Authors: Mohamed E. Abd El-Hack, Elwy A. Ashour, Fatemah AlMalki, Asmaa F. Khafaga, Mahmoud Moustafa, Mohammed O. Alshaharni, Islam M. Youssef, Ahmed A. Elolimy, Sylwester Świątkiewicz
Categories: PROCESSING AND PRODUCT, Biodegradation, Microorganisms, Microplastic removal, Pollution, Poultry
Source: Poultry Science
Microplastics (MPs) are small plastic particles less than five millimeters in size. Microplastic pollution poses a serious threat to ecosystems, affecting both biotic and abiotic components. Current techniques used to eliminate microplastics include recycling, landfilling, incineration, and biodegradation. Microplastics have been detected in various animal species, including poultry, fish, mammals, and invertebrates, indicating widespread exposure and potential bioaccumulation. In the Middle East, MPs contamination was discovered in chicken purchased from food shops, chain supermarkets, and open markets. The contamination levels ranged from 0.03±0.04 to 1.19±0.72 particles per gram of chicken meat. In poultry, microplastics negatively affect production and harm vital organs such as the kidneys, spleen, and lungs. In humans, exposure to microplastics can lead to inflammation, immune responses, metabolic disturbances, DNA damage, neurological damage, and even cancer upon contact with mucosal membranes or absorption into the body. Several studies have explored the use of microorganisms, including bacteria, fungi, and algae, to degrade microplastics, offering an economical and environmentally friendly solution. Different polymers were cultured with strains of Bacillus spp. (SB-14 and SC-9) and Streptococcus spp. (SC-56) for a duration of 40 days. Degradation rates for LDPE were 11.8 %, 4.8 %, and 9.8 %. The rates of deterioration for HDPE were 11.7 %, 3.8 %, and 13.7 %. Rates for polyester beads were 17.3 %, 9.4 %, and 5.8 %. This review focuses on the effects of microorganisms in removing microplastic pollution, the detrimental impact of microplastics on poultry production, and the connection between microplastic pollution and human health.
**Key ** Microplastic removal, Microorganisms, Biodegradation, Poultry, Pollution
Plastic pollution produces millions of tons of waste annually, one of the worst environmental catastrophes brought on by human activity, with more than 430 million tons of plastic produced annually. Two-thirds are short-lived products that soon become waste, and, often, work their way into the human food chain (Naz et al., 2024). Research indicates that microplastic pollution is ubiquitous in many ecosystems, including freshwater bodies, terrestrial areas, and oceans. It is a global environmental concern. The wide dispersion of microplastics in marine habitats has been emphasized by several systematic reviews and research, recent studies estimate that about 5–13 million tons of plastic enter the oceans annually highlighting the seriousness of the problem (Al Nahian et al., 2023; Pourebrahimi and Pirooz, 2023; Sharma and Vidyarthi, 2024). Microplastics have been found in various animal species, including birds, fish, invertebrates, and mammals, indicating extensive exposure and bioaccumulation potential. Consumption can affect gut bacteria composition, nutrient absorption, and digestion efficiency. Microplastics can also transport chemical contaminants, increasing their bioavailability and potentially causing oxidative stress, inflammation, and endocrine disruption. Livestock consumption can indirectly affect human health (Khan et al., 2024).
Microplastics and other environmental pollutants can cause the poultry business to become increasingly polluted, negatively impacting the industry's economic efficiency and growth. Thus, it is imperative to look into the harm that microplastics cause to chickens. According to reports, a portion of the eating MP molecules may quit the body by the digestive system (Wu et al., 2021). Zhang et al. (2022c) demonstrated that the concentrations of microplastics in chicken, and goat compost fertilizers were 150, 150, and 144 items/kg, respectively. Moreover Zhang et al. (2022d) found in a recent investigation that the number of microplastics in the compost made from chicken compost was 14,720 ± 2,468 items kg^−1^. Removing all contaminants from recovered food, including heavy metals, mycotoxins, biogenic amines, microplastics and anti-nutritional factors is not always possible. As a result, it is advised to use infrastructure to evaluate the pollution levels in recovered food in conjunction with comparing methods to effectively remove these contaminants (Simmons et al., 2023). In a novel study on Japanese quail, Zhang et al. (2024) showed that microplastics caused microstructural damage, cell disarray, and splenic inflammation. The spleen was exposed to oxidative stress, increased levels of malondialdehyde (MDA) and reactive oxygen species (ROS), and decreased proinflammatory cytokines. Microplastics also stimulated tumor necrosis factor (TNF) signaling, activating the p38 mitogen-activated protein kinases pathway, causing splenic cell death.
Microplastic treatments made possible by the activity of microorganisms (bacteria, fungus, and algae) are thought to be attractive instruments for economically viable and environmentally acceptable degradation techniques. Recently, scholarly works and studies have been released on remediation strategies and microorganism-mediated degradation (Kotova et al., 2021; Qin et al., 2021; Chen et al., 2022; Cholewinski et al., 2022).
