Page 221 - Soil Degradation, Conservation and Remediation

210 6 Soil Pollution

Table 6.10 (continued)
Heavy metals Common toxicities of heavy metals in human
b
Selenium It can cause nausea, vomiting, and diarrhea. Chronic oral exposure to high
concentrations can produce selenosis. Major signs of selenosis are hair
loss, nail brittleness, and neurological abnormalities. Brief exposures to
high levels in air can result in respiratory tract irritation, bronchitis,

difficulty breathing, and stomach pains. Longer-term exposure can cause
respiratory irritation, bronchial spasms, and coughing
c
Zinc Zinc is considered to be relatively nontoxic, especially if taken orally.
However, excess amount can cause system dysfunctions that result in
impairment of growth and reproduction. The clinical signs of zinc
toxicosis have been reported as vomiting, diarrhea, bloody urine, icterus,
liver failure, kidney failure, and anemia (Fosmire 1990 )
a Yu ( 2005 )
b Bradl ( 2005 )
c Duruibe et al. ( 2007 )

There are some good reviews of the heavy metal remediation techniques (USEPA
1997 ; Stegmann et al. 2001 ; Bradl and Xenidis 2005 ; Wang et al. 2010 ). However, the
choice of the method depends on the degree and kind of contamination, contaminating
metal(s), cost involved, farm facilities, technology available, etc. As mentioned in
relation to organic pollutant remediation, the methods may be on-site or off-site, in
situ or ex situ, and physical, chemical, and biological. Physical methods include soil
washing, encapsulation, vitrification, and electrokinesis; chemical methods include

solidification, precipitation, and ion exchange; and biological methods use microor-

ganisms or plants to remove heavy metals.

Physical Remediation

Soil Washing
Soil washing is usually done as an ex situ remediation process. Soil washing
employs physical and/or chemical procedures to extract metal contaminants from
soils. During soil washing, (1) those soil particles which host the majority of the
contamination are separated from the bulk soil fractions, (2) contaminants are
removed from the soil by aqueous chemicals and recovered from solution on a solid
substrate, or (3) a combination of both (Dermont et al. 2008 ). The separated contami-
nants are disposed in landfill or further treated by chemical, thermal, or biological

processes. By removing the majority of the contamination from the soil, the bulk

fraction that remains can be (1) back filled, (2) used on another site as fi ll, or (3)
disposed of relatively cheaply as nonhazardous material. Soil washing is a popular
practice because it (1) completely removes the contaminants and hence ensures

the rapid cleanup of a contaminated site, (2) meets specific criteria, (3) reduces or
eliminates long-term liability, (4) may be the most cost-effective, and (5) may produce
recyclable material or energy (GOC 2003 ). The disadvantages include the fact that