To the editor:
The International Agency for Research on Cancer is the world's most respected carcinogen classification entity. Over the course of the past several decades, IARC has invested a great amount of effort in determining the carcinogenicity of numerous persistent organic pollutants (POPs). During February 2013 IARC meetings, an expert panel decided to classify polychlorinated biphenyls (PCBs) as carcinogenic to humans. This is the highest carcinogen rating used by IARC.
The new classification for PCBs is of major importance in the determination of how significant a role exposure to POPs takes in cancer causation. Current IARC classifications for POPs are provided below.
PCBs are classified as carcinogenic to humans.
2,3,7,8-Tetrachlorodibenzo-p-dioxin is classified as carcinogenic to humans.
Chlordane and DDT are classified as possibly carcinogenic to humans.
Hexachlorobenzene and hexachlorocyclohexanes are classified as possibly carcinogenic to humans.
Many other POPs are listed as not classifiable due to data limitations.
The IARC classifications for POPs make clear the fact that total POPs exposure, which includes exposure to many PCBs, is carcinogenic to humans. This means that the total POPs exposure entailed in consumption of mainstream food supply animal-fat-containing foods, including meats, fish, dairy products and eggs, causes cancer in humans. Total POPs exposure is what matters in public health protection efforts due to the fact that many POPs are present in animal-fat-containing foods. Consumers are exposed to mixtures of POPs, not individual POPs. The IARC classifications for POPs make clear the fact that minimizing POPs exposure will lead to decreases in cancer incidence.
POPs exposure causes cancer in several ways. Gestational POPs exposure leads to changes in the packaging of the DNA in the chromosomes of the developing organism. These changes are referred to as epigenetic effects. Additionally, gestational dioxin exposure has been reported to cause abnormalities in the morphology of breast tissue, which are believed to be associated with increased breast cancer risk. Morphological abnormalities in prostate tissue have been associated with gestational dioxin exposure. These abnormalities are considered to correlate with increased prostate cancer risk. Dioxin exposure that takes place during the life of the individual organism leads to increased rate of growth of cancer cell lines. This process is referred to as promotion. When cancer cells grow faster, the clinically diagnosable stage of the disease occurs at an earlier age.
Much of the scientific research has been conducted using animal models. This is done because of ethical and practical matters. Humans cannot legally be given doses of POPs. Laboratory animals have shorter life spans, making studies less time consuming. Cancer has been found to develop in similar ways in all mammals, making the use of laboratory animals a valid means of conducting research.
The IARC classifications are available at the URL named below: http://monographs.iarc.fr/ENG/Classification/index.php.
Donald L. Hassig, director
Cancer Action NY