National Survey of Persistant Organic Pollutants in Human Milk in China
The Stockholm Convention which is designed to lead to a gradual decrease of the presence of persistent organic pollutants in the environment is a global treaty whose purpose is to safeguard human health and the environment from highly harmful chemicals that persist in the environment and affect the well-being of humans as well as wildlife. The Convention requires parties to eliminate and/or reduce POPs, which have a potential of causing devastating effects such as cancer and diminished intelligence and have the ability to travel over great distances.
China is a party to the Convention and and has a National Implantation Plan which aims to eliminate or restrict the production and use of the intentionally produced POPs. POPs are chemical substances that remain in the environment, can be transported over large distances, bioaccumulate through the food web, and pose a risk of causing damage to the environment and human health. POPs include pesticides such as DDT, industrial chemicals such as polychlorinated biphenyls (PCB) and unintentionally generated chemicals such as polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF). While the Convention initially focused on 12 intentionally and unintentionally produced chemicals (the "Dirty Dozen"), the Convention began adding additional substances to the agreement in May of 2009 and will continue to do so Presently, there are 23 POPs listed, see www.pops.int.
The Stockholm Convention evaluates the effectiveness of its strategies by monitoring activities under the global monitoring plan (GMP) which provides a harmonized organizational framework for the collection of comparable monitoring data on the presence of POPs from all regions. The GMP focuses on generating measurement data from core media: ambient air, human milk and human blood, and surface water for water-soluble POPs (perfluorooctane sulfonic acid, its salts and perfluorooctane sulfonyl fluoride). Monitoring of human milk allows countries and regions to identify contamination problems and formulate measures to reduce and prevent human and environmental exposure to these chemicals.
CFSA is responsible for carrying out the national surveys of POPs in human milk in China. So far, two surveys have been conducted in 2007 and 2011 respectively. For evaluation of the effect of various dietary habits and variety of contamination levels between regions, the survey was performed in the same regions as the Total Diet Survey carried out simultaneously. In the first survey, the samples were collected from 12 provinces including Heilongjiang, Liaoning, Hebei, Henan, Shanxi, Ningxia, Jiangxi, Fujian, Shanghai, Hubei, Sichuan and Guangxi. In the second survey, Inner Mongolia, Jilin, Qinghai and Guangdong were added. The population of the provinces involved in the surveys accounts for about 50% of the total population of China. In each province, one urban site and two rural sites were selected for sampling. In each urban area, 50 donors were selected, and in each rural area, 30 donors were selected. The approach for donor selection and sampling human milk was based on the ‘Guidelines for Developing a National Protocol’ of the Fourth WHO-Coordinated Survey of Human Milk for Persistent Organic Pollutants in Cooperation with UNEP (WHO, 2007). Some modifications were made for the special conditions within China, for example, the maximum age mothers was 35 in this study instead of 30 in the Guidelines. Mothers donating milk were informed of the nature and purpose of the study and signed the consent forms. A written questionnaire was completed to record the content of the face-to-face interview of each mother. The information collected included date of birth, place of birth, residence record, dietary habits (vegetarian/non vegetarian), consumption of animal origin food including aquatic food, meat, egg and milk, occupation before pregnancy, and the indoor usage of DDT at home. The sampling was carried out from August to November in 2007. Mothers provided the samples at the specific local contact places where collection was supervised. At least 50 mL of milk was collected from each mother. The samples were collected directly in pre-washed collecting jars and were stored at -20℃ until analysis.
Most of POPs in the Stockhom Convention list e.g. dioxins/furans (PCDD/Fs) and polychlorinated biphenyls (PCBs), Organic chlorine Pesticides (OCPs), polybrominateddiphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), hexabromocyclododecanes (HBCDDs), Tetrabromobisphenol A (TBBPA) and perfluorinated substances (PFAS) were included in the surveys.
Human milk is a unique biological matrix for monitoring certain environmental contaminants because it can provide exposure information about both the mother and the breastfed infant through a non-invasive method of collection. Human milk is considered to be one of the most important biota to be monitored for the presence of POPs, known to accumulate in the food chain. Consequently, human milk monitoring can yield information about the kinds and quantities of POPs in the environment as well as in our bodies. Better understanding of our exposure to harmful environmental chemicals will help us better manage such chemicals by eliminating or reducing emissions of such POPs or by limiting their presence in the food supply. Furthermore, the uptake of these chemicals by the infant via human milk is of high toxicological relevance. The risk-benefit assessment of breastfed infants represents one of the most challenging aspects of human toxicology, as possible adverse health effects associated with exposure to POPs concur with significant health benefits of breastfeeding.