Page 189 - Plant-Based Remediation Processes

10 Phytostabilization as Soil Remediation Strategy 181

into groundwater. Studies show that some plants can take up and accumulate Ni.
However, it has been shown that Ni does not accumulate in small animals living on
land that has been treated with Ni-containing sludge. In humans, food is the major
source of exposure to nickel. Also, the exposure to Ni may be breathing air,
drinking water, or smoking tobacco containing Ni. The most common harmful
health effect of nickel in humans is an allergic reaction. Approximately 10–20 % of
the population is sensitive to nickel.

10.1.5 Lead

Lead is not essential for plant or animal life, and in the environment it is mainly
particulate bound with relatively low mobility and bioavailability. Lead does, in
general, not bioaccumulate and there is no increase in concentration of the metal in
food chains. In humans, Pb can result in a wide range of biological effects
depending upon the level and duration of exposure. For infants and young children
Pb in dust and soil often constitutes a major exposure pathway and this exposure has
been one of the main concerns as to the exposure of the general population.
Absorbed Pb is rapidly taken up into blood and soft tissue, followed by a slower
redistribution to bone. Bone accumulates Pb during much of the human life span
and may serve as an endogenous source of Pb that may be released slowly over
many years after the exposure stops. In the environment Pb binds strongly to
particles, such as soil, sediment, and sewage sludge. Because of the low solubility
of most of its salts, Pb tends to precipitate out of complex solutions. Consequently,
the fate of Pb in the soil is affected by the specific or exchange adsorption at mineral
interfaces, the precipitation of sparingly soluble solid phases, and the formation of
relatively stable organo-metal complexes or chelates with the organic matter in soil
(Gustafsson et al. 2012). The tendency of inorganic Pb to form highly insoluble
salts and complexes with various anions together with its tight binding to soils
drastically reduces its availability to terrestrial plants via the roots. Lead is taken up
by terrestrial plants through the roots and to a lesser extent through the shoots.
Translocation of the ion in plants is limited and most bound Pb stays at root or leaf
surfaces. As a result, in most experimental studies on lead toxicity, high lead
concentrations in the range of 100–1,000 mg kg 1 soil are needed to cause visible
toxic effects on photo synthesis, growth, or other parameters. Thus, Pb is only likely
to affect plants at sites with very high environmental concentrations.

10.1.6 Chromium

Chromium is the 21st most common element in the earth’s crust. Also, Cr is found
in all phases of the environment, including air, water, and soil. Naturally, occurring
in soil, Cr ranges from 10 to 50 mg kg 1 depending on the parental material. Cr and