Healthy Milk, Healthy Baby
Chemical Pollution and Mother's Milk
BACK TO CHEMICAL OVERVIEW
Hexachlorobenzene (HCB) is a persistent organochlorine chemical that is both a pesticide and an industrial byproduct. Its main use is as a fungicide on seed grains, including wheat, barley, oats and rye.1 It also occurs as an impurity in other fungicides at low levels.2 It also had other uses in the past, including as a disinfectant in soaps.
HCB is formed as an industrial byproduct in chlorination processes, such as wastewater treatment. It also forms as a byproduct in the manufacturing and production of the wood preservative pentachlorophenol, of such chlorinated solvents as perchloroethylene and carbon tetrachloride and of various pesticides.3
HCB in the Body
HCB can contaminate air, soil, grass and food. Once it enters the environment, it breaks down very slowly, making it extremely persistent.
One reason for its slow breakdown is that it does not dissolve well in water. It tends to stick very strongly to soil particles, as well as to sediment on the bottom of lakes and rivers. It can also build up in wheat, grasses, some vegetables and other plants when it is present in soil.4 Soil contamination by HCB has occurred as a result of the improper disposal of HCB-containing industrial waste (often referred to as "hex waste").5
Because of HCB's persistence in soil and water, humans can be exposed to it in a number of ways. The major route of human exposure is through food: eating food produced in contaminated soil, eating contaminated fish and drinking milk or eating dairy products or meat from cattle that grazed on contaminated pastures.6 Other, less common, routes of human exposure to HCB include drinking contaminated water, breathing low levels in contaminated air, eating or touching contaminated soil and working at a factory or in an industry that produces HCB as an unintentional byproduct.7
In Europe, the importance of diet as an exposure pathway was shown in a circumstance where livestock were fed HCB-treated grain. The meat and meat products made from the exposed cattle and pigs were contaminated with HCB.8 A similar incident occurred in the United States in the mid-1970s in an industrial area of Louisiana, when cattle were quarantined because of especially high levels of HCB in their milk and fat. The cattle were exposed because the soil and grass they ate were contaminated from the disposal of hex wastes.9
HCB can be eliminated from the human body in urine, feces and breast milk. HCB may also be transferred to the fetus across the placenta during pregnancy.10 Levels of HCB in women have been found to decrease with each successive breast-fed child and with increased breastfeeding time.11
Controlling Exposures: Bans and Restrictions
As of 2003, HCB had been banned or restricted as a pesticide in 23 nations, and it had been made illegal for import in 69 nations.12 While many countries have restricted the use of HCB as a pesticide, its occurrence as an industrial byproduct is less strictly controlled.
Moreover, listing a chemical as banned or restricted does not guarantee that all use has truly stopped. Considerable time can pass before a country fully enforces a ban, sometimes because companies are allowed to use up their stockpiles of the chemical and sometimes because of weak government enforcement. Also, countries sometimes permit chemicals that are otherwise banned to be used for special purposes.
HCB has not been used for commercial purposes in the United States since 1965. It has been listed as a pollutant of concern to the EPA's Great Waters Program because of its persistence in the environment, its potential to bioaccumulate and its toxicity to humans and the environment.13
Assessing the Extent of Exposure: Limits and Benchmarks
Most chemicals that are either in widespread use or that have caused widespread contamination are subject to national and international benchmark levels, established to protect public health. But different agencies may have markedly different levels they consider "safe." These differences usually reflect the agencies' varying perspectives, as well as the kind of data they reviewed in setting levels. Conclusive evidence demonstrating that any one of these benchmarks is protective or superior to the others does not exist.
The Canadian Health Protection Branch has set a tolerable daily intake (TDI) level of 0.27 micrograms per kilogram per day (µg/kg/day).14 Infant consumption of breast milk with average detected levels of HCB can frequently surpass this benchmark. The U.S. EPA has set a maximum contaminant level (MCL) of one part per billion (ppb) in drinking water.
Breast Milk monitoring Studies Measuring Hexachlorobenzene
Studies looking at HCB in breast milk have been conducted in the following countries:
Data from these studies are not all complete, however. In addition, countries not on this list may also have detectable levels of HCB residues in breast milk, since the list reflects only those areas where studies have been conducted, not just where HCB is measurable. The following section discusses issues that make it difficult to interpret the data.
