This is actually from low grade fertilizer. The marijuana plant sucks up everything from nutrients . . . to heavy metals and can be transported from the stems and into the flower. I realize this thread is old but made an account just to warn and encourage people to evaluate your marijuana before consuming it!! So many people, especially people that dont know any better (novices), dont realize how harmful marijuana can be in FLOWER form. I will not even get into cartridges right now because that's a whole different topic. Just inspect your herb and never buy more than a small amount (8th), unless you trust the person especially if SWIM is in a state where it's illegal because that's where your more prone to find flower with HEAVY GRADE METALS! BUYER BEWARE!