1. Features of contamination
The Soil Contamination Countermeasures Law specifies ten items of inorganic matter, for instance heavy metals as Second Class Specific Toxic Substance. Among these particular substances, cadmium, lead, chromium hexavalent, arsenic, mercury (including alkyl mercury), and selenium are examples of heavy metals. Fluoride, boron, and cyanogen are also considered “heavy metals” and are classified under the same group since the investigation technique applies to the remediation of soil polluted with such metals.
When taking into account the contamination due to heavy metals, the migration of contaminants is a slow process as compared with volatile organic compounds. The heavy metals exist near the surface of the soil because they are easily adsorbed into the soil, as well. Moreover, in the case of a highly concentrated contamination, especially with relatively soluble substances, such as chromium hexavalent and cyanogen, the occurrence of rainfall is likely to expand the contamination into groundwater.
2. Technology for the measures against soil contamination due to heavy metals
The measures against soil contaminated with heavy metals are classified into two general processes. 1) Purification is the process of separating polluted substances from the contaminated soil and allowing subsequent decomposition of the heavy metals. 2) Containment is a manner of isolating the contaminated soil from the environment and preventing the spread of the contamination from diffusion into nearby soil. (Table) In this paper, the soil purification process, which is classified as a purification measure, the insolubilization treatment, which is often performed prior to containment, and the cyanogen bioremediation, which has been studied recently, are outlined.