**2. Origin of heavy metal contamination**

Heavy metals are found generally in soil due to bioturbation, degradation and weathering of parent materials in small concentrations are considered as trace (less than 1000 mg kg−1) but very occasionally toxic [3, 4]. As a consequence of man's destruction and amplification of essence's slowly developing geochemical cycle, soils often accumulate heavy metals above-established background values which are sufficient to pose a risk to human health, livestock, crops, and other media [5].

Heavy metals eventually set off pollutants in the environment when:


The significant sources contributing to heavy metal accumulation in our ecosystems are:

#### **2.1 Fertilizers**

Plants needs both macronutrients and micronutrients to develop and complete their life cycle. Heavy metals (like Co, Cu, Fe, Mn, Mo, Ni, and Zn) required for plant growth and development [6] are insufficient in certain soils and can be applied as a foliar spray or soil application in fields. In intensive farming systems, substantial amount of fertilizers is used frequently to provide plants with adequate *Remediation of Soil Impacted by Heavy Metal Using Farm Yard Manure, Vermicompost, Biochar… DOI: http://dx.doi.org/10.5772/intechopen.105536*

nutrients for plant growth development. However, few heavy metals such as Cd and Pb are present as impurities in the compounds used to supply essential elements, and regular application of fertilizer can remarkably boost their concentration into the soil [7]. Lead and cadmium are known to have little or no physiological activity. Phosphorus containing fertilizers unintentionally introduce Cd and some other certainly harmful elements [such as iron (F), mercury (Hg), and (Pb)] to the soil [8].

#### **2.2 Pesticides**

In historical agriculture and horticulture, several prevalent insecticides had a considerable amount of metal concentrations. For example, around 10 percent of the chemicals licensed are used as fungicides and insecticides in the United Kingdom in recent years were based on compounds containing Manganese (Mn), Copper (Cu), Zinc (Zn), Hg, and Pb. Fungicidal sprays containing Cu, for instance, Bordeaux mixture (copper sulfate) and copper oxychloride [7], are examples of such pesticides. For many years, lead arsenate was employed in fruit orchards to control parasitic insects. Compounds that contain arsenic have also been widely used to prevent livestock ticks and bananas in New Zealand and Australian countries, where wood timber has been conserved with Cu, Cr, and Arsenic (CCA) formulations. Many abandoned sites now surpass the background concentrations of the soil of these elements. Such pollution may lead to problems, significantly when areas are restored for agricultural or non-agricultural activities. The usage of such materials was more confined, restricted to specific sites or crops than fertilizers [9].

#### **2.3 Manures and biosolids**

Inadvertently, the manures application (e.g., animal manures or municipal sewage loam) onto the soil results in the build-up of heavy metals like chromium (Cr), arsenic (As), Cu, mercury (Hg), cadmium (Cd), lead, nickel (Ni), selenium (Se) and molybdenum (Mo) [10]. Some animal wastes like poultry, cattle, or pig dung produced in farming are often used as solids and slurries on crops and pastures [11]. While most manures are regarded as helpful fertilizers, Zn or Cu are given in diets as growth enhancers and added as supplements could have the capacity to bring about metal pollution of the soil, livestock and poultry industries [11, 12]. Manures produced by animals consuming those diets have significant concentrations of Zn, As, and Cu, leading to the substantial accumulation of heavy metals in the soil if it is frequently applied to restricted sections of land.

Biosolids are predominantly waste materials having organic origin created by wastewater treatment procedures that can also be reused to benefit the environment [13]. Biosolids materials are applied to the soil in many countries to reuse the biosolids produced by urban populations [14]. More than 30% of the wastewater is used as a fertilizer in the farming sector in the European Community [15]. Approximately 2.8 MT of dry sewage sludge utilized or get rid of per annum in the United States is anticipated to be land applied, and biosolids are utilized in agriculture throughout the country.

The possibility of composting biosolids with other organic substances like sawdust, stroke, or garden waste is also of considerable curiosity. Biosolids' potential to contaminate the soils with heavy metals has prompted widespread review about their usage in agricultural sector [16]. The most frequent heavy metals in these are Zn, Cd, Cu, Ni, Cr, and Pb, and the metal content depend on the nature, intensity, and techniques used to treat biosolids [17]. These metals applied to soils as part of biosolids treatments can seep into the soil profile and pollute groundwater in certain conditions [18]. For example, increased amounts of Zn, Ni, and Cd in drainage leachates have been found in recent investigations on certain New Zealand soil amended with biosolids [19, 20].

### **2.4 Wastewater**

Municipal and polluted wastewater is being applied to agricultural land for over four 100 years, a prevalent exercise in many sections of the world [21]. Such liquid waste is being used to irrigate 20 million hectares of agricultural land around the world. As per studies, wastewater irrigation-based agriculture is responsible for 50% of the vegetable supply to metropolitan parts in many African and Asian cities. Farmers are unconcerned about environmental impact or consequences and only focus on enhancing their production and profitability. Irrigation with such water leads to accumulation of heavy metal in the soil even though metals in industrial wastewaters are typically low.

## **2.5 Mining of metal, milling processes and industrial wastes**

Across many countries have been vouchsafed by the mining and milling of metals and the fabrication, the legacy of vast disseminating pollutants of metal contamination in soil. At the time of mining, the residues of ores are straightaway released into natural depressed geologic formation and swamps, resulting in upraised contents [22]. Voluminous mining and smelting of Zn and Pb, thus polluting the soil, risk ecological and human health risks. Furthermore, various recovery methods applied at these sites can be long and exorbitant, and soil productivity may not be restored. Comprehend pathways comprise the absorption of plant material being grown in or direct absorption of polluted soil [10].

More materials are produced by diverse industries like petrochemicals, textile, tanning by fortuitous oil spills, petroleum-based products being used, pesticides, and pharmaceutical provisions significantly fluctuating in the constitution. Though some are inclined of on land, some have suitable for forestry or agriculture. Moreover, numerous are certainly precarious due to their concentration of weighty metals (Zn, Pb, and Cr) or poisonous biological compounds that are rarely, if by any chance, used on land. Rest are highly deprived of nutrients or possess no soil improving properties [11].
