PCBs are Associated with Lymphoma

by | Sep 16, 2013 | 2007, Cancer, Pollution

Written by Tatjana Djakovic, Staff Writer. This article discusses synthetic chemicals called  poly-chlorinated Biphenyls (PCBs) which are used in industrial processes and are implicated in Non-Hodgkin Lymphoma, a cancer of white blood cells. 

PCBs (Polychlorinated biphenyls) are carcinogenic substances that are directly involved in causing cancer. They are synthetically made substances, with no natural origin, which has been linked to a type of cancer of the immune system called Non-Hodgkin Lymphoma (NHL). Non-Hodgkin Lymphoma is a group of white blood cell malignancies that originate in B cells, T cells, or natural killer (NK) cells that protect the immune system from foreign invaders. In the United States, the incidence of NHL has increased by an average of 3.6% per year from 1975 to 1991, and continued to rise from 1991 to 2008 at a slower rate of 0.5% per year on average. Scientists noticed a substantial increase in the incidence of lymphomas in the years of 1983 to 1992 across all age groups, which was in accord with environmental exposures from polychlorinated biphenyls (PCB’s) 1.

PCB’s are used in the industrial processes due to their inability to become oxidized (gain oxygen atoms) in the natural environment. In addition, they are nonflammable with high boiling points and work well as an electrical insulator. However, the chemical stability is a downfall when it comes to human health because it has a long half-life (8 to 15) years, which is the time for half of it to decay, and therefore accumulates in soil, air, water and animals such as fish for long periods of time 2. In order to assess the risk of developing Non-Hodgkin Lymphoma after due exposure to PCBs has been determined in the current population based case-control study in British Colombia, Canada.

The study included 455 subjects that were newly diagnosed with Non-Hodgkin Lymphoma aged 20-79 years old. The subjects provided blood samples before starting chemotherapy, as it is known to change the levels of PCBs in the blood. In addition, a total of 463 healthy subjects were used as a control. Different types of PCBs were tested which include slight variations in the chemical structure, but still pose a risk for cancer formation.  Overall, there was a significant association between total levels of PCBs and NHL; in fact those with highest concentration of PCBs (more than 220 nanograms/gram) were more than twice as likely to develop NHL as those that had the lowest levels (p<0.001).

In addition, scientists found that six pesticides whose chemical structure included a benzene ring and chlorine as in the case of PCBs, were also significantly associated with formation of NHL (p=0.045) 3.  The mechanism of how PCBs cause cancer has not yet been determined. Scientists speculate that it may be due to alterations in the immune system so that it is not able to initiate an attack on a foreign substance before it does harm to the body 4. Exposure to PCBs have been associated with increased incidence of infections in children of capacitor manufacturing workers that have breast-fed for a long time, which is indicative of PCBs causing an immune disruption 5.

Another study has determined that PCBs altered the levels of natural killer cells, which are cells of the immune system that eliminate early malignant cells. In the study, participants that consumed fatty-fish (which has high accumulation of PCBs) had reduced levels of natural killer cells (p=0.01) 6.

There is strong evidence on the causal role of PCBs in the formation of NHL due to suppression of immune system. The PCBs have been banned from being commercially produced in the United States in 1979, however some products and materials made before then still may contain PCB’s. These materials include electrical equipment such as transformers and capacitors, medical equipment (such as X-ray machines) and household appliances (such as refrigerators and microwave ovens).

PCB’s can easily be absorbed through the skin or inhaled as a vapor from overheated equipment that contains PCBs. In order to prevent exposure to PCB, it is important to check equipment labels, inspect for leaks or damage. It is recommended to wear protective clothing, and if one becomes exposed, wash with soap and water and dispose of damaged clothing. As with most carcinogenic substances, the accumulation of exposures has detrimental effects, rather than one single exposure 7.

Source: Spinelli, John J., et al. “Organochlorines and risk of non‐Hodgkin lymphoma.” International journal of cancer 121.12 (2007): 2767-2775.

© 2007 Wiley-Liss, Inc.

Posted September 9, 2013.

References:

  1. Howlader N, Noone A, Krapcho M, et al. SEER Cancer Statistics Review. Bethesda, MD: National Cancer Institute; 1975-2008. In:2011.
  2. Wimmerova S, Lancz K, Tihanyi J, et al. Half-lives of serum PCB congener concentrations in environmentally exposed early adolescents. Chemosphere. 2011;82(5):687-691.
  3. Spinelli JJ, Ng CH, Weber JP, et al. Organochlorines and risk of non-Hodgkin lymphoma. Int J Cancer. 2007;121(12):2767-2775.
  4. McConnachie PR, Zahalsky AC. Immune alterations in humans exposed to the termiticide technical chlordane. Archives of environmental health. 1992;47(4):295-301.
  5. Hara I. Health status and PCBs in blood of workers exposed to PCBs and of their children. Environmental health perspectives. 1985;59:85-90.
  6. Svensson BG, Hallberg T, Nilsson A, Schutz A, Hagmar L. Parameters of immunological competence in subjects with high consumption of fish contaminated with persistent organochlorine compounds. Int Arch Occup Environ Health. 1994;65(6):351-358.
  7. EPA. Polychlorinated Biphenyls (PCBs). https://www.epa.gov/pcbs.