Healthy Milk, Healthy Baby
Chemical Pollution and Mother's Milk
Chemicals: Dieldrin, Aldrin, and Endrin
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Dieldrin, aldrin, and endrin are closely related organochlorine insecticides that are extremely persistent in the environment. They are more acutely poisonous than such organochlorine pesticides as DDT, but tend to be less persistent.
Aldrin has been used as a soil insecticide to control root worms, beetles, and termites. Dieldrin has been used in agriculture for soil and seed treatment as well as for control of mosquitoes and tsetse flies.[1, 2] Other uses for dieldrin include veterinary treatments for sheep, wood treatment against termites, and mothproofing of woolen products. Endrin has been used as an agricultural insecticide on tobacco, apple trees, cotton, sugar cane, and grain, as well as to control rodents and birds.
Dieldrin is both a pesticide product in its own right and the oxygenated metabolite of aldrin. The two chemicals are often discussed together because they occur simultaneously. Endrin, although very similar in structure and function, has some differences that distinguish it from aldrin and dieldrin.
Dieldrin, Aldrin, and Endrin in the Body
Dieldrin, aldrin, and endrin enter the environment when they are used as pesticides. When used in agriculture, the chemicals can enter the soil, wash into nearby surface water, or volatize in air. Once in the environment, they can accumulate in living organisms. The chemicals are also used for termite control in home settings, and can enter soil, water and air in those circumstances as well.
In both plants and animals, aldrin quickly converts to dieldrin. In soil and water, aldrin's conversion to dieldrin is aided by sunlight and bacteria. Once present in soil or water, dieldrin breaks down very slowly, does not easily evaporate into the air and can bind very tightly to soil particles. Plants take up aldrin and dieldrin residues directly from the soil. In animals, including humans, dieldrin is stored in the fat and leaves the body very slowly.
Endrin also accumulates in soil and water. In water, it does not dissolve, but instead binds strongly to sediment and soil particles. In soil, endrin can persist for as long as ten years. The extent of endrin's persistence depends somewhat on local climate conditions - high temperatures or intense light can cause endrin to break down more rapidly.
Humans can be exposed to aldrin, endrin, and dieldrin in a number of ways, but the chief avenue of exposure is by eating contaminated fish, poultry, beef, or other animal-derived food products, or food grown in treated soil. In countries where dieldrin is still used for termite control, household air may be a significant exposure pathway as well.
Dieldrin is ubiquitous in breast milk; it is found in more than 99 percent of samples tested in most countries. Because dieldrin is attracted to fat, the level of dieldrin in a mother's milk is generally about six times higher than the level in her blood. However, despite dieldrin's widespread presence in breast milk, the World Health Organization (WHO) has concluded that dieldrin residues in breast milk may not pose a significant risk to the infant. WHO found, surprisingly, that the concentration of dieldrin in the blood and bodies of breastfeeding babies did not increase with age during their first six months of life. In addition, WHO found that the blood levels of dieldrin in breast-fed and bottle-fed babies were the same. Several factors might account for these findings. Infant exposure to dieldrin may occur primarily in the womb via transplacental transfer. Alternatively, non-breast-fed babies may be exposed to dieldrin from infant formulas and baby foods, although most studies have failed to show organochlorine contamination in infant formula.
Controlling Exposure: Bans and Restrictions
In most industrialized countries, dieldrin, aldrin, and endrin are banned for agricultural use, and either banned or severely restricted for non-agricultural settings. Indeed, according to a 1990 report by the United Nations Food and Agriculture Organization, dieldrin, aldrin, and endrin are the most widely banned and restricted class of pesticides in the world. In some countries, restrictions on dieldrin, aldrin, and endrin were imposed in stages. In the United States, for instance, dieldrin was banned from agricultural use in 1974, but was still permitted for mothproofing and to fight termite infestations until 1987. Similarly, most uses of endrin were restricted in the United States by 1986, although it could still be used as a toxicant on bird perches until 1991.[3, 4]
As of 1995, aldrin and endrin had been banned or severely restricted in more than 60 countries, while dieldrin had been banned or severely restricted in more than 70. The table below is a partial list of countries that have taken steps to reduce the use of dieldrin, aldrin, and endrin.
|Countries that have imposed bans or severe restrictions |
Despite these countries' restrictions, dieldrin, aldrin, and endrin are still in use around the world. Agricultural use continues in developing nations, often the result of "unsolicited pesticide donations" from countries where the chemicals are prohibited, but still in supply. Excess inventory is sometimes exported to developing countries, where it is introduced into the environment, either by use or by improper or inadequate disposal.[9, 10] Recently, industrialized nations and the United Nations Environment Program (UNEP) have begun assistance efforts to provide financial support and technology for clean-ups, but such efforts have only begun to address the problem.
