An approximated one-quarter of IARC Group 3 (unclassifiable) chemicals fit more appropriately into IARC Group 4 (probably not carcinogenic)

Abstract

International Agency for Research on Cancer (IARC) classifies agents as to their potential carcinogenicity in humans. Monographs 1-123 categorize 120 agents as group 1 (carcinogenic to humans); 82 agents as group 2A (probably carcinogenic to humans); 311 agents as group 2B (possibly carcinogenic to humans); 499 agents as group 3 (not classifiable as to its carcinogenicity to humans); but only a single agent, caprolactam, a precursor for the manufacture of Nylon 6, fibers, and plastic as group 4 (probably not carcinogenic to humans). The evidence regarding carcinogenic potential to humans for a randomly selected sample of 100 group 3 agents was studied to determine whether the paucity of agents classified as group 4 represented the state of the scientific evidence or a reluctance on the part of IARC to classify a chemical into the lowest risk category. Of the 100 agents evaluated, a significant minority estimated at 24% did not possess structural elements of carcinogenicity, mutagenic activity in the Ames Salmonella assay or activity in a cell transformation assay. The results of this analysis suggest that the lack of agents classified as group 4 represents a reluctance on the part of IARC to place agents into the lowest category of risk. Failure to appropriately place agents into group 4 unnecessarily exhausts valuable staff resources as these low risk compounds require periodic updating of the evidentiary basis of their classification as a group 3 agent. It would be advantageous for both IARC and public health agencies if a clearer differentiation of group 3 and group 4 agents was employed.

Ecotoxicity and Associated Threat of Polycyclic Aromatic Hydrocarbons (PAHs) to Biodiversity: A Review

“…Placed by IARC grouping in group 3, it was not classified as to its carcinogenicity potential in human (Kamata et al, 2018). Therefore, this PAH has not demonstrated any evidence to be considered carcinogenic to both human and animals (Smith & Perfetti, 2019).…”

Health Risk Assessment of Toxic and Harmful Air Pollutants Discharged by a Petrochemical Company in the Beijing-Tianjin-Hebei Region of China

“…In other words, when people are exposed to certain toxic and harmful air pollutants, will these toxic and harmful air pollutants cause harm to human health or adversely affect health? The 2019 International Agency for Research on Cancer (IARC) special report [27] divided carcinogens into three categories and four groups (category 1, category 2A, category 2B, and category 3), as shown in Table 3. According to Section 2.1 of this thesis, we can see that this thesis takes benzene, toluene, and xylene as research objects.…”