Limitations of Studies Measuring Hexachlorobenzene
It is often difficult to draw conclusions about national and international trends in HCB contamination because of the many factors affecting measured levels, and because of limitations in the way data are reported. Some of these challenges include:
- Absence of standardized methodology. No accepted and standardized method for conducting breast milk monitoring studies has been established. Thus, differences may arise in the sampling time -- when the breast milk is collected or in the birth histories of the mothers -- women who have breast-fed multiple children might be mixed in with women who are breastfeeding for the first time.
- Distinct regional differences in HCB use and contamination. HCB is both an agricultural pesticide and an industrial byproduct, so its concentration in a given area depends on what is produced or grown in that area. Therefore, national averages may obscure the different exposure scenarios in the various regions of a given country.
- Few studies. Many countries do not have multiple studies over time. Instead, the information on HCB residues may be just a snapshot of a particular time. Where that is the case, it is difficult to generalize about how the conditions in a country may have changed over time.
- Small study populations. Because of the cost and time involved, many studies measuring HCB levels in breast milk test only a few people. In instances where the only data on a country's HCB exposure levels are from studies with small sample sizes, it is difficult to draw reliable conclusions about the entire population's exposure.
- Bias. The selection of study participants often presents challenges. In many studies, women may have been chosen to participate based on potentially high exposure to the chemical of interest, thereby driving average values from the study higher.
Some Important Examples of Hexachlorobenzene in Breast Milk
Several useful studies on hexachlorobenzene are available.
HCB has been detected in breast milk around the world. It is also commonly found in other fatty tissues.15 Historically, women in areas with less industrialization have had significantly lower levels of HCB in their breast milk. For instance, average HCB levels detected in breast milk in Kenya in the mid-1980s were just 1/100th of average levels found in Sweden and Germany at a similar time.16
HCB levels in breast milk have declined in some countries over the past two decades, probably the result of changes in fungicide use and procedural improvements in industry that have resulted in a reduction in the production of HCB byproducts.
The examples of HCB breast milk studies presented here are divided into four types:
- Unique exposure situations caused by diet
- Time trend examples -- studies that have looked at average levels of HCB in breast milk in a given location over a number of years
- Differences in average levels among different countries
- Comparisons and differences within countries depending on different regional use and exposure patterns
Unique Exposure Situations: Diet and Industrial Exposure
The most notorious example of breast milk contamination by HCB occurred in Turkey in the 1950s. During a period when bread wheat was unavailable, HCB-treated seed wheat intended for agriculture was used for food. Between 1955 and 1959, 500 people were fatally poisoned by eating bread made with the contaminated seed. More than 4,000 people fell ill as a result of the exposure. Most of the sick were affected with a liver condition called porphyria cutanea tarda, which disturbs the metabolism of hemoglobin and results in skin lesions. The poisoning was often fatal for children. In some villages, almost all breastfeeding children under the age of two, whose mothers had eaten tainted bread, died. Locally, this condition was called "pembe yara" and probably resulted from high doses of HCB passed on through the breast milk. In one mother's breast milk during the incident, the HCB level was found to be 20 parts per million in lipid, approximately 2,000 times the average levels of contamination found in breast milk samples around the world.17 Follow-up studies 20 to 30 years after the poisoning found average HCB levels in breast milk were still more than seven times the average for unexposed women in that part of the world,18 and 150 times the level allowed in cow's milk.19
Severe health effects from HCB exposure in breast milk are not common. In Turkey, the "pembe yara" outbreak occurred because of direct exposure to acutely poisonous levels. In most cases where HCB is detected in breast milk, the dose is far lower. However, the Turkey example illustrates the potential for dietary HCB exposure and lactational transfer.
