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Chemicals: Chlordane

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Chlordane is a manufactured chemical, used as a pesticide throughout the world. A mixture of more than 26 compounds, it is classified as an organochlorine cyclodiene pesticide. Trade names for chlordane include Octachlor and Velsicol 1068.1 Chlordane has been used as an agricultural pesticide on such crops as corn and citrus, and is often used on home lawns and gardens. One of chlordane's most common uses has been against termites.2 For the sake of this discussion, "chlordane" refers to the multiple chemical breakdown products that persist in the environment and that bioaccumulate.

Chlordane was once used widely in the United States and Japan, but it was banned in 1986 in Japan and in 1988 in the United States, and is no longer manufactured for export in either country. Its use in European countries has always been fairly limited.3

Chlordane in the Body

Chlordane enters the environment as a result of its use on crops and in home gardens and in termite control. Once it enters the environment, it sometimes evaporates. But it can also bind itself to soil particles, particularly to particles in the upper layers of soil, or to sediment in bodies of water.4 The breakdown of chlordane once it has attached to soil particles or sediment is very slow -- in some cases, it has been found in soil up to 20 years after initial treatment.5 So persistent is the residue that a recent study showed that detectable levels of chlordane are still present in some food grown in the United States, even though it has been decades since chlordane was used in agriculture.6

Chlordane does not usually remain in living organisms in its original form for long. Instead, it breaks down into metabolites such as oxychlordane and gamma-chlordane or into impurities such as trans-nonachlor or cis-nonachlor. It is these breakdown products that persist in the tissue of fish, birds and mammals.7 It is these metabolites and breakdown impurities that can be measured in human breast milk.

Human beings are exposed to chlordane in various ways.8 The most common path for exposure is through consumption of fish or shellfish taken from water contaminated by chlordane. Because the fish and shellfish have already bioaccumulated chlordane, the human dose is significantly increased. Other less significant routes of exposure may include eating crops grown in soil containing chlordane; breathing air or touching soil near homes treated for termites with chlordane; and breathing air or touching soil near waste sites or landfills. The seriousness of these minor routes depends on the extent of the chlordane contamination, but significantly, none of them involve bioaccumulation.

Some of the chlordane humans take in leaves the body in a few days through feces and urine, but some breaks down into persistent products that are stored in body fat. Months or years can pass before the chlordane byproducts stored in fat are released from the body.9 One way chlordane is excreted is through breast milk.

Controlling Exposure: Bans and Restrictions

Chlordane has been banned in 47 countries and severely restricted in an additional 14.10 In some countries, the banning of chlordane has proceeded in stages. For instance, in the United States, chlordane was used as a pesticide and agricultural fumigating agent until 1983, when its use was restricted to termite control. Finally in 1988, all uses were banned.11

The table below is a partial list of countries that have taken steps to reduce the use of chlordane. It is important to remember, however, that banning or restricting a chemical does not necessarily stop its use. Often, a considerable period of time can pass before a ban is fully enforced, either because of provisions allowing the use of existing stockpiles of the chemical or because of weak government enforcement. In addition, special limited uses of a chemical may continue, even after it has been banned for general use. Indeed, even in countries with fully enforced bans, chlordane exposure may still occur. For example, chlordane can persist in treatments for termites for many years, and it can remain in soil years after agricultural treatments have stopped. Thus, although the effects of a ban on human accumulation levels are positive, results may take years.

Some countries where chlordane has been banned or severely restricted12
Austria, Belgium, Bolivia, Brazil, Chile, Colombia, Costa Rica, Denmark, Dominican Republic, Ecuador, El Salvador, Fiji, Germany, Guatemala, Hong Kong, China, Ireland, Italy, Kenya, Korea, Lebanon, Lichtenstein, Mozambique, Netherlands, Norway, Panama, Paraguay, Philippines, Poland, St. Lucia, Singapore, Spain, Sweden, Switzerland, Tonga, Turkey, United Kingdom, United States, Yemen, Yugoslavia.

Assessing the Extent of Chlordane 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. Different benchmarks also reflect different endpoints. For example, benchmarks set to protect against cancer are different than those seeking to protect against a less serious health condition. Conclusive evidence demonstrating that any one of these benchmarks is protective or superior to the others does not exist.

