**3. Source of heavy metal in irrigation water**

Heavy metals are commonly found in the environment as a result of substrate erosion. These naturally occurring heavy metals are generally in forms that are inaccessible to plant roots [15]. However, due to a rise in human activities that release more biologically accessible forms of heavy metals into the environment, this has altered in recent years [16] Agriculture is one of the most major human activity that contributes to heavy metals being released into the environment [17]. Using wastewater to irrigate agricultural soils resulted in considerably greater amounts of heavy metals in the edible parts of the crops produced on these soils, according to [18]. Heavy metals may be present in factory wastewater, which build over time in soil deposits along waste water routes as well as in creatures that live near them. Human exposure to polluted wastewater is common, especially in densely populated metropolitan areas or when wastewater is utilized for agricultural purposes.

Multiple businesses (textile, dyeing, garment, pharmaceutical, ceramic, paint, packing, etc.) dump untreated wastewater into neighboring canals, causing heavy metal pollution in irrigation water in Bangladesh's Gazipur District. Due to wastewater discharge from businesses, it was found that the surface water and soil of the industrial region in Dhaka and Gazipur District are significantly contaminated with Zn, Cr, Cu, Pb, and Cd. Farmers irrigate their crops with polluted water, resulting in heavy metal pollution in the district's veggies. Vegetables are polluted with high amounts of Cr, Zn, Cu, Fe, Pb, Ni, and Cd in the industrial region of the Dhaka Export Processing Zone (DEPZ). The majority of these veggies are sold at Dhaka's wholesale market and are consumed by a large number of people [19–21]. (**Table 1**) demonstrate the concentrations of heavy metals (mg L−1) in effluent-contaminated water for irrigation within the DEPZ in Dhaka, Bangladesh [21].

#### **3.1 Source of heavy metal in agricultural soil**

Heavy metals and metalloids may be accumulated in soils as a result of discharges from rapidly expanding modern regions, mine tailings, removal of high metal


**Table 1.**

*Concentrations of heavy metals (mg L−1) in effluent-contaminated water [21].*

squanders, leaded gas and paints, land use of composts, animal excrement, sewage slop, pesticides, wastewater water system, coal burning buildups, petrochemical spillage, and environmental statements [22, 23]. Frequently recognized heavy metals like Lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), mercury (Hg), and nickel (Ni) are the pollutants. Soils are a significant sink for heavy metals delivered into the climate by recently referenced anthropogenic exercises, and dissimilar to regular unfamiliar substances that are oxidized to carbon (IV) oxide by microbial movement, most metals do not go through microbial or compound degradation, and their complete obsession in soils goes on for quite a while after discharge [24, 25]. Regardless, changes in their substance structure (speciation) and bioavailability are conceivable. The presence of harmful metals in soil can keep regular pollutants from biodegrading appropriately [26]. Significant metal contamination of soil can jeopardize individuals and the organic framework through: direct ingestion or contact with spoiled soil, the normal lifestyle (soil–plant-human or soil–plant–animal-human), drinking defiled ground water, decline in food quality (security and appeal) because of phytotoxicity, and reduction in land usability for agrarian creation because of phytotoxicity [27]. The adequate security and rebuilding of heavy metaltainted soil biological systems need their depiction and repair. At both the public and global levels, current legislation on natural insurance and general well-being is based on data that describes the compound qualities of ecological wonders, particularly those that exist in our developed way of life [28]. Risk assessment is a powerful logical tool that enables leaders to manage contaminated areas in a cost-effective manner while protecting public and biological system health [29]. Heavy metals happen spontaneously in the soil environment as a result of pedogenetic cycles of parent material lasting at levels that are considered safe (1000 mg/kg-1) and occasionally hazardous (1000 mg/kg-1) [29]. In view of man's exacerbation and acceleration of nature's progressively happening geochemical example of metals, most soils in country and metropolitan regions may collect at any rate one of the heavy metals above described establishment regards adequately high to represent a danger to human wellbeing, plants, animals, organic frameworks, or other media [30]. Significant metals basically become toxins in soil conditions since (I) their paces of maturing through counterfeit cycles are quicker than normal ones, (ii) they are moved from mines to self-assertive regular regions with higher odds of direct receptiveness, and (iii) the metal unions in discarded things are tolerably high contrasted with those in get items. Critical metals in soil from anthropogenic sources will be more adaptable and henceforth bioavailable than those from pedogenic or lithogenic sources [30]. Metal-bearing solids in spoiled regions can emerge out of an assortment

### *Heavy Metal Contamination of Food Crops: Transportation via Food Chain, Human… DOI: http://dx.doi.org/10.5772/intechopen.101938*