The importance of dietary exposure to HCB has been demonstrated in many studies. In Germany, women who followed a healthy diet (low meat consumption and high vegetable and fruit intake) for at least three years had much lower levels of HCB in their breast milk. Conversely, women who ate more than 700 grams (1.5 pounds) of meat per week were found to have higher levels of HCB.20
Sweden has witnessed a clear decline in the levels of HCB detected in breast milk. Figure 1 illustrates this marked decrease. In 1980, HCB was withdrawn in Sweden from use as a fungicide. In addition, HCB's production as an industrial byproduct decreased with improvements in industrial technologies. The average concentrations found in breast milk varied in the 1970s, but scientists have measured a steady decline since the ban.21
Norway experienced a similar decrease, with levels of HCB in breast milk dropping by 65 percent between the mid-1970s and early 1990s. HCB was never used as a fungicide in Norway, so it is thought that the decreased levels are a result of improvements in industrial processes, especially in wood treatment.22
Figure 2 shows how HCB levels in breast milk have drastically decreased in the North Rhine Westphalia region of Germany.23 Over the course of a decade, HCB levels in breast milk declined by more than 85 percent. Again, the decline may be a result of changes in fungicide use and improvements in various production practices.
Japan banned HCB and most other organochlorine compounds in the early 1970s, and organochlorine compounds have been measured in breast milk in the city of Osaka since 1972. HCB levels were not recorded before 1980, but Figure 3 shows that Osaka women's breast milk HCB contamination levels fell by 70 percent between 1980 and 1998, in line with the available time-trend data from Europe.24 Studies conducted in Belgium, Canada, Denmark, the Netherlands and Switzerland suggest a decline in the HCB levels found in breast milk there also.25
In the Czech Republic, HCB levels found in breast milk in Prague appear to have fallen by nearly 50 percent in just six years. Figure 4 compares data collected in 1993 and 1994 with data collected with similar methodology in 2000. The data from the latter study may be somewhat downwardly biased, as a third of the milk sample donors were nursing their second child, while all of the rest of the donors in both studies were nursing their first child. (Normally, breast milk pollutant levels are measured during a woman's first lactation because pollutant concentrations decrease significantly with additional lactations and duration of breastfeeding.26) However, this large reduction in contamination seems noteworthy, regardless of this potential bias.27
Figure 5 shows high international variability in HCB levels in breast milk measured in 17 countries during the 1990s. The data from various international studies in this graph reflect the most recent research, and are the product of similar methodologies and adequate sample sizes. That said, international comparisons of contaminants in breast milk are difficult to make because of wide variations in data-collection and reporting methods, because few studies were conducted in the same year and because some of the sample populations may reflect higher or lower exposure levels than the national averages.
The concentration levels shown for Australia, the Czech Republic, the Slovak Republic and the Ukraine in Figure 5 were included as examples of unique or particularly high HCB exposures that may not reflect true national averages, but which may represent large portions of the nations' populations. The available data can not elucidate the exact causes of these elevated levels, but conditions in the regions where the studies took place indicate that these exposures may be related to the proximity of the study populations to heavy industrial areas or to the use of HCB for pest control.
Some of the breast milk donors in Australia were from urban neighborhoods close to an industrial area in Victoria that had a history of industrial accidents, and others were from a rapidly developing suburban area, where numerous new houses had recently been treated for termites.28 The sample populations from the Czech Republic, the Slovak Republic and the Ukraine were made up of mothers living in Prague, Bratislava and Kyiv and Dniprodzerzhinsk -- cities that support much of their respective nations' heavy industry. The breast milk donors in these Eastern European studies were not specifically chosen from neighborhoods close to industrial facilities, however, so the very high breast milk HCB levels in these studies most likely reflect widespread problems with urban industrial pollution in these regions and related contamination of food sources.29