Ecosystems and our surroundings are seriously threatened by microplastics. Their persistence and ubiquity in both terrestrial and marine habitats have given rise to grave worries over their possible effects on human health and wildlife. The effects of microplastic pollution are extensive, ranging from the ingestion of these particles by poultry strains to the possibility of their entering the food chain. The microplastic crisis calls for a multimodal response. This entails cutting back on the use of plastic, enhancing waste management, and creating cutting-edge approaches to recycling and biodegradable materials. We can lessen the negative consequences of microplastics and save our world for future generations by banding together. So, the primary goal of this review is to show the consequences of microplastics in poultry production, which are most significant, as well as biological ways to remove microplastics and the microplastic food chain that reaches people from poultry.
Small plastic molecules, known as microplastics (MPs), are less than five millimeters in size and are considered a popular environmental pollutant in poultry and aquatic ecosystems. Because of their accumulation and ability to advance up the food chain, concerns have been expressed regarding the consequences of microplastics on different animal's nutrition and health (Khan et al., 2024). Plastics consist of seven main categories based on how often they are used. Two species of polyethylene are low-density (LDPE) and high-density (HDPE), polyethylene terephthalate (PET or PETE), polystyrene (PS or Styrofoam), polypropylene (PP), and others. Many can be broken down (Thakur et al., 2022). Furthermore, the arrangement and makeup of microplastics are intimately linked to the materials from which they originate. The most prevalent plastic molecules are polypropylene (PP), polystyrene (PS), polyethylene (PE), cellulose acetate (CA), nylon (PA) and thermoplastic polyester (PET) (Campanale et al., 2020).
Anand et al. (2023) state that there are 2nd distinct sources of microplastics. Patel et al. (2009) reported that the main sources of microplastics are drug delivery systems, cosmetics, home goods, and polymeric raw substances (fakes, pellets and powders) made of polystyrene, polyethylene, polyvinyl chloride, polypropylene and polyamide nylon 6, among other materials. According to Fendall and Sewell (2009), personal care products like scrubs, toothpaste, cleaning supplies, and cosmetics have been found to contain irregular microplastics with a diameter of 0.5 < to 0.1 mm. These microplastics, which are a source of primary microplastics, are sold as "micro-beads" or "micro-exfoliates." But while microplastic pollution is effectively eliminated by the settling and skimming treatment operations, the treatment of wastewater plants now in operation has demonstrated that tertiary water treatment is not a main exporter of microplastic pollution (Carr et al., 2016). When big plastic objects or particles are extensively fragmented in the presence of environmental conditions such as high temperatures, UV radiation exposure, reactive ozone, oxidation, stress and air pressure, secondary microplastics are produced (Tiwari et al., 2020; John et al., 2021). Polymeric materials can only resist oxidative-thermal breakdown if stabilizers and antioxidants are introduced. Secondary microplastics are also produced through physical abrasion. Furthermore, it is well-recognized that a wide variety of enzymes secrete by biological factors, like bacteria, algae and fungus, are essential to the breakdown of microplastics (Chia et al., 2020; John et al., 2021; Othman et al., 2021; Chen et al., 2022; Manzi et al., 2022; Zhu et al., 2022; Miri et al., 2022).
Large plastic bodies composed of the same polymers incorrectly disposed of in land and water systems are the main source of secondary microplastics. Physical wear and tear on the items result in oxidative-thermal degradation and weakening of the chemical bonds (Gerritse et al., 2020). The breakdown of synthetic fibers while washing clothing and industrial processes like thermal cutting of polystyrene are two other secondary sources of microplastics. The overproduction of items made of polypropylene, polyethylene and polyethylene terephthalate has been attributed to the growing use of single-use plastics. Additionally, different sectors such as paint, electronics, automotive, textile, and paint release goods made of microplastics into river catchment areas and bodies of water, potentially contributing to microplastic contamination (Kay et al., 2018; Chia et al., 2021).
Microplastics can enter poultry breeding systems through various sources, including contaminated feed, bedding, and water. Here are the main release forms of microplastics in poultry breeding. Microplastics from feed can seep out of its plastic packaging, particularly if it is kept in storage for a long time or is heated. Furthermore, feed components include grains, vegetable leftovers, and animal dung could include microplastics from contaminated environments or agricultural methods. Microplastics may also be present in some feed additives or supplements as a transporter or processing help. Microplastics can seep into water systems used in chicken houses through plastic fittings, pipelines, and other plumbing parts. Microplastics from agricultural runoff or environmental pollution may also be present in poultry water sources. Additionally, dust and airborne particles may contain microplastics that land on chickens, bedding, or feed. Additionally, over time, plastic feeders, drinks, and cages used in poultry equipment may release microplastics (Jadhav et al., 2021).
