Page 187 - Soil Degradation, Conservation and Remediation

176 6 Soil Pollution

released from these wastes can give rise to human exposure by transport through the
atmosphere, aquatic systems, or through soil subcompartments.
A catastrophic accident occurred at the Chernobyl Nuclear Power Plant in
Ukraine on April 26, 1986. The explosion caused radiation to be released into the
atmosphere over a 9-day period, with prevailing winds sending the plume generally
in a north to northeasterly direction. The plume eventually spread over Europe,

resulting in significant fallout of radiation associated with precipitation events in
Austria, Switzerland, Germany, and Sweden. High levels of radioactive deposition
were also reported in Italy and Britain. The releases during the accident contami-
2
nated about 125,000 km of land in Belarus, Ukraine, and Russia with radiocesium
2
−2
levels greater than 37 kBq m and about 30,000 km with radiostrontium greater
−2
than 10 kBq m . Soil and water pollution from the accident is extensive, having
been recorded in 22 oblasts of Russia and considerable areas of some other countries.
In these areas, radionuclides have been measured in the soil to depths up to 25 cm. This
quarter-meter represents the vertical zone in which crop cultivation takes place. As
a result, in northern Ukraine, over 100,000 ha of agricultural land containing some
of the world’s richest soils has had to be abandoned (Savchenko 1995 ).
The movement of radionuclides in soil varies with soil type, pH, rainfall, and
agricultural tilling. Radiocesium is generally confi ned to particles with a matrix of
uranium dioxide, graphite, iron–ceramic alloys, silicate-rare earth, and silicate com-
binations of these materials. Cesium-137 behaves like potassium and strontium-90
behaves like calcium in soil. Cesium-137 is not adsorbed strongly in soil and is
readily taken up by plants. The movement of these radionuclides in the soil depends
also on the chemical breakdown of these complexes by oxidation to release more
mobile forms. The bulk of the fission products are distributed between organomineral

and mineral parts of the soil largely in humic complexes. Radionuclides deposition

can be a significant pathway to human exposure by ingestion of contaminated
pasture by animals and then by the ingestion of contaminated animal products (meat
and milk). Plant foods also accumulate radionuclides.
Various soil pollutants and their sources are summarized in Table 6.4 .

6.2.11 Organic Pollutants in Soil

Organic pollutants can reach the soil by dry or wet deposition after either long- range
aerial transport from diffuse sources or from short-range transport from point sources
such as industrial discharges, waste deposits, sludge amendments, and pesticide
spraying. The contaminants are partitioned between soil particles, interstitial water,
and interstitial air, and uptake by plants may occur from the water or air phases. The

fate of a specific compound in a specific soil depends on the physical and chemical

properties of both the compound and the soil. Organic pollutants in soil include
short-chain alkanes; chlorinated solvents such as polychloroethylene (PCE, CCl 2 CCl 2 ),
trichloroethylene (TCE, C 2 HCl 3 ), dichloroethylene (DCE, CHClCHCl), and vinyl
chloride or chloroethylene (VC, CH 2 CHCl); monoaromatic hydrocarbons; chlorinated