of anthropogenic sources, including metal mine tailings, expulsion of high metal wastes from inappropriately got landfills, leaded gas and poisonous paints, land utilization of fertilizer, creature feces, biosolids (sewage sludge), compost, pesticides, coal start developments, petrochemicals, and air contamination [31]. Fertilizer. Horticulture was the most important human effect on the land in general [32]. Plants require not just macronutrients but also essential micronutrients to build up and complete the lifecycle. Some soils are deficient in heavy metals which are necessary for solid plant development, and harvests might be supplemented with them as a soil development or foliar spray. Grain crops grown on Cu-deficient soils are treated with Cu on a regular basis as a soil expansion, and cereal and root crops may also be given Mn. In major cultivating frameworks, large volumes of compost are frequently applied to soils to provide adequate N, P, and K for crop development. Following measurements of heavy metals (e.g., Cd and Pb) as contaminants are present in the mixes utilized to supply these components [33] which may fundamentally extend their substance in the soil after being applied with compost. Cd and Pb, for example, have no recognized physiological effects. The use of some phosphatic composts accidentally introduces Cd and other potentially toxic components to the soil, such as F, Hg, and Pb [34]. Pesticides. In the past, a few common insecticides used widely in agribusiness and agriculture included significant metal centralizations. For example, in the recent past, around 10% of the synthetics used as insecticides and fungicides in the United Kingdom were based on intensities containing Cu, Hg, Mn, Pb, or Zn. Copper-containing fungicidal splashes like Bordeaux mixture (copper sulphate) and copper oxychloride are examples of such pesticides [35]. For a long time, lead arsenate was used in natural product plantings to suppress parasitic microorganisms. In New Zealand and Australia, arsenic-containing compounds were additionally broadly used to control dairy cows ticks and banana bugs, woods have been saved with Cu, Cr, and As (CCA) plans, and there are currently various disregarded regions where soil groupings of these parts endlessly outperform establishment obsessions. The narrative of arsenic pollution, infiltration, and its impact on a variety of crops, foods, mushrooms, fruits, vegetables, sea animals, and fish and animal products is being revealed via ongoing research [36]. Such contamination may cause issues, particularly if areas are revamped for non-horticultural or agrarian reasons. Rather than excrements, the utilization of such materials has been more compelled, in light of indicated objections or yields. Biosolids and Manures. The inadvertent social affair of heavy metals and others in the soil is brought about by the utilization of different biosolids (e.g., creature composts, fertilizers, and civil sewage ooze). In agribusiness, some living thing squanders like chickens, dairy cattle, and pig waste products are commonly applied to harvests and fields as solids or slurries [37]. In spite of the way that most fertilizers are viewed as significant excrements, the Cu and Zn added to things down as improvement advertisers and advertisers in the pig and poultry businesses. Metal spoiling of the dirt may happen because of the fixings in poultry wellbeing items. Fertilizers made by creatures on such weight reduction regimens incorporate high centralizations of As, Cu, and Zn, which, whenever applied a few times to restricted spaces of land, can bring about significant development of these metals in the soil over the long haul. Biosolids (sewage slop) are essentially regular, amazing items that might be used subsequent to being given by wastewater treatment systems. Land utilization of biosolids materials is a typical procedure in numerous nations that consider the reuse of biosolids given by metropolitan populaces [38–40]. In view of its far and wide acknowledgment and authoritative significance, the expression sewage waste is utilized in an assortment of contexts [41]. In any case, the word biosolids is

getting more utilized as a substitute for sewage overflow, since it is considered to better precisely portray the gainful properties inborn in sewage ooze. Most of the 5.6 million dry truck heaps of sewage waste utilized or unloaded in the United States are assessed to be land applied, and biosolids are utilized in provincial regions around the country. Over 30% of sewage ooze is utilized as manure in agriculture in the European social class [42]. The major urban expert in Australia gives around 1,75,000 tons of dry biosolids consistently, and most biosolids applied to agrarian land are presently utilized in arable managing circumstances where they might be united into the dirt. There's likewise a great deal of buzz about the chance of enhancing soil biosolids with other regular assets like sawdust, straw, or nursery squander. There will be suggestions for metal polluting of soils if this inclination proceeds. Biosolids' penchant to debase soils by eliminating substantial metals has started to worry about their use in agrarian activities. Significant metals are probably not going to be foundare Pb, Ni, Cd, Cr, Cu, and Zn, and the metal obsessions are addressed by the nature and the force of the advanced development, similarly as the sort of connection used during the biosolids treatment [43]. Wastewater. The practise of dumping urban and mechanical wastewater and associated effluents on land dates back 400 years and is now commonplace in countless parts of the world [44]. Squander water has been estimated to cover 20 million hectares of fertile land throughout the world. Considerations suggest that horticulture depending on wastewater water systems contributes 50% of the vegetable supply to metropolitan regions in certain Asian and African cities. Ranchers, for the most part, are unconcerned with ecological benefits or risks, and are only interested in increasing their profits and benefits. Despite the fact that metal fixations in wastewater effluents are typically modest, a long-distance water system with such might eventually result in significant metal accumulation in the ground. Industrial Wastes and Metal Mining and Milling Cycles Mining and handling of metal assets, in mix with organizations, has given numerous nations the legacy of inescapable metal contamination transport in soil. Tailings are essentially released into customary dejections, including neighboring wetlands, bringing about expanded obsessions. Contamination of soil has come about because of far and wide Pb and zinc Zn metal mining and filtration, representing a danger to human and organic wellbeing. A significant number of the recuperation techniques utilized here

**Figure 1.** *Source of heavy metal contamination.*

*Heavy Metal Contamination of Food Crops: Transportation via Food Chain, Human… DOI: http://dx.doi.org/10.5772/intechopen.101938*

are tedious and costly, and they will most likely be unable to reestablish soil utility. Bioavailability has been featured as a soil heavy metal natural danger to individuals. Retention of plant material filled in (normal hierarchy) or quick ingestion (oral bioavailability) of contaminated soil are instances of assimilation courses. Various materials are created by an assortment of organizations, including material, tanning, petrochemicals from unplanned oil spills or the utilization of oil-based items, pesticides, and medication workplaces, and they assume a critical part in the arrangement as shown in (**Figure 1**). Despite the way that some appear on shore, few have agrarian or officer administration benefits. Moreover, a few are conceivably perilous in light of the fact that to the presence of huge metals (Cr, Pb, and Zn) or poisonous normal mixes, and are simply applied to arrive on uncommon events, if by any means. Others are insufficient in plant supplements or do not have the capacity to shape soil [32].
