Salt comes from the sea. The sea is full of plastic, which we put there. So now 90% of table salt contains plastic.
Of 39 salt brands tested, 36 had microplastics in them, according to a new analysis by researchers in South Korea and Greenpeace East Asia. Using prior salt studies, this new effort is the first of its scale to look at the geographical spread of microplastics in table salt and their correlation to where plastic pollution is found in the environment.
The brands aren't listed and the study is behind the academic wall, but apparently include inland-sourced rock salt. They use seawater to dissolve, extract and filter it, see.
P.S. The Himalayan stuff is mostly inauthentic. Free plastic, though.