Heroin Forum: Purity, Use And Addiction Treatment Is Up, Cost Is Down QUINCY - Heroin use and the purity of the drug are way up, and its cost is way down. That, says Norfolk County District Attorney William Keating, is a lethal combination. ''Janis Joplin overdosed at a 16 percent purity level,'' Keating told a Quincy audience last night, referring to the rock singer who died in 1970. ''Kids today are using 80 percent, which is high enough to possibly make their first time their last.'' [continues 449 words]