Based on everything I know about the mechanism of action and the impact of dietary fiber in general on microplastic adsorption I would need to see a study with protocols and raw data published to be convinced that barley is lacking and your solution is superior but I'm open to it.
Hulled Barley is a combination of both IDF and SDF's, that study is for DF across the board. Frankly a barley drink made with unfiltered french press coffee would probably be the single best/easiest validated drink for reducing absorption of microplastics and heavy metals.
But it is an under researched area for sure.
edit because I can't reply: the above paper I linked references coffee grounds and MP.