The impacts of microplastics on poultry production are summarized in Fig. 1. According to Dong et al. (2023), animals can come into contact with microplastics through three different (i) ingestion (by food and drink), (ii) inhalation (mostly by lungs), and (iii) skin contact. According to Sheriff et al. (2023), microplastics can result in several toxicodynamics (toxicity) and toxicokinetics outcomes after they enter an animal's body. According to Gehring and van der Merwe (2014) and Richardson (2020), a chemical's or toxicant's toxicodynamic effect is what happens to an organism following a certain or predetermined exposure duration, dose, frequency and amount. Conversely, toxicokinetics refers to a foreign chemical or toxicant absorbed, distributed, metabolized, and excreted within the biological organism's system (van der Merwe et al., 2018; Asati et al., 2022). As will be covered in the following sections, toxicokinetic and toxicodynamic investigations of microplastic in cattle and poultry are a relatively young field of study with a little body of literature (Sheriff et al., 2023). Table 1 shows the impact of microplastics on poultry. When MPs are consumed by birds, they can cause inflammation, gastrointestinal obstructions, and poor nutrient absorption, which can interfere with regular digestive processes and jeopardize general health. (Fig. 2). By upregulating Caspase 8, damaging the intestinal vascular barrier, upsetting the intestinal flora, and encouraging the buildup of lipopolysaccharide, MPs shifted the death mode from apoptosis to necrosis and pyroptosis. Through the liver-gut axis, pathogenic flora and metabolites were transferred to the liver, inducing hepatic immune responses, hepatic lipid metabolism abnormalities, and apoptosis. Liver injury is associated with several molecular effects, including disruption of mitochondrial dynamics, oxidative stress, stress in the endoplasmic reticulum, and disruption of the cell cycle (Yin et al., 2023).
Fig. 1 Impacts of microplastics on poultry production.
Fig. 2 Distribution of microplastics in poultry tissue.
Moreover, Susanti et al. (2021) studied the presence of microplastics in ducks housed in five Indonesian towns and grown in intensive farming. The duck intestines had a large amount of microplastics; in certain areas, the number of microplastics per bird was 39 and 49. The duck intestines included fragment and filament microplastics that ranged in size from 100 µm to 5000 µm. Susanti et al. (2021) found that pellet and filament-shaped microplastics predominated in the intestines under examination and that the polymer types identified were nylon, PBM, PET, PVC, and PE. In a related investigation, microplastics in the form of film, fragments and pellets were found in the gizzards and intestines of chickens purchased from damp markets in South Caloocan, the Philippines (Leon et al., 2022). Also, Huerta Lwanga et al. (2017) showed that 16.45 % of the microplastics smaller than 5 mm were found in the gizzards of chickens in Mexico. The amount of microplastic found in poultry gizzard and intestines in the Philippines may have come from two sources of exposure, according to Leon et al. (2022): polluted poultry feed and exposure to ambient pollution. According to Huerta Lwanga et al. (2017), the primary route for microplastic detected in chicken gizzards in Mexico is oral exposure through soil consumption from home gardens.
The negative impacts of microplastics on the reproductive systems of chickens exposed to 1 and 100 mg/L of PS microplastic for twenty-eight and forty-two days, respectively, were studied by Hou et al. (2022). According to the findings, the microplastics injured the testicular tissue of the hens and induced oxidative stress and "inflammatory infiltration" (Hou et al., 2022). According to another recent study, chickens exposed to PS-microplastics (5 µm) for forty-two days suffered kidney damage, oxidative stress, and changes in their "mitochondrial status," especially when exposed to microplastics at concentrations of 10 mg/L and 100 mg/L by Meng et al. (2022).
Additionally, Zhang et al. (2022a) investigation discovered that the microplastics, particularly at higher dose levels, induced "myocardial dysplasia" in chicks and chickens. It has been observed that microplastics induce "myocardial pyroptosis" in chickens, specifically inducing inflammation and impacting "energy metabolism" and "mitochondrial homeostasis" (Zhang et al., 2022b). In the stomachs of hens who suffer from microplastics for twenty-eight days, a recent study discovered a significant decrease in microbial diversity and plentiful. The investigation also found that polluted microplastics caused harm to the gut, liver, kidney, and spleen in hens (Li et al., 2023). For instance, hens exposed to polyethylene through feed showed a decrease in body weight (Li et al., 2023); yet, hens treated to varying doses of microplastics by drinking water showed no discernible change in body weight or myocardial weight (Zhang et al., 2022b). In addition to their toxicological effects, research on the behavioral and physiological impacts of microplastics on poultry and livestock models, including their effects on feeding, sexual behaviors and social movement, broodiness, aggression, and cannibalism, is important to improve our understanding of how microplastics affect various species (Sheriff et al., 2023).
Huerta Lwanga et al. (2017) showed that only larger plastic particles (MaPs) were found in the chicken's digestive system, known as the crops, while both larger (>5 mm; 84 % MaPs) and smaller (16 % microplastics, 5 mm) MaPs were found in the gizzards. On the other hand, the feces only had tiny particles (microplastics, 1 mm). This implies that during digestion, MaPs are changed into microplastics (Huerta Lwanga et al., 2017). Plastic particles may be retained in poultry for an extended period if the crop is used to store food (Zhao et al., 2016). It has been shown that plastics used as vectors can biomagnify some chemicals, such as polybrominated diphenyl ethers, in aquatic bird tissues (Tanaka et al., 2013). The biomagnification of microplastics has also been studied in birds with higher nutrition levels (Carlin et al., 2020).
