Pesticides and Breast Cancer

Two recent studies in the US implicate the pesticide DDT as a possible cause of breast cancer. Women in Connecticut and New York with breast cancer had higher levels of DDE (a metabolite of DDT) in their breast tissue(1) and blood (serum)(2) than women without the disease. In Helsinki, Finland, tissue from women with breast cancer (pooled samples) had higher levels of the pesticide hexachlorocyclohexane (beta-HCH), but not DDE, compared to tissue from women without the disease(3). In Israel, the only country to report a decrease in the incidence of breast cancer, the authors postulate the lower rates were due to a banning of the heavily used pesticide, hexachlorocyclohexane (HCH, BHC)(4). By Marion Moses.

Breast cancer is the most prevalent cancer in women in the US where estimates are that two million will be diagnosed with the disease in the 1990s, and 460,000 will die of it. From 1950 to 1989 the incidence of breast cancer increased by 53%(5); since 1940 mortality rates have been increasing by about 1% a year in industrialised countries(6). The cause is unknown for 70% of the cases. For the 30% with known risk factors, the most significant one is lifetime exposure to female hormones (oestrogens) which play a critical role in the development of breast cancer.

          Many xenobiotics(7), including pesticides, PCBs (polychlorinated biphenyls), and PAHs (polyaromatic hydrocarbons), affect oestrogen production and metabolism, Such oestrogenic substances which are foreign to the body are called xenoestrogens(8). Pesticides that are xenoestrogens or affect reproduction include DDT and its metabolite DDE; chlordane, dieldrin, heptachlor, hexachlorobenzene, and hexachloro-cyclohexane (alpha, beta, gamma-HCH). Since these pesticides or their metabolites break down slowly and are stored in fatty tissue, residues can remain in the body years after exposure. All of the above mentioned pesticides are animal carcinogens.

      Xenoestrogenic pesticides currently in wide use in agriculture are the chlorinated hydrocarbons endosulfan and methoxy-chlor. They are much less persistent than DDT and are not stored in body fat. Other pesticides besides the chlorinated hydrocarbons, however, may increase the risk of breast and other cancers in women. Atrazine, a persistent herbicide that is the most widely used pesticide in the US, and an extensive groundwater contaminant, causes mammary cancer in rats and is linked to ovarian cancer in an agricultural area of Italy(9). 

      Other pesticides besides atrazine, not in the chlorinated hydrocarbon family, that cause mammary tumours in rats include the herbicides cyanazine and ethafluralin; the fungicide captafol, the insecticides dichlorvos (DDVP) and flucythrinate; and the fumigants ethylene dibromide, and ethylene dichloride(10).

      Human breast milk is contaminated with xenoestrogenic and carcinogenic pesticide residues, and results from selected studies throughout the world are summarised in Table 1. Pesticide contamination of breast milk has been found even in remote villages in Papua New Guinea and India. All of the pesticides in Table 1, except gamma-HCH (lindane), are banned in the US. Most are still widely used in developing countries in agriculture and for vector control for malaria and other tropical diseases. Third World women thus suffer the greatest exposure to pesticide residues; their children are much more likely to be breast fed and for a much longer period of time. The transfer of pollutants to the nursing infant is well documented, and mothers nursing their second or later child have lower levels of pesticides in their milk than mothers nursing their first child(11). Lactation is thus a way to decrease the mother’s body burden of pesticides—by passing the burden to her infant.

      Reviewing the breast milk contamination data for Table 1 makes clear the need to establish international protocols for the collection, measurement, and bio-monitoring of pesticides and other xenobiotics in human breast milk. Cross-cultural comparisons within and between different countries are valuable epidemiological tools in the study of the health of women and children of all ages and races. Suitable populations of pre-adolescents and adolescents should be included in any plan to document and monitor exposures of women and children to toxic substances. It has been stated that if we know how cancer changes cells, what the basic mechanism of action is, then we can figure out how to stop it, and the exposure to a carcinogen would not matter. While this may be true for cancer, it ignores the fact that carcinogenicity is only one aspect of toxicity. In the case of pesticides important non-cancer endpoints are neurotoxicity, teratogenicity, infertility, subfertility, and immunotoxicity among others. Reliance on a single end point—cancer—to determine health risks of pesticide exposure is inappropriate as a basis of regulatory or public health policy.

      The failure to regulate toxic pesticides has resulted in contamination of the bodies of the millions of inhabitants of the earth. The indiscriminate use of the persistent pesticides such as DDT, dieldrin, chlordane, hexachlorobenzene and hexa-chlorocyclohexane results in contamination of the entire ecosystem(12). That we continue to allow billions of pounds of toxic pesticides to be deliberately put into the global environment is a public health failure of enormous magnitude.

      The preliminary findings of a possible link between pesticides and breast cancer is already having an impact on the pesticide debate. Women with breast cancer are a cross-section of the US and many are very active in breast cancer action coalitions both locally and nationally. It is the efforts of these citizen activists that are the major impetus for getting scientific resources and government attention to this important disease of women.

