Healthy Milk, Healthy Baby
Chemical Pollution and Mother's Milk
BACK TO CHEMICAL OVERVIEW
Polychlorinated biphenyls (PCBs) are a group of common chemicals that are no longer manufactured but that remain in the environment. The term "PCBs" refers to a large group of 209 individual congeners -- members of the same structural group of chemicals with different configurations. PCBs generally occur as a complex mixture of some assortment of these congeners.1
PCBs were used for numerous purposes, including:2
- stabilizers in polymers, paint and adhesives;
- industrial lubricants and coolants in transformers, capacitors and other electrical equipment; and
- insulating materials in electrical transformers, fluorescent lighting fixtures and electrical appliances.
Health Effects of PCBs
PCBs are a complex and hazardous group of chemicals. While their acute toxicity is much lower than many of the organochlorine pesticides and the dioxins, they have serious long-term health effects at relatively low levels. High levels of exposure can cause effects in infants ranging from low birth weight; to abnormalities of the skin, hair and nails; to hearing loss.
The most serious effects of PCBs, however, are on the brain. PCB exposures, particularly before birth, have been linked in humans to lower IQ, hyperactivity, shortened attention span and delayed acquisition of reading skills. PCBs interfere with thyroid hormone, and some researchers believe that this mechanism may explain some of the neurological effects of PCBs. Thyroid hormone is essential for normal growth and development of the brain before birth and throughout infancy. Some PCBs also mimic estrogen, leading to questions about possible associations with such diseases as breast cancer later in life. PCBs are also probable human carcinogens, based on animal studies and some studies of exposed workers.
PCBs in the Body
PCBs are extremely persistent and accumulate in the environment and in living organisms. The chemical properties of PCBs allow them to travel long distances on global air currents, resulting in contamination in such remote northern locations as the Arctic.3
PCBs do not readily dissolve in water. So when PCBs are released into water, most end up binding to sediments.4 PCBs released into the environment eventually enter the food chain and can build up in fish and other marine animals, eventually reaching levels thousands of times higher than their original concentration in water.
Humans are exposed to PCBs in a number of ways, but eating PCB-contaminated food, especially fish, meat and dairy products, is by far the most common exposure route.5 Other less common exposure scenarios include PCB leaks in old appliances or fluorescent lighting fixtures, living near leaking hazardous waste sites that contain PCBs and repairing old PCB-containing transformers.
Historically, mass PCB poisonings have occurred as a result of food contamination.6 In Japan in 1968, poisonings occurred because of PCB-contaminated rice oil.7 A similar incident occurred in Taiwan, China in 1979 from PCB-contaminated cooking oil.8
PCBs occur as an environmental contaminant around the world. Because of their pervasive nature, PCBs' contribution to the overall human body burden of chemicals is significant. Many researchers report that almost all samples of human blood, fat or breast milk show some detectable level of PCBs.9 The majority of breast milk samples tested throughout the world show at least trace levels of PCBs.10
Many studies looking at PCBs in women's bodies have found concentrations in breast milk that are four to ten times higher than in the mothers' blood. However, it is prenatal exposure (via trans-placental transfer) of PCBs that is believed to be more significant to the later health of the child.11 Many researchers have investigated the effect of PCB exposure on infants' neurobehavioral development, and a consensus is emerging that prenatal exposure to PCBs is much more important than exposure in breast milk.12
Controlling Exposure: Bans and Restrictions
PCBs were recognized as hazardous in the 1970s, at least in part as a result of the poisoning incidents in Asia. As a result, international pressure to restrict the use of PCBs has grown.
Because of the evidence of widespread environmental damage, the manufacturing of PCBs in the United States was halted in 1977.13 In many countries, the use of PCBs has been restricted to closed electrical systems.14 As of May 17, 2004, the date the Stockholm Convention entered into force, countries must begin to develop replacements for PCBs and have them in place by 2025. Not later than 2028, governments must dispose of their PCBs in an environmentally sound manner.15
In most of the world, the main risks from PCBs are associated with exposure from the destruction of materials containing them. Thus, although production may have decreased, a vast number of products with high levels of PCBs remain in use. The degradation and disposal of these products is the area of greatest concern.
Assessing the Extent of PCB 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." In the case of PCBs, conclusive evidence demonstrating that any one of these benchmarks is protective or superior to the others does not exist.
The U.S. EPA has set a maximum contaminant level (MCL) of 0.5 parts per billion (ppb) for PCBs in water. The most relevant benchmark level was set by the U.S. Food and Drug Administration: a limit of 0.2 to 3 parts per million (ppm) for PCB residues in milk, eggs, other dairy products, poultry fat, fish, shellfish and infant foods.16 Levels of PCBs in breast milk today in many countries exceed this benchmark level.