Because dieldrin is still used as an agricultural insecticide in some parts of the world, it can still enter any country as a food contaminant or in global air currents. Thus, dieldrin, aldrin, and endrin will remain in the environment and in breast milk until a total international ban is achieved.
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. 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 international regulatory board, Codex Alimentarius, has set a benchmark for dieldrin in breast milk, a maximum residue level (MRL) of 6 parts per billion in milk. Many countries' average levels of dieldrin in breast milk are now below this MRL, but in many instances, that is a recent accomplishment.
The World Health Organization (WHO) has set another benchmark, known as the acceptable daily intake level (ADI). The ADI for dieldrin is 0.1 µg/kg body weight. Various studies have found average levels well above this benchmark. For instance, in Uganda, researchers found that the national average for dieldrin residues in breast milk would result in intake by a nursing infant 3.2 times WHO's ADI (0.32 µg/kg body weight). More than 70 percent of the collected samples in the Ugandan study had residue levels that would result in an infant exceeding the maximum ADI.
Breast-milk Monitoring Studies Measuring Dieldrin, Aldrin, and Endrin
Studies looking at residues of aldrin, endrin, and dieldrin have been conducted in the following countries:
Data from the studies of these countries' breast milk are not all complete. Also, countries not included in this list may also have detectable levels of dieldrin, aldrin, and endrin in breast milk, since the list reflects only those areas where studies have been conducted, not just where pesticides are measurable. The following section discusses issues that make it difficult to interpret the data.
Limitations of Studies Measuring in Breast Milk
Although humans may be exposed to aldrin, endrin, or dieldrin, it is dieldrin that is most often detected in tissues. That is the case for two principal reasons: first, because aldrin in animals and plants quickly converts into dieldrin; and second, because dieldrin is the most persistent of the three. The majority of the studies discussed here measured only dieldrin residues in breast milk. But because of the likely conversion of aldrin to dieldrin, dieldrin levels should be considered a proxy for combined exposure to aldrin and dieldrin. Because endrin is not as persistent as aldrin and dieldrin, the data do not adequately assess exposure to endrin.
It is often difficult to draw conclusions about national and international trends in dieldrin contamination because of the many factors affecting their levels and because of the 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 use. Dieldrin and aldrin have been used for a wide range of purposes, including agricultural applications, veterinary treatments, and vector control. These different settings employ different quantities of the chemicals, resulting in very different exposure situations. For that reason, a country where the pesticides have been used for different reasons may have a national average that obscures much more troubling data in individual regions.
- Few studies. Many countries do not have multiple studies over a range of time. Instead, the information on dieldrin residues may be just a snapshot of a particular time period. 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 dieldrin levels in breast milk have tested only a few people. If the only data for a country are from studies with very small sample sizes, it is difficult to draw 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 Dieldrin in Breast Milk
Several useful studies on dieldrin are available.
Dieldrin detection in breast milk has been heavily influenced by use patterns. When dieldrin and aldrin first came into widespread international use, detection in breast milk rose dramatically. As countries have restricted and banned the use of dieldrin, levels detected in breast milk dropped significantly. Some countries have seen up to a tenfold decrease in the level of detectable dieldrin in the years following these restrictions. It is important to note than even in countries with longstanding bans, the levels of dieldrin in breast milk have never returned to zero. The persistence of dieldrin makes it impossible to completely prevent bioaccumulation in breast milk; therefore, changes in breast-milk residue levels often mirror changes in use. Some countries have witnessed unique increases of dieldrin levels in breast milk because of specific modifications in distribution and application.
Increasing levels of dieldrin in breast milk have often been correlated with continued dieldrin use. A study in the late 1970s in Australia found that dieldrin levels in breast milk rose because of the increased use of dieldrin for household termite control.[11, 13] Breast-milk levels of dieldrin in Uganda have remained high because the chemical continues to be used to control banana weevils and termites, as a tree trunk treatment for tsetse fly control, and for soil pests.
The following examples of dieldrin detected in breast milk are broken into two categories: time-trend data, and data demonstrating distinct regional differences.
Figure 14 combines a series of studies from Canada, chiefly from Alberta and Ontario. [11, 15] The graph shows a clear decrease in the average levels of dieldrin detected in breast milk over several decades.
