Plastic nurdles, as small resin pellets, are a significant pollutant across the north- and southwestern Gulf of Mexico (America) coasts from Texas to the Yucatán Peninsula. This study identified the potential source of nurdle pollution using a combination of chemical analysis and numerical modeling. Chemical data of the nurdles collected from over 70 sites from Houston to the Yucatán Peninsula during 2021–2024 revealed distinct patterns in polymer type, color distribution, and weathering status, providing strong evidence for Texas as the primary source of these nurdles. Color distribution results showed that white nurdles, representative of fresher nurdles, dominated the Texas sites and more weathered, yellow nurdles, were found in Mexico regions. This color trend suggests an increased surface degradation as nurdles move southward. Analysis through Fourier transform infrared spectroscopy shows polyethylene (PE) as the dominant polymer across all sampled sites, showcasing a linked homogeny through the regions, and the data were further used to build chemical weathering indices, which provided a way of quantifying the degree of oxidation nurdles have undergone. Results showed that the Mexico nurdles had higher indices than those in Texas, reinforcing the hypothesis that the Mexico nurdles have undergone longer environmental exposure. Physical oceanographic modeling, incorporating wave and current dynamics, confirmed that nurdles released from Texas can be transported to Mexican coastlines, while nurdles released from Mexico do not reach deep into the US. shorelines due to strong prevalent downcoast currents along the inner shelf. This movement pattern, together with chemical and weathering evidence, strongly supports Texas as the primary source of nurdle pollution along the gulf coast. Identification of the pollutant source will assist management practices and international cooperation to tackle nurdle pollution.

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