This research summary from University of Plymouth gives a pretty good picture of the sheer volume of plastic flowing into the Bay of Bengal.
Quote below (my bold):
The study represents the first investigation of microplastic abundance, characteristics and seasonal variation along the river and was conducted using samples collected by an international team of scientists as part of the National Geographic Society’s Sea to Source: Ganges expedition.
Over two expeditions in 2019, 120 samples (60 each in pre- and post-monsoon conditions) were gathered at 10 sites by pumping river water through a mesh filter to capture any particles. The samples were then analysed in laboratories at the University of Plymouth with microplastics found in 43 (71.6%) of the samples taken pre-monsoon, and 37 (61.6%) post-monsoon. More than 90% of the microplastics found were fibres and, among them, rayon (54%) and acrylic (24%) — both of which are commonly used in clothing — were the most abundant.
Combining predicted microplastic concentration at the mouth of the river (Bhola, Bangladesh) with the discharge of the river, scientists estimate that between 1 billion and 3 billion microplastics might be being released from the Ganges Brahmaputra Meghna River Basin every day.
The authors answer the obvious question of ‘why does this study matter?’
Quote: “Professor Richard Thompson OBE, Head of the International Marine Litter Research Unit at the University and one of the study’s co-authors, said: “We know that rivers are a substantial source of microplastics in the ocean. But the information like this can help identify the key sources and pathways of microplastic and hence inform management interventions. With this type of evidence, we can progress toward using plastics more responsibly so as to get the many benefits they can bring without unnecessary contamination of the environment.”