Hexabromocyclododecanes in breast milk from residents in Shenzhen, China: Implications for infant exposure
Graphical abstract
Hexabromocyclododecanes (HBCDs) exposure for general population and infants.
Introduction
Hexabromocyclododecanes (HBCDs) are widely used as flame retardants for expanded polystyrene (EPS) foam, extruded polystyrene (XPS) foam, textile products, and various electronic products. In 2001, the global consumption of HBCDs was 16,700 tons, and reached 28,000 tons in 2011 (9000–15,000 tons in China, and 13,426 tons in Europe and the United States; POPRC, 2011). Unlike tetrabromobisphenol A, which is chemically bound to products, HBCDs are additives and thus are easily released into environmental compartments from the products. HBCDs are ubiquitous pollutants, they have been frequently detected in air, soils, sediments, and human fluids (Law et al., 2014, Yi et al., 2016). Although animal experiments suggest that HBCDs have low acute toxicity via oral, inhalation, and dermal routes (Wang et al., 2011, Wikoff and Birnbaum, 2011), repeated oral doses lead to chronic toxicity such as hepatotoxicity and thyroid toxicity (Ema et al., 2008, Palace et al., 2008, Ibhazehiebo et al., 2011, Villanger et al., 2011). Previous in vitro studies suggest that HBCDs are cytotoxic (Al-Mousa and Michelangeli, 2012, An et al., 2014, Huang et al., 2016). Moreover, some studies show that HBCDs have adverse effects on the development of juvenile animals (Anselmo et al., 2011, Du et al., 2012b, Usenko et al., 2016).
After entering the human body, HBCDs can remain in bodily fluids such as breast milk (Geyer et al., 2004, Kakimoto et al., 2008, Toms et al., 2012) and blood (Bjermo et al., 2017, Drage et al., 2017), or in tissues such as scalp hair (Malarvannan et al., 2013) and adipose tissue (Johnson-Restrepo et al., 2008, Pulkrabova et al., 2009). In contrast to environmental measurements, the biomonitoring of HBCDs in bodily fluids directly reflect the overall exposure via different sources and pathways. Although previous studies have determined environmental pollution of HBCDs in China (Zhang et al., 2009, Hu et al., 2011, Li et al., 2012a), data on the levels of HBCDs in human samples are still very limited.
Shenzhen is a coastal city locating east of the Pearl River Delta, which is one of the most economically developed regions in China. In the past three decades, Shenzhen has undergone rapid economic growth and has become a manufacturing center of electronic products in China, and income from the electronic industry reached 1600 billion yuan in 2016 (Xu, 2017). A large amount of brominated flame retardants is required in the production of electronic products. Previous studies have frequently reported polybrominated diphenyl ethers, tetrabromobisphenol A, and HBCDs in soil, air, indoor dust (Li et al., 2012b, Ni and Zeng, 2013), and ecological food chains (Liu et al., 2011) in Shenzhen. A recent study has found that polybrominated diphenyl ethers exist at relatively high levels in human breast milk of Shenzhen residents (Zhang et al., 2012). Breast milk is the most important food for infants, making infants exposed to residual HBCDs. Therefore, more attention should be paid to this issue. Nevertheless, there is still no study on HBCDs in the residents of Shenzhen.
The aims of this study were, therefore, to investigate the concentrations and profiles of HBCDs in human breast milk samples in Shenzhen, to estimate the daily intake of HBCDs of infants, and to analyze the probable sources of HBCD exposure for the local residents. This is the first study to report levels of HBCDs in samples from the residents in the city.
Section snippets
Chemicals and reagents
α-, β-, and γ-HBCD and their corresponding internal standards (13C12-α-, 13C12-β- and 13C12-γ-HBCD, respectively) with the purity of 98% were purchased from Cambridge Isotope Laboratories (Andover, MA, USA). Methanol, hexane, cyclohexane, toluene, and acetonitrile of high-performance liquid chromatography (HPLC) grade were purchased from Merck (Darmstadt, Germany). HPLC-grade ethyl acetate was purchased from Honeywell Burdick & Jackson (Muskegon, MI, USA). Sulfuric acid (98% purity) and
Concentrations of HBCDs in breast milk samples from Shenzhen
The mean, median, percentile, and range of concentrations of α-, β-, γ-HBCD, and ΣHBCDs in the breast milk samples are listed in Table 1. The concentrations of individual HBCD diastereoisomers and ΣHBCDs in the samples varied greatly. Diastereoisomer of α-HBCD was detected in all samples. Its concentration ranged from 0.103 to 14.3 ng/g lipid and had a median of 1.79 ng/g lipid. β-HBCD and γ-HBCD were detected only in some of the samples. The detection rates for β-HBCD and γ-HBCD were 21.1% and
Conclusions
Results from this study suggest that infants from Shenzhen are exposed to moderate doses of ΣHBCDs. The duration of residence in Shenzhen was positively correlated with the HBCD levels in breast milk. Electronic products, EPS foam, and XPS foam may therefore be important sources of HBCD exposure in Shenzhen. To identify the exposure sources of HBCDs, the levels of indoor environments and diets should be investigated in future studies. This is the first study to report the body burden of HBCDs
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 21677103), the Natural Science Foundation of Guangdong Province (No. 2015A030313869) and Shenzhen Municipal Science and Technology Innovation Commission (No. JCYJ20170413102320786). We thank all the mother donors and doctors who participated in this study. Also our sincere thanks are given to Professor Lingeng Lu who is in Department of Chronic Disease Epidemiology, Yale School of Public Health, Yale Cancer Center,
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