The mean body length and mean body weight of Japanese quails in the microplastics groups were lower than birds in the control group, according to a final study by Zhang et al. (2024). Specifically, the microplastics group's mean body weight of quails exposed for two, three, and four weeks was considered lower than birds in the control group. Furthermore, following a 5-week exposure, the mean body length of birds in all three transaction groups dropped by 1.27 %, 3.14 %, and 2.83 %, respectively, and their average body weight dropped by 0.54 %, 2.33 %, and 4.04 %, respectively, in comparison to the birds in the control group. In the meantime, the quails' average daily consumption of feed and water from the microplastic transaction was also reduced compared to birds from the control group. We can conclude that the poultry production is seriously threatened by microplastics. Their pervasiveness in the environment, ranging from water sources to feed, has profound effects on the health and welfare of chickens. Research has shown that microplastics in poultry can have a variety of negative impacts, including as stunted growth and development, weakened immune systems, decreased fertility and irregular egg production, and tissue damage due to the accumulation of microplastics in different organs.
Because macro-polymers are not immediately utilized by biofilm microorganisms, they break down microplastics (Dhiman et al., 2023). Once microplastics have entered the biofilm, several extracellular oxidases and hydrolases remove the macro molecular polymers into oligomers and monomers. The bacteria then take up and begin converting these short-chain polymers (Zhang et al., 2021). Lastly, when bacteria are present, microplastics can mineralize and produce water and carbon dioxide. Typically, the biofilm technique calls for four processes to remove microplastics. First, bacteria, fungi, and prokaryotes gather on the surface of microplastics and alter them. The breakdown of microplastic additives and monomers is the next stage of microbial degradation. After that, microplastic and their additives are attacked by biologically produced enzymes and free radicals, which erode them and cause mechanical instability. As a result of water seeping into the polymer matrix and microbial filament disintegration, microorganisms eliminate microplastics in the fourth stage (Sun et al., 2023). Mechanism of microorganisms to remove microplastics in (Fig. 3).
Fig. 3 Mechanism of microorganisms to remove microplastics.
Numerous parameters, such as surface area, hydrophobicity, particle weight, crystallinity, chemical structure, functional groups, etc., influence how biologically plastic pollutants deteriorate. Because it becomes harder for bacteria to ingest plastics via the cell membrane, an increase in particle weight causes a drop in the rate of deterioration and a decrease in solubility, making the plastics less vulnerable to microbial attack (Siracusa et al., 2008). According to Slor et al. (2018), another significant element influencing biodegradability is crystallinity, where polymers with amorphous domains are more susceptible to the enzymes produced by microbes. Microalgae and their toxins and enzymes can be employed to break down polymeric material biologically, as demonstrated by (Moog et al., 2019; Chia et al., 2020; Manzi et al., 2022; Anand et al., 2023). The main feature is that they don't need a rich carbon exporter like the bacterial system does supply for growth and can develop in various environments, like those that are home to most microplastics (Yan et al. 2016). It is commonly known that in wastewater streams, microalgae adhere to plastic surfaces and create ligninolytic and exopolysaccharide enzymes, leading to plastic degradation. These polymers mainly serve as a carbon source, increasing the quantity of proteins and carbohydrates within cells and accelerating their growth. Scanning electron microscopy has just been used to identify the breakdown or surface degradation of low-density polyethylene sheets caused by algal colonization (Sanniyasi et al., 2021). According to Chia et al. (2020), the key processes that lead to algal biodegradation are corrosion, hydrolysis, penetration, fouling, and others. The biodegradation of plastic trash is linked to several catabolic processes. The first stage of biodegradation is known as biodeterioration and is typified by alterations in the polymer's surface structure and form (Ali et al., 2021a). Mineralization, assimilation, and biofragmentation are later phases. Extracellular enzymes accelerate biodeterioration by encouraging microbial growth and improving the collection and adhesion of additional pollutants onto the plastic surface (Ali et al., 2021b).