Breast Milk Monitoring Studies Measuring PCBs
PCBs have been measured in the breast milk of women from the following countries:
The extent of nation-specific information about PCBs in breast milk only reflects what has been examined thus far. Based on what we know about the pervasive nature of PCB contamination in the food chain and its ability to move great distances, PCBs are likely to occur throughout the world.
Limitations of Studies Measuring PCBs in Breast Milk
Unlike many other chemicals on the POPs list, it is extremely difficult to compare different measurements of PCBs in breast milk -- both within individual countries and between different countries and studies. The challenges arising from PCB data in breast milk include:
- Differences in analytical techniques. The last several decades have seen important changes in the techniques used to measure PCB levels in human tissue, making it difficult to compare recent data with older measurements. In addition, no accepted standardized method for analyzing breast milk for PCBs has emerged, so the problem of incomparable results continues even in new research.
- Number of congeners measured. Reported PCB levels in breast milk vary depending on how many congeners are measured. Some studies measure just one (Webb-McCall method) or only a few congeners considered to be the most prevalent or the most toxic. Others report a group of congeners thought to be an "indicator group" of total PCB contamination. Still others measure all congeners that analytical tools can detect. As a result, reported PCB levels in milk may differ greatly, depending on the choice of congeners sampled in each individual study, making comparisons virtually impossible.
- Differences in reporting. Because PCBs often are present in the environment along with other contaminants, their detection may be reported as a combined toxic equivalency factor that also includes dioxins and furans. In such cases, it is quite challenging to tease out just the component attributable to PCBs.
Some Important Examples of PCBs in Breast Milk
Because of the challenges presented by the data measuring PCBs in breast milk, it is difficult to assess trends. There are some indications that, over the last 25 years, levels have decreased slightly.17
The examples of PCB breast milk studies presented here are divided into four types:
- time trend examples -- long-term studies that have looked at average levels of PCBs in breast milk at one location over a number of years;
- dietary differences and their influence on PCB levels in breast milk;
- differences in average levels of seven of the most abundant and commonly reported PCB congeners among different countries; and
- comparisons and differences within countries depending on different regional use and exposure patterns.
In Sweden, where data have been collected following fairly consistent methods over time, evidence of a downward trend has emerged.18 Figure 1 shows this data.
Another ongoing study of total PCB levels being conducted in Osaka, Japan shows a similar trend in the published data from 1972 to 1998.19
In New Zealand, researchers demonstrated a 68 percent decrease in the six most abundant PCB congeners in breast milk between 1988 and 1998, shown in Figure 3. The study procedures and selection criteria for the 1988 study were replicated in 1998 to test the breast milk of a very similar group of women in the same four areas of New Zealand. The principal objective of the second study was to test whether a number of New Zealand regulatory measures that went into effect during or just before this time helped to reduce exposures to organochlorine pollutants, as intended. These regulatory measures included a 1986 prohibition on importation of PCBs and a 1995 prohibition on PCB storage in the country.20
It would be difficult to prove that the PCB reductions witnessed in this period of time resulted solely from this regulatory action, since a number of other factors, such as non-regulatory incentives and subtle differences in the study population could have contributed to the results. However, this study is valuable because it shows that it may be possible for nations to make rapid progress in decreasing breast milk levels of PCBs through regulatory efforts.
Although most other studies are difficult to interpret and compare, it is clear that diet is very important in determining PCB levels in breast milk.
Many researchers have looked into the role of diet in the level of PCBs present in breast milk. In the United States, fish consumption in the Great Lakes area has been associated with a higher body burden of PCBs.21 In Canada, Inuit and fisherman populations have shown higher breast milk levels than urban populations. This is attributable to higher fish consumption.22 Figure 4 shows the difference in breast milk levels of Inuit and Caucasian women in Quebec, Canada.23 This study looks at just one group of PCBs (the di-ortho substituted PCB congeners), but it illustrates that the Inuit women with higher fish consumption have much higher breast milk levels. Fish consumption is not the only dietary exposure of concern. Other unique scenarios involving food contamination have resulted in increased breast milk levels. For instance, in the Czech Republic, the use of a PCB-containing paint in grain silos led to breast milk levels higher than those found in neighboring regions and countries.24
International ComparisonsFigure 5 compares international measurements of seven abundant PCB congeners often used as indicators of total PCB contamination. The seven indicator congeners are PCB #s 28, 52, 101, 118, 138, 152 and 180. Figure 5 shows high variability in levels of these indicators detected in breast milk in 12 nations around the world 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. Thus, Figure 5 should be considered a rough overview of general trends, rather than a precise comparison.
