Food and human safety: the impact of microplastics

Abstract

Plastic waste pollution is one of the biggest problems in the world today. The amount of plastic in the environment continues to increase, and human exposure to microplastic (MP) has become a reality. This subject has attracted the attention of the whole world. The MP problem has also been noticed by the scientific community. The term microplastic is mostly used to define synthetic material with a high polymer content that can have a size range from 0.1 to 5000 µm. This paper aims to characterize the routes of exposure to MP, define its pollution sources, and identify food types contaminated with plastics. This review addresses the current state of knowledge on this type of particles, with particular emphasis on their influence on human health. Adverse effects of MP depend on routes and sources of exposure. The most common route of exposure is believed to be the gastrointestinal tract. Sources of MP include fish, shellfish, water as well as tea, beer, wine, energy drinks, soft drinks, milk, salt, sugar, honey, poultry meat, fruits, and vegetables. Studies have shown that particles of PET, PE, PP, PS, PVC, PA, and PC are the most frequently found in food.

Keywords:

• Polymer
• microplastic
• packaging
• microplastic exposure route
• human health risk

Introduction

Plastics are materials composed of polymers and additives such as fillers, plasticizers, pigments, stabilizers, flame retardants, anti-static, and foaming agents that improve physical and processing properties. In the beginning of 1950s, the production of plastic products has steadily increased (Novotna et al. 2019). In 2021, the plastics and rubber products’ market were worth approx. $1,229.98 billion. This market is expected to grow to $1357.49 billion in 2022 (+10.4%) and to $1923.6 billion in 2026 (+9.1% of each year) (“Plastics and rubber products global market report 2022” 2022).

Plastics can be found in all branches of life and economy. Goods made of this material show many positive features, such as lightness and durability – resistance to mechanical damage, corrosion, and weather conditions (Bott, Störmer, and Franz 2014). Unfortunately, the popularity of such products has also its negative consequences. One of the biggest problems of the modern world is plastic waste, the amount of which increased significantly during the COVID-19 pandemic (Shi 2021). In the EU, 80–85% of marine litter is plastics, of which 50% are single-use products (Yuan, Nag, and Cummins 2022).

Nearly 40% of global plastic production is used by packaging (Hirt and Body-Malapel 2020; Shlush and Davidovich-Pinhas 2022). Therefore, it is one of the main sources of microplastic (MP) (Koelmans et al. 2022; Lozano et al. 2021).

Microplastic is a synthetic material with a high polymer content (Jadhav et al. 2021). It characterizes with a size range from 0.1 to 5000 µm (Figure 1). However, due to technical limitations, detection at sizes smaller than 1 μm does not yet have adequate technical support. Therefore, the minimum size for MP recognition is currently considered to be 1 µm. Depending on the size, these materials are usually divided into small and large MPs. 50% of MPs in aquatic systems are between 500 and 1000 µm, 29.8% are between 1000 and 2500 µm, while 17.6% are between 2500 and 5000 µm. Large MPs in the marine environment decompose into smaller particles by mechanical action, photooxidation, and hydrolytic degradation (Batool et al. 2022; Liu, Xu, et al. 2022). The toxicity of MPs is related to their size, the smaller the size, the greater the predicted toxicity (Kwon et al. 2020; Yang, Man, et al. 2022).

Figure 1. Sizes of plastics.

This contaminant is ubiquitous in the environment, the air we breathe and in the food we eat. Various types of plastics can be found in food. The largest amounts of MP are made from the following polymers: poly(ethylene terephthalate) – PET (Oßmann et al. 2018; Schymanski et al. 2018), polyethylene – PE (Çobanoğlu et al. 2021; Wang et al. 2022), polypropylene – PP (Hwang et al. 2019), polystyrene – PS (Huang et al. 2022; Liu, Hou, et al. 2022), poly(vinyl chloride) – PVC (Qin et al. 2022), polyamide – PA (Deshoulles et al. 2022), and polycarbonate – PC (Shi et al. 2021) (Table 1).

Table 1. The properties of microplastic present in food.

