(USEPA) 2006). Primordial radionuclides (
235 U,
238 U,
232 Th and
40 K) are basically
remain-over from the creation of the earth and have half-lives of hundreds millions
of years. Primordial radionuclides end up in soil due to weathering of rocks.
Cosmogenic radionuclides are produced by cosmic rays in the atmosphere and
have long half-lives, while majority have shorter half-lives than the primordial
radionuclides. Cosmogenic radionuclides include
14 C,
3 T and
7 Be. Anthropogenic
activities such as nuclear testing and radiological events like the Chernobyl accident
lead to deposition of radioactive particles in soil through air and water
(Romanovskaia et al. 1998). Inappropriate disposal of radioactive substances also
contributes to increasing contents of radionuclides in the soil (USEPA 2006).
16.3.2 Organic Pollutants
Organic pollutants include POPs, VOCs and semi-volatile (SVOCs) organic
compounds (Fig. 16.3). POPs are recalcitrant towards degradation, highly toxic
and are carcinogenic as well as mutagenic (Ashraf 2017). It includes pesticides,
chlorinated solvents, industrial fluids and flame retardants (Bartrons et al. 2016).
Short- and long-distance transportation of gaseous or particulate forms of POPs in
the atmosphere is facilitated by air and water (Ashraf 2017). Besides, atmospheric
dry and wet depositions constitute the main input of these compounds to the soil
(Cousins et al. 1999). Indirect deposition of compounds in soil occurs through
decomposition of litter fall from plants (Wania and Mclachlan 2001). Accumulation
of POPs in soil horizons rich in organic matter may lead to their persistence for years
(Masih and Taneja 2006). For an instance, it has been reported that 90% of United
Kingdom’s land are rich in POPs (Cousins and Jones 1998). There are about 7 key
POPs, viz. PCBs, DDT, hexachlorocyclohexane (HCH), dieldrin,
perfluorooctanesulfonate (PFOS), hexabromocyclododecane (HBCD) and endosulfan, which are restricted as per Stockholm Conference held in 2001 (Ashraf 2017).
Organic pollutants such as gasoline and hydrocarbons as a result of fossil fuel
burning and automobile exhaust are volatile in nature. World Wildlife Fund enlisted
67 different types of environmental hormones in 1997 that were considered harmful
for the soil biota (Lyons 2005).
A myriad of organic pollutants such as biocides, pesticides, flame retardants,
pharmaceuticals, surfactants, PAHs, PCBs, polychlorinated dibenzo-p-dioxins
(PCDDs), polychlorinated dibenzofurans (PCDFs), etc. end up in the soil as a
consequence of human activities (Rhind 2009). The most commonly found organic
pollutants in soils are chlorinated compounds (e.g., PCDDs, PCBs and PCDFs), oil
hydrocarbons (e.g., alkanes, alkenes and cycloalkanes), monomeric aromatic
hydrocarbons (e.g., toluene, xylene, benzene and ethylbenzene), PAHs (e.g.,
chrysene, benzo(a)pyrene and fluoranthene), pesticides (e.g., alachlor, acetochlor,
atrazine and bifenox), fungicides (e.g., penconazole, procymidone and metalaxyl),
insecticides (e.g., endosulfan, heptachlor, captan, benomyl and endrin),
pharmaceuticals (e.g., antibiotics, analgesics, nonsteroidal anti-inflammatories,
antiparasitics and antimicrobials), hormones (e.g., oestrogens and androgens),
16 Causes, Effects and Sustainable Approaches to Remediate Contaminated Soil
459
235 U,
238 U,
232 Th and
40 K) are basically
remain-over from the creation of the earth and have half-lives of hundreds millions
of years. Primordial radionuclides end up in soil due to weathering of rocks.
Cosmogenic radionuclides are produced by cosmic rays in the atmosphere and
have long half-lives, while majority have shorter half-lives than the primordial
radionuclides. Cosmogenic radionuclides include
14 C,
3 T and
7 Be. Anthropogenic
activities such as nuclear testing and radiological events like the Chernobyl accident
lead to deposition of radioactive particles in soil through air and water
(Romanovskaia et al. 1998). Inappropriate disposal of radioactive substances also
contributes to increasing contents of radionuclides in the soil (USEPA 2006).
16.3.2 Organic Pollutants
Organic pollutants include POPs, VOCs and semi-volatile (SVOCs) organic
compounds (Fig. 16.3). POPs are recalcitrant towards degradation, highly toxic
and are carcinogenic as well as mutagenic (Ashraf 2017). It includes pesticides,
chlorinated solvents, industrial fluids and flame retardants (Bartrons et al. 2016).
Short- and long-distance transportation of gaseous or particulate forms of POPs in
the atmosphere is facilitated by air and water (Ashraf 2017). Besides, atmospheric
dry and wet depositions constitute the main input of these compounds to the soil
(Cousins et al. 1999). Indirect deposition of compounds in soil occurs through
decomposition of litter fall from plants (Wania and Mclachlan 2001). Accumulation
of POPs in soil horizons rich in organic matter may lead to their persistence for years
(Masih and Taneja 2006). For an instance, it has been reported that 90% of United
Kingdom’s land are rich in POPs (Cousins and Jones 1998). There are about 7 key
POPs, viz. PCBs, DDT, hexachlorocyclohexane (HCH), dieldrin,
perfluorooctanesulfonate (PFOS), hexabromocyclododecane (HBCD) and endosulfan, which are restricted as per Stockholm Conference held in 2001 (Ashraf 2017).
Organic pollutants such as gasoline and hydrocarbons as a result of fossil fuel
burning and automobile exhaust are volatile in nature. World Wildlife Fund enlisted
67 different types of environmental hormones in 1997 that were considered harmful
for the soil biota (Lyons 2005).
A myriad of organic pollutants such as biocides, pesticides, flame retardants,
pharmaceuticals, surfactants, PAHs, PCBs, polychlorinated dibenzo-p-dioxins
(PCDDs), polychlorinated dibenzofurans (PCDFs), etc. end up in the soil as a
consequence of human activities (Rhind 2009). The most commonly found organic
pollutants in soils are chlorinated compounds (e.g., PCDDs, PCBs and PCDFs), oil
hydrocarbons (e.g., alkanes, alkenes and cycloalkanes), monomeric aromatic
hydrocarbons (e.g., toluene, xylene, benzene and ethylbenzene), PAHs (e.g.,
chrysene, benzo(a)pyrene and fluoranthene), pesticides (e.g., alachlor, acetochlor,
atrazine and bifenox), fungicides (e.g., penconazole, procymidone and metalaxyl),
insecticides (e.g., endosulfan, heptachlor, captan, benomyl and endrin),
pharmaceuticals (e.g., antibiotics, analgesics, nonsteroidal anti-inflammatories,
antiparasitics and antimicrobials), hormones (e.g., oestrogens and androgens),
16 Causes, Effects and Sustainable Approaches to Remediate Contaminated Soil
459