2) Fishing nets are a common issue, but make a low percentage of micro plastic waste to reach the ocean. (Though they are a significant percentage of all plastic in the ocean.)
3) This is the main issue, but anti littering laws and sewage treatment make a huge difference in output. This means South America, Indonesia, and yes Africa are disproportionately causing micro plastic pollution.
https://wwtonline.co.uk/features/microplastics-plastics-plas...
> Domestic and commercial wastewater is certainly a major route for microplastics entering the environment – but by no means the exclusive one. When comparing the samples upstream of the wastewater treatment plants with those downstream, the Leeds study found that all of the plants were linked to an increase in microplastics in the rivers – on average up to three times higher, but in one instance by a factor of 69.
The large volume means that even reducing 95% of all microplastic will still be releasing large numbers of microplastic. And because it's a waste water treatment plant these microplastics are going to be heavily contaminated with bioavailable pollutants -- these are higher risk microplastics.
We currently don't know how well wastewater treatment plants remove microplastics. We do know that some of them will be releasing hundreds of microplastics per cubic metre.
> even reducing 95% of all microplastic
Yea, no scale matters. Micro plastics where only detected on the world’s oceans in 2004, they are an issue but far from the most critical one facing the world’s oceans.
> We currently don’t know how well wastewater treatment
Sure, but this is still a massive issue with the study. If they are say 50% vs 99.9% effective that’s a big deal.
https://www.acsh.org/news/2018/07/26/asia-africa-cause-90-pl...
Please can you support this with a cite, because I think you've misunderstood what you've read.
Plastic in the ocean comes from roughly 3 sources.
1) Microfibres in clothing. It's likely that the West dumps significantly more of these into the environment because of greater numbers of plastic clothing and increased amounts of washing of those clothes.
2) industrial equipment, mostly lost fishing nets. I haven't seen anything that says these nets are disproportionately from African boats.
3) plastics from sewage systems, and plastics washed from land into rivers and thus into the ocean.
It's this last one that I think you're talking about. But it's important to realise that 1) many of these rivers aren't in Africa, but in Asia and 2) most of that plastic was exported from the West to Asia.