**4. Effect of heavy metals on plant**

Soil heavy metal pollution would result in two major issues: loss of soil value and increased health risks for persons living near affected areas. Soil that has been poisoned by heavy metals will lose at least some of its function. When heavy metal concentrations are within legal limits, soils may be able to continue to function. However, more attention should be made to soil heavy metal intervention and goal values [57]. In light of the phytotoxicity and biological relevance of the metal species that control various plant processes, the term "heavy metal" is coined. Few metals, such as Zn, Fe, Cu, Mn, Ni, and Co, are important micronutrients for plants, but others, such as Hg, Al, Cd, Pb, As, Ga, Ag, and Cr, are non-essential for plants and have no recognized physiological function. The HMs' critical limit thresholds and reactions at the cellular and whole-plant levels are summarized [58]. The overall visual toxic reaction differs between heavy metals due to their varied locations of action inside the plant. The most common visual indication of heavy metal toxicity is a reduction in plant development, which includes leaf chlorosis, necrosis, turgor loss, a drop-in seed germination rate, and crippled photosynthetic machinery, which is commonly linked to senescence or plant mortality [59]. The concentration of this element in food varies depending on where it comes from, how it's stored, and how it's processed. These metals have several peculiar characteristics, including the fact that (1) they do not degrade over time (2) they can be necessary or beneficial to plants at certain levels but can be toxic when levels exceed specific thresholds, (3) they are always present at a background level of non-anthropogenic origin, with their input in soils being related to weathering of parent rocks and paedogenesis, and (4) heavy metals in soils can become mobile as a result of changing environmental conditions because they frequently appear as cations that interact strongly with the soil matrix [5]. Multiple studies have found that anthropogenic sources are the principal contributors of heavy metal contamination in the environment. Traffic emission (vehicle exhaust particles, tire wear particles, weathered street surface particles, brake lining wear particles, etc.), industrial emission (power plants, coal combustion, metallurgical industry, auto repair shop, chemical plant, etc.), domestic emission, building and pavement surface weathering, and atmospheric deposited heavy metals are all anthropogenic sources of heavy metals in urban soils and urban road dust [60]. Soil bacteria have been shown to alter heavy metal mobility and bioavailability by solubilizing metal phosphates, releasing chelating agents, producing redox changes, and acidification [61]. Due to the textural composition of distinct soil strata, heavy metals differ in different soil horizons. Different remediation strategies have been developed to avoid metal deposition and movement within the soil profile. Those based on the addition of materials capable of immobilizing mobile forms of metals, such as compost and biosolid, are sufficient. Another approach is phytoremediation, which is based on heavy metal absorption by various plant species [62]. pH, organic matter, and redox conditions are all factors that affect the chemistry of metals in soil and their intake by organisms; of these, pH is the most important and easiest controllable. Soil pH influences the availability and plant uptake of micronutrients [63].

#### **4.1 Treatment of soil contaminated with heavy metals**

Soil washing, which comprises pretreatment, separation, coarse-grained treatment, fine-grained treatment, water treatment, and residual management, can reduce heavy metal concentrations in soils by physical/chemical desorption, chelation, dissolution, and oxidation processes. The distribution of heavy metal compounds between soil and washing solution impacts soil cleaning performance. The efficacy of treatment varies depending on the washing technique and solution agents utilized [57]. Heavy metals and metalloids can accumulate in soils due to emissions

### *Heavy Metal's Environmental Impact DOI: http://dx.doi.org/10.5772/intechopen.103907*

from rapidly expanding industrial areas, mine tailings, disposal of high metal wastes, leaded gasoline and paints, fertilizer application, animal manures, sewage sludge, pesticides, wastewater irrigation, coal combustion residues, petrochemical spillage, and atmospheric deposition [64]. Minerals are dissolved in most cases by reacting with carbonic acid and water. Insoluble minerals are distributed into fine particles. Metals and metalloids from metal wastes, gasoline, animal feces, sludge, wastewater irrigation, and atmospheric deposition contaminate soils. Heavy metals can be removed from soil and water via phytobiological remediation, which is a costeffective and environmentally benign method. Heavy metals are removed from soil and water through phytobial remediation, which incorporates plants and bacteria. Plants are used to ingest heavy metals, and microbes aid in the breakdown of those metallic elements in phytobial-based remediation [65]. Integrating an appropriate bacteria that can release numerous plant growth-promoting substances can improve these mechanisms [66]. Phytobial remediation, in contrast to other invasive technologies, is widely considered the safest and most cost-effective option. It's in situ treatment method has also been demonstrated to reduce heavy metal distribution in soil and aid in topsoil preservation. Phytoremediation is aided by the mobilization and volatilization of free-living microorganisms. Metals are mobilized through a variety of processes, including volatilization, redox transformation, leaching, and chelation. Endophytes are bacteria and fungus that dwell on the inside of plants. They spend at least part of their life cycle inside the plant without harming it. They are found in almost every plant, with certain of them having the ability to encourage plant development [67]. Secondary metabolites are produced by a few fungal endophytes. Heavy metal tolerance has been discovered in Methylobacterium strains from the *Pteris vittata* plant [68]. Algae are considered an essential constituent of the aquatic system, playing a significant role in the biogeochemical cycle. Because of its exceptional absorption and sequestration capability, it has piqued the interest of researchers all over the world [69]. Though several integrated techniques, recombinant genetic engineering of bacteria and plants has also proven to be worthwhile in terms of heavy metal removal applications. If microbes are genetically modified, they can perform better than the natural variety, which has enormous remedial potential. Similarly, genetic engineering can be used to stimulate phytoremediation to increase heavy metal accumulation and absorption [70].
