Healthy Milk, Healthy Baby
Chemical Pollution and Mother's Milk
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Hexachlorocyclohexane is a commercial insecticide. It is persistent in the environment, and has been noted in breast-milk monitoring studies, but it is not one of the chemicals currently included in the International POPs Elimination Treaty. That is a mistake, in the view of environmentalists and health experts.
Hexachlorocyclohexane (HCH) is made up of a mixture of eight isomers. Isomers are related but different forms of a chemical. A sample of HCH is usually a mixture of at least four different HCH isomers including the alpha, beta, delta, and gamma forms.[1, 2] The chart below illustrates what a normal HCH mixture would look like. The composition of HCH is important because different isomer forms have different levels of persistence and bioaccumulate in breast milk differently.
The gamma-isomer of HCH, also known as lindane, is also used separately as an insecticide that is directly applied to the body and scalp to treat head and body lice and scabies.
The beta-isomer of HCH is the most persistent and bioaccumulative form. The alpha- and gamma-isomers of HCH are converted into the beta-isomer in living organisms. As a result of this conversion, as much as 90 percent of HCH detected in human tissues and breast milk is the beta-HCH.
HCH in the Body
The different chemical forms of HCH can move through air once they are released into the environment. The alpha-, beta-, gamma-, and delta-isomers can all be present as a vapor or can attach to such small airborne particles as soil and dust. Lindane (the gamma-isomer) can remain in the air for up to 17 weeks, and can travel long distances. Airborne particles with attached HCH may be removed from the air by rain.
As with many other POPs, HCH attaches to soil and sediment particles. However, fungi and bacteria can break HCH down into less harmful substances. HCH isomers, including lindane, are broken down quickly in water. All HCH isomers can accumulate in the fatty tissue of fish and other animals.
Humans may be exposed to HCH isomers in different ways, including:
- eating contaminated foods, including plants grown in HCH-contaminated soils, and meat and dairy products from contaminated animals;
- through the skin, when lindane is applied as a lotion or shampoo to control head lice and scabies; and
- drinking contaminated water or breathing contaminated air near waste sites, landfills, or sites where HCH is produced or used.
Controlling Exposure: Bans and Restrictions
HCH is banned or severely restricted in more than 60 countries. Lindane is specifically banned or restricted in 46 countries, but is often permitted for special uses by exemption. For instance, in the United States, mixed HCH has been banned as an insecticide, but lindane may still be used, either as a pesticide or as a pharmaceutical for topical application against head lice and scabies.
Countries with bans or severe restrictions|
Along with other commonly banned pesticides, surplus stockpiles of technical grade HCH and lindane are often exported to developing countries. In Africa and Asia, large quantities of obsolete HCH have been sent to remote locations where their use and storage have endangered drinking water, food sources, and humans.
Assessing the Extent of Exposure: Bans and Restrictions
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. In the case of HCH, a number of agencies have established benchmarks, but conclusive evidence demonstrating that any one of these benchmarks is protective or superior to the others does not exist.
For direct human intake of beta-HCH, the Canadian Health Protection Branch has set a tolerable daily intake level (TDI) of 0.3 micrograms per kilogram per day (µg/kg/day). The World Health Organization (WHO) has set an acceptable daily intake level (ADI) for lindane of 8 µg/kg. The U.S. EPA has set a maximum contaminant level (MCL) of 0.2 parts per billion (ppb) in drinking water.
Breast-milk monitoring Studies Measuring HCH
Studies looking at HCH contamination of breast milk have been conducted around the world, including reported results in the following countries:
Although studies have been conducted in all of these countries, data are not always complete. The following section discusses issues that make it difficult to interpret the data. In addition, countries not on this list may also have detectable levels of HCH residues in breast milk since this list reflects only those areas where studies have been conducted.
Limitations of Studies Measuring HCH in Breast Milk
It is often difficult to draw conclusions about national and international trends in HCH contamination because of the numerous factors affecting levels and limitations in the way the data is 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.
- Different measurement methodologies. Because HCH contamination can occur in several different isomeric forms, it can be reported either as individual isomer concentrations or as a sum value of total HCH presence. In cases where different individual isomer concentrations are reported, it may be difficult to compare across studies. This is especially relevant since different isomeric forms of HCH have different levels of persistence. Without a measurement of beta-HCH, it may be difficult to assess the full extent of contamination.
- Few studies. Many countries have not conducted multiple studies over a range of time. Instead, the information on HCH residues may just be a snapshot of a particular time. It is difficult, therefore, to draw conclusions about trends or to assess the effects of bans and restrictions.
- Small study populations. Because of the cost and time involved, many studies measuring HCH residue levels in breast milk test only a few people. In instances where the only data on a country's HCH 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 HCH in Breast Milk
Several useful studies on HCH are available.
Technical grade hexachlorocyclohexane and its isomers have been found in breast milk throughout the world. That said, HCH levels vary widely across the globe, with the highest values found in areas of extensive use.
Several additional factors may affect the levels of HCH found in breast milk. Like DDT, HCH breaks down more quickly in tropical climate zones than in temperate zones. Thus, levels of HCH in the environment, and perhaps in breast milk, are likely to be relatively lower in warm climates if all other factors are equal. Also, as with other persistent organic compounds that bioaccumulate through the food chain, the concentration of HCH in breast milk is strongly related to diet. A German study found that women who followed a low-fat diet had lower beta-HCH levels in their breast milk than women whose diet included large quantities of meat.
Especially high levels of HCH in breast milk have been associated with areas of high use. In China and Japan, HCH was commonly used as an insecticide in rice fields, and levels as high as 6,500 ppb of HCH in milk fat have been measured in these countries. Since Japan banned HCH in the 1970s, however, levels of the pesticide in breast milk have decreased. Figure 23 shows data measuring average levels of HCH in breast milk in Japan. Over the course of the decade studied, levels dropped significantly.
Very high levels have also been found in parts of the former Soviet Union. In the Kola Peninsula, levels were found to be 20 times higher than those in neighboring Norway. It is thought that these increased levels may be diet-related, because high rates of fish consumption in the circumpolar region have been linked to high levels of other organochlorine compounds.
A 1982 study in Norway, a decade after HCH was banned in that country, found higher levels of the beta-isomer of HCH in women who had immigrated from developing countries. Immigrant women had an average level of 433 ppb beta-HCH in their milk fat, while native Norwegian women had an average of 80 ppb in theirs. The difference was attributed to the likelihood of higher exposures in developing countries.
In general, countries that have monitored breast milk for HCH residues over time have witnessed a steady decrease. Figure 24 demonstrates a clear downward trend in residues in the North Rhine Westphalia region of Germany. Figure 25 illustrates a similar downward trend of average lindane levels in Stockholm, Sweden, while Figure 26 shows the same trend for levels of beta-HCH found in Swedish breast milk.
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last revised 5.22.01