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[MAG33-P08] Vertical distribution of mercury in soils
Keywords:Mercury, Vertical distribution, Soil characteristics
1. Introduction
Heavy metals in soil exist in various forms, and their behavior is different depending on the form. Mercury is a heavy metal that is easily released into the atmosphere, and some mercury emitted into the air by natural or anthropogenic factors is deposited on the ground surface by rain. Soils are composed of clay minerals, organic matter etc., and heavy metals such as mercury are easily adsorbed by clay minerals and organic matter in soil, but their mobility is thought to vary depending on soil properties. Research on the distribution and dynamics of mercury in the natural environment is a major issue. In this study, we measured the vertical distribution of mercury in soil in order to investigate the dynamics of mercury deposited on soil from the atmosphere.
2. Methods
Undisturbed Soils in Hiroshima were sampled at 1 cm intervals from the surface to a depth of 30 cm. Mercury concentrations in the soils were measured using the thermal decomposition mercury analyzer (MA-3000; Nippon Instruments, Co., Ltd., Japan).
3. Results
The concentration of mercury in the soil peaked at the surface layer 0-10 cm, with smaller values in the deeper layers at many locations. It is speculated that mercury retained in soil changes over time to mercury chloride, organically bound mercury, and mercury sulfide, and exists as the stable form that is not dissolved by rain [1]. Therefore, it tends to accumulate in the upper layers of the soil rather than the lower layers, and similar results were obtained in this study.
Background values of mercury in soil are said to be representative of the mercury content in wildland soil or agricultural land without anthropogenic mercury contamination, and a geochemical background level in soil is considered to be approximately 0.03 mg/kg [2]. The origin of mercury in soil can be analyzed by normal probability plot of the data, and divided into three groups: (A) soil matrix, (B) an increase due to natural cycles, and (C) anthropogenic contamination [3]. In this study, the mercury concentration could be estimated to be naturally or artificially derived.
The content of mercury showed peaks in the 0-10 cm depth range at most of the sites. On the other hand, in some sites, the concentration of mercury in the soil increased as the depth increased. It is thought that mercury concentrations are higher in the lower layers because of permeability and less organic matter in the soil [4]. Therefore, the organic matter concentration in the soil was measured and found to be lower in the surface layer than at other sites, indicating that the behavior differs depending on soil characteristics.
The peak of concentration of Cs-137 was observed at different depth from that of mercury. The behavior of Cs-137 and mercury such as vertical migration may vary based on their chemical forms, whereas the origin of Cs-137 in the soil was thought to be different from mercury.
This study indicated that mercury deposited from the atmosphere was accumulated in the upper layers, and that the concentration of mercury was greater in the lower layers because of the small amount of organic matter in the soil.
4. References
[1] Nakagawa et al.: Behavior of residual mercury in urban soils, Safety Engineering, Vol.39, No.1, p.12-18, 2000.
[2] Shimada: The essence of problems on groundwater and soil pollutions caused by naturally occurring heavy metals and harmful elements: Mercury, Oyo Technical Report, Vol.30, p.33-61, 2011.
[3] Nakagawa et al.: Behavior of residual pesticide mercury in soils of paddyfield, Chemical Society of Japan, Vol.1991, No.5, p.470-477, 1991.
[4] Gotoh: Mercury in the soil environment, Soil Science and Plant Nutrition, Vol.53, No.6, p.550-558, 1982.
Heavy metals in soil exist in various forms, and their behavior is different depending on the form. Mercury is a heavy metal that is easily released into the atmosphere, and some mercury emitted into the air by natural or anthropogenic factors is deposited on the ground surface by rain. Soils are composed of clay minerals, organic matter etc., and heavy metals such as mercury are easily adsorbed by clay minerals and organic matter in soil, but their mobility is thought to vary depending on soil properties. Research on the distribution and dynamics of mercury in the natural environment is a major issue. In this study, we measured the vertical distribution of mercury in soil in order to investigate the dynamics of mercury deposited on soil from the atmosphere.
2. Methods
Undisturbed Soils in Hiroshima were sampled at 1 cm intervals from the surface to a depth of 30 cm. Mercury concentrations in the soils were measured using the thermal decomposition mercury analyzer (MA-3000; Nippon Instruments, Co., Ltd., Japan).
3. Results
The concentration of mercury in the soil peaked at the surface layer 0-10 cm, with smaller values in the deeper layers at many locations. It is speculated that mercury retained in soil changes over time to mercury chloride, organically bound mercury, and mercury sulfide, and exists as the stable form that is not dissolved by rain [1]. Therefore, it tends to accumulate in the upper layers of the soil rather than the lower layers, and similar results were obtained in this study.
Background values of mercury in soil are said to be representative of the mercury content in wildland soil or agricultural land without anthropogenic mercury contamination, and a geochemical background level in soil is considered to be approximately 0.03 mg/kg [2]. The origin of mercury in soil can be analyzed by normal probability plot of the data, and divided into three groups: (A) soil matrix, (B) an increase due to natural cycles, and (C) anthropogenic contamination [3]. In this study, the mercury concentration could be estimated to be naturally or artificially derived.
The content of mercury showed peaks in the 0-10 cm depth range at most of the sites. On the other hand, in some sites, the concentration of mercury in the soil increased as the depth increased. It is thought that mercury concentrations are higher in the lower layers because of permeability and less organic matter in the soil [4]. Therefore, the organic matter concentration in the soil was measured and found to be lower in the surface layer than at other sites, indicating that the behavior differs depending on soil characteristics.
The peak of concentration of Cs-137 was observed at different depth from that of mercury. The behavior of Cs-137 and mercury such as vertical migration may vary based on their chemical forms, whereas the origin of Cs-137 in the soil was thought to be different from mercury.
This study indicated that mercury deposited from the atmosphere was accumulated in the upper layers, and that the concentration of mercury was greater in the lower layers because of the small amount of organic matter in the soil.
4. References
[1] Nakagawa et al.: Behavior of residual mercury in urban soils, Safety Engineering, Vol.39, No.1, p.12-18, 2000.
[2] Shimada: The essence of problems on groundwater and soil pollutions caused by naturally occurring heavy metals and harmful elements: Mercury, Oyo Technical Report, Vol.30, p.33-61, 2011.
[3] Nakagawa et al.: Behavior of residual pesticide mercury in soils of paddyfield, Chemical Society of Japan, Vol.1991, No.5, p.470-477, 1991.
[4] Gotoh: Mercury in the soil environment, Soil Science and Plant Nutrition, Vol.53, No.6, p.550-558, 1982.