It is notable that the sample population used to determine the comparatively low HCB level shown for the United States on this graph was comprised of members and spouses of a New York State anglers' club living in counties adjacent to Lake Ontario. Lake Ontario fish have been shown to have high levels of some organic pollutants, and this study cohort was developed to assess whether consumption of fish from Lake Ontario was contributing to elevated organic pollutant levels in women's breast milk in the region. Thus, the low HCB level shown for the United States in Figure 5 could actually be somewhat higher than the national average.30
National Variations In HCB Levels
HCB concentrations in breast milk differ depending on regional exposure patterns. For example, in France, breast milk from recent Algerian immigrants contained three times as much HCB as that of native French women, suggesting a marked difference in their exposure early in life.31
In many countries, a clear difference emerges between HCB exposures in industrial and non-industrial areas. In the Czech Republic, Figure 6 shows incrementally higher levels of HCB measured in breast milk in more heavily industrialized areas. The more industrial areas (Prague and Kladno) are home to a variety of industries using combustion processes that emit heightened levels of HCB. The agricultural region of Uherske Hradiste has experienced high environmental chemical burdens from emissions and PCB contamination from a paint factory, but there is little other industry in the area, and HCB levels in the region are lower than in the other two areas.32
In Russian Siberia, exposures to HCB have been difficult to analyze, due to the area's variety of contamination pathways and the possibility that more than one factor has heavily influenced HCB levels in breast milk. A study in 1992 found that HCB levels in the breast milk of women living in the highly industrialized Kola Peninsula of the arctic Russian Siberia were twice as high as in Norway and the Netherlands.33
The same principal researcher measured HCB levels in four areas of arctic and sub-arctic Russian Siberia again between 1996 and 1997. Figure 7 shows that the latter study found HCB levels in Naryan-Mar, a small, non-industrial arctic town, equal to levels found in industrial regions of the Kola Peninsula. Levels found in sub-arctic towns were all significantly lower, although one of these towns, Arkhangelsk, was home to a paper mill, along with chemical and wood industries. Researchers have suggested that in addition to the influence of industry, higher levels of organic pollutants such as HCB in arctic locations could be due to higher consumption of contaminated fish in arctic populations, atmospheric transport and deposition or collection and transport of contaminants in rivers that flow northward, such as the Pechora, along which Naryan-Mar is situated.34
The discrepancy between breast milk HCB levels in northern and southern regions can be seen in the Western Hemisphere as well. Figure 8 shows that breast milk samples donated in 1996 by indigenous mothers in the District of Keewatin in northern Canada were 66 percent higher than pooled samples from the Great Lakes region of southern Canada in 1992. Since the District of Keewatin is not industrialized, this difference is likely due to atmospheric deposition of organic pollutants and consumption of greater amounts of contaminated fish in northern Canada.35
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Chlordane | DDT | Dieldrin, Aldrin and Endrin | Hexachlorobenzene | Hexachlorocyclohexane | Heptachlor | Mirex | Nitro Musks | Toxaphene | Dioxins and Furans | PBDEs | PCBs | Solvents | Lead, Mercury, Cadmium and Other Metals
1. Jensen, A.A. and S.A. Slorach, Chemical Contaminants in Human Milk, Boca Raton Ann Arbor Boston: CRC Press, Inc. (1991); Courtney, K.D. "Hexachlorobenzene (HCB): A Review," Environmental Research; 20 (1979): pp. 225-266.
15. Abbott, D.C., et al. Organochlorine "Pesticide Residues in Human Fat in the United Kingdom 1976-77," British Medical Journal ; 283 (1981): pp. 1425-1428; Mes, J., D.J. Davies, and D. Turton, "Polychlorinated Biphenyl and Other Chlorinated Hydrocarbon Residues in Adipose Tissue of Canadians," Environ Contam Toxicol 28 (1982): pp. 97-104.
17. Jensen, A.A. and S.A. Slorach, Chemical Contaminants in Human Milk , Boca Raton Ann Arbor Boston: CRC Press, Inc. (1991); Courtney, K.D. "Hexachlorobenzene (HCB): A Review," Environmental Research 20: (1979): pp. 225-266.
18. Gocmen, A., et al. "Hexachlorobenzene Episode in Turkey," Biomedical Environmental Science 2(1) (1989): pp. 36-43; Cripps, D.J., et al. "Porphyria Turcica Due to Hexachlorobenzene: A 20 to 30 Year Follow-up Study on 204 Patients," British Journal of Dermatology 111(4) (1984): pp. 413-422.
20. Schade, G. and B. Heinzow, "Organochlorine Pesticides and Polychlorinated Biphenyls in Human Milk of Mothers Living in Northern Germany: Current Extent of Contamination, Time Trend from 1986 to 1997 and Factors that Influence the Levels of Contamination," The Science of the Total Environment 215 (1998): pp. 31-39.
22. Johansen, H.R., et al. "Congener-specific Determination of Polychlorinated Biphenyls and Organochlorine Pesticides in Human Milk from Norwegian Mothers Living in Oslo," Journal of Toxicology and Environmental Health 42 (1994): pp. 157-71.