This demonstrates the vital role that secretions and extracellular enzymes from microorganisms play in the biodegradation process. Laccase, which is produced by fungi, speeds up the oxidative division of the amorphous high-density polyethylene (HDPE) structure, allowing MPs to be broken down (Othman et al., 2021). Also, the oxidase enzyme helps break down polymers by extracting the carbonyl groups from the polymer chains. Sumathi et al. (2016) investigated the laccase-producing Cochliobolus sp.'s capacity to break down PVC and improve laccase synthesis conditions. The results demonstrated that the PVC samples' physical and chemical characteristics had changed, leading to erosion and the addition of carbonyl groups (CeO) to the microplastic material's surface. Microorganisms, like fungi and bacteria, release extracellular enzymes called hydrolases and depolymerases. These enzymes can hydrolyze complicated compounds into monomers, dimers, and oligomers, among other simpler forms. The results of Lepcha et al. (2023) show that a variety of organic acids (such as gluconic, oxalic, glyoxylic, and citric acid) and some chemicals can be produced by certain chemoorganotrophic microbes (Thiobacillus, Nitrobacter and Cladosporium sp.,). These substances exhibit significant activity for the duration of the biodeterioration phase. Numerous other factors, like pH, which varies due to metabolic activity in the medium, also impact this stage (Ali et al., 2021a, b).
To aid in their growth and development, microbial types can integrate the monomers created during the bio-deterioration phase into their structural makeup. These monomers can withstand mineralization and cross microbial cell membranes. In anaerobic settings, mineralization activities involving cell monomers can produce CH4, CO2, and H2O (Cai et al., 2023). Conversely, under aerobic conditions, monomers can mineralize into H2O and CO2, generating biomass and energy. Polyethylene and thermoplastic polyester materials have been significantly destroyed by the chitinase enzyme derived from fungi, specifically Rhizopus oryzae (Seenivasagan et al., 2022). By generating proteins such as hydrophobins, cysteine-rich proteins, and polysaccharides, fungi can adhere to the plastic surface. Extracellular enzymes can be produced by the fungal cell. Fungi can adhere to plastic surfaces and pierce the polymeric structure thanks to certain compounds and enzymes (Temporiti et al., 2022). The infiltration process creates pores and voids, changing the plastic surface's physical characteristics. The polymer's resistance is now decreased via a physicochemical transition (Ali et al., 2023). Using a consortium of yeast that originated from the symbiotic bacteria present in the termite stomach, high molecular weight polymers were broken down. Plastic waste was utilized in this procedure to encourage the growth of yeast (Elsamahy et al., 2023), It is noteworthy that the biodegradation efficiency may be enhanced by adding a carbon source to the growth medium.
Moreover, to accelerate the degradation process, more creative approaches are needed to improve the degrading bacteria and optimize the environment. Research has shown that harmful byproducts are usually produced when a single bacterium biodegrades (Dobretsov et al., 2013). These byproducts can be eliminated in a fix microbial community (Singh and Wahid, 2015). Therefore, the employment of a consortium of bacteria is typically favored. The primary degradation process is physic-chemical degradation, which shortens the polymer chain and modifies the functional groups of microplastics to increase their susceptibility to the action of microbial enzymes. esterases, Lipases, laccases, cutinases, amidases, hydrolases and carboxylesterases are among the enzymes that are involved in biodegradation employing enzymes (Barth et al., 2016; Gómez-Méndez et al., 2018; Chen et al., 2020; Inderthal et al., 2021; Amobonye et al., 2021). Therefore, a thorough understanding of the metabolic routes and the related enzymes is required to carry out the biodegradation process in an impact manner. It is advised to do physiochemical pre-treatment on plastics, which includes UV irradiation, thermo oxidation, and chemical oxidizing agents. Pre-treatments that increase the biodegradability of polypropylene include nitric acid treatment, UV irradiation, and blending with polymers such as starch derivatives, polyhydroxybutyrate, cellulosic esters, polycaprolactone and poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (Gironi and Piemonte, 2011). It has been observed that prooxidative and biodegradable materials such as starch can improve the biodegradability of low- and high-density polyethylene (LDPE and HDPE), and polyvinyl.
Microbes can break down plastics, but different tactics must be developed to maximize their ability to do so (Thakur et al., 2022). Polymers are utilized in many different industries. Specifically, butylene adipate-co-terephthalate, acetyl cellulose, acrylic, cellulose triacetate, cellophane, alkyd, polyamide, epoxy resin and polyacrylonitrile are among the biodegradable polymers (Thakur et al., 2022). Many researchers conducted in the last several years have documented the potential of various microbes to break down various synthetic polymers. An estimated 50 % or more of plastic garbage is disposed of in landfills, with the remaining 19 % being burned. 22 % of poorly managed plastic trash is in terrestrial and marine habitats, with only around 9 % of plastic garbage being recycled. Pseudomonas species have the highest ability in the bio-degradation of plastics among the Gram-negative bacilli species that make up the majority of those that can break down plastic (Nanda et al., 2010; Usha et al., 2011; John et al., 2012; Kyaw et al., 2012; Tribedi et al., 2012). A summary of the microorganisms used to eliminate the microplastics is in Table 2.
