**5. Ways to reduce heavy metal penetration into crops and inactivation in animals**

Accumulation of heavy metals by crop plants varies genotypically. The transfer coefficient of elements from soil to plant is expressed as the ratio of the concentration in the plant to the total concentration in the soil. For example, low transfer coefficients for cadmium are found in maize, pea, oat, and wheat grains, while high Pb and Cd are found in wheat grains. Low coefficients are found for Zn transfer in spinach and lettuce leaves and roots of various plants. Therefore, it is better to grow crops with low metal uptake (some cereals, legumes, vegetables) on polluted soils, while leafy vegetables on unpolluted soils [41].

The mechanisms of plant tolerance to metal are important in plant breeding. It depends on the species, plant growth phase, tissue or organ, type of metal, time of action, and applied dose. In zinc tolerance, mainly processes related to its detoxification by organic acids and storage in vacuoles are involved. In tolerance to lead mainly processes in the cell walls are immobilized, while for cadmium mainly detoxification

#### *Influence of Heavy Metals on Quality of Raw Materials, Animal Products, and Human… DOI: http://dx.doi.org/10.5772/intechopen.102497*

by phytochelatins or accumulation in the cell walls are involved. Due to the existing network of mechanisms in plants that protect against toxic effects of heavy metals, in the future, it may be a way to restore the biocenotic balance in ecosystems destroyed by industrial human activities [42].

Some plants have a natural ability to accumulate heavy metals, which is used in the process of environmental cleanup (so-called phytoremediation). Known species accumulate 1–2% of metals in tissues (so-called hyperaccumulators), for example, boll weed (Thlaspi sp.). However, due to the low biomass yields of these species, the practical usefulness of the plants is limited. Plants that are to be effective in the uptake of heavy metals should be characterized by the following features—fast growth, high biomass yield and easy harvesting, deep root system, and accumulation of large amounts of heavy metals in the aboveground parts. Several phytoremediation technologies can be distinguished—phytoextraction, i.e., removal of heavy metals by accumulation in the above-ground parts of plants, phytostabilization, i.e., immobilization of metals in soil and reduction of their availability in the environment, phytostimulation, i.e., support by plants of naturally occurring microbial degradation processes in the rhizosphere, phytodegradation, i.e., decomposition of organic substances by plants and related microorganisms and phytovolatilization, i.e., transformation of contaminants into a volatile state. The plants most commonly used for bioaccumulation belong to many families, of which the crucifers (Cruciferae), grasses (Poaceae), butterflies (Papilionacae), composite plants (Asteraceae), willow plants (Salicaceae), and clove plants (Caryophyllaceae) deserve special attention [17].

Barrero-Moreno et al. [43] conducted biofilter modeling using rice husk as filter material to remove heavy metals from water. The use of bioadsorption represents great potential because lignocellulosic materials can be obtained in large quantities, are inexpensive, and can selectively remove Cd (II), Cu (II), and Cr (VI) from aqueous solutions. Based on the results, rice husk was found to be a good alternative for making filters with the ability to remove Cd (II), Cu (II), and Cr (VI) with 83.21%, 67.11%, and 92.18% efficiency, respectively, for specific values of filter height, temperature, and pH.

In sustainable agricultural production, one of the ways to reduce environmental and human, and animal health risks is to use fertilizer from agricultural biogas plants. It can be used in liquid or solid form as fresh matter, granulate, or compost. The introduced organic matter can prevent the leaching of toxic elements on the one hand, and their uptake by plants on the other [41]. Studies on the content of selected heavy metals (Fe, Zn, Mn, Pb, Cd, Ni, and Cu) in soils fertilized with mineral fertilizers (NPK and CaNPK) and with digestate and granulate did not show exceeding of permissible standards. The content of elements was compared to unfertilized objects. It was found that the applied post-fermentation masses are safe for fertilizer use. Statistically lower contents of Zn, Cu, and Mn were found after fertilization with fresh digestate compared to control objects, while lower amounts of Cu, Fe, and Cd were found after the application of granules [44].

Compost from digestate is also a product used in fertilization. The content of selected heavy metals (Fe, Zn, Mn, Pb, Cd, Ni, and Cu) in soils fertilized with mineral fertilizers (NPK and CaNPK) and with compost was analyzed to demonstrate its environmental safety and, indirectly, animal and human health. The content of elements was compared to objects not fertilized with mineral fertilizers (object 0) and with compost (K—control). The study showed that the long-term application of nitrogen, phosphorus, or potassium fertilizers increased the content of available forms of heavy metals in the soil. On the other hand, application of compost from

post-fermentation mass caused a statistically significant decrease in bioavailable forms of metals, especially in object CaNPK—Ni, Pb, and Fe and object 0—Zn and Ni. In the case of the NPK object, a significant reduction in the content of all the metals studied except Cu occurred [45].

Detoxification of contaminated natural environments is based on different solutions—the use of antagonistic type interactions in reducing bioaccumulation in animal tissues and the use of properties of compounds of organic and mineral origin.

Vitamins play a special role in reducing the bioaccumulation of heavy metals in the animal organism. They actively participate in body protection by increasing the absorption and cellular bioavailability of elements that are antagonists, maintaining the physiological concentration of ions of these elements, and participating in free radical reactions. Vitamin C in animal feed rations reduces cadmium retention and increases the effectiveness of elements antagonistic to this element, such as Fe, Cu, and Ca. Vitamin C can reduce cadmium concentration in the kidney and liver by 35–40%. Vitamin D, with Ca and Zn, and vitamin A with calcitriol and fluorine can also significantly reduce Cd concentration in tissues. On the other hand, vitamin E can counteract the activity of dehydrogenases, lowered by cadmium [46, 47]. Antagonists of cadmium are elements, such as Zn, Cu, Se, Fe, Mn, Mg, and Ca. In the case of lead, the antagonists are: Fe, Cu, Zn, Mg, Se, Ca, P, and K, while mercury may be selenium. Interactions involve competition in absorption for common transport sites and mutual displacement from metalloproteins, enzymes, DNA, RNA, and cell receptors [46].

Aluminosilicates (e.g., zeolites bentonites, kaolin), humic acids, or flavonoids play a special role in the process of heavy metals reduction in the animal organism. Aluminosilicates, due to their complex-forming, sorption, and ion-exchange properties, counteract the bioaccumulation of heavy metals in animal tissues. Studies using kaolin and zeolite as litter additives for broiler chickens showed a reduction of Hg by over 93%, Pb by almost 31%, and Cd by over 31% in birds' livers. The use of aluminosilicates in animal feed rations resulted in a reduction of Cu, Pb, Cd, Cr, and Ni content in animal tissues. The study with the application of a mixture of humic acids (brown coal and peat) and aluminosilicates (bentonite) showed more than twofold decreased Pb accumulation in animal livers. From the group of flavonoids, quercetin is an organic compound showing the ability to attach metal ions and form complex compounds. Flavonoids that are present in propolis can form chelate compounds with heavy metals, which contributes to the detoxifying effect of this bee product [46].
