**5. Strategies to control heavy metal pollution**

In order to minimize soil pollution issues and heavy metal contamination, efforts must be made to close nutrient cycles on farms by recycling nutrients in livestock manure [109]. As a result, numerous studies have been conducted to discuss methods for reducing heavy metal levels in soil and livestock waste [110–112]. Reducing the input/output ratio of heavy metals in animals should be the main objective of effective solutions [113]. For this reason, several multidisciplinary strategies should be taken into consideration to reduce animal intake, excretion in feces, and concentration in manure [1, 114, 115]. Since nutrients found in manure or in compounds come from the portion of feed that is not absorbed by the animals, adjusting the diet may be an effective strategy to influence the amount of manure generated as well as its composition [1, 116]. A formulated diet is required to increase the efficiency of nutrient retention by animals and decrease their excretion in feces [117]. For instance, using commercial amino acids to minimize nitrogen excretion in pigs and poultry is a very effective method. As a result, imports of feedstuffs high in protein, including soybean meal, are significantly reduced at the farm level. In several species, it has been proven effective to add enzymes to the meal to increase the biological availability of some particular nutrients [118]. Animal nutrition is a key factor in controlling nutrient flows on livestock farms [119]. Utilizing trace mineral supplements may help stop

the "waste." Alternative innovative compounds to antibiotics as well as to Zn and Cu should be used to control enteric diseases, and the maximum permitted level should not be thought of as the ideal level for animal requirements [120]. There is a need for various technologies to remove the content of heavy metals from contaminated soil and water in agricultural land because an excessive amount of heavy metal output from manures can still seep into the soil and water [121]. Different manure treatment methods have been researched and can be used in the field to lower the heavy metal output from animals [112].

Metal concentrations can be lowered using electro-remediation, which involves running an electric current through liquid manure to cause metal ions to precipitate on an electrode [122]. The technique has not been tested on farms yet, so it's unlikely to be economical at this time. In order to reduce the environmental impact and guarantee high nutrient efficiency, the recycling loop of manure back into food production should, from a whole-farm viewpoint, be as brief as feasible [123]. A group of researchers claim that phytoremediation, a straightforward clean-up technique, has the potential to get rid of metals from agricultural land by using plants that accumulate significant amounts of heavy metal contamination [124] . The discovery that plants might metabolize harmful pesticides led to the development of this technique a few decades ago [125]. It is seen by the communities as an acceptable, efficient, and novel technology that is also cost-effective. The term "phytoremediation" refers to a group of methods that use plants and related bacteria to remove contaminants from matrices by transfer, confinement, accumulation, or dissipation [126]. Its costeffectiveness and potential to limit the exposure of the polluted substrate to people, animals, and the environment are both facilitated by the fact that phytoremediation is typically carried out in situ [124]. The four types of phytoremediation are phytoextraction, phytofiltration, phytostabilization, and phytovolatilization, depending on the circumstances, the extent of clean-up necessary, the plants used, and the contaminants [127]. Since nutrients found in manure or in compounds come from the portion of feed that is not absorbed by the animals, adjusting the diet may be an effective strategy to influence the amount of manure generated as well as its composition [124]. Phytoremediation is a straightforward clean-up technique that makes use of plants that accumulate significant levels of heavy metal pollutants and offers hope for the removal of metals from agricultural land. The discovery that plants might metabolize harmful pesticides led to the development of this technique a few decades ago [125]. It is seen by the communities as an acceptable, efficient, and novel technology that is also cost-effective. The ideal plants for heavy metal removal ought to possess the following traits:

### i. rapid growth;


vii.increased accumulation of the desired heavy metals from soil; and

viii.translocation of the accumulated heavy metals from the soil.

A formulated diet is required that decreases the efficiency of nutrient retention by animals, increases their excretion in for instance, using commercial amino acids to minimize nitrogen excretion in pigs and poultry is a very effective method [117]. Alternative innovative compounds to antibiotics as well as to Zn and Cu should be used to control enteric diseases, and the maximum permitted level should not be thought of as the ideal level for animal requirements [128].

Heavy metals are absorbed, precipitated, and concentrated by plant or seed roots that have been raised in aerated water [129]. In order to stop contaminants from migrating to groundwater or entering the food chain, phytostabilization is employed to minimize their mobility and bioavailability in the environment [130]. Phytovolatilization is the process by which pollutants are taken up by plants from the soil, transformed into a volatile state, and then released into the atmosphere [131]. The primary and most effective method for removing heavy metals and metalloids from contaminated soils or water is phytoextraction [132]. The bioavailability of metals in soil, which is affected by a variety of factors such as chemical composition, pH, geochemical properties of metals, environmental variables, and agricultural soil management, has a significant impact on phytoremediation effectiveness [133]. Bioavailability can be increased by lowering the pH of the soil, using fertilizers, soil microorganisms, and root exudates, and adding chelating agents [134]. In order to accomplish the homeostasis of agriculture with natural habitats and to maintain balanced production systems, it is crucial to control environmental losses and the spread of toxins from livestock manure [1]. The unintentional discharge of farm waste into water has led to outbreaks of dangerous infections, even though it is unlawful to spread manure close to surface water and on frozen land, as it is in the majority of European nations [135]. Technologies and approaches are consequently required to manage these environmental issues.