Pseudomonas spp. was isolated to degrade polyethylene from three distinct sources. Among these, the most effective in biodegrading both natural and manufactured polyethylene was Pseudomonas species isolated from sewage sludge dump. Pseduomonas species produced the stickiest and most flocculent surface biofilms in three weeks compared to the other species (Nanda et al., 2010). In addition to Pseudomonas species, Klebsiella, Streptomyces, Ideonella, Mycobacterium, Rhodococcus, Escherichia, Flavobacterium and Azotobacter are among the other bacterial species that can biodegrade plastics. Fungi also contribute to the biodegradation of plastics, speeding up the process by exchanging metabolic intermediates with bacteria (Orr et al., 2004). Additionally, it was found that pro-oxidative pretreatments and chemicals were unnecessary for the colonization and destruction of LDPE surfaces by Phormidium lucidum and Oscillatoria subbrevis (Sarmah and Rout, 2018). A variety of bacteria and algae, like Chlorella fuscavar. Chlamydomonas mexicana, Chlorella vulgaris, vacuolated and Stephanodiscus hantzschii, broke down bisphenol A, an additive with estrogenic vigorously that is frequently present in molecular (Hirooka et al., 2005; Li et al., 2009; Ji et al., 2014).
Most of the time, the development of biofilms on the molecular surface is linked to removing microplastics. Several cyanobacterial strains were also able to form films on the microplastic polymers, such as genus Microcystis, the species Pleurocapsa, Rivularia, Leptolyngbya Calothrix, Synechococcus, Prochlorothrix, and Scytonema (Bryant et al., 2016; Debroas et al., 2017; Dussud et al., 2018; Muthukrishnan et al., 2019). In addition to cyanobacterial species, the biofilms contain diatoms, which aid in photosynthesis (Amaral-Zettler et al., 2020). Novel developments in various biotechnological techniques have made it possible to establish several genetically altered microalga cell factories that can secrete and produce the enzymes needed to break down plastic (Shen et al., 2019). The breakdown of terephthalic acid and polyethylene terephthalate films is accomplished by polyethylene terephthalate hydrolase, which was produced by genetic alteration of the green microalgae Chlamydomonas reinhardtii (Kim et al., 2020). Prochlorothrix tricornutum produced polyethylene terephthalate hydrolase and demonstrated strong catalytic activity against polyethylene terephthalate and its polyethylene terephthalate glycol, copolymer (Moong et al., 2019). In summary, microalgae may be useful microplastic degraders because they are easy to cultivate and can use microplastics as a carbon source by creating degradation enzymes. Using microalgae and synthetic biology, a promising ecologically benign method of biologically degrading polyethylene terephthalate has been made possible by the potential to modify algal strains to increase their capacity for genetic degradation.
The majority of the broad varieties of organisms that include fungi are saprotrophs, sometimes known as obligatory or opportunistic parasites. They are incredibly adaptable and may flourish in different terrestrial and aquatic ecosystems with a wide range of environmental status. They generate many natural bio surfactants, including hydrophobins, and extracellular enzymes that can degrade complex polymers into simpler monomers and provide microbes with carbon and electrons. According to Hernández et al. (2019), this resistance to several hazardous substances and metals aids in the decomposition and mineralization of complex contaminants. Penicillium simplicissimum is the main genus linked to the degradation of a variety of polymers, including polypropylene, polyethylene terephthalate and polyethylene (de Oliveira et al., 2020). These microorganisms use microplastic as their only carbon exporter after being broken down by extracellular enzymes. They lessen their hydrophobicity and promote the formation of various chemical component linkages with ester, carboxyl, and carbonyl functional groups. Fungal strains like Penicillium chrysogenum, and species of Pestalotiopsis microspora all showed similar degradation of polyurethane (Álvarez-Barragán et al., 2016; Magnin et al., 2020). Serine hydrolase is usually a key player in the breakdown of polyurethane.
Alcanivorax borkumensis is one of the marine hydrocarbonoclastic bacteria that can break down branched aliphatic compounds, alkanes, alkyl cycloalkanes and isoprenoid hydrocarbons (Davoodi et al., 2020). The same isolate used in the study by (Delacuvellerie et al., 2019) conducted the production of biofilms on LDPE (low-density polyethylene) when hexadecane, pyruvate, and yeast extract were present. Additionally, it was mentioned that the presence of alkanes alters the hydrophilicity of cell membranes, creates biosurfactants that interact with plastic surfaces, and causes COOH/OH and C=O functional groups to develop. The biodegradation of polyethylene was also aided by many actinomycetes, such as Streptomyces and Rhodococcus ruber (Sivan 2011). Overall, Pseudomonas accounted for 21 % of the various species of bacteria linked to the breakdown of microplastics, Bacillus for roughly 15 %, and combinations of these two genera for 17 % of the bacteria (Matjašič et al., 2021). Ideonella sakaiensis and Exiguobacterium sp. (Tanasupawat et al. 2016), Also, Pseudomonas putida, Thermomonospora fusca and Pseudomonas chlororaphis, (Ghosh et al. 2013) were among the other bacteria linked to the biodegradation of microplastics. These include Bacillus sp., Enterobacter asburiae, Nocardia asteroids and Rhodococcus rhodochrous (Bonhomme et al., 2003), Streptomyces badius, Clostridium thermocellum, Comamonas acidovorans and Rhodococcus ruber, (Paço et al., 2019).
