Elsevier

Chemosphere

Volume 266, March 2021, 129180
Chemosphere

Contamination levels and temporal trends of legacy and current-use brominated flame retardants in a dated sediment core from Beppu Bay, southwestern Japan

https://doi.org/10.1016/j.chemosphere.2020.129180Get rights and content

Highlights

  • PBDEs and DBDPE were examined in a sediment core from Beppu Bay, Japan.

  • BDE-209 was the most predominant congener in all the sediment layers.

  • BDE-209 concentrations peaked at the mid-1990s, then decreased and kept constantly.

  • DBDPE/BDE-209 ratios gradually increased during 1991–2011.

  • No serious ecological risk of PBDEs and DBDPE was estimated.

Abstract

Contamination levels and temporal trends of polybrominated diphenyl ethers (PBDEs) and some alternative brominated flame retardants (BFRs) were examined in a dated sediment core from the deepest part of the Beppu Bay, southwestern Japan. PBDEs were found in the upper layers of 0–15 cm depth at concentrations ranging from 5200 to 32,600 pg g−1 with the peak estimated at 1995. Decabromodiphenyl ether (BDE-209) was the most abundant congener, accounting for 96% in average of total PBDEs. The vertical profile of BDE-209 observed in our sediment core generally agreed with the historical pattern of domestic demand of commercial deca-BDE mixtures in Japan, and perfectly matched with maximum stock of these products (i.e., 42,000 tons in 1995). Among alternative BFRs, only decabromodiphenyl ethane (DBDPE), a replacement of deca-BDE, was found at significant levels with concentrations of 69–850 pg g−1 in sediment layers dated between 1991 and 2011. Ratios of DBDPE to BDE-209 gradually increased during this period, implying opposite trends of these two compounds and the role of DBDPE as a deca-BDE’s alternative. The occurrence of deca-BDE components in sediments may pose medium risk to benthic aquatic life, while the ecological risk of other PBDE homologs and DBDPE was negligible.

Introduction

Brominated flame retardants (BFRs), for example, tetrabromobisphenol A (TBBPA), polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), hexabromocyclododecanes (HBCDs), and a variety of other organobromine compounds have been widely produced and applied in different materials and products to protect them from fire hazard (Alaee et al., 2003; Guerra et al., 2010). Environmental contamination and ecological and human health risk related to BFRs (with special focus on PBDEs) have become issues of concern since the 1980s, especially in countries where these substances were extensively manufactured and used like the US, Sweden, Japan, etc. (de Wit, 2002; Darnerud, 2003; Sjodin et al., 2003; Watanabe and Sakai, 2003; Hites, 2004). Several BFR classes were listed under the Stockholm Convention on Persistent Organic Pollutants (POPs) as chemicals need to be eliminated, including PBDEs, PBBs, and HBCDs due to their persistence, widespread dispersal, and toxic effects (Stockholm Convention, 2018). The phase-out of these legacy BFRs has resulted in the introduction alternative formulations such as decabromodiphenyl ethane (DBDPE), 1,2-bis-(2,4,6-tribromophenoxy)ethane (BTBPE), TBBPA derivatives, etc. (de Wit et al., 2010; Covaci et al., 2011). These current-use BFRs, however, in following the footsteps of legacy formulations, have been detected in the environment (even in remote areas like the Polar regions) with not fully answering questions regarding their environmental behavior and fate and toxicities (Kierkegaard et al., 2004; de Wit et al., 2010; Ricklund et al., 2010; Covaci et al., 2011; Vorkamp et al., 2019).

In Japan, the production of PBDEs started in the mid-1970s and reached a peak of 2600 tons in 1990 with a total domestic production of about 35,000 tons between 1975 and 2014 (Abbasi et al., 2019). Domestic demand of PBDEs in this country was estimated to be 120,000 tons during the past four decades, which was dominated by deca-BDE products (about 90% of total PBDE demand) (MOE, 2018). The production and demand of tetra- and octa-BDE mixtures in Japan decreased drastically after 1990 due to voluntary phasing out (Watanabe and Sakai, 2003). The domestic demand of deca-BDE mixtures declined gradually after reaching a peak in 1990 (Xue et al., 2017), and then the use of these formulations was stopped in 2017 according to the Stockholm Convention on Persistent Organic Pollutants (POPs). As a result, consumption of alternative BFRs such as DBDPE has increased since the early 1990s and surpassed those of deca-BDE in 1997 (MOE, 2018). Although usage history of DBDPE was much later than PBDEs, cumulative demand of its products was equal to PBDE products in 2016 with a slight increasing trend of annual consumption (MOE, 2018). The early evidences on environmental pollution caused by PBDEs in Japan were reported since the late 1980s by using aquatic biota and sediment archives (Watanabe et al., 1986, 1987). Spatial and vertical profiles of PBDEs were evaluated for surface and core sediments collected from Tokyo Bay, indicating municipal and industrial wastewater as potential contamination sources and showing an increasing trend of their sedimentary concentrations from the 1980s to the early 2000s (Minh et al., 2007). Since then, updated information on temporal trends of BFRs in the Japanese environment is probably not available, especially for current-use formulas like DBDPE.

