**5. Heavy metals (HMs)**

Finding a variety of toxic substances in animal feed or food additives, such as arsenic, lead, cadmium, mercury, and a host of other toxins is very common [63]. In general, it refers to a group of metals with high densities, atomic weights, or atomic numbers that are either not required or only required in trace amounts [64]. As a result of their widespread use in the manufacturing, medical, and agricultural sectors, these chemicals have begun to accumulate in the environment, raising questions about their potential dangers to both human and animal health as well as the environment [65]. Ingestion, inhalation, or dermal exposure to heavy metals can cause a wide range of health issues, including neurological and neurobehavioral disorders, abnormal blood chemistry, cancers, and cardiovascular disease in humans [62].

Poultry can be exposed to a variety of toxic metals from a variety of sources [66]. The application of sewage sludge, the disposal of industrial waste, the use of pesticides and fertilizers, and atmospheric deposition are all methods by which heavy metals can contaminate soil and water [67]. These heavy metals can be found in the air, water, and soil, it is difficult to remove them from animal feed and feed supplies [68]. Heavy metal bioaccumulation and indestructibility raise the possibility of these substances serving as toxins [69]. Metals cannot be catabolized, so chelation is an option for their removal [63].

*The Impact of Heavy Metals on the Chicken Gut Microbiota and Their Health and Diseases DOI: http://dx.doi.org/10.5772/intechopen.105581*

#### **5.1 Classification of heavy metal**

Heavy metals can be classified into four major groups on their health importance. Essential: Cu, Zn, CO, Cr, Mn and Fe. These metals also called micronutrients [70] and are toxic when taken in excess of requirements [69].

Non-essential: Ba, Al, Li and Zr.

Less toxic: Sn and Al.

Highly toxic: Hg, Cd and Cd.

Heavy metals are also called trace element due to their presence in trace (10 mg Kg−1) or in ultra-trace (1 μg kg−1) quantities in the environmental matrices [69, 70].

## **6. Channels of heavy metals exposure in broiler production**

Poultry feed is a common source of heavy metal pollution, as are the majority of animal feeds [71]. Heavy metal contamination in poultry birds can occur from feed or water [66]. Bioaccumulation and the food chain can transfer heavy metals from the soil to plants, animals, and ultimately humans [62]. Due to the use of plants in poultry feeding, contamination of the plant is likely to be found in poultry feed [71]. Rice bran, rice polish, solvent extracted rice and wheat bran, and molasses are all common ingredients in poultry feeds [72]. Calcium, phosphorus, trace minerals (such as Fe, Zn, Mn, Cu, CO, and Me), and vitamins A, D3, E, K, and B complex are among the other minerals and vitamins that can be found [73].

#### **6.1 Feed**

Mineral nutrition is required by all animals and heavy metals have been shown to be essential nutrients [73]. It is essential to maintain animal health and productivity because of the numerous enzymes that coordinate many biological processes, such as Co, Cu, Fe, I, Mn, Mo, Se, Zn [74]. Catalysis and regulation are two other important functions that essential metals perform [75]. Minerals are frequently added to commercial feeds to promote optimal growth, functional bioactivity, and antimicrobial properties from the standpoint of mineral nutrition, as well as to prevent mineral deficiencies that could compromise production [73]. There are many factors to consider when it comes to the optimal concentration of essential metals in feed [76]: genetic influences, diet, interactions between nutrients, bioavailability, and subclinical toxic effects [74, 77]. Since soil and climate conditions around the world have a significant impact on farming practices, the levels of heavy metal contamination in feed can vary widely, making it difficult to generalize across locations and legal restrictions [74]. In order to accurately predict the risk of metal exposure, it is necessary to consider the production system [78]. The majority of chicken feed contains trace amounts of heavy metals.

#### **6.2 Water**

Water pollution is the term used to describe the process of polluting waterways (e.g. lakes, rivers, oceans and groundwater). This type of pollution happens when contaminants are not properly handled before returning to the environment via rivers [79]. Water pollution has a negative impact on all aquatic life, including individual

species and populations, as well as natural biological ecosystems [80]. "Heavy" or "toxic," when it comes to metals, is defined as having a density larger than five times the water density. It is important to note that these elements are stable (i.e., those that cannot be digested by the body) and bio-accumulative [63]. Among the heavy metals (the metallic form against the ionic form required by the human body) are mercury, nickel, lead, arsenic and cadmium, alluminum, platinum, and copper.

There are a lot of heavy metals in proteins that have a lot of sulfur in them. The heavy metal concentration in streams, lakes, and rivers is normally less than 0.1 ppm [81]. However, some water sources contained up to 80 ppm of heavy metals. A lack of research has been done on heavy metal concentrations in rainfall and snow [82]. Mono-methyl mercury salts and diethyl mercury salts are the most common watersoluble mercury compounds. Environmental contaminants such as heavy metals have been related to adverse effects on human and animal health [64]. When an animal consumes a large amount of an important metal, it becomes hazardous [66].