The U.S. Agency for Toxic Substance and Disease Registry (ATSDR) set an intermediate-duration oral minimum risk level (MRL) for chlordane of 0.0006 milligram per kilogram per day (mg/kg/day) -- equivalent to a concentration of 0.003 milligrams per day for an 11-pound infant.13 Average levels found in breast milk in various countries would result in exposures below this level.14 The U.S. EPA has set a maximum contaminant level (MCL) in drinking water of 2 parts per billion.

Breast Milk Monitoring Studies of Chlordane

Studies examining chlordane (oxychlordane, trans-nonachlor, cis-nonachlor and other breakdown products) in breast milk have been conducted in at least the following countries:

KazakhstanUnited States

Data from these studies are not all complete, however. For example, a country on this list may have had only one study of chlordane done, or such studies may not have met standard protocols. In addition, countries not on this list may also have detectable levels of chlordane residues in breast milk, since the list reflects only those areas where studies have been conducted, not just where chlordane is measurable. The following section discusses issues that make it difficult to interpret the data.

Limitations of Studies Measuring Chlordane in Breast Milk

It is often difficult to draw conclusions about national and international trends in chlordane 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 chlordane use. Many countries have a clear demarcation between agricultural and urban zones. In such cases, general averages are inadequate because they do not reveal peak levels in areas with heavy agricultural use. The same problem arises in countries where chlordane has been used for pest control only in specific regions. Average values will not adequately represent the unique exposure situations in these areas.

  • Few studies. In general, the data on chlordane residues in breast milk are extremely limited. Most studies were conducted between the late 1970s and the mid-1980s. With the exception of data from regions of the former Soviet Union, scientists have gathered almost no information from the 1990s. It is difficult, therefore, to draw conclusions about trends or to assess the effects of bans and restrictions. Since most restrictions of chlordane were established in the 1980s and persistence can be decades long, current data are necessary to draw conclusions about current conditions.

  • Small study populations. Because of the cost and time involved, many studies measuring chlordane residue levels in breast milk test only a few people. In instances where the only data on a country's chlordane exposure come from studies with small sample sizes, it is difficult to draw reliable conclusions about the entire population's exposure.

  • Differences in measurement methodology and data reporting. The data also present challenges in assessing the overall impact of chlordane exposure. As noted earlier, chlordane can turn up in several different chemical forms in breast milk (oxychlordane, trans-nonachlor, cis-nonachlor, etc.). The quantity and presence of these different metabolites and impurities reflect different exposure scenarios and different stages in metabolism. But some studies report levels only for certain forms of chlordane, so it is difficult to determine if these gaps are a result of analytical limitations or if the data truly reflect different types of 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 Chlordane in Breast Milk

Several useful studies on chlordane are available.

One mid-1970s study of chlordane in the United States found significant levels of oxychlordane in breast milk throughout the country, with the highest levels in the Southeast. (Chlordane was still in use in the United States at the time.) The authors of this study attribute the higher levels found in the Southeast to the greater use of agricultural pesticides in this area, as well as to more intensive use of chlordane for home termite control in the region.15 Figure 1 shows the results of this study, with average concentrations of chlordane in breast milk broken down by region.16

Figure 1

Figure 1

Another study looked at chlordane exposure in Japan. Not banned there until 1986, chlordane was heavily used for household termite control, especially during the early 1980s.17 Most of the data recording chlordane residues in breast milk predate the ban, making it difficult to draw conclusions regarding the effectiveness of these restrictions on breast milk levels. That said, some interesting information is available concerning pre-ban levels. In a study done in Osaka, Japan, women living in households using chlordane for termite control had breast milk chlordane levels 4.4 times higher than women whose households used no form of chlordane.18 Figure 2 shows the average concentrations of chlordane found in the breast milk of the women in this study. The "controls" are women who lived in homes where no chemicals were used to control termites, while the "exposed" women are those who lived in households where chlordane was regularly sprayed to control termites. Although a notable difference between the breast milk levels of chlordane of these two groups of women emerges, it is important to compare the levels to those shown in Figure 1. The higher levels found in the "exposed" women in Japan are much lower than the average levels reported in the regional study in the United States.

Figure 2

Figure 2

Another study examined chlordane residues in breast milk in Finland in the early and mid-1980s.19 The discovery of the chemical in the breast milk of Finnish women was disturbing because chlordane has never been used in Finland and was used in extremely restricted ways in neighboring Scandinavian countries. The chlordane metabolites in Finnish breast milk may have been the result of dietary exposure. In the 1970s and 1980s, scientists detected an increase in the concentration of insecticides in Baltic fish.20 The chlordane in these fish probably originated in distant countries and was carried to the Baltic Sea in water runoff and in the air.