The historical profiles of a typical POP class, polychlorinated biphenyls (PCBs), were reasonably reconstructed by using a well-preserved sediment core from Beppu Bay, southwestern Japan (Takahashi et al., 2020). As information about temporal trends of PBDEs and their alternatives in Japan is still scarce, the same sediment core was examined to provide insights into the occurrence and historical inputs of these flame retardants. In the present study, vertical profiles of PBDEs and alternative BFRs (notably DBDPE) were investigated in the sediment core deposited continuously for over 60 years (i.e., 1952–2011). The compositional profiles of PBDEs and DBDPE were analyzed by using correlation analysis and several diagnostic ratios to estimate their potential emission sources and environmental behavior and fate. Estimation of deposition fluxes and inventories of PBDEs and DBDPE was performed. Ecological risk assessment of these BFRs was also conducted by using risk quotient approach. To our knowledge, this is among the first studies to simultaneously investigate the contamination status, depositional history, inventory, and risk of legacy and current-use BFRs in a coastal area of Asia–Pacific countries.

Section snippets

Sampling location and sample collection

Beppu Bay is located in the northeastern coast of Kyushu Island, Japan. The southern area of the bay receives discharges from Oita River and Ono River, which are affected by industrial, urbanization, and tourism activities of Oita Prefecture (Amano et al., 2011). Previous geochronological studies suggested that sediments in the deepest and innermost part of Beppu Bay are continuously deposited with high sedimentation rates and minor tidal mixing because of specific basin shape with a barrier

Concentrations and temporal trends of PBDEs and DBDPE in the sediment core from Beppu Bay

In our sediment samples, PBDEs were only quantified in 8 upper layers of 0–15 cm in depth. Among 41 PBDEs and 4 alternative BFRs examined in this study, 14 tetra-to decabrominated congeners (i.e., BDE-47, -99, −153, −154, −180, −183, −196, −197, −201, −203, −206, −207, −208, and −209) and DBDPE were detected, while levels of the remaining compounds were lower than detection limits. Therefore, concentrations of total PBDEs (ΣPBDEs) refer to the sum of detected congeners with descriptive

Conclusions

This study reports one of the most updated datasets about temporal trends of PBDEs and DBDPE in a coastal area of southwestern Japan, which was reconstructed by combining geochronological and chemical methods. In our sediment core samples, PBDEs (notably BDE-209) have been detected in the layers dated from the 1980s onwards. Concentrations of total PBDEs reached a peak at the mid-1990s and then rapidly decreased to relatively constant levels from the early 2000s–2010s. Compositional profiles of

Credit author statement

Anh Quoc Hoang: Methodology, Writing – original draft. Daichi Aono: Methodology, Formal analysis. Isao Watanabe: Conceptualization, Methodology, Formal analysis. Michinobu Kuwae: Conceptualization, Resources, Formal analysis, Writing – review & editing. Tatsuya Kunisue: Conceptualization, Resources, Writing – review & editing. Shin Takahashi: Supervision, Conceptualization, Resources, Project Administrator, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was supported by the Environment Research and Technology Development Fund (SII-3-2) of the Environmental Restoration and Conservation Agency of Japan (ERCA). The cooperative research program (18A024) of the Center for Advanced Marine Core Research, Kochi University also supported this study. We thank Ms. Kana Kadota and the staff and students of CATE and CMES (Ehime University) for their support in sampling, preparation, and analysis of the samples.

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      In contrast, Beppu Bay, Japan (Fig. 1), is the only basin located within the Japanese coastal zone which exhibits clear autumnal oxygen depletions in bottom waters (0–0.2 mg L−1) (Kameda and Fujiwara, 1995) as well as annual varve sedimentation during the late Holocene (Kuwae et al., 2013b). The high sedimentation rates (0.23–0.30 cm yr−1) observed in Beppu Bay have allowed for the precise dating of surface sediments using lead-210 (210Pb) (Takahashi et al., 2020) and the reconstruction of excellent proxy records of anthropogenic markers, including increases in concentrations of cesium-137 (137Cs) (Kuwae et al., 2013b; Takahashi et al., 2020), polychlorinated biphenyls (PCB; Takahashi et al., 2020), dichlorodiphenyltrichloroethane (DDT; Nishimuta et al., 2020), brominated fire retardants (Hoang et al., 2021) and microplastics (Masumoto et al., 2018) since 1950. In addition, Beppu Bay sediments may have a plutonium-239 (239Pu) signature arising from atmospheric deposition of radio-isotopes that could act as a marker to define the lower boundary of the Anthropocene (Yokoyama et al., 2021).

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