The sample populations from the Czech Republic, the Slovak Republic and the Ukraine were comprised of mothers living in Prague, Bratislava, Kyiv and Dniprodzerzhinsk, cities that support much of the three nations' heavy industry. The breast milk donors in these studies were not specifically chosen from neighborhoods close to industrial facilities, however, so the elevated breast milk PCB levels reported most likely reflect widespread problems with urban industrial pollution and related contamination of food sources in these regions.25
National Variations In PCB Levels
It is difficult to draw broad conclusions from the few studies available that compare PCB levels in different regions of the same country, but the following studies offer examples of the kinds of differences in regional exposures that have been found.
Data from Finland shows a common pattern of higher breast milk PCB levels in and around urban areas supporting heavy industrial activity than in nonindustrial rural areas. Figure 6 shows that PCB levels in breast milk in urban Helsinki were 40 percent higher than in the rural area of Kuopio in samples collected between 1992 and 1994.26
In the Czech Republic, breast milk PCB concentrations measured in three regions of the country between 1993 and 1994 did not follow this pattern. Figure 7 shows that samples collected in the urban, industrial city of Prague were 22 percent higher than those found in Kladno, a small, nonindustrial city outside Prague, but samples collected from a rural agricultural area were 44 percent higher than those in Kladno, and 28 percent higher than those in Prague. This may be because Uherske Hradiste, the agricultural area, had a history of high environmental PCB burdens. Specifically, a local factory produced paints containing PCBs, and these paints were heavily used on local agricultural buildings and grain silos. Researchers suggest that atmospheric deposition of contaminated emissions and direct contact with the paints caused widespread contamination of food in the area.27
Figure 8 shows data from 1996 and 1997 from four sub-arctic and arctic towns in Russian Siberia. The mothers who participated in this study were exclusively Caucasian, except in the arctic town of Naryan-Mar, where half of the study participants were from the Nenets indigenous group. The data indicate that the levels of breast milk PCB contamination could be related to the respective levels of industrial activity in the sub-arctic towns of Kargopol, Arkhangelsk and Severodvinsk. However, this does not seem to be the likely cause for the higher PCB contamination levels reported in non-industrial Naryan-Mar. The researchers involved in this study suggested that higher levels of organic pollutants in arctic women's breast milk could be due to higher consumption of contaminated fish in arctic populations. Fish may be contaminated through atmospheric transport and deposition of pollutants, or collection and transport of contaminants in rivers that flow northward, such as the Pechora, along which Naryan-Mar is situated.28
Because of methodological challenges, it is hard to sustain final conclusions regarding the status of PCB levels in breast milk. Many researchers have looked into the risks posed to breastfeeding children by PCBs in breast milk,29 and most have concluded that the small increased risk associated with breast milk exposure to PCBs is outweighed by the benefits of breastfeeding. However, at least one recent study has found slightly worse neurological performance (slower response times and worse performance on a standardized test of higher-level problem solving) in nine-year-old Dutch children whose mothers had higher PCB levels in their breast milk and who breast fed for a longer time, as compared to children whose mothers had lower levels of PCBs and who breastfed for a somewhat shorter time. On the other hand, prolonged breastfeeding in this study was associated with better spatial organizational skills in these children.30
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6. Jensen, A.A. and S.A. Slorach, Chemical Contaminants in Human Milk, Boca Raton Ann Arbor Boston: CRC Press, Inc. (1991); Fisher, B.E. "Most Unwanted," Environmental Health Perspectives Journal 107(1) (1999): pp. A18-21; Longnecker, M.P., W.J. Rogan, and G. Lucier, "The Human Health Effects of DDT (Dichlorodiphenyltrichloroethane) and PCBs (Polychlorinated Biphenyls) and an Overview of Organochlorines in Public Health," Annual Reviews of Public Health 18 (1997): pp. 211-44; 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; Rogan, W.J., A. Bagniewska, and T. Damstra, "Pollutants in Breast Milk," The New England Journal of Medicine 302(26) (1980): pp. 1450-3.
9. Longnecker, M.P., W.J. Rogan, and G. Lucier, "The Human Health Effects of DDT (Dichlorodiphenyltrichloroethane) and PCBs (Polychlorinated Biphenyls) and an Overview of Organochlorines in Public Health," Annual Reviews of Public Health 18 (1997): pp. 211-44.
