Lead Induced Toxicity, Detoxification and Bioremediation 189
therefore less accessible for plant uptake (Punamiya et al. 2010). An investigatory report given by
Kumpiene et al. (2017) showed that lead is a versatile element present in the soil with a background
amount of 27 mg kg–1. Lead-contaminated soil is divided into five categories depending on the level
of contamination, i.e., extremely low (< 150 ppm), low (150–400 ppm), moderate (400–1000 ppm),
high (1000–2000 ppm) and extremely high (> 2000 ppm). The degree of Pb contamination also
varies from one season to another, and in different mediums (Patel et al. 2010). Reports suggested
that a high level of lead is reported in some places where anthropogenic activities are prominent. For
example—at smelting sites, lead concentration in soil ranged from 10 to 7100 mg kg–1 (Chlopecka
et al. 1996), road dust (105–110 mg kg–1) (Bi et al. 2018), mining site (132–45016 mg kg–1) (Higueras
et al. 2017). Further, the industrial site contained lead at a level of 42–131 mg kg–1 (He et al. 2017);
in previous garden soil, it was 1020–1030 mg kg–1 (Egendorf et al. 2018). Similarly, Pb in flooded
soil was in between 105–115 mg kg–1 (Antić-Mladenović et al. 2017), and in the soil of shooting
ranges was 32,500–33,500 mg kg–1 (Mariussen et al. 2018).
11.2.1.1 How Lead Toxicity Affects Soil Ecosystem
The presence of Pb in excessive concentrations in the soil affects the soil ecosystem in several ways:
11.2.1.1.1 Reducing Nutrient Availability to Plants
Nutrients inside the soil ecosystem play a vital role in the growth of plants and animals. An increase
in the amount of lead in the soil decreased the other metal ions’ availability to the plants. Soil
contaminated with Pb may generate abiotic stress to the living flora, which further reduces the
uptake of other macronutrients ions like potassium, calcium and magnesium and micronutrients like
zinc, copper, nickel as well as nitrogen uptake (Wu et al. 2011). For example, enhancement of Pb
level reduces the nickel ion concentration in spinach in Madhya Pradesh, India. Further, elevated
concentrations of Pb in black soil also affected its enzymatic properties (Pipalde and Dotaniya
2018).
11.2.1.1.2 Effect on soil Forming Processes
There are various pedogenic processes like oxidation-reduction, mineralization-immobilization,
dissolution-precipitation, sorption-desorption, etc., which are responsible for the formation of soil.
These reactions are involved in regulating the dynamics of various nutrient cycles and ultimately,
soil biodiversity by creating competition among the nutrients. Once elevation occurs in the
concentration of Pb, it leads to disruption in these reactions and affects the dynamics, ultimately
pedogenesis (Dotaniya and Pipalde 2018).
11.2.1.1.3 Effect on Soil Health and Microbiota
Lead toxicity affects the microbial count in the soil ecosystem by direct or indirect effects. The
decomposition rate of organic material was suppressed due to the presence of moderate or excessive
concentrations of metal ions inside the soil (Bahar et al. 2012). According to reports, approximately
8–16 times higher concentration of lead was discovered in crops developed on polluted sites
(smelter plant) in France (Douay et al. 2013). Further, enhancement in the level of Pb leads to a
decline in the biodiversity, richness and population count of microorganisms (Banat et al. 2010).
If Pb concentration was reached to 100 mg/kg, it reduced the rate of carbon mineralization as well
as enzymatic activities such as dehydroascorbate reductase. Reports suggested that lead toxicity
reduces the amount of nitrogen fixation organisms, thus affecting the rate of biological nitrogen
fixation (Dotaniya et al. 2020).
11.2.1.1.4 Crop Quality and Productivity
Crop loss and fall in quality are among the most typical consequences of Pb toxicity. Lead
accumulation in crops reduce the food grain quality, which has detritus effects on human health
after consuming these crops. Vegetables and their parts are more prone to the accumulation of toxic