      The involvement of such women in the pesticides issue, even if only peripherally, can only benefit efforts towards pesticide reform. It also benefits the hundreds of thousands of farm workers in the US, by focusing attention on an issue that so directly affects their health and that of their children.

      In breast cancer research pesticides are only one of several environmental exposures that are being considered as risk factors for the disease. But it is important that we look at what we are doing now, what current pesticide exposures are that may put pre-adolescent girls in particular at greater risk. In the US, we may not be using most of the pesticides on the list in Table 1 but we are using others that may be risk factors. Most of the pesticides being used are not persistent and are not stored in the body. Tissue and blood levels will not be useful for finding markers (such as DDE) of past exposure.

      For this reason it is very important to set up comprehensive monitoring programmes, including tissue and other specimen banks for archiving and testing samples, as part of the study of environmental causes for human cancer and other chronic diseases. Good candidates to include, along with blood and urine, are tissues routinely discarded such as placenta and liposuction fat.

      Although the current focus is on breast cancer, we must broaden our vision in the case of pesticides to include other cancers, especially in children, because of placental and breast milk transfer, and the ubiquity of environmental exposure to pesticides, in the home, workplace and community.  

Dr. Marion Moses is the Director of the Pesticide Education Center, PO Box 420870, San Francisco, CA 94142- 0870, US, Tel. +1 415 391 8511.

References:  

1. Falck, F., Ricci, A., et. al., 1992, Pesticides and chlorinated biphenyl residues in human breast lipids and their relation to breast cancer. Archives of Environmental Health, 47:143-146.  

2. Wolf, M.S., Toniolo, P.G., et. al., 1993, Blood levels of organochlorine residues and risk of breast cancer, Journal of National Cancer Institute, 85:648-652.  

3. Mussalo-Rauhamaa, H., Häsánen, Pyysalo, H., et. al., 1990, Occurrence of beta-hexachlorocyclohexane in breast cancer patients, Cancer 66:21224-2128.  

4. Westin, J.B. & Richter, E., 1990, The Israeli breast-cancer anomaly, Annals New York Science 609:269-279.  

5. President’s Cancer Panel Special Commission on Breast Cancer, 1993, A National Strategy, a report to the Nation. National Cancer Institute, Bethesda, Maryland, US.  

6. Davis, D.L., Bradlow, H.L., et. al., 1993, Medical Hypothesis: xenoestrogens as preventable cause of breast cancer, Environmental Health Perspectives, 101:372-377.

7. Xenobiotics—biologically active substances that are not produced by or normally found in the body, i.e. are foreign to it.  

9. Donna, A., Crosignani, P., et. al., 1989, Triazine herbicides and ovarian epithelial neoplasms, Scandinavian Journal Work Environment and Health, 15:47-53.  

10. State of California, Dept of Pesticide Regulation, SB-950 Medical Toxicology Summaries, Sacramento California, US, 1985-current.  

11. Rogan, W.J., Gladen, B.C., et. al., 1986, Polychlorinated biphenyls (PCBs) and dichlorodiphenyl dichloroethane (DDE) in human milk: effects of maternal factors and previous lactation, American Journal of Public Health, 76:172-177.  

12. Colburn, T., Vom Saal, F.S., et. al., 1993, Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environmental Health Perspectives, 101:378-384. 

Table References: 

1. Stacey, C.I., Perriman, W.S., Whitney, S. 1985. Organochlorine pesticide residue levels in human milk: Western Australia, 1979-1980. Archives Environmental Health 40:102-108.

2. Stevens, M.F., Ebell, G.F., Psaila-Savona, P. 1993. Organochlorine pesticides in Western Australian nursing mothers. Medical Journal Australia 158:238-241.

3. Matuo, Y.K., Lopes, J.N.C., Casanova, I.C., et al. 1992. Organochlorine pesticide residues in human milk in the Ribeirão Preto region, state of São Paulo, Brazil. Archives Environmental Contamination Toxicology 22:167-175.

4. Davies, D., Mes, J. 1988. Comparison of the residue levels of some organochlorine compounds in breast milk of the general and indigenous Canadian populations. Bulletin Environmental Contamination Toxicology 40:647-654.

5. Mes, J., Doyle, J.A., Adams, B.R., et al. 1984. Polychlorinated biphenyls and organochlorine pesticides in milk and blood of Canadian women during lactation. Archives Environmental Contamination Toxicology 13:217-223.

6. Zahradnicek, L., Jodl, J., Sevcik, J., et al. 1989. [Foreign substances in maternal milk]. Ceskoslovenska Pediatrie 44(2):80-83. Czech. (Abstract).

7. Wickstrom, K., Pyysalo, H., Siimes, M.A. 1983. Levels of chlordane, hexachlorobenzene, PCB and DDT compounds in Finnish human milk in 1982. Bulletin Environmental Contamination Toxicology 31:251-256.

8. Bordet, F., Mallet, J., Maurice, L., et al. 1993. Organochlorine pesticide and PCB congener content of French human milk. Bulletin Environmental Contamination Toxicology 50:425-432.

