heavy metals

[zuf]

For me it not a concern of chemical  fertilizers so much. What you are looking for in this potting soils are heavy metals, that’s your reall concern. And they are not in those beads, but are in general present in proccess of creating potting soil, compost etc. They get materials from sewege and elsewhere. Not always the case, but here in Slovenia we have this a lot, when potting soil is imported. You have no other option than taking that soil on tests. Than you can be totally sure.