I'm writing a paper rpg scenario, and even if we don't need to be 100% accurate about chemistry and physics in such games, one of my players has an advanced level in chemistry and I don't want him to cringe at the situation (and I can't ask him, obviously, or he'll be spoiled).
So, I need a river to be polluted with an invisible and odorless product, that slowly destroys the fauna. As it happens in Siberia, I thought about tritium first, but I don't think it's easy to clean. So I thought about a product that could be cleaned with a flocking agent. Problem is, when I was searching for "products reacting to flocking agent" on Google I didn't find any name of product that I could use.
So, which invisible, toxic and odorless product react to flocking agent to the point the river is cleaned in one or two months maximum (and eventually produced in the 1980's) ?
Thanks a lot, and sorry if it's not the SE to ask this question.