9:00 AM - 9:15 AM
[MZZ51-01] The analysis of the chemical form of insoluble bromine in sediment by XANES
Keywords:X-ray absorption near edge structure, Insoluble bromine, Persistent organic pollutants, Natural origin organic bromine compounds, Sediment, Beppu Bay
Introduction and Purpose
Some organobromine compounds are classed as Persistent Organic Pollutants (POPs) and are subject to international restrictions, but the number of compounds registered as POPs is increasing. A comprehensive evaluation of POPs-like substances including substitutes and analogues of POPs is necessary. As the evaluation, insoluble bromine fraction (Insoluble-Br)1 and extractable organobromine low (<1000 g/mol) molecular weight fraction (EOBr-L)2, which focus on the characteristics of POPs is noted. While the investigation of EOBr-L, which is close to the characteristics of POPs, is progressing, it is also necessary to clarify the insoluble bromine fraction, which is more comprehensively evaluated. After POPs are released into the environment, they are known to be migrated and distributed in sediment3. Dated sediment core samples are therefore suitable for exploring the trends in contaminants4. Organobromine compounds are also produced naturally. It has been reported that natural organic bromine compounds are generated from seaweeds and contained in sediment and that they are dehalogenated by bacteria5, and the concentration of bromine in sediment has been pointed out to be related to the total organic carbon and marine organic carbon6. As these facts, the vertical change in bromine concentration reflects both the trend of anthropogenic compounds and the formation and decomposition of naturally occurring compounds, and it is important to understand the bromine cycle in nature by understanding the form of bromine existence. In this study, we aimed to clarify the vertical variation of bromine and the regional differences in the sediment. Sediment samples collected from several locations were cut into 1 cm layers and washed to remove water-soluble bromine and measured the X-ray absorption near-edge structure (XANES) of each layer to compare the depth dependence of the spectra and the differences between the sampling locations.
Materials and Methods
Sediment samples were collected from three sites: Beppu Bay, Osaka Bay, and Lake Biwa. Cores were cut into layers of 1cm each, freeze-dried, and washed three times with potassium nitrate solution, and the residue was dried and used as Insoluble-Br. The samples were irradiated with X-rays at BL-12C of the Photon Factory in Tsukuba, Ibaraki, and the XANES around the Br-K absorption edge was measured (Project No:2021G064). The bromine concentration in the Insoluble-Br was measured by combustion ion chromatography.
Results and Discussions
The bromine spectra at each site were almost unchanged in the depth direction, and no significant difference appeared at the three sites. This is noteworthy when compared to the fact that the chlorine spectrum was different depending on depths and locations. This result suggests that insoluble bromine in sediment contains some dominant compound regardless of the region or freshwater, or that multiple compounds are present in a certain ratio, and the shape of the spectra suggests that the compounds are likely to be aromatic rather than aliphatic. Furthermore, this compound is not of anthropogenic origin, which can vary greatly from year to year and region to region, but is of natural origin, which does not cause much variation. The concentrations of Insoluble-Br were similar in the seawater areas of Beppu Bay and Osaka Bay but different in the freshwater areas of Lake Biwa. The concentrations of bromine in all core samples decreased from the surface layer to the lower layer. It is possible that the dominant or the other bromine compounds in the sediment are dehalogenated by microorganisms in the same proportion.
Conclusion
In this study, it was found that the abundance of bromine compounds in the insoluble fraction of sediment was the same in depths less than 30 cm, regardless of depth, location, or freshwater and seawater, and the same could be said on a global scale. On the other hand, since there are many bromine compounds considered to be naturally occurring, the Insoluble-Br as a risk assessment of pollutants is uncertain, and EOBr-L is more suitable for this purpose.
Acknowledgments
This research was supported by a Grant-in-Aid for Scientific Research (A) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Project Number: 20H00646.
1Mukai et al., (2019) ACS Omega. 4(4), 6126-6137.2Mukai et al., (2021) Sci. Total Environ. 69, 133-148.3Anh et al., (2021) Chemosphere. 266, 129180.4Atashgahi et al., (2018) Environ. Microbiol. 20(3). 934-948.5Leri et al., (2010) Global Biogeochem. Cycles. 24(4), 1-15.6Mayer et al., (2007) Mar. Chem. 107, 244-254.