Bacillus gottheilii and Bacillus cereus, two species of Bacillus strains obtained from mangrove sediments were used in Auta et al. (2017)'s investigation into the treatment of various microplastics made of polystyrene, polyethylene, polypropylene and polyethylene terephthalate. Apart from examining the morphology and structure alterations by electron microscopy and FTIR investigations, the microplastics weight loss was used to gauge the biodegradation rate. Using Bacillus cereus isolate and polystyrene microplastics, the quickest mass reduction (0.0019/day) and the shortest degradation half-life (363.16 days) were discovered; in contrast, Bacillus gottheilii on polyethylene produced 0.0016/day and 431.25 days. Scanning electron microscopy (SEM) can also be used to monitor the biodegradation of microplastics, revealing several holes, fissures, and erosions (Sowmya et al., 2014). Bacillus gottheilii emerged as a more promising candidate for microplastic degradation when FTIR analysis was used to compare the degradation results, bond cleavages, and chemical modifications (Mohsen et al., 2020). In summary, microbiota, polluted sediments, sludge, compost, wastewater, extreme conditions and municipal landfills have all been found to include bacteria that can break down microplastics. The capability of bacteria to break down microplastics has been investigated using both microbial consortiums and pure cultures. Specifically, the bacterial consortium exhibits increased community stability and efficiency. While the mechanisms employed by microorganisms to degrade microplastics are multifaceted, the potential of these tiny organisms to mitigate this global environmental challenge is undeniable. Their capacity to disassemble complicated polymers into simpler molecules presents a viable path toward long-term fixes. With further research, we should be able to predict the creation of tailored bioremediation techniques and microbial strains that are specifically designed to counteract microplastic pollution in diverse environments. We might be able to bring our world back into balance and protect its delicate ecosystems for future generations by using the power of nature.
Three distinct routes of exposure to microplastics have been eating food including microplastics, breathing in microplastics from the air, and coming into contact with these molecular via the skin (Revel et al., 2018). Research by Cox et al. (2019) indicated that individuals consume 39,000-52,000 microplastics annually, which clog the intestines, trigger an inflammatory response, and alter gut microbes' composition and metabolism. As previously mentioned, microplastics can also be ingested. According to Dris et al. (2017), the concentration rate of microplastics outdoors ranges from 0.3 to 1.5 particles per m3, whereas interior concentrations range from 0.4 to 56.5 particles per m3. The size and density of the particles have a significant impact on how microplastics deposit. According to Oliveira et al. (2020), the smaller, less dense particles have a tendency to lodge deeper in the lungs, releasing chemotactic factors and leading to persistent inflammation. It was only recently confirmed that human blood and lung tissue contain microplastics (Leslie et al., 2022; Jenner et al., 2022). Furthermore, according to Revel et al. (2018), there is a possibility that nanoparticles can pass through the skin barrier, leading to fibrous encapsulation and minimal inflammatory responses (Oliveira et al., 2020). Once they come into touch with mucosal membranes or are absorbed by the body, microplastics can induce inflammation, immunological reactions, neurological damage, metabolic changes, damage to deoxyribonucleic acid (DNA), and even cancer. The main causes of this are the leaking of hazardous compounds and their tendency to be persistent in the body (Wright and Kelly, 2017; Revel et al., 2018; Vethaak and Legler, 2021; Rahman et al., 2021; Gruber et al., 2022).
Moreover, all trophic levels of organisms are susceptible to the harmful impacts of microplastics and nanoplastics originating from many sources, most notably the environmental degradation of waste plastics. They can penetrate the food chain of aquatic fauna, where they can cause intestinal obstruction, changes in the adsorption of nutrients, endocrine disruption, and impacts on the nervous system, immune system, and loss of reproductive functions. Toxic leachate, microplastics and nanoplastics, and impaired metabolic processes can harm the cell walls of microalgae and hinder photosynthesis by creating shadows. Micro and nanoplastics can cause inflammatory and immunological responses when they reach the human body by ingestion, inhalation and skin contact. The chain of microplastics in poultry and humans is presented in Fig. 4.
Fig. 4 Impact of microplastics across the poultry food chain on human health.
The researchers found a favorable correlation between inflammatory bowel illness and microplastics found in feces. Either inflammatory bowel disease patients retain microplastics in their feces as a result of the condition, or the disease is caused by exposure to microplastics. Even though microplastics can damaging to humans’ health, additional experimental research is needed to confirm these impacts on the human's body (Thakur et al., 2022). Furthermore, they concluded that display to microplastics alters metabolic pathways and causes oxidative stress and neurotoxic reactions through research on biochemical biomarkers and metabolomic profiles. Lack of appropriate analytical instruments for the isolation, quantification, detection and characterization of microplastics particles. It has been reported that diesel exhaust-derived particulate matter smaller than 2.5 µm in size can enter cells, causing more production of reactive oxygen species (ROS) and inflammation, which in turn increases the risk of dying from cardiovascular, respiratory diseases and lung cancer. It is possible to evaluate the risk of microplastics on human health by drawing a connection between these results and smaller-sized microplastics (Vethaak and Legler, 2021).
