The use of microplastics in offshore oil and gas activities could be substantial. However, systematic understanding of the occurrence patterns and ecological risks of microplastics within platform discharges remains limited. To characterize the abundance, morphological features and polymer types of microplastics in discharges from offshore oil and gas platforms, and to quantitatively assess the ecological risks, this study investigated 21 platforms in the Bohai Sea, East China Sea, and South China Sea. Thirty-six samples covering four discharge types (produced water, domestic sewage, drilling muds and cuttings) were collected and analyzed. Microplastics were detected in all samples. Rayon and polyethylene terephthalate fibers were dominant in produced water and domestic sewage. In contrast, fibrous and pelletized microplastics were abundant in drilling muds and cuttings. Pollution load index results suggested that the vast majority of samples exhibited low-to-moderate microplastic pollution levels. Meanwhile, polymer risk index results suggested that 89% of samples posed low-to-moderate ecological risks. Potential ecological risk index results revealed that over half of the samples attained extreme risk grades, a result attributable to either trace amounts of highly toxic polymers or exceptionally high microplastic loads. The microplastic features in discharges from platforms were highly consistent with those in sediments of the Bohai offshore oil and gas fields, suggesting that discharges from offshore oil and gas platforms may represent potential sources of microplastics in the surrounding sediments. This work provides the first comprehensive microplastic dataset of China's offshore platform discharges, supporting targeted marine pollution regulation and mitigation.
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