17. Longnecker, M.P., W.J. Rogan, and G. Lucier, "The Human Health Effects of DDT (Dichlorodiphenyltrichloroethane) and PCBs (Polychlorinated Biphenyls) and an Overview of Organochlorines in Public Health," Annual Reviews of Public Health 18 (1997): pp. 211-44.
19. KonishiY., 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): pp. 571-578.
25. Cajka and 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, 913-919 (2003); Prachar et al., "Levels of Polychlorinated Biphenyls and Some Other Organochlorine Compounds in Breast Milk Samples in Bratislava," Science and the Total Environment , Supplement Pt. 1 (1993): pp. 237-242; Kocan et al., "Levels of PCBs and Some Organochlorine Pesticides in the Human Population of Selected Areas of the Slovak Republic, I. Blood.," Chemosphere , vol. 29, nos. 9-11 (1994): pp. 23125-2325; Gladen et al., "Organochlorines in Breast Milk from Two Cities in Ukraine," Environmental Health Perspectives , vol. 107, no. 6 (June 1999): pp. 459-462.
27. 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): pp.1485-1494.
28. Polder et al., "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 (2003): pp. 179-195; Polder, A., J.O. Odland, A. Tkachev, S. Foreid, T.N. Savinova, J.U. Skaare, "Dioxins, PCBs, and some Chlorinated Pesticides in Human Milk from the Kola Peninsula, Russia," Chemosphere vol. 37, no 9-12 (1998): pp. 1795-1806.
29. Longnecker, M.P., W.J. Rogan, and G. Lucier, "The Human Health Effects of DDT (Dichlorodiphenyltrichloroethane) and PCBs (Polychlorinated Biphenyls) and an Overview of Organochlorines in Public Health," Annual Reviews of Public Health 18 (1997): pp. 211-44; Rogan, W.J., A. Bagniewska, and T. Damstra. "Pollutants in Breast Milk," The New England Journal of Medicine 302(26) (1980): pp. 1450-3; Dekoning, E.P. and W. Karmaus, "PCB Exposure in Utero and Via Breast Milk, A Review," Journal of Exposure Analysis and Environmental Epidemiology 10 (2000): pp. 285-293; Huisman, M., et al. Neurological Condition in 18-month-old Children Perinatally Exposed to Polychlorinated Biphenyls and Dioxins, Early Human Development 1995; 43: p. 165-76; Patandin, S., et al. "Dietary Exposure to Polychlorinated Biphenyls and Dioxins from Infancy Until Adulthood: A Comparison Between Breast-feeding, Toddler, and Long-term Exposure," Environmental Health Perspectives Journal 107(1) (1999): pp. 45-51; Rogan, W.J., et al. "Polychlorinated Biphenyls (PCBs) and Dichlorodiphenyl Dichloroethane (DDE) in Human Milk: Effects on Growth, Morbidity, and Duration of Lactation," American Journal of Public Health 77(10) (1987): pp. 1294-1297; Koopman-Esseboom, C., et al. "Dioxin and PCB levels in Blood and Human Milk in Relation to Living Areas in the Netherlands," Chemosphere 29(9-12) (1994): pp. 2327-2338.
30. Vreugdenhil H.J., Mulder P.G., Emmen H.H., Weisglas-Kuperus N. "Effects of perinatal exposure to PCBs on neuropsychological functions in the Rotterdam cohort at 9 years of age," Neuropsychology vol. 18, no. 1 (2004): pp. 185-193.
Cites for International Studies Used in Comparison Chart
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, "PCB and Organochlorine Pesticides in Canadian Human Milk - 1992," Chemosphere vol. 30, no. 11 (1995): pp. 2143-2153.
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.
Finland - Kiviranta, H., R. Purkunen, T. Vartiainen, "Levels and Trends of PCDD/Fs and PCBs in Human Milk in Finland," Chemosphere vol. 38, no. 2, (1999): pp. 311-323.
The Netherlands - Tuinstra, T.G., M. Huisman, E.R. Boersma, "The Dutch PCB/Dioxin Study, Contents of Dioxins, Planar and Other PCBs in Human Milk from the Rotterdam and Groningen Area," Chemosphere vol. 29, no. 9-11, (1994): pp. 2267-2277.
New Zealand - Bates M.N., 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," The Science of the Total Environment vol. 306, no. 1-3 (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 2000; vol. 40, no. 9-11, p. 1111-1123.
Turkey - Cok, I, E. Gorucu, M.H. Satiroglu, G.C. Demircigil, "Polychlorinated Biphenyl (PCB) Levels in Human Milk Samples from Turkish Mothers," Bulletin of Environmental Contamination and Toxicology vol. 70, no. 1 (2003): pp. 41-45.
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 (June 1999): pp. 459-462.
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