Healthy Milk, Healthy Baby
Chemical Pollution and Mother's Milk
BACK TO CHEMICAL OVERVIEW
Heptachlor is an organochlorine cyclodiene pesticide that has been used in various parts of the world.1 Heptachlor has been sold and distributed under many trade names, including Heptagran, Basaklor, Drinox, Soleptax, Termide and Velsicol 104.2 Heptachlor has been used to control termites in home and commercial settings. It also has been used as an insecticide in seed grains and on food crops, most notably corn. In the United States, heptachlor is currently used for fire ant control inside power transformers.3
Heptachlor in the Body
In living organisms, heptachlor is most commonly converted into its oxygenated metabolite, heptachlor epoxide. Heptachlor epoxide is an extremely persistent form of the chemical, both in the environment and in humans. Both chemicals evaporate slowly in air and bind strongly to soil particles. Heptachlor does not easily dissolve in water, but heptachlor epoxide is more soluble.4
Heptachlor can enter surface waters through agricultural drift and runoff. Once in water, microorganisms can break heptachlor down to heptachlor epoxide.5 Both forms of heptachlor bind to sediment, and the ingestion of contaminated sediment by fish and other aquatic organisms leads to a buildup of the chemicals.6
Heptachlor epoxide is extremely persistent in soil. In some cases, trace amounts of heptachlor have been found in soil 14 to 16 years after application.7 Plants can take in heptachlor directly from the soil. That, in turn, leads to bioaccumulation of heptachlor, as cattle and other range animals eat contaminated plants.
Humans can be exposed to heptachlor and heptachlor epoxide by:
- Eating crops that have been grown in soil containing heptachlor
- Eating fish, dairy products and fatty meats from animals exposed to heptachlor in their food
- Breathing air, drinking water or skin contact with soil near waste sites or landfills
In the discussion that follows, "heptachlor" refers to heptachlor epoxide, since this is the form that is examined in most analyses of breast milk.
Controlling Exposure: Bans and Restrictions
As of 2003, heptachlor had been banned or restricted in 39 countries, and been made illegal for import in 93 countries.8 However, some of the countries with restrictions still permit its use for termite and other pest control, and many Asian countries and other developing nations still use heptachlor for agricultural purposes.9 Despite the imposition of a ban in the United States in 1988, U.S. customs data showed that heptachlor was exported in large quantities through 1994. In 1997, the sole U.S. producer of heptachlor, Velsicol Chemical Corporation, ceased production of the pesticide.10
Assessing the Extent of Heptachlor 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. A number of benchmarks have been established for heptachlor, but no conclusive evidence demonstrates that that any one of these benchmarks is protective of health, or that one may be superior to the others.
Some recommendations for acceptable daily intake levels (ADIs) have been set for heptachlor. The World Health Organization (WHO) set an ADI for heptachlor in adults at 0-0.5 micrograms per kilogram of body weight (µg/kg body weight) in 1988.11 Rogan et al. recommended an ADI for heptachlor epoxide intake by infants via breast milk of 4.0 µg/kg body weight (estimated for intake of a 5kg infant drinking 700 milliliters of 2.5 percent fat milk per day).12
Breast Milk Monitoring Studies Measuring Heptachlor
Studies looking at residues of heptachlor and heptachlor epoxide 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 heptachlor residues in breast milk, since the list reflects only those areas where studies have been conducted, not just where heptachlor is measurable. The following discusses issues that make it difficult to interpret the data.
Limitations of Studies Measuring Heptachlor in Breast Milk
It is often difficult to draw conclusions about national and international trends in heptachlor 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 heptachlor use. Many countries have a clear demarcation between agricultural and urban zones. In such situations, general averages are inadequate because they do not reveal peak levels in areas with heavy agricultural use. The same problem arises in countries where heptachlor 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 breast milk levels of heptachlor are extremely limited. Most studies were conducted between the late 1970s and the mid-1980s; almost no information has been collected and analyzed from the 1990s. It is difficult, therefore, to draw conclusions about the effectiveness of bans since most restrictions occurred in the 1980s, after the majority of the studies were conducted. Also, many countries do not have multiple studies over a range of time. Instead, the information on heptachlor residues may be simply a snapshot of a particular time. In such cases, it is difficult to generalize about how the conditions in a country have changed over time.
- Small study populations. Because of the cost and time involved, many studies measuring heptachlor levels in breast milk test only a few people. In instances where the only data on a country's heptachlor exposure come 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 Heptachlor in Breast Milk
Several useful studies on heptachlor are available.
Judging from available data, the trend line for heptachlor epoxide residue levels in breast milk appears to be pointed downward. However, in the time frame where data are available, the incidence of contamination at any level increased. Early studies often detected heptachlor and heptachlor epoxide in less than 10 percent of samples tested, while later studies approached 100-percent detection.
Detected levels of heptachlor epoxide in breast milk have been heavily influenced by patterns of use -- as countries have restricted and banned heptachlor, levels detected in breast milk have dropped. But even in countries with long-standing bans, the levels of heptachlor epoxide in breast milk have never returned to zero because the persistence of heptachlor and heptachlor epoxide makes the chemicals almost impossible to eradicate completely. Changes in breast milk residue levels often mirror fluctuations in use. Some countries have witnessed increases of heptachlor levels in breast milk that result from identifiable changes in distribution and application -- for example, in cases where heptachlor's use against termites has increased suddenly.
Because of the limited data from monitoring of heptachlor and heptachlor epoxide levels in breast milk, only two types of case example are available. In a limited number of countries, consistent studies over time provide data on trends. In countries with few studies and with varied internal use patterns, data illustrating the impacts of differences in pest control and agricultural use are available.
In Alberta, Canada, between 1966 and 1978, average levels of heptachlor epoxide increased more than ten-fold, from an average of 2 parts per billion lipid to 29 parts per billion lipid. More striking, however, was the increase in the incidence of detection. From 1966 to 1970, only 5 percent of collected samples contained detectable levels of heptachlor epoxide. By the time of a 1977-78 study, the detection incidence had increased to 94 percent of collected samples.13 This increase may be due to increased use, or it could be the result of increased persistence resulting from widespread contamination. The use of heptachlor in Canada was discontinued in 1985.14 The limited data available suggest that levels in breast milk have probably begun to decrease.
Figure 1 shows a clear decline in the levels of heptachlor epoxide in Osaka, Japan, as measured by a long-term study between 1986 and 1998.15
In the United States in the mid-1970s, significant levels of heptachlor epoxide were found in the breast milk of women throughout the country. This is illustrated in Figure 2. The Southeast region had the highest levels, most likely due to more intensive termite control efforts in this region.16
In Belgium, large differences were seen in average residue levels of heptachlor epoxide in breast milk between the North and South. This variation, shown in Figure 3, reflected different regional patterns in the agricultural industry and differences in heptachlor use.
In Spain, a more than twofold difference in heptachlor epoxide levels was found between rural and urban populations. Again, this was attributed to the increased agricultural use in the rural areas.17
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15. 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 40 (2001): pp. 571-578.
last revised 3.25.05