Hmm good to know more about what is in the game.
Your own comment seems to indicate an understood inference. Micro-organisms that live in and around the plant. Road side living suck up vehicle emmissions as do most similar plants at just about any road side.
The exact percentage is more for game mechanics than real life hard fact. As these are wild plants that are edible and not something taken into a lab for study. But rinsing something off in water isn’t much different than shaking dirt of your pants. You are likely to have something remain that you do not perceive with the naked eye.
Since we are on the topic. Check out this thread. Add to it as you like:
