Journal of Geography (Chigaku Zasshi)
Online ISSN : 1884-0884
Print ISSN : 0022-135X
ISSN-L : 0022-135X
Geological Approach to Soil Contamination Caused by Natural Processes
Katsumi MARUMO
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2007 Volume 116 Issue 6 Pages 877-891

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Abstract

The soil Contamination Countermeasures Law (referred to hereafter as the Law) was legislated to prevent damage to health from toxic substances (e.g. As, Cd, and Pb) in soils and sediments, caused by oral ingestion of these toxic substances through drinking ground water and eating foods containing fine-grained soil and sediment particles.
To apply the Law, we must judge whether soils have high toxic metal concentrations or high leachabilities caused by anthropogenic or natural processes. If high toxic metal concentrations or high leachabilities are caused by natural processes, administration of the Law should not oblige landowners, managers, and occupiers of contaminated sites to remedy them. Therefore, it is essential to determine natural levels of As, Cd, and Pb concentrations and their leachabilities in soils and sediments. We also need to evaluate the potential risk of natural contamination and potential harm to human health.
We obtained toxic metal concentrations of rocks, sediments, and soils in the Anesaki and Sendai areas, as well as their leachabilities, to publish “Geochemistry of rocks, sediments, and soils of these areas”. Arsenic, Cd, and Pb concentrations in these areas are lower than the regulated level (150 mg/kg) under the Law. However, the leachabilities of some marine sediments are higher than regulated levels (0.01 mg/L) under the Law.
The arsenic leachabilities of some marine sediment samples become higher as the pH of the leaching test solution increases, because As occurs as an anion in the test solution, and is absorbed efficiently by allophane and iron oxyhidrite as pH increases. The arsenic concentration of the leaching test solution will be higher than regulated levels, when the sediment releases calcium ions and pH increases.
Meanwhile, cadmium leachabilities of some marine sediment samples become higher as the pH of the test solution decreases, because Cd occurs as a cation in the solution and will be absorbed by these minerals efficiently as pH decreases. The cadmium concentration of the leaching test solution will be higher than regulated levels, when the sediment releases sulfate ions and pH decreases.<BRSome Tatsunokuchi sediments in the Sendai area are characterized by high Cd (>10 mg/ kg) and high Cd/Zn ratio (>0.2). These values are similar to those of seawater suggesting that seawater is the main source of Cd and Zn, and that they were concentrated in the sediment. Such a high Cd sediment must be treated carefully to prevent soil and river contamination.

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