Bromine and iodine in Japanese soils determined with polarizing energy dispersive X-ray fluorescence spectrometry

The bromine (Br) and iodine (I) status of Japanese soils was investigated by analyzing around 900 soil samples and related materials with polarizing energy dispersive X-ray fluorescence spectrometry (EDXRF). The samples consisted of the following five groups: (1) 468 soil samples collected from 70 sites in the mainland of Japan (mainland soils); (2) 139 agricultural soils collected nationwide; (3) 93 samples taken from the southwestern island (island soils); (4) 52 coastal marine sediments; and (5) 137 tsunami deposits by the 2011 off the Pacific coast of Tohoku Earthquake. The geometric mean of Br was highest in marine sediments (30.6 mg kg⁻¹), followed by that in island soils (24.8 mg kg⁻¹), although the difference between these two groups was not significant. The values for the other three groups were significantly lower at p < 0.05 by Welch’s t test, and were in the following order: mainland soils (10.4 mg kg⁻¹) > tsunami deposits (8.52 mg kg⁻¹) > agricultural soils (7.86 mg kg⁻¹). For I, the geometric mean of island soils (31.9 mg kg⁻¹) was significantly higher than that of other soils at p < 0.05 by Welch’s t test, and was more than three times higher than that of mainland soils (9.11 mg kg⁻¹), which was the second highest group. The values for the other three groups were in the following order: marine sediments (5.68 mg kg⁻¹) > tsunami deposits (4.66 mg kg⁻¹) > agricultural soils (3.50 mg kg⁻¹). The contents of I were higher than those of Br for around two thirds of the island samples. As a result, the geometric mean of the Br/I ratio was less than 1.0 only in this group. The contents of both elements were significantly higher in upland soils than in paddy fields soils. These differences could be partly attributed to the higher ratio of Andosols containing higher amounts of Br and I in upland samples, in addition to the difference in the chemical forms of both elements in paddy field and upland samples. The correlation coefficients among rare earth elements, for example, were more than 0.9 for a considerable number of combinations, whereas more than 80% of the absolute values of correlation coefficients for Br and I against 60 other elements were less than 0.4. These results strongly suggest that the behavior of Br and I in the terrestrial environments differs considerably from that of most other metallic elements.