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Due to the bioaccumulation of persistent organic pollutants in fatty tissues, varying levels of these have been consistently found in human breast milk samples worldwide. Persistent organic pollutants (POPs) are synthetic chemicals that are highly resistant to degradation and that bioaccumulate in fatty tissues of biota through dietary intake and environmental exposure (Ennaceur et al., 2008) and can have adverse effects on breast-feeding children. Human breast milk is an important sampling specimen for the measuring of chemical residues in humans. It gives a measure of the mother’s chemical burden as well as a measure of the intake of breast-fed infants. Breast milk is easily obtainable, non-invasive and indicates levels well in maternal fat.

Background
Presently, human biomonitoring results are the most reliable estimate of human exposure resulting from multiple sources. Risk assessment can be determined from these results, and measures can be taken from there to create programs to lessen the effect of these chemicals. Many research projects have been undertaken in both industrialized and developing countries in order to collect and monitor chemical levels (Porta et al., 2008). Levels of these chemicals vary from place to place and depend on environmental and dietary patterns.

Compounds
Dichlorodiphenyltrichloroethane and its metabolites (DDTs, p,p’DDE), hexachlorobenzene (HCB), hexachlorocychlohexane isomers (HCHs), polychlorinated bipenyls (PCBs), polychlorodibenzodiocins (PCDDs), polychlorodibenzofurans (PCDFs), chlordane compounds (CHLs) and dioxins are the major organic pollutants in question that are being analyzed. There are many other pollutants found in human breast milk samples, such as mercury. The chemical stability of many of these POPs is responsible for their long persistence in humans, and their high lipophilicity means that they are stored and accumulated in lipids (Abballe et al., 2008). The monitoring of levels of these chemicals is important in understanding infant exposure as well as determining certain effects in general populations.

Political Involvement
The Stockholm convention (and thus, the Stockholm Treaty) called for more research on chemical levels in breast milk. Article 11 of this treaty calls for research and examinations of POPs, their sources, trends of use, levels in humans and in the environment as well as all social impacts. Certain POPs have been banned since the convention, but continue to be found in the environment due to their bioaccumulation in food chains (Porta et al., 2007) and their limited usage with vector-borne diseases in developing countries. Studies have resulted in a large base of results from which trends have been derived, allowing assessment for proper regulatory actions (Abballe et al., 2008) around the globe. All levels of POPs have been decreasing in the last 25 years (Abballe et al., 2008; Ennaceur et al., 2008; Devanathan et al., 2008) which reflects the positive effects of restrictions and bans on uses of DDT and other chemicals (Devanathan et al., 2008). Levels of dioxins decreased between 1973 and 1996 by 85% in Japan (Strogi, 2008). These declining levels are good news. The effects of exposure to these chemicals are wide ranging, and even with these lower levels, recommended daily intakes are often surpassed, even just with environmental levels of contamination (Devanathan et al., 2008). Although such initiatives as the Stockholm treaty have warranted monitoring concentrations of POPs, there are many countries worldwide that do not know and have not researched the distributions of these chemicals in their populations via any type of biomonitoring analysis. Although many studies have been conducted in countries ranging from developed to developing, there are fewer reports that focus on representative samples of the population than once thought (Porta et al., 2007). The studies report a need for more comprehensive studies to be undertaken to determine trends in order to understand the sources and risks of long-term exposure of OCs (Devanathan et al., 2008; Ennaceur et al., 2008) now that they have been discovered to possibly affect the majority of the population.

Factors
Many factors affect chemical concentrations in breast milk such as diet, parity age, smoking habits, and environmental exposure. Since POPs bioaccumulate, mothers with diets high in animal protein generally have higher concentrations of PCBs (Emmaceur et al., 2008) and of DDT in Indian urban areas (Devanathan et al., 2008) than those with diets having less animal content. The general global trend is that PCB contamination increases and shows positive correlations with fish-rich diets (Abballe et al., 2008; Ennaceur et al., 2008) and that dietary food intake is one of the major sources of increased OC body burden. Developed countries that have been studied report, on average, lower concentrations of HCB and HCHs and DDTs than developing countries, but higher levels of PCBs (Ennaceur et al., 2008). Parity, the number of children borne from a mother, is also an important factor in noting concentrations of POPs. Lactation is the main route of discharge for organochlorine compounds from the body, therefore mothers will have higher concentrations of OCs before the breast-feeding of their first child than before the breast-feeding of their second. Concentrations of DDTs have the tendency to decrease with increasing number of breast-fed children (Strogi, 2008). Breast-feeding reduces women’s organochlorine compound levels by transferring the contaminants to the infant (Ennaceur et al., 2008).

Health Consequences
Slowed neurodevelopment (Ennaceur et al., 2008), potential adverse effects on cognitive-motor skills, thyroid problems (Abballe, 2008) and cretinism are but a short list. Research was conducted in Japan to determine the relation between cretinism and OC concentration in breast milk. The milk of mothers who gave birth to children with cretinism was contaminated with OCs 1.9–2.5 times higher than that of mothers who gave birth to normal children. According to findings, PCBs and DDT were the most effective compounds among the OCs to influence the incidence of cretinism; of dioxin-like compounds, PCDFs seemed the most influential. This study also strongly suggests that long-term and multiple exposures to these OCs truly have an effect on the thyroid hormone system in the fetus (Nagayama et al., 2007). The estimated daily intake of infants is useful in determining when levels of OCs are harmful or not. In India and in Tunisia, the intake levels were close to or even higher than the recommended daily intake as proposed by Health Canada (Devanathan et al., 2008; Ennaceur et al., 2008). Breast-feeding may pose serious risks to infants because of the transmitted compounds and their adverse effects: thyroid hormone disruption (Abballe et al., 2008), long-term impacts on intellectual function and delayed effects on central nervous system functions (Devanathan et al., 2008) negative impacts on neurodevelopment, lower birth weight and premature birth (Ennaceur et al., 2008). Although breast milk may be contaminated with damaging levels of OCs, the benefits of breast-feeding outnumber the risks; international organizations continue to recommend breast-feeding because of its immunological, developmental, mental and nutritive advantages (Ennaceur et al., 2008).