A decline in environmental quality can be brought on by the presence of heavy metals in water, soil, or the air [64, 68]. Pollution sources can be traced back to airborne particles. It can be brought to the ground by wind or by raindrops, for example [83]. Contamination of soil layers with Cd is one cause of toxic amounts of Cd in groundwater [83]. Cd will be more concentrated in the water in the pipe duct. Environmental damage occurs when heavy metals in groundwater influence organisms directly or indirectly through adverse effects on human and animal health [84].

HMS can have an impact on our gut microbiota.

In addition to morphological harm, long-term heavy metal ingestion can cause gut flora dysfunction and potentially lead to host metabolic disorders [85]. These germs can impose selection pressure on bacteria that cannot adhere to the mucosal surface [5] and hence affect gut health.

#### **6.3 The impact of heavy metals on the makeup of the gut microbiota**

HMs have been shown to limit bacterial growth in several studies [86]. When it comes to microorganisms, Cd has been proven to have harmful effects on growth and development, particularly through disrupting protein synthesis as well as numerous enzymatic processes [83]. Because HMs come into direct touch with the gut microbiota, they have a profoundly negative impact on its composition [85]. After exposure to HM, the majority of studies have shown a drop in Firmicutes and Proteobacteria abundance and a rise in Bacteroidetes abundance at the phylum level. Cd, Pb, Cu, and aluminum (Al) were shown to elicit metal-specific and time-dependent alterations in the gut microbiota of mice, and the quantity of Akkermansia reduced following exposure to these four HMs.

Antibiotics, like heavy metals, may be poisonous to microorganisms as well as dangerous to mammals [5]. As a result, antibacterial metals are being used more frequently in goods. If animals are exposed to heavy metals, their health can be affected both directly and indirectly through their toxicological effects on cells and systems as well as the impact on their animal microbiome [12]. Microbiota imbalance, or dysbiosis, has been associated to several chronic health consequences, including infection [5]. As the immune system matures, the microbiota plays an increasingly important role in ensuring that it stays in a state of homeostasis [13]. Mucus production, epithelial barrier function and inflammation are all affected by beneficial bacteria in the microbiota [27]. The microbiota and the immune system might both be weakened as a result of heavy metal exposure, raising the risk of infection. Furthermore, these

#### *The Impact of Heavy Metals on the Chicken Gut Microbiota and Their Health and Diseases DOI: http://dx.doi.org/10.5772/intechopen.105581*

exposures might have a negative influence on health because of the rise in antibioticresistant bacteria [85]. Metal resistance, like antibiotic resistance, has been thoroughly documented across many different bacteria for many different metals, despite the fact that heavy metals may be hazardous to microorganisms [36]. Bacteria that are resistant to both metals and antibiotics are often found together. Co-selection of metal and antibiotic resistance genes in bacteria can be caused by a variety of methods. Antibiotic resistance and metal resistance are both coded by two different genes that microbes may have, with one stimulus triggering transcription of both genes either physically or transcriptionally coupled inside a genetic unit like a plasmid. It is also possible that bacteria may have just one gene that makes a protein set that is capable of resisting both metals and antibiotics. As a result of any of these scenarios, bacteria would be able to select for antibiotic resistance as well.

The health impacts of HMs after changes in gut microbiota caused by HMs.

Toxicity-induced gut microbiota alterations have been found to disrupt gut integrity and contribute to a number of downstream consequences [36].

Cucumber toxicity resulted in a deterioration of chicken cecum structure, with the mucosa falling off, vacuoles forming in the lamina propria, and an inflammatory response that was time-dependent. In addition to morphological harm, long-term heavy metal ingestion can cause gut flora dysfunction and possibly host metabolic disorders [11]. Another study found that alterations in the microbiota of the digestive tract have been linked to a number of ailments, including intestinal barrier permeability and inflammation [38]. It is believed that copper exposure might lead to an imbalance in the gut flora, which could have negative consequences for the health of chickens [21].

### **7. Conclusion**

Heavy metals in the broiler chicken production environment affect the gut flora, which in turn affects the health of the animals. In order to minimize or eliminate any impact on the gut microbiota, proper rules for the use of heavy metals in feed and water should be put in place. This is critical for the consumer's health, as heavy metals may build up in the body over time and pose a health risk. Toxic heavy metals may lead to the growth of bacteria that are resistant to heavy metals and antimicrobial resistance at the same time. Regulators and testing should be put in place to limit the discharge and exposure of hazardous materials.

*Broiler Industry*
