Dr. Kurunthachalam Kannan of the Wadsworth Center’s Division of Environmental Health Sciences (DEHS) serves on the working group of the International Agency for Research on Cancer (IARC) to evaluate the carcinogenicity of butyl benzyl phthalate (BBzP), dibutyl phthalate (DBP), and diisononyl phthalate (DINP).
BBzP, DBP, and DINP are all high-production-volume chemicals that have been used primarily as plasticizers for flexible polyvinyl chloride (PVC) applications such as flooring and cables, but also in adhesives and sealants, paints and coatings, cosmetics, and industrial solvents, and (for DBP) pharmaceuticals. Production of BBzP and DBP has declined now that several countries have imposed restrictions on use in toys, childcare products, and food contact materials. Production of DINP has increased since the 1980s. Human exposures to these three chemicals are ubiquitous and they are reproductive toxicants.
The IARC working group is comprised of 23 scientists, including Dr. Kannan, and represents 13 countries. The working group thoroughly assessed literature related to sources and pathways of human exposure, human epidemiological evidence and laboratory animal and mechanistic studies linking the three phthalates to carcinogenicity.
The documents will be published as monographs by the IARC and the monographs are used by national and international authorities to make risk assessments, formulate decisions concerning preventive measures, provide effective cancer control programs and decide among alternative options for public health decisions. Following several rounds of review of the compiled documents, the working group met in person at IARC in Lyon, France, from June 9-17, 2026, to finalize their evaluation.
For each of the agents assessed by this working group, the mechanistic evidence was strong, and the evidence for cancer in animals was either sufficient (BBzP and DINP) or limited (DBP). The evidence for cancer in humans was inadequate in each case. The classification options were as follows:
• Group 1 (carcinogenic to humans)
• Group 2A (probably carcinogenic to humans)
• Group 2B (possibly carcinogenic to human)
• Group 3 (not classifiable as to its carcinogenicity to humans)
• Group 4 (not carcinogenic to humans)
The Working Group evaluated BBzP, DBP, and DINP each as possibly carcinogenic to humans (Group 2B).
The full scientific assessment will be published as Volume 142 of the IARC Monographs. A summary of the assessment is published in Lancet Oncology (Sun M, Glass DG, Josephy PD, Mancini FR, Ogawa K, Blanc EB, et al. Carcinogenicity of butyl benzyl phthalate, dibutyl phthalate, and diisononyl phthalate. Lancet Oncol, Published online 3 July 2026; https://doi.org/10.1016/S1470-2045(26)00334-7). Dr. Kannan is an author.