I came here with the same question -- the ink. Why do you feel that the ink is an organic compound? Not sure if there is an easy answer here but this site: https://home.howstuffworks.com/pen4.htm seems to suggest colored inks are inorganic and contains heavy metals.
But if you just compost the fungi, you are just back to where you started. With phytoextraction you have to incinerate the plant material afterwards. I know fungi aren’t plants, but similar principle.
The fruiting body of a mushroom often represents only a fraction of total biomass. It depends on the species, but what we see above ground is more analogous to a flower than an entire plant.
