Seeking answers, NBC News commissioned one of the nation's leading cannabis testing facilities to test a sampling of THC cartridges — 18 in all — obtained from legal dispensaries and unlicensed dealers. The findings were deeply troubling. Of the three purchased from legal dispensaries in California, the CannaSafe testing company found no heavy metals, pesticides or residual solvents like Vitamin E. But 13 out of the other 15 samples from black market THC cartridges were found to contain Vitamin E. CannaSafe also tested 10 of the unregulated cartridges for pesticides. All 10 tested positive. The products all contained myclobutanil, a...