If you are worried you can try putting it in some water (so it doesn't bake

) and zap it in the microwave or boil it on the stove, or you can bake it in the oven as well, but for moss I find the microwave to be the best
The worst stuff youw ill probably find in moss are wood mites, which are totally harmless anyways. I used to zap anything natural before using it but, though I don't use much natural stuff anymore, I don't really treat it and haven't encountered any subsequent problems.