9. Ip, H.M.H., Phillips, D.J.H. 1989. Organochlorine chemicals in human breast milk in Hong Kong. Archives Environmental Contamination Toxicology, 18:490-494.

10. Basu, N., Murugesan, K., Bhide, N.K. 1991. DDT levels in human body fat and milk samples from Delhi. Indian Journal Medical Research [B] 94:115-118.

11. Jani, J.P., Patel, J.S., Shah, M.P. 1988. Levels of dichlorodiphenyltrichloroethane and hexachloro-cyclohexane in human adipose tissue of the Indian population. Scandinavian Journal Work Environmental Health 14:201-204.

12. Al-Omar, M.A., Tawfiq, S.J., Al-Ogaily, N. 1985. Organochlorine residue levels in human milk from Baghdad. Bulletin Environmental Contamination Toxicology 35:65-67.

13. Weisenberg, E., Arad, I., Grauer, F., et al. 1985. Polychlorinated biphenyls and organochlorine insecticides in human milk in Israel. Archives Environmental Contamination Toxicology 14:517-521.

14. DiMuccio, A., Camoni, I., Dommarco, R., et al. 1990. Evaluation of p,p’-DDE, p,p’-DDT and polychlorobiphenyls (PCBs) levels in samples of human milk from Rome, Florence, and the surrounding areas. Annali dell Instituto Superiore di Sanita 26(2):155-160. Ital. (Abstract).

15. Taguchi, S., Yakushiji. 1988. Influence of termite treatment in the home on the chlordane concentration in human milk. Archives Environmental Contamination Toxicology 17:65-71.

16. Alawi, M.A., Ammari, N., Al-Shuraiki, Y. 1992. Organochlorine pesticide contaminations in human milk samples from women living in Amman, Jordan. Archives Environmental Contamination Toxicology 23:235-239.

17. Kanja, L.W., Skaare, J.U., Ojwang, S.B.O., et al. 1992. A comparison of organochlorine pesticide residues in maternal adipose tissue, maternal blood, cord blood, and human milk from mother/infant pairs.                       Archives Environmental Contamination Toxicology 22:21-24.

18. Albert, L., Vega, P, Portales, A. 1981. Organochlorine pesticide residues in human milk samples from Comarca Lagunera, Mexico, 1976. Pesticides Monitoring Journal 15:135-138.23:235-239

19. Skaare, J.U., Tuveng, J.M., Sande, H.A. 1988. Organochlorine pesticides and polychlorinated biphenyls in maternal adipose tissue, blood, milk and cord blood from mothers and their infants in Norway. Archives Environmental Contamination Toxicology 17:55-63.

20. Spicer, P.E., Kereu, R.K. 1993. Organochlorine insecticide residues in human breast milk: a survey of lactating mothers from a remote area in Papua New Guinea. Bulletin Environmental Contamination Toxicology 50:540-546.

21. Bouwman, H., Cooppan, R.M., Reinecke, A.J., et al. 1990. Levels of DDT and metabolites in breast milk from Kwa-Zulu mothers after DDT application for malaria control. Bulletin World Health Organization 68:761-768.

22. Karakaya, A.E., Burgaz, S., Kanzik, I. 1987. Organochlorine pesticide contaminants in human milk from different regions of Turkey. Bulletin Environmental Contamination Toxicology 39:506-510.

23. Rogan, W.J., Gladen, B.C., McKinney, J.D. et al. 1986. Polychlorinated biphenyls (PCBs) and dichlorodiphenyl dichloroethane (DDE) in human milk: effects of maternal factors and previous lactation. American Journal Public Health 76:172-177.

24. Takei, G.H., Kauahikaua, S.M., Leong, G.H. 1983. Analyses of human milk samples collected in Hawaii for residues of organochlorine pesticides and polychlorobiphenyls. Bulletin Environmental Contamination Toxicology 30:606-613.

25. Jacobson, J.L., Fein, G.G., Jacobson, S.W., et al. 1984. The transfer of polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) across the human placenta and into maternal milk. American Journal Public Health 74:378-379.

26. Jan, J. 1983. Chlorobenzene residues in human fat and milk. Bulletin Environmental Contamination Toxicology 30:595-599.

27. Krauthacker, B. 1991. Levels of organochlorine pesticides and polychlorinated biphenyls (PCBs) in human milk and serum collected from lactating mothers in the northern Adriatic area of Yugoslavia. Bulletin Environmental Contamination Toxicology 46:797-802.

28. Vukavic, T., Pavkov, S., Cusic, et al. 1986. Pesticide residues in human colostrum: seasonal variations, Yugoslavia. Archives Environmental Contamination Toxicology 15:525-528.

29. Chikuni, O., Skare, J.U., Nyazema, N., et al. 1991. Residues of organochlorine pesticides in human milk from mothers living in the greater Harare area of Zimbabwe. Central African Journal Medicine 37:136-140.

[This article first appeared in Pesticides News No. 22, December 1993, pages 3-5]