Easy on the hyperbole. Let's assume that this study is correct, and everyone at median age of 50 is walking around with this level of microplastics in the stated organs. Are we all dead? Disabled? Dying? No. Our lifespans are amongst the longest in human history. I'm doing OK. How about you?
Far bigger practical concerns are that we're fat and lethargic and suffering from metabolic disease, heart disease, cancer and diabetes en masse because we eat too much. About the only thing you can do with this finding is wave your hands around and make hypothetical links to this and that (as they do in the paper), or try to claim that this is really, secretly the underlying cause of the stuff that is actually, observably killing us.
I'm not saying there's no concern here, but I am not "terrified" of this. I am actually scared of getting fat, or falling down when I get old from being weak. These are things that happen to nearly all of us.
Anyway, first rule of science: when we look for things, we find things. If you are "terrified" by everything new you find, you are applying an emotional judgment to what you see, and not being objective enough.