Figure 15 shows data from Denmark. Average levels of dieldrin found in breast milk in Denmark in the 1960s and 1970s were substantially higher than those found in Canada, Sweden, and Germany in the same time. Levels have since decreased in Denmark and are now in line with those in the other countries'.
Figure 16 shows data from Sweden. The average level of dieldrin found in Swedish women's breast milk has steadily decreased, even though the earliest breast-milk monitoring studies found that the highest levels of dieldrin in Sweden were much lower than levels in other parts of the world.
Figure 17 shows a clear decline over time in the average dieldrin levels found in breast milk in Germany. These data may obscure differences between levels in the pre-unification East and West Germany.
Figure 18 shows the decrease in detected levels of dieldrin in Japanese women's breast milk.
Insufficient studies of dieldrin in breast milk have been conducted in the United States. Therefore it is impossible to reliably document changes in dieldrin residues over time. We can assume that the ban in the United States resulted in similar decreases.
Regional Differences in Dieldrin Breast-milk Levels
In some countries with ongoing dieldrin use, it is clear that breast-milk levels relate closely to local use patterns. In areas where dieldrin is used more heavily, levels in breast milk are often significantly higher.
For example, measurements in Kenya have shown distinct regional differences. Kenya still uses dieldrin in agriculture, and areas with intensive agricultural production (such as Loitokitok) have much higher levels of dieldrin in women's milk compared to non-agricultural areas. The data presented in Figure 19 show the differences found in average dieldrin levels detected in women's breast milk around the country.[12, 18]
Similarly, studies have shown that women in Southern European countries have higher concentrations of dieldrin residues in their breast milk than do women in Northern European countries. This has been attributed to more agricultural industry in the Southern regions and, thus, higher pesticide use.
A nationwide study conducted in the United States in 1975 mirrored the findings in Europe. It showed that the Southeastern United States, where agricultural and termite control uses of dieldrin were higher, had higher average levels in breast milk. Figure 20 presents the average levels measured from each region in this study.
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1. Jensen, A.A. Chemical Contaminants in Human Milk. Residue Reviews 1983; 89: p. 1-128.
2. ATSDR. Public Health Statement for Aldrin and Dieldrin, 1989, Agency for Toxic Substances and Disease Registry.
3. ATSDR. ToxFAQs for Endrin, 1997, ATSDR.
4. ATSDR. ToxFAQs for Aldrin/Dieldrin, 1993, ATSDR.
5. WHO. Aldrin and Dieldrin, 1989, World Health Organization: Geneva.
6. PANNA. Demise of the Dirty Dozen Chart, 1995.
7. Siedenburg, K. Demise of the Drins, Global Pesticide Campaigner 1991; January 1991.
8. Barclay, B. and J. Steggall. Obsolete Pesticides Crisis, Global Pesticide Campaigner 1992.
9. Gajurel, D. Obsolete Hazardous Pesticides Poison Nepal, 2000, Environment News Service.
10. Thorton, J. Adding Insult to Injury: Disposal of Obsolete Pesticides in Africa, Pesticide Action Network's Dirty Dozen Campaigner 1990.
11. Jensen, A.A. and S.A. Slorach. Chemical Contaminants in Human Milk, 1991, Boca Raton Ann Arbor Boston: CRC Press, Inc.
12. Ejobi, F., et al. Organochlorine Pesticide Residues in Mother's Milk in Uganda, Bulletin of Environmental Contamination and Toxicology 1996; 56: p. 873-880.
13. Stacey, C.I. and T. Tatum. House Treatment with Organochlorine Pesticides and Their Levels in Human Milk, Perth, Western Australia, Bulletin of Environmental Contamination and Toxicology 1985; 35: p. 202-208.
14. Mes, J. and D.J. Davies. Presence of Polychlorinated Biphenyl and Organochlorine Pesticide Residues and the Absence of Polychlorinated Terphenyls in Canadian Human Milk Samples, Bulletin of Environmental Contamination and Toxicology 1979; 21: p. 381-87.
15. Currie, R.A., et al. Pesticide Residues in Human Milk, Alberta, Canada, Pesticides Monitoring Journal 1979; 13(52).
16. 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.
17. 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 1994; 102: p. 187-93.
18. Kanja, L., et al. Organochlorine Pesticides in Human Milk from Different Areas of Kenya 1983-85, Journal of Toxicology and Environmental Health 1986; 19: p. 449-464.
19. Savage, E. National Study of Chlorinated Hydrocarbon Insecticide Residues in Human Milk, USA, American Journal of Epidemiology 1981; 113(4): p. 413-422.
last revised 5.22.01