Because of the harm that microplastic contamination does to organisms, the entire society is concerned about it. In the event of a long-term accumulation, the impact of microplastics on liver damage and fibrosis is still unknown. According to certain studies, even at low concentrations, 0.1 μm microplastic can cause injury to the liver by entering hepatocytes through circulation. Exposure to microplastics has the potential to cause DNA damage in the nucleus and mitochondria. This damage results in the translocation of a double-stranded DNA (dsDNA) fragment into the cytoplasm, which activates the DNA sensing adaptor stimulator of interferon genes (STING). The downstream cascade reaction was triggered by the activation of the cyclic GMP-AMP synthase (cGAS) / STING pathway. This resulted in the translocation of NFκB into the nucleus, where it elevated the production of pro-inflammatory cytokines and ultimately facilitated liver fibrosis (Fig. 5). Moreover, inhibiting STING could lessen liver fibrosis by preventing fibronectin production and NFκB translocation (Shen et al., 2022).
Fig. 5 Microplastic-induced liver fibrosis via the cGAS-STING pathway.
Because microplastics in poultry may have negative effects on human health, this is a developing concern. These minuscule particles can enter people's systems directly when they eat poultry that has been infected with microplastics. Thus, microplastics have the potential to cause chronic health problems in people by causing inflammation in the digestive system. Furthermore, certain microplastics could include substances that prevent the body from producing hormones. Furthermore, human exposure to microplastics may cause major health problems such as inflammatory bowel disease, respiratory conditions, and a variety of malignancies. Microplastics can carry hazardous substances or bacteria, which could contaminate chickens and then humans (Winiarska et al., 2024). Customers can pick organic or sustainably grown poultry to limit their exposure to microplastics; these techniques may lessen the risk of exposure.
The information that is currently available points to a disturbing connection, even if research on microplastics in poultry and their possible effects on human health is still in its early phases. The possibility that microplastics could build up in the human body and have harmful effects on health is raised by the discovery of microplastics in poultry products. By encouraging sustainable practices, minimizing plastic waste, and making educated food choices, customers can help to mitigate the problem. We may fight to protect the environment and human health by being aware of the possible threats and promoting responsible behavior.
It is imperative to recognize the obstacles and deficiencies in current understanding regarding the effects of microplastics on poultry products to propel this area of study forward and create practical solutions for mitigation. Among the major obstacles and areas of ignorance
These limitations underline the need for additional research to close the knowledge gaps regarding the potential impacts of microplastic pollution in poultry products on the health of humans and the environment, even though the study provides informative information. To improve our understanding of the effects of microplastics on poultry and human health, interdisciplinary research collaborations and the development of sophisticated detection tools are essential. These obstacles and information gaps must be addressed. Conducting thorough studies to assess the long-term effects of eating poultry contaminated with microplastics on environmental ecosystems and human health has to be a top priority for future research endeavors. Future research should closely monitor the levels of microplastic in poultry products and conduct comprehensive toxicological studies to elucidate the causes and effects of exposure. Stronger waste management practices to prevent the release of microplastics into the environment, encouraging the utilization of alternative feed resources, and imposing stringent regulations on the use of plastic additives in chicken feed are some suggestions for interventions to mitigate these consequences. The creation of educational initiatives and public awareness campaigns is also necessary to encourage sustainable consumer choices and raise knowledge of the risk of microplastic contamination. Prioritizing research projects that clarify the causes, toxicity, and long-term effects of microplastic pollution is crucial. Robust regulatory measures must also be developed to reduce hazards to the environment and public health.
Microplastic pollution, a significant environmental issue driven by human activity, results in millions of tons of waste annually. These plastic particles, less than 5 mm in size, have become widespread in terrestrial, freshwater, and marine ecosystems. Microplastics impact animal health, particularly in poultry, through ingestion, inhalation, and dermal contact. Exposure to microplastics can lead to stunted growth, compromised immune function, reduced fertility, and tissue damage in affected animals, posing a substantial risk to both environmental and animal health.
Microorganisms like fungi, bacteria, and algae can degrade microplastics through stages such as biodeterioration, bio-fragmentation, assimilation, and mineralization. Extracellular enzymes enhance biodegradation by promoting microbial growth and pollutant adhesion. However, concerns exist over harmful by-products formed during the degradation process. Microbial consortia can mitigate these effects by neutralizing by-products, but more research is needed for large-scale use. Reducing microplastic exposure also involves choosing sustainably raised poultry and conducting interdisciplinary research to understand microplastic contamination pathways in the food chain.
Data Availability Statement: No data are available.
All authors contributed equally to writing this review article. All authors read and approved the final version of this manuscript.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The authors extend their appreciation to the Deanship of Research and Graduate Studies at King Khalid University for funding this work through Large Research Project under grant number RGP2/289/45.