Mikroplastik adalah plastik berukuran sangat kecil ≤ 5 mm, dan merupakan limbah yang dapat mencemari lingkungan perairan dan menimbulkan efek toksik. Ketika mikroplastik masuk ke dalam sedimen, hal ini dapat mengganggu rantai makanan bagi organisme. Penelitian bertujuan mengidentifikasi keberadaan mikroplastik pada sedimen di Perairan Pesisir Sungai Kayan, Kalimantan Utara. Penelitian dilaksanakan pada bulan Februari-Maret 2023 dengan melakukan pengambilan sampel sebanyak tiga kali. Terdapat 6 stasiun pengambilan sampel di wilayah perairan pesisir Sungai Kayan, Kalimantan Utara. Pengambilan sampel sedimen dilakukan dengan menggunakan metode purposive sampling di keennam stasiun pengamatan dengan tiga kali pengulangan. Hasil penelitian menunjukkan ada empat bentuk mikroplastik yang teridentifikasi, yaitu fragmen, film, fiber, dan pellet. Bentuk mikroplastik yang dominan adalah fragmen 69%. Ukuran yang paling dominan sekitar 100-500 µm dengan presentase 60%, Ditemukan warna mikroplastik yaitu warna hitam, biru, merah, transparan, coklat dan warna kuning dimana warna coklat mendominasi (53%). Keberadaan mikroplastik berasal dari kegiatan pemukiman, fragmnetasi kantong plastik dan sampah makro yang terpapar sinar ultraviolet dan terpengaruh oleh arus. Variabilitas warna dikaitkan dari berbagai sumber dan berubah warna seiring dengan terjadinya pelapukan di alam. Rentang ukuran disebabkan oleh fisik dan kimia yang berpengaruh terhadap degradasi mikroplastik sehingga memiliki ukuran yang beragam.

Kata Kunci: Bentuk, Mikroplastik, Sungai, Sedimen, Ukuran, Warna

Microplastics, defined as plastic particles measuring ≤ 5 mm, pose significant environmental threat, polluting aquatic ecosystems and triggering toxic effects. Infiltrating sediments, microplastics disrupt the food chain for organisms. The study aimed to identify the presence of microplastics in sediments in the Coastal Waters of Kayan River, North Kalimantan. The study was conducted in February-March 2023 by incorporating three sampling intervals across six distinct stations along the river's coastline. Employing a purposive sampling technique, sediment samples were meticulously collected from each of the designated stations, with three repetitions to ensure accuracy. The results revealed four identified forms of microplastics: fragments, films, fibers, and pellets, where fragments were the most dominant form with 69% of the total. Microplastics in the size range of 100-500 µm dominated, constituting 60%. The diverse colors observed included black, blue, red, transparent, brown, and yellow, where brown was the most prevalent at 53%. The presence of microplastics into the ecosystem was primarily stemmed from residential activities and the fragmentation of plastic bags and macro waste was influenced by ultraviolet exposure and prevailing currents. The color variability was attributed to multiple sources and the color changes occurred along with weathering in nature. The size range resulted from physical and chemical factors influencing microplastic degradation, resulting in a variety of sizes. Keywords: Shape, Microplastics, River, Sediments, Size, Color