Elsevier

Chemosphere

Volume 247, May 2020, 125950
Chemosphere

Concentrations and distributions of polybrominated diphenyl ethers (PBDEs) in surface soils and tree bark in Inner Mongolia, northern China, and the risks posed to humans

https://doi.org/10.1016/j.chemosphere.2020.125950Get rights and content

Highlights

  • PBDEs pollution is widespread in Inner Mongolia.

  • BDE-28 concentrations in bark of AGR areas were significantly higher than in IND areas.

  • The exposure risk in pristine areas can be higher than in polluted areas due to LRAT of lower-brominated congeners.

Abstract

Three functional zones, namely the industrial (IND), the agricultural (AGR), and the grassland (GRA) areas from Inner Mongolia (a remote province in northern China), were selected to evaluate the levels and distributions of PBDEs and the risks posed to local humans. PBDEs concentrations in surface soils and tree bark were detected and the air levels were estimated based on bark measurements. The total concentrations (∑8PBDEs) of BDE-28, -47, −100, −99, −154, −153, −183, and −209 in soils were 1.71–64.9 ng/g dry weight (d.w.), 0.720–4.08 ng/g d.w., and 0.604–3.76 ng/g d.w. in the IND, AGR and GRA areas respectively. The average total concentrations in bark and air were 0.792 ng/g d.w. and 0.125 ng/m³ in the AGR areas respectively, which were lower than those (1.69 ng/g d.w. in the bark and 0.476 ng/m³ in the air) in the IND areas. BDE-209 was the dominant congener, consistent with DeBDE being the dominant commercial products used in China. However, except for BDE-209, BDE-28 and BDE-47 in the AGR and GRA areas averagely contributed about half of the total PBDEs concentrations in soils. BDE-28 concentrations in the bark samples of the AGR areas were significantly higher (p < 0.05) than in the IND areas, and the average total hazard quotients (∑8PBDEs) were higher for humans in the AGR areas (0.12) than in the IND areas (0.08). Degradation of higher-brominated congeners (e.g., BDE-209) and migration of lower-brominated congeners (mainly BDE-28 and BDE-47) may increase the risks to humans in pristine areas.

Introduction

Large amounts of polybrominated diphenyl ethers (PBDEs) have been manufactured and used in textiles, furniture, and electronic appliances as one of the most widely used brominated flame retardants (BFRs) (Leung et al., 2007). PBDEs, as a kind of additive (without chemical bonds) BFRs, can enter the environment from PBDEs-treated products through volatilization when the products are in use or discarded (particularly if the products are combusted) (de Wit, 2002). There are also great concerns about the behaviors and effects of PBDEs in the environment since they are toxic (particularly the lower-brominated congeners), persistent, and can migrate globally through “global fractionation” and the “grass-hopping” and accumulate in organisms (Wania and Mackay, 1996; Gouin et al., 2004; Hites, 2004). PeBDE, OcBDE, and DeBDE are 3 main PBDE-based flame retardant commercial products (de Wit, 2002). It is generally considered that PeBDE has never been produced in China and OcBDE was added in the Stockholm Convention in 2009 (Qiu et al., 2010). However, DeBDE, which is the dominant commercial PBDE-based flame retardant commercial product (consisting of 97–98% BDE-209), is still not regulated in China (WHO/ICPS, 1994; Li et al., 2016c). Meanwhile, domestic demand for BFRs in China has continued to grow by 8% each year from 2000 (Mai et al., 2005).

Much research on the occurrence of PBDEs in the environment has been conducted in recent years, and these studies have mainly been performed in heavily polluted or populated areas such as electronic waste recycling sites (Leung et al., 2007; Luo et al., 2009), waste plastic disposal sites (Deng et al., 2014; Tang et al., 2016), and big cities such as Guangzhou, Toronto, and Zurich (Chen et al., 2006; Bogdal et al., 2014; Melymuk et al., 2014). Few studies have been performed in pristine areas while concerns about PBDEs in these regions are growing (Ikonomou et al., 2002; Wang et al., 2009; Gao et al., 2012; Bossi et al., 2016; Carlsson et al., 2018; Liu et al., 2018). PBDEs concentrations in Arctic biota increased exponentially between 1981 and 2000 and it was estimated that, at current rates of bioaccumulation, PBDEs would become the most abundant organohalogen compounds by 2050 (Ikonomou et al., 2002). PBDEs were also detected in the Tibetan Plateau (southwest China) where there were no direct sources of PBDEs and it was indicated that the lower-brominated congeners, especially BDE-28 and BDE-47, which were more toxic and persistent than BDE-209 (UNEP, 2006), contributed most (exceeded 40%) to the total PBDEs concentrations in environmental and biological matrices in pristine sections of China (Wang et al., 2009; Gao et al., 2012; Liu et al., 2018). Lower-brominated congeners’ light weights and high volatility make them easier to undergo long-range atmospheric transport (LRAT) than heavier congeners, which can help explain their predominance in pristine areas (Betts, 2002). Studies also have shown that lower-brominated congeners can be formed from higher-brominated congeners through biodegradation (Kim et al., 2007; Chang et al., 2012), photochemical degradation (Eriksson et al., 2004; Kuivikko et al., 2007), and reductive debromination by zerovalent iron (Keum and Li, 2005; Lin et al., 2012). Debromination of higher-brominated congeners may be an important source of lower-brominated PBDEs in the environment. To sum up, our understanding of PBDEs transport to pristine areas far from PBDEs sources is still poor, and it is not clear whether lower-brominated PBDEs concentrations in pristine environments have reached the level that could pose risks to local humans.

