Then what happens to them? Some – perhaps most – wash off the soil and into the rivers: in other words, whether sewage is screened or not, the microplastics it contains end up in the same place. Others accumulate in the soil.
Which, I don't know, is an accurate picture of what happens? We do know that sizable quantities of what is put onto the land—be it littered plastic bags or fertilizer spread on fields—does end up in the water ways. This is in no way hand-wavy. No hard figures or references to peer-reviewed literature is given, but then this is the Guardian, not the Lancet. It is also not a long read, more of a short reminder.
I don't know what you're up against, but we do put lots and lots of forever chemicals into the environment, compounds that do not occur in nature, that are hardly affect by any processes that would break them down, compounds of which many have been shown to be harmful to organisms, including people. This article highlights one particular aspect of it: how chemicals that are put into paints, into fertilizers, into many products make their way from their one-time useful application into the soil and the seas to stay there, essentially forever.
A constructive criticism of this would be to show research that demonstrates this is not a bad thing, instead all you do is accusations of hand-waving.
FUD articles like this are not helpful.
