It is a very rational thought. People have been eating used filters for millions of years. In particular, just 60 years ago you could find small clams almost i

It is a very rational thought. People have been eating used filters for millions of years. In particular, just 60 years ago you could find small clams almost in any beach and we believe homo erectus ate those. But just less than 80 years ago, rivers started carrying all kind of new chemical compounds, like mines' waste, from coal cleaning particles to mercury and cadmium compounds. Then we added other chemicals like detergents, or machine oils, or silver halides from photography, plastifiers and plastic or resins synthesis residues, Hormones like "the pill", fertilizers, heavy metals like Pb, industrial acids, pharmaceutical residues and I could go on and on. In some places like in the Mediterranean sea clams just have been dissolved by acid waters or pollution just killed most of them. This is specially true in the river mouth of big industrial rivers. It is not lack of rationality, quite the contrary, people with information,like those that do quality analysis of waters will never eat things like fish coming out of some of them.