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metals as compared to edible crops. Further, crops grown on land continuously supplied by sewage
water also have a high level of lead, which ultimately leads to a bad color of the crops (Bhupal Raj
et al. 2009). Onion crops quality was found inferior in the soil irrigated by lead-contaminated water
in Ratlam, India (Meena et al. 2020).
Severe loss of yield in crops was observed in soybean, gram, fenugreek and garlic. These crops
got affected by Pb contaminated water, which decreased farmers’ output (Panwar et al. 2010).
11.2.1.2 Factors Affecting Pb Toxicity in Soil
Lead toxicity in the soil is affected by several factors. These factors might be topographic, climatic
or due to human activities. Some of these factors are:
11.2.1.2.1 Soil Properties
Soil properties like pH, porosity, amount of organic matter, cation exchange capacity, clay content,
soil structure and the presence/absence of other ions inside soils are the key factors that ultimately
determine lead toxicity (Meena et al. 2020). If clay content is high in the soil, it forms complexes with
humus, which ultimately reduces the mobility of Pb (Dotaniya et al. 2016). These complexes also
serve as sources of carbon for soil microorganisms, enhancing their growth and variety. Further, the
organic matter containing the carboxyl group binds with Pb and forms complexes, which ultimately
decrease its availability (Dotaniya et al. 2020). Solubility and accumulation of Pb in the soil are
influenced by the presence of phosphates and carbonates. Additionally, the availability of lead to
plants is typically low in the pH range from 5 to 7 (Blaylock et al. 1997). The presence of several
metal ions like zinc, copper, nickel and chromium also had adverse effects on Pb accumulation in
soil (Orroño et al. 2012). Rhizosphere containing soil fauna has a vital role in Pb availability, as
found in the case of Thlaspi caerulescens and Lantana camera (Jusselme et al. 2012).
11.2.1.2.2 Concentration of other Elements
An increase in the level of nickel ion to the level of 100 mg kg–1 leads to a reduction in Pb toxicity
(Pipalde and Dotaniya 2018). By introducing acid-neutralizing material into the soil, the mobility of
Pb can be reduced. Water stress might be helpful in lowering Pb concentration as on adding water,
Pb concentration is diluted (Dotaniya et al. 2018b). The toxicity of soil also depends upon the forms
of Pb. For example, Pb is present in oxyanion complexes in soil and water streams (Dotaniya et al.
2018c). Similarly, an increased amount of phosphatic fertilizers could be helpful in reducing the Pb
accumulation (Lenka et al. 2016).
11.2.1.2.3 Industries
Agricultural soil/lands that are situated closer to industrial areas are more prone to lead contamination
because of leakage of lead-containing pollutants (Saha et al. 2013). Pb level was found greater in
the soil surrounding the Coimbatore area near an electroplating and paint industry. Similarly, in
Tamil Nadu’s Dindigul district, the cement factory is the major source of lead poisoning (Meena
et al. 2020). Lead contamination into the soil is also caused by industries that make daily life
products such as Pb-based paints, solder, ceramics and pesticides. Industries that are involved in
mining smelting and tailing release high amounts of lead into nearby soil (Mitra et al. 2020, Anju
and Banerjee 2011).
11.2.1.2.4 Urbanization
Lead increase in urban soils might be due to increasing industrialization. Combustion of leaded
petrol results in vehicular emission containing tetraethyl Pb, which contributes significantly to lead
in urban areas. As per USEPA standards, the threshold limit of Pb in the soil is 400 mg/L, and in
portable water, it is 0.01 mg/L (Bureau of Indian Standard) (Mitra et al. 2020).