concentration higher than normal causes adverse effects on non-targeted organism.
Soil pollution often cannot be directly evaluated, constructing it a hidden hazard
(Rodríguez-Eugenio et al. 2018). The status of the World’s Soil Resources Report
(SWSR) identified soil pollution as one of the main soil threats affecting global soils
and the ecosystems services provided by them. The main anthropogenic or manmade
(Brookes 1995) sources of soil pollution are the chemicals used in or produced as
byproducts of industrial activities (Vorobeichik et al. 2012), domestic (Nyenje et al.
2013), livestock (Zhang et al. 2012a, b), municipal wastes (Ali et al. 2014), agrochemicals (Wimalawansa and Wimalawansa 2014), and petroleum-derived products
(Pinedo et al. 2013). These chemicals are released to the environment accidentally
(Kim et al. 2018; Awad et al. 2011), for instance, from oil spills or leaching from
landfills, or deliberately, as is the case with the use of fertilizers and pesticides,
irrigation with untreated wastewater, or land application of sewage sludge. Soil
pollution also results from atmospheric deposition from smelting (Zhang et al.
2012a, b; Gunawardena et al. 2013), transportation (Wiłkomirski et al. 2011),
spray drift from pesticide applications, and incomplete combustion of many substances as well as radionuclide deposition from atmospheric weapons testing and
nuclear accidents. Recently, new types of pollutants are developed such as pharmaceuticals, endocrine disruptors, hormones and toxins, among others, and biological
pollutants, which include bacteria and viruses (Rodríguez-Eugenio et al. 2018)
called micropollutants in soil. All these types of soil pollution need to be remediated
by the development of a novel and science-based method, which includes a newly
emerging method, i.e., bioremediation.
Bioremediation is an ecofriendly and an efficient method, in which live microorganism and its products can be utilized for the alleviation of environment contamination (Ojuederie and Babalola 2017). These processes facilitate to crop
reestablishment on treated soil. Microorganisms such as plant growth–promoting
rhizobacteria (PGPR) and plants employ various mechanisms for the bioremediation
of polluted soils (Chibuike and Obiora 2014), and it has been suggested to play a
significant and vital role in alleviating the toxicity in different contaminated soils
(Khan et al. 2009; Jayabarath et al. 2009; Cardón et al. 2010; Cetin et al. 2011). Use
of PGPR strains with many properties, like metal resistance/reduction ability (Joseph
et al. 2007; Kumar et al. 2008; Wani and Khan 2010) and capacity to facilitate plant
growth through variable mechanisms in contaminated soils (Khan et al. 2009), is
considered enormously important for the attainment of the bioremediation program.
8.2 Soil Pollution
Soil pollution includes disturbance of major ecosystem services provided by soil. It
can also adversely affect the yield of plants due to toxic levels of contaminants. It can
be defined as a chemical or a substance out of place and/or present at a higher than
the normal concentration that has adverse effects on any non-targeted organism
(Rodríguez-Eugenio et al. 2018). The main anthropogenic sources of soil pollution
8 Bioremediation of Polluted Soil by Using Plant Growth–Promoting Rhizobacteria
205
Soil pollution often cannot be directly evaluated, constructing it a hidden hazard
(Rodríguez-Eugenio et al. 2018). The status of the World’s Soil Resources Report
(SWSR) identified soil pollution as one of the main soil threats affecting global soils
and the ecosystems services provided by them. The main anthropogenic or manmade
(Brookes 1995) sources of soil pollution are the chemicals used in or produced as
byproducts of industrial activities (Vorobeichik et al. 2012), domestic (Nyenje et al.
2013), livestock (Zhang et al. 2012a, b), municipal wastes (Ali et al. 2014), agrochemicals (Wimalawansa and Wimalawansa 2014), and petroleum-derived products
(Pinedo et al. 2013). These chemicals are released to the environment accidentally
(Kim et al. 2018; Awad et al. 2011), for instance, from oil spills or leaching from
landfills, or deliberately, as is the case with the use of fertilizers and pesticides,
irrigation with untreated wastewater, or land application of sewage sludge. Soil
pollution also results from atmospheric deposition from smelting (Zhang et al.
2012a, b; Gunawardena et al. 2013), transportation (Wiłkomirski et al. 2011),
spray drift from pesticide applications, and incomplete combustion of many substances as well as radionuclide deposition from atmospheric weapons testing and
nuclear accidents. Recently, new types of pollutants are developed such as pharmaceuticals, endocrine disruptors, hormones and toxins, among others, and biological
pollutants, which include bacteria and viruses (Rodríguez-Eugenio et al. 2018)
called micropollutants in soil. All these types of soil pollution need to be remediated
by the development of a novel and science-based method, which includes a newly
emerging method, i.e., bioremediation.
Bioremediation is an ecofriendly and an efficient method, in which live microorganism and its products can be utilized for the alleviation of environment contamination (Ojuederie and Babalola 2017). These processes facilitate to crop
reestablishment on treated soil. Microorganisms such as plant growth–promoting
rhizobacteria (PGPR) and plants employ various mechanisms for the bioremediation
of polluted soils (Chibuike and Obiora 2014), and it has been suggested to play a
significant and vital role in alleviating the toxicity in different contaminated soils
(Khan et al. 2009; Jayabarath et al. 2009; Cardón et al. 2010; Cetin et al. 2011). Use
of PGPR strains with many properties, like metal resistance/reduction ability (Joseph
et al. 2007; Kumar et al. 2008; Wani and Khan 2010) and capacity to facilitate plant
growth through variable mechanisms in contaminated soils (Khan et al. 2009), is
considered enormously important for the attainment of the bioremediation program.
8.2 Soil Pollution
Soil pollution includes disturbance of major ecosystem services provided by soil. It
can also adversely affect the yield of plants due to toxic levels of contaminants. It can
be defined as a chemical or a substance out of place and/or present at a higher than
the normal concentration that has adverse effects on any non-targeted organism
(Rodríguez-Eugenio et al. 2018). The main anthropogenic sources of soil pollution
8 Bioremediation of Polluted Soil by Using Plant Growth–Promoting Rhizobacteria
205