BACKGROUND Hexabromocyclododecanes (HBCDs) have been identified as organic pollutants with the properties of persistence, long-distance migration, bioaccumulation, and biological toxicity. HBCDs have been detected in all kinds of biological and abiotic samples around the world, and have adverse effects on the environment and human body. As a non-invasive biological sample, human milk is a good medium for evaluating the exposure of HBCDs in the human body, and is widely used in the study of the exposure level of HBCDs in various countries, especially in nursing infants and young children. According to the survey, the production and use of HBCDs in Beijing has continued to rise since the use and production restriction of HBCDs in 2016, and the total use of HBCDs in 2019 increased by 60.8% compared with 2018. Therefore, in recent years in Beijing, especially before and after the use and production restriction of HBCDs, the residual characteristics and change trend of HBCDs in breast milk have attracted much attention.

OBJECTIVES To investigate the residual characteristics and trends of HBCDs in breast milk in Beijing from 2010 to 2018, evaluate the health risks for infants to intake HBCDs via breastfeeding, and provide basic data support for the scientific use, management, control, and human exposure risk assessment of HBCDs.

METHODS Breast milk samples (n=233) were obtained from 85 volunteer donors living in Beijing from 2010 to 2018. All volunteers have been living in Beijing for more than 5 years, are healthy, and do not directly engage in HBCDs production, processing, and other related occupations. Each sample was about 30mL, which was manually collected by volunteers into a 30mL clean glass bottle with a Teflon lined screw cap, and then transferred to a laboratory refrigerator for cryopreservation at -20℃. All volunteers were informed of the objective of this study. Pretreatment was conducted by liquid-liquid extraction and ammonia, ethanol, ether and n-hexane were added in turn. After liquid-liquid extraction, concentrated sulfuric acid sulfonation was combined with solid phase extraction (SPE) to purify the samples. Finally, 200μL methanol was added for constant volume. After centrifugation, the upper layer solution was transferred to a brown sample bottle (including lined tube) for storage. The qualitative and quantitative analysis of HBCDs was performed by Waters UPLC CLASS ultra-high performance liquid phase tandem API 4000 triple quadrupole mass spectrometry(LC-MS/MS). The isotope internal standard method was used for quantitative analysis to reduce the matrix effect.

RESULTS The detection rate of HBCDs in breast milk was 100%, indicating that HBCDs have been widespread in the human body. The concentration range of HBCDs was 0.46-93.5ng/g lw (lipid weight), with the average and median values of 7.27ng/g lw and 5.77ng/g lw, respectively. The 95th percentile of high-end exposure was 15.6ng/g lw. There were individual differences in the milk samples. The detection rates of α, β and γ-HBCD in all breast milk samples were 100%, 35.6% and 70.8%, respectively. α-HBCD had the most abundant diastereomers in breast milk samples, accounting for 80.1%, followed by γ-HBCD and β-HBCD in order. There were also a small number of breast milk samples that were dominated by γ-HBCD, accounting for 52.2%-83.5%. Even samples taken by the same volunteer in different months had different major diastereomers. The median EDI of HBCDs via human milk for infant was 20.5ng/kg bw/day, and the 95th percentile value was 71.4ng/kg bw/day, which was comparable to the previous research in Beijing, but higher than Japan, Ghana and other cities in China.

CONCLUSIONS Compared with the HBCDs in breast milk from other regions at home and abroad, the level of HBCDs in breast milk in this study is close to the previous research data in Beijing, but higher than that of Shanghai, Shenzhen and other cities in China, as well as higher than the results of recent studies in Japan, the United Kingdom, the United States, Canada, India, the Philippines and some African countries, which may be related to the continuous use of HBCDs in China and the large amount of use. In human breast milk, α-HBCD is the main diastereomers, while in a small number of samples, γ-HBCD is the main diastereomers. The differences in the distribution characteristics of these diastereomers may be due to the differences in the absorption, metabolism and excretion mechanisms among individuals, and the transformation of HBCDs among different isomers in vivo, and the differences in the main external exposure pathways. The level of HBCDs showed an obvious upward trend from 2010 to 2013, reached the highest value of 6.84ng/g lw in 2013, and then decreased slightly and remained constant, which may be related to the production, use and prohibition of HBCDs globally and domestically. The time trend of α-HBCD and HBCDs is basically the same, while the content of β-HBCD and γ-HBCD in breast milk is low, and the change trend is stable with time. The concentration of HBCDs in breast milk changed slowly from 2014 to 2018 but did not show a significant downward trend after the initial ban of HBCDs in China in 2016, which may indicate that there are still a large number of HBCDs in production and use on the market, and human intake of HBCDs through air, dust, diet and other ways does not decrease. The risk assessment results indicate that the Hazard Quotient (HQ) of 99% breast milk samples is less than 1, which indicates that the intake of HBCDs through breast-feeding during lactation would not bring significant health risk to infants, but the HQ value of 1% breast milk samples is greater than 1, which suggests that breastfeeding may bring health risks to infants. More research is needed to further investigate the major sources of exposure and the effect of each potential factor.