This is not just a problem with these things. Many products out of china have a lot of impurities not removed from metals used in construction. There has been some really kooky things too, like water soluble polymers formed into 'rice', and I remember in Australia there was a big fuss about chinese toys with those beads that you add a solvent and they stick together, because the solvent was Gamma Butyrlactone, the precursor (and itself psychoactive) of GHB. A small amount of this stuff could put a child to sleep, forever.