23. Furst, P., C. Furst, and K. Wilmers, "Human Milk as a Bioindicator for Body Burden of PCDDs, PCDFs, Organochlorine Pesticides, and PCBs," Environmental Health Perspectives Journal 102 (1994): pp. 187-93.
24. Konishi, Y., K. Kuwabara, S. Hori, "Continuous Surveillance of Organochlorine Compounds in Human Breast Milk from 1972 to 1998 in Osaka, Japan," Archives of Environmental Contaminants and Toxicology vol. 40, no. 4 (2001): pp. 571-578.
26. Schecter, A., J.J. Ryan, O. Papke, "Decrease in Levels and Body Burden of Dioxins, Dibenzofurans, PCBs, DDE, and HCB in Blood and Milk in a Mother Nursing Twins Over a Thirty-Eight Month Period," Chemosphere vol. 37, no. 9-12 (1998): pp. 1807-1816.
27. Cajka, T. and J. Hajslova, "Polychlorinated Biphenyls and Organochlorine Pesticides in Human Milk from the Locality Prague, Czech Republic: A Comparative Study," Bulletin of Environmental Contaminants and Toxicology vol. 70, no. 5 (2003): p. 913-919; Schoula, R., J. Hajslova, V. Bencko, J. Poustka, K. Holadova, V. Vizek, "Occurrence of Persistent Organochlorine Contaminants in Human Milk Collected in Several Regions of Czech Republic," Chemosphere vol. 33, no. 8 (1996): 1485-1494.
29. Cajka, T. and J. Hajslova, "Polychlorinated Biphenyls and Organochlorine Pesticides in Human Milk from the Locality Prague, Czech Republic: A Comparative Study," Bulletin of Environmental Contaminants and Toxicology vol. 70, no. 5 (2003) pp. 913-919; Prachar V., M. Veningerova, J. Uhnak, " Levels of Polychlorinated Biphenyls and Some Other Organochlorine Compounds in Breast Milk Samples in Bratislava," The Science of the Total Environment ; supp. pt. 1 (1993): pp. 237-242; Kocan, A., J. Petrik, B. Drobna, J. Chovancova, "PCBs and Some Organochlorine Pesticides in the Human Population of Selected Areas of the Slovak Republic, I. Blood.," Chemosphere ol. 29, no.9-11 (1994): pp. 231-2325; Gladen et al., Organochlorines in "Breast Milk from Two Cities in Ukraine," Environmental Health Perspectives , vol. 107, no. 6 (June 1999): 459-462.
30. Kostyniak, P.J., C. Stinson, H.B. Greizerstein, J. Vena, G. Buck, P. Mendola, "Relation of Lake Ontario Fish Consumption, Lifetime Lactation, and Parity to Breast Milk Polychlorobiphenyl and Pesticide Concentrations," Environmental Research Section A vol. 80, 2 pt. 2 (1999): pp. S166-S174.
34. Ibid; Polder, A., J.O. Odland, A. Tkachev, S. Foreid, T.N. Savinova, J.U. Skaare, "Geographic Variation of Chlorinated Pesticides, Toxaphenes, and PCBs in Human Milk from Sub-Arctic and Arctic Locations in Russia," The Science of the Total Environment vol. 306, no. 1-3 (2003): pp. 179-195.
Cites for International Studies Used in Comparison Chart
Australia - Quinsey, P.M., D.C. Donohue, J.T. Ahokas, "Persistence of Organochlorines in Breast Milk of Women in Victoria, Australia," Journal of Food and Chemical Toxicology vol. 33, no. 1 (1995): pp. 49-56.
Brazil - Paumgartten, F.J., C.M. Cruz, I. Chahoud, R. Palavinskas, W. Mathar, "PCDDs, PCDFs, PCBs, and Other Organochlorine Compounds in Human Milk from Rio de Janeiro Brazil," Environmental Research Section A vol. 83,no. 3 (2000): pp. 293-297.
Canada - Newsome, W.H. and J.J. Ryan, "Toxaphene and Other Chlorinated Compounds in Human Milk from Northern and Southern Canada: A Comparison," Chemosphere vol. 39, no. 3 (1999): pp. 519-526.