Soils act as a major sink and reservoir for PBDEs because of their large sorption capacity and PBDEs can be released from soils to air even though they have been legally prohibited, and therefore, soils are frequently used to monitor PBDEs in the environment (DeCarlo, 1979; Hassanin et al., 2004; Zou et al., 2007; Li et al., 2016b). Tree bark makes an excellent natural passive sampler to monitor persistent organic pollutants (POPs) originating from the air, particularly in remote areas because (1) Tree bark is rich in lipids and has large and porous surface areas so that it can accumulate both vapor-phase and particle-phase lipophilic PBDEs from its surrounding air (Samecka-Cymerman et al., 2006; Peverly et al., 2015). (2) POPs in tree bark are almost all from the atmosphere unless the soil is very much polluted (Kipopoulou et al., 1999; Pier et al., 2002). Moreover, a mathematical model describing the stable partitioning of POPs between bark and air was established to evaluate atmospheric POPs levels based on those recorded in bark (Zhao et al., 2008; He et al., 2016). (3) The lifetime of tree bark is normally in a 3–5 year range (Peverly et al., 2015) and that the airborne pollutants absorbed in the bark are almost inert because of the absence of metabolic processes (Schulz et al., 1999), which means tree bark indicates long-term air pollution. (4) Tree bark is a widely distributed, cost-effective and energy-efficient natural sampler (Schulz et al., 1999). Hence for those remote areas where instrumental monitoring is difficult, tree bark can be useful biosamplers for atmospheric pollutants (Tarcau et al., 2013). Therefore, tree bark has become a useful biomonitor for POPs in air and been used constantly in estimating airborne POPs concentrations and tracing potential POPs sources (Zhao et al., 2008; Fu et al., 2014; Peverly et al., 2015; He et al., 2016; Li et al., 2016a).

The Inner Mongolia Autonomous Region is the largest area that is relatively unaffected by anthropogenic activities in northern China. Nevertheless, rapid industrial development is also occurring here. Meanwhile, Inner Mongolia is dominated by the Mongolian plateau, which has a mean elevation of 1000 m and an annual mean temperature of 6.5 °C (Inner Mongolia Meteorological Bureau, 2017). PBDEs can therefore be enriched in the Inner Mongolian environment through cold condensation (Simonich and Hites, 1995). To our knowledge, the occurrence of PBDEs in soils, bark, and air in Inner Mongolia was first measured simultaneously in this work and it is an important study to have a good knowledge of global PBDEs concentrations. The levels, distributions and human exposure risks of PBDE were analyzed in our study, the results of which will improve our understanding of PBDEs transport patterns, environmental impacts and health risks posed by PBDEs in relatively pristine areas.

Section snippets

Sample collection

As for the locations, we selected 6 sites of Inner Mongolia and every two of the sites represent one functional zone, namely, the industrial areas (IND; site S1, a steel production base in Baotou; site S2, a thermal power plant in Huhhot), agricultural areas (AGR; site S3 in Baynnur and S4 in Tongliao, both were cornfields) and grassland areas (GRA, site S5 in Ulanqab and S6 in Xilingol, with a population of 2.1 and 1.1 million respectively) (Fig. 1). Surface soils (0–15 cm deep) and tree bark

Soil

Detailed PBDEs concentrations in soil, bark, and air at different sites were listed in Table 1. Eight PBDEs congeners (BDE-28, -47, −100, −99, −154, −153, −183, and −209) were detected and analyzed in the soil samples. The average total PBDEs concentrations (∑8PBDE, the sums of BDE-28, -47, −100, −99, −154, −153, −183 and −209) in the studied functional areas ranged from 1.25 ng/g d.w.(S5, GRA area) to 13.3 ng/g d.w. (S1, IND area), with an average of 3.62 ng/g d.w. and a median of 2.91 ng/g

Conclusions

PBDEs concentrations in soil and bark were detected in three functional areas of Inner Mongolia and the risks posed to local humans were also evaluated. It was found that Inner Mongolia has been somewhat contaminated with PBDEs and the PBDEs levels in soils of the IND areas were a bit higher than in those developed regions across China. The overall PBDEs concentrations in tree bark were comparable to the average global level. BDE-209 was the most abundant congener at all the sampling sites. The

CRediT authorship contribution statement

Yijing Chen: Conceptualization, Formal analysis, Investigation, Visualization, Writing - original draft, Writing - review & editing, Project administration, Funding acquisition. Aiqin Zhang: Conceptualization, Formal analysis, Resources. Huixiang Li: Formal analysis, Investigation, Writing - original draft, Funding acquisition. Yu Peng: Formal analysis, Investigation, Writing - original draft, Funding acquisition. Xinyu Lou: Formal analysis, Investigation, Funding acquisition. Minghui Liu:

Acknowledgments

This work was financially supported by the National Undergraduate Innovative Training Project of China (GCCX2018110041), the Collaborative Innovation Center for Ethnic Minority Development of Minzu University of China (0910KYQN50), the Fundamental Research Funds for the Central Universities (2015MDTD23C), and the Institution of Higher Education Innovation Talent Recruitment Program (111 Program) (B08044).

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