You are probably right that industrial and packaging are probably major sources, but microfibers in clothes is a big problem too

https://www.unep.org/news-and-stories/story/fashions-tiny-hidden-secret#:~:text=Laundry alone causes around half,almost three billion polyester shirts.

Laundry alone causes around half a million tonnes of plastic microfibres to be released into the ocean every year—the equivalent of almost three billion polyester shirts.