Czech Republic - Cajka, T. and J. Hajslova, "Polychlorinated Biphenyls and Organochlorine Pesticides in Human Milk from the Locality Prague, Czech Republic: A Comparative Study," Bulletin of Environmental Contamination and Toxicology vol. 70, no. 5, (2003): pp. 913-919.
Ghana - Ntow, W.J., Organochlorine "Pesticides in Water, Sediment, Crops, and Human Fluids in a Farming Community in Ghana," Archives of Environmental Contamination and Toxicology vol. 40, no. 4 (2001): pp. 557-563.
Indonesia - Burke. E.R., A.J. Holden, I.C. Shaw, "A Method to Determine Residue Levels of Persistent Organochlorine Pesticides in Human Milk from Indonesian Women," Chemosphere vol. 50, no. 4 (2003): pp. 529-535.
Iran - Cok, I., A.E. Karakaya, B.L. Afkham, S. Burgaz, "Organochlorine Pesticide Contaminants in Human Milk Samples Collected in Tebriz (Iran)," Bulletin of Environmental Contamination and Toxicology vol 63. no. 4 (1999): p. 444-450.
Japan - Konishi, Y., K. Kuwabara, S. Hori, "Continuous Surveillance of Organochlorine Compounds in Human Breast Milk from 1972 to 1998 in Osaka, Japan," Archives of Environmental Contamination and Toxicology vol. 40, no. 4 (2001): p. 571-578.
Kazakhstan - Lutter, C., V. Iyengar, R. Barnes, T. Chuvakova, G. Kazbekova, T. Sharmanov, "Breast Milk Contamination in Kazakhstan: Implications for Infant Feeding," Chemosphere vol. 37, no. 9-12, (1998): pp. 1761-1772.
Mexico - Waliszewski, S.M., A.A. Aguirre, R.M. Infanzon, C.S. Silva, J. Siliceo, "Organochlorine Pesticide Levels in Maternal Adipose Tissue, Maternal Blood Serum, Umbilical Cord Serum, and Milk from Inhabitants of Veracruz, Mexico," Archives of Environmental Contamination and Toxicology vol. 40, no. 3 (2001): pp. 432-438.
New Zealand - Bates, M., B. Thomson, N. Garrett, "Reduction in Organochlorine Levels in the Milk of New Zealand Women," Archives of Environmental Health vol. 57, no. 6 (Nov./Dec. 2002): pp. 591-597.
Russia - Polder, A., J.O. Odland, A. Tkachev, S. Foreid, T.N. Savinova, J.U. Skaare, "Geographic Variation of Chlorinated Pesticides, Toxaphenes, and PCBs in Human Milk from Sub-Arctic and Arctic Locations in Russia," Science and the Total Environment vol. 306 (May 1, 2003): pp. 179-195.
Slovak Republic - Prachar, V., M. Veningerova, J. Uhnak, "Levels of Polychlorinated Biphenyls and Some Other Organochlorine Compounds in Breast Milk Samples in Bratislava," Science and the Total Environment Supp. pt. 1 (1993): pp. 237-242.
Sweden - Noren, K. and D. Meironyte, "Certain Organochlorine and Organobromine Contaminants in Swedish Human Milk in Perspective of Past 20-30 Years," Chemosphere vol. 40, no. 9-11 (2000): pp. 1111-1123.
Ukraine - Gladen, B.C., S.C. Monaghan, E.M. Lukyanova, O.P. Hulchiy, Z.A. Shkyryak-Nyzhnyk, J.L. Sericano, R.E. Little, "Organochlorines in Breast Milk from Two Cities in Ukraine," Environmental Health Perspectives vol. 107, no. 6 (1999): pp. 459-462.
United Kingdom - Harris, C.A., S. O'Hagan, G.H. Merson, "Organochlorine Pesticide Residues in Human Milk in the United Kingdom 1997-8," Human and Experimental Toxicology vol. 18, no. 10 (1999): pp. 602-606.
United States - Kostyniak, P.J., C. Stinson, H.B. Greizerstein, J. Vena, G. Buck, P. Mendola, "Relation of Lake Ontario Fish Consumption, Lifetime Lactation, and Parity to Breast Milk Polychlorobiphenyl and Pesticide Concentrations," Environmental Research Section A vol. 80, 2 pt. 2, (1999): pp. S166-S174.
last revised 3.25.05