Some organobromine compounds are classed as Persistent Organic Pollutants (POPs) and are subject to international restrictions, but the number of compounds registered as POPs is increasing. A comprehensive evaluation of POPs-like substances including substitutes and analogues of POPs is necessary. As the evaluation, insoluble bromine fraction (Insoluble-Br)1 and extractable organobromine low (<1000 g/mol) molecular weight fraction (EOBr-L)2, which focus on the characteristics of POPs is noted. While the investigation of EOBr-L, which is close to the characteristics of POPs, is progressing, it is also necessary to clarify the insoluble bromine fraction, which is more comprehensively evaluated. After POPs are released into the environment, they are known to be migrated and distributed in sediment3. Dated sediment core samples are therefore suitable for exploring the trends in contaminants4. Organobromine compounds are also produced naturally. It has been reported that natural organic bromine compounds are generated from seaweeds and contained in sediment and that they are dehalogenated by bacteria5, and the concentration of bromine in sediment has been pointed out to be related to the total organic carbon and marine organic carbon6. As these facts, the vertical change in bromine concentration reflects both the trend of anthropogenic compounds and the formation and decomposition of naturally occurring compounds, and it is important to understand the bromine cycle in nature by understanding the form of bromine existence. In this study, we aimed to clarify the vertical variation of bromine and the regional differences in the sediment. Sediment samples collected from several locations were cut into 1 cm layers and washed to remove water-soluble bromine and measured the X-ray absorption near-edge structure (XANES) of each layer to compare the depth dependence of the spectra and the differences between the sampling locations.
Materials and Methods
Sediment samples were collected from three sites: Beppu Bay, Osaka Bay, and Lake Biwa. Cores were cut into layers of 1cm each, freeze-dried, and washed three times with potassium nitrate solution, and the residue was dried and used as Insoluble-Br. The samples were irradiated with X-rays at BL-12C of the Photon Factory in Tsukuba, Ibaraki, and the XANES around the Br-K absorption edge was measured (Project No:2021G064). The bromine concentration in the Insoluble-Br was measured by combustion ion chromatography.
Results and Discussions
The bromine spectra at each site were almost unchanged in the depth direction, and no significant difference appeared at the three sites. This is noteworthy when compared to the fact that the chlorine spectrum was different depending on depths and locations. This result suggests that insoluble bromine in sediment contains some dominant compound regardless of the region or freshwater, or that multiple compounds are present in a certain ratio, and the shape of the spectra suggests that the compounds are likely to be aromatic rather than aliphatic. Furthermore, this compound is not of anthropogenic origin, which can vary greatly from year to year and region to region, but is of natural origin, which does not cause much variation. The concentrations of Insoluble-Br were similar in the seawater areas of Beppu Bay and Osaka Bay but different in the freshwater areas of Lake Biwa. The concentrations of bromine in all core samples decreased from the surface layer to the lower layer. It is possible that the dominant or the other bromine compounds in the sediment are dehalogenated by microorganisms in the same proportion.
Conclusion
In this study, it was found that the abundance of bromine compounds in the insoluble fraction of sediment was the same in depths less than 30 cm, regardless of depth, location, or freshwater and seawater, and the same could be said on a global scale. On the other hand, since there are many bromine compounds considered to be naturally occurring, the Insoluble-Br as a risk assessment of pollutants is uncertain, and EOBr-L is more suitable for this purpose.
Acknowledgments
This research was supported by a Grant-in-Aid for Scientific Research (A) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Project Number: 20H00646.
1Mukai et al., (2019) ACS Omega. 4(4), 6126-6137.2Mukai et al., (2021) Sci. Total Environ. 69, 133-148.3Anh et al., (2021) Chemosphere. 266, 129180.4Atashgahi et al., (2018) Environ. Microbiol. 20(3). 934-948.5Leri et al., (2010) Global Biogeochem. Cycles. 24(4), 1-15.6Mayer et al., (2007) Mar. Chem. 107, 244-254.