treatments are ineffective in practical use as well as very expensive; it can be easily
adopted for low-level contaminated sites, where only superficial treatment is
required for the long term. Phytoremediation can also be employed as a final step
in conjunction with other technologies. The use of phytoremediation is limited
because of the chance of introducing a contaminant or its metabolites into the food
web. The process is slow to achieve regulatory levels, and toxic establishment and
acclimatization in encountered sites also can result.
1.1 Background
Following the rapid development of industry and intensive agricultural activities,
potent hazardous HMs are released into nature; as a consequence, the very basic and
essential part of the ecosystem, the soil, becomes heavily contaminated. Up to the
present, approximately 16.7% of farmland all over the world has been polluted by
HMs such as Cr, Zn, and Pb. In addition, most of the HMs in farmland soil has
exceeded the environmental quality limit, where the percentage of the exceedance
was even greater at 19.4% (Liu et al. 2005). HM pollution in soil causes millions of
tons loss of crop production every year. In addition to developed countries (American and European Union), developing countries such as China and India also have
large areas of heavy metals-contaminated soil. It was estimated that in the European
Union more than 3.5 million sites are heavily contaminated and 0.5 million sites
have been seriously polluted. In America, HM-contaminated sites cover 600,000 ha
(De Sousa and Ghoshal 2012; Perez 2012; Orooj et al. 2015). Compared to organic
pollutants, the HMs are indestructible, which can result in their accumulation in the
ecosystem and subsequent contamination of the food web with consequent harm to
human health (Ali et al. 2013). As already mentioned, remediation of
HM-contaminated soil has become a pressing problem worldwide.
In the past few years, many approaches such as biological, physical, and chemical
processes have been used in remediating HM-contaminated soil; for example, the
soil replacement and leaching method, chelate extraction method, animal remediation, and phytoremediation (Sarwar et al. 2017). In all available approaches, the
physical and chemical methods revealed serious limitations such as high cost,
manpower, potential concomitant pollution, and alteration of soil character and
native microflora, whereas phytoremediation uses the plants, rhizosphere, and
microbially assisted collaboration in reducing the toxicity from HMs in soil
(Rajkumar et al. 2012). When compared to other remediation methods,
phytoremediation seem to be better for solving this problem, being also costeffective, eco-friendly, and clean. Many researchers have discussed the mechanism
of phytoremediation for HM removal in contaminated soils and its development
(Mahar et al. 2016; Sarwar et al. 2017).
4 Recent Advances in Phytoremediation of Toxic Metals from Contaminated. . .
79
adopted for low-level contaminated sites, where only superficial treatment is
required for the long term. Phytoremediation can also be employed as a final step
in conjunction with other technologies. The use of phytoremediation is limited
because of the chance of introducing a contaminant or its metabolites into the food
web. The process is slow to achieve regulatory levels, and toxic establishment and
acclimatization in encountered sites also can result.
1.1 Background
Following the rapid development of industry and intensive agricultural activities,
potent hazardous HMs are released into nature; as a consequence, the very basic and
essential part of the ecosystem, the soil, becomes heavily contaminated. Up to the
present, approximately 16.7% of farmland all over the world has been polluted by
HMs such as Cr, Zn, and Pb. In addition, most of the HMs in farmland soil has
exceeded the environmental quality limit, where the percentage of the exceedance
was even greater at 19.4% (Liu et al. 2005). HM pollution in soil causes millions of
tons loss of crop production every year. In addition to developed countries (American and European Union), developing countries such as China and India also have
large areas of heavy metals-contaminated soil. It was estimated that in the European
Union more than 3.5 million sites are heavily contaminated and 0.5 million sites
have been seriously polluted. In America, HM-contaminated sites cover 600,000 ha
(De Sousa and Ghoshal 2012; Perez 2012; Orooj et al. 2015). Compared to organic
pollutants, the HMs are indestructible, which can result in their accumulation in the
ecosystem and subsequent contamination of the food web with consequent harm to
human health (Ali et al. 2013). As already mentioned, remediation of
HM-contaminated soil has become a pressing problem worldwide.
In the past few years, many approaches such as biological, physical, and chemical
processes have been used in remediating HM-contaminated soil; for example, the
soil replacement and leaching method, chelate extraction method, animal remediation, and phytoremediation (Sarwar et al. 2017). In all available approaches, the
physical and chemical methods revealed serious limitations such as high cost,
manpower, potential concomitant pollution, and alteration of soil character and
native microflora, whereas phytoremediation uses the plants, rhizosphere, and
microbially assisted collaboration in reducing the toxicity from HMs in soil
(Rajkumar et al. 2012). When compared to other remediation methods,
phytoremediation seem to be better for solving this problem, being also costeffective, eco-friendly, and clean. Many researchers have discussed the mechanism
of phytoremediation for HM removal in contaminated soils and its development
(Mahar et al. 2016; Sarwar et al. 2017).
4 Recent Advances in Phytoremediation of Toxic Metals from Contaminated. . .
79