drinking water to rivers, lakes and streams, and the oceans, where more than 98% of all buoyant microplastics are unaccounted for in loading estimates. The hypothesis for this research is that sunlight is responsible for degrading floating microplastics to dissolved organic carbon (DOC) on relatively short time scales (years). This hypothesis will be tested through a series of field, experimental, and analytical studies. The second hypothesis is that DOC released from photochemical breakdown will impact microbial growth. This hypothesis will be tested through bioassays with natural marine and freshwater microbes to assess the degradation kinetics (dissolution, fragmentation, and oxidation) of microplastics in seawater and freshwater in the light and dark, and with and without microbes. Experiments with plastics of variable polymer chemistry, size, and previous oxidation history will reveal the role of these factors in explaining variability in degradation rates to inform future modeling studies of plastic loss. The project brings together scientists with complementary educational, field, experimental, and analytical skills to transform our understanding of the fate and impact of buoyant microplastics in surface waters. Results will be disseminated to other scientists, the press, and incorporated into high school classroom learning via publication in the Science Journal for Kids, an open access journal which adapts primary, peer-reviewed research papers with age-appropriate language and illustrations geared towards middle and high school students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.