Quantification of THC, heavy metals, pesticides, mycotoxins, and microbial contaminants in cannabis inflorescence reveals higher levels in illicit samples than in the licensed Canadian market

Background Following the legalization of recreational cannabis in Canada under the Cannabis Act (2018), regulatory frameworks were implemented to ensure product safety, quality, and consistency within the legal market. Previous studies revealed significantly greater pesticide contamination in illicit cannabis than in licensed products. In light of these findings, the present study expands contaminant surveillance to include the quantification of Δ⁹-tetrahydrocannabinol (THC) and a broader range of potential toxicants, including heavy metals, pesticides, mycotoxins, and microbial agents. Methods Fifty licensed cannabis products were purchased across Canadian provinces, and 50 illicit samples were obtained via law enforcement seizures. All the samples were tested via validated, accredited/attested methods. THC content was assessed using LC-UV-MS. Pesticides were analyzed via LC-MS/MS and GC-MS/MS; heavy metals via ICP-MS/MS; mycotoxins via LC-MS/MS; and microbial contamination using MALDI-TOF. Results THC levels in 48% of licensed products deviated by more than 20% from their labeled concentrations. Microbiological testing revealed that 20% of legal products exceeded the European Pharmacopoeia microbial limits, prompting regulatory responses and voluntary recall. In contrast, 55% of the illicit products exceeded the aerobic plate count thresholds, and 73% surpassed the yeast and mold limits. Mycotoxins were undetected in licensed products but were present in 12% of illicit samples. Pesticide residues were found at trace levels (0.01 µg/g) for myclobutanil and dichlobenil in two licensed samples, whereas 94% of illicit samples contained pesticides, averaging 3.4 compounds per sample across 24 unique active ingredients. Heavy metal analysis revealed higher levels of arsenic, cadmium, lead, and mercury in illicit products than in their licensed counterparts. However, licensed samples presented higher chromium concentrations, with peak values approximately threefold greater than those observed in illicit cannabis. The concentrations of arsenic, barium, chromium, copper, molybdenum, nickel, and vanadium exceeded the permissible daily exposure limits of the United States Pharmacopeia (USP) in one or both product categories. Conclusion These findings demonstrate significant differences in licensed THC levels compared with their label claims as well as in contaminants between licensed and illicit cannabis products. The results provide evidence to inform regulatory oversight, enhance public health risk assessments, and support informed decision-making by consumers and policymakers in the context of a legal cannabis framework.