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There are trillions of microplastic particles, ranging in size from about one micrometer to a few millimeters, on Earth. Many of these particles end up in the oceans, where they disrupt nutrient cycles, are ingested by marine animals or transport pollutants. To better understand how microplastics accumulate and disperse in marine environments, new research published in ACS’ Environmental Science & Technology reflects efforts to locate hotspots — areas with high concentrations of microplastics — in Texas coastal bays.

Coastal environments are important habitats for juvenile fish, oysters and protective salt marshes. Microplastics, which look like small grains or elongated filaments, can settle to the bottom of river mouths, estuaries (areas where freshwater mixes with salt water) and bays. There, they can accumulate in the sediment or float freely in the water, disturbing ecosystem balance. The problem is particularly worrisome for the Texas bay systems, which have documented incidents of microplastic pollution. For example, the Formosa Plastic Corporation in Point Comfort, Texas, spilled billions of small plastic pellets, known as nurdles, into coastal waters in 2019. The presence of microplastics in estuarine environments is understudied, despite the critical nature of these locations. So, William Bailey and colleagues investigated estuaries and bays along the Texas coast to understand how many microplastics are being transported to the Gulf Coast, and later, the ocean.    

To study microplastic accumulation and dispersion patterns, the team members sampled sediment in several locations along the Gulf shore. They identified plastic particles and plastic filaments using microscopy and spectroscopy techniques, as well as a process that sorts particles by size, shape and density. Overall, they found fewer microplastic particles than expected, given the documented incidences of nurdle spillage. The highest amounts of microplastics were by river mouths; but otherwise, the plastic particles were just as prevalent in deep water as shallow water closer to the shore.

The researchers reasoned that the lower-than-expected levels and even distribution of microplastics in coastal waters were a result of shrimp and oyster fishing, which scours the bottom of the bay and kicks up and redistributes sediments and microplastics. Winds are also capable of generating bottom-scraping waves, especially during strong Gulf storms. And because microplastics are less dense than natural sediments, they’re more likely to be transported by big waves out of the bays and into the Gulf, and eventually, the open ocean.

The team’s future work will incorporate their microplastic transport and deposition data into numerical models that “can be applied to the Gulf shore and other understudied, high-risk areas to effectively inform conservation efforts and pollution mitigation strategies,” says Bailey.

The authors acknowledge funding from the Matagorda Bay Mitigation Trust and the Jackson School of Geosciences at the University of Texas at Austin.

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