In addition, scientists gathered information on oxychlordane and trans-nonachlor residues in Swedish breast milk between 1972-1989.21 Chlordane was restricted in Sweden in 1970.22 Levels of the two chlordane residues oxychlordane and trans-nonachlor have fluctuated and seem to be decreasing. However, the period during which these chemicals were measured was limited, and it is therefore difficult to draw any final conclusions. Figures 3 and 4 show the average levels of oxychlordane and trans-nonachlor found in Swedish women's breast milk. Again, it is useful to compare the results of this study with the others referred to here. The highest concentrations of oxychlordane and trans-nonachlor found in the early 1970s in Sweden are about the same as the levels found in the Japanese controls and much lower than the average concentrations found in the United States.

Figure 3

Figure 3

Figure 4

Figure 4

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1. ATSDR, Toxicological Profile for Chlordane, (1994).

2. Ibid; Jensen, A.A. and S.A. Slorach. Chemical Contaminants in Human Milk, Boca Raton Ann Arbor Boston: CRC Press, Inc. (1991); Sonawane, B. "Chemical Contaminants in Human Milk: An Overview," Environmental Health Perspectives, (1995): 103 (Suppl 6): p. 197-205.

3. Jensen, A.A. and S.A. Slorach. Chemical Contaminants in Human Milk, Boca Raton Ann Arbor Boston: CRC Press, Inc. (1991).

4. ATSDR, Toxicological Profile for Chlordane, (1994).

5. Savage, E. "National Study of Chlorinated Hydrocarbon Insecticide Residues in Human Milk," USA, American Journal of Epidemiology, (1981): 113 (4): p. 413-422.

6. Mattina, M.J.I., W. "Iannucci-Berger and L. Dykas. Chlordane Uptake and Its Translocation in Food Crops," Journal of Agriculture and Food Chemistry, (2000): 48: p. 1909-1915.

7. Jensen, A.A. and S.A. Slorach. Chemical Contaminants in Human Milk, Boca Raton Ann Arbor Boston: CRC Press, Inc. (1991).

8. ATSDR, Toxicological Profile for Chlordane, (1994).

9. ATSDR, Toxicological Profile for Chlordane, (1994).

10. PANNA, Demise of the Dirty Dozen Chart, (1995).

11. ATSDR, Toxicological Profile for Chlordane, (1994).

12. WWF, Summary of Where POPs are Being Used, Banned, or Restricted, World Wildlife Fund (2000).

13. Pohl, H.R. and C.A. Tylenda. "Breast-feeding Exposure of Infants to Selected Pesticides: A Public Health Viewpoint," Toxicology and Industrial Health, (2000): 16: p. 65-77.

14. Ibid; Bordet, F., et al. "Organochlorine Pesticide and PCB Congener Content of French Human Milk," Bulletin of Environmental Contamination and Toxicology, (1993): 50: p. 425-32.

15. Savage, E. "National Study of Chlorinated Hydrocarbon Insecticide Residues in Human Milk," USA, American Journal of Epidemiology, (1981): 113(4): p. 413-422.

16. Ibid.

17. Taguchi, S. and T. Yakushiji. "Influence of Termite Treatment in the Home on the Chlordane Concentration in Human Milk," Archives of Environmental Contamination and Toxicology, (1988): 17: p. 65-71.

18. Ibid.

19. Wickstrom, K., H. Pyysalo, and M. Siimes. "Levels of Chlordane, Hexachlorobenzene, PCB and DDT Compounds in Finnish Human Milk in 1982," Bulletin of Environmental Contamination and Toxicology, (1983): 31: p. 251-56.

20. Ibid.

21. Noren, K. and D. Meironyte. "Certain Organochlorine and Organobromine Contaminants in Swedish Human Milk in Perspective of Past 20-30 Years," Chemosphere, (2000): 40: p. 1111-1123; Noren, K. "Contemporary and Retrospective Investigations of Human Milk in the Trend Studies of Organochlorine Contaminants in Sweden," The Science of the Total Environment, (1993): 139/140: p. 347-355.

22. Noren, K. and D. Meironyte. C"ertain Organochlorine and Organobromine Contaminants in Swedish Human Milk in Perspective of Past 20-30 Years," Chemosphere, (2000): 40: p. 1111-1123.

last revised 3.25.05

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