In order to pass regulations, they'll need to establish a level of toxicity, as they do with other contaminants.
There's not much research on that level that I could find, but there is some research into how lethal microplastics are.
There are a few animal studies available that measured lethal doses of microplastics: https://oceanconservancy.org/n...
- Sea birds - 12 grams of plastic will kill a bird weighing 320 grams, about 1:26
- Sea turtles - 280 grams of plastic will kill a turtle weighing 180 kg, about 1:642
- Porpoises - 1200 grams of plastic will kill a porpoise weighing 77 kg, about 1:64
Let's compare salt.
- Humans - 50 grams of salt can kill a 100-kg person, about 1:2000
So salt seems to be about 3x more lethal than the worst case (sea turtles) cited by the Ocean Conservancy above.
This type of comparison will no doubt influence the level of regulation, whichever party ultimately controls Congress.