Eric Berger/Kaiser Health News

The concerns about delta-8 are largely focused on how it’s made. Delta-8 is typically produced by dissolving CBD — a compound found in cannabis plants — in solvents, such as toluene that is often found in paint thinner. Some people in the marijuana industry say that process leaves potentially harmful residue. A study published in the journal Chemical Research in Toxicology last year found lead, mercury, and silicon in delta-8 electronic cigarettes.