Polymer type	Monomer	Health effectsmonomer	Sources	References
Polyethylene (PE)	Ethylene	Asphyxia	Shopping bags, wrap film	(Çobanoğlu et al. 2021; Wang et al. 2022)
Polypropylene (PP)	Propylene	Asphyxia	Bottle caps, reusable food containers, wrap film, insulation material, single-use face masks	(Hwang et al. 2019)
Poly(ethylene terephthalate) (PET)	Terephthalic acid	Irritating to eyes, respiratory system and skin	Bottles, textile fibers	(Oßmann et al. 2018; Schymanski et al. 2018)
	Ethylene glycol	Kidney damage
Poly(vinyl chloride) (PVC)	Vinyl chloride	Skin and respiratory irritation, eye hazard, liver damage, proven carcinogenic	Pipes, shoe soles, window frames	(Qin et al. 2022)
Polystyrene (PS)	Styrene	Skin and respiratory irritation, neurotoxic, possibly carcinogenic	Insulation boards (styrofoam)	(Huang et al. 2022; Liu, Wang, et al. 2022)
Polyamide (PA)	Adipic acid	Eye damage	Carpets, sportswear, textile	(Deshoulles et al. 2022)
Polycarbonate (PC)	Bisphenol A	Skin and respiratory irritation, hazardous to eyes, burns, cardiovascular damage, arrhythmia, hypotension, damages kidneys and liver, causes blood hemolysis, coma, convulsions and spasms	Construction materials, roofs of greenhouses, CD, DVD, glasses lens, reusable bottles	(Shi et al. 2021)

Microplastic is a health problem, raising ecological, and food safety concerns (Lee and Fang 2022). It attracts the attention of the whole world: authorities, public opinion, media, as well as ecological and non-governmental organizations (Yuan, Nag, and Cummins 2022). This problem has also been noticed by the scientific community (Sridhar et al. 2022). The number of papers dealing with MP has increased more than 100-fold over the last ten years (Figure 2). There is also a growing awareness of the problem and number of questions that the scientific community is trying to answer. A key question with respect to MP is to what extent and in what way does it cause risk to human health? This article will attempt to answer this question. This paper aims to characterize the routes of exposure to MP, define its pollution sources, and identify food types contaminated with this material.

Figure 2. The number of articles concerning microplastic from 2012 to 2021 (based on source: ScienceDirect).

Methods

The analysis of the current state of knowledge was based on studies on MPs published in international databases: ScienceDirect, PubMed, and Scopus. The databases were filtered by search terms in title, abstract, and keywords with the following expressions: microplastic and food. The most relevant literature sources were included in this review. Priority was given to articles published during the last three years. Over 190 studies on microplastic were reviewed.

Classification

Until recently, MP analysis has focused on aquatic environments, primarily the living organisms. However, these contaminants are also considered an emerging threat to terrestrial ecosystems. Many food products of different origins can be contaminated with MP. The derivation, size, shape as well as polymer type (Table 1), and concentration are key properties when studying the effects of these types of particles on the aquatic and terrestrial environment (Lozano et al. 2021).

Primary and secondary microplastics

Microplastics can be classified according to their origin, and there can be distinguished primary and secondary types (Kwon et al. 2020; Yang, Man, et al. 2022).

Primary MPs are particles of manufactured products, such as personal hygiene. They can be residues of toothpaste, hair gel, cleansing lotion, and particulate air fresheners. They usually enter the environment with discharged domestic wastewater (Anagnosti et al. 2021; Hwang et al. 2020; Xu et al. 2022). Investigations of MP presence in toothpaste resulted in findings of PP, PVC, and PA particles within 100 and 399 μm. Irregularly shaped microparticles – fragmentary – were the most abundant and accounted for 63–98% of all MPs, followed by fibrous particles in an amount of 2–35% (Madhumitha et al. 2022).

Secondary MPs are the unintentional debris of plastic degradation. They are obtained from “meso (5–25 mm)” and “macro (>25 mm)” plastic waste by physical, chemical, and biological processes (Olewnik-Kruszkowska et al. 2020; Olewnik-Kruszkowska, Nowaczyk, and Kadac 2016, 2017). Plastic waste undergoes several processes but the photodegradation was found to be the most common route of MPs formation (Periyasamy and Tehrani-Bagha 2022; Xi et al. 2022). Their main sources besides plastic waste fragments (e.g. packaging) are paints removed from various types of plastic products and fibers from fishing equipment and textiles (Muthu 2021).

Shape

Microplastics can be found in different forms. Their categorization is enabled by the size and color sorting system (SCS), which is used to characterize these particles according to their appearance (Crawford and Quinn 2017). There are ten shape categories in the SCS system (Table 2). Some authors suggest further categorization of MPs shapes as spheres, cylindrical, disc-shaped, flat, egg-shaped, elongated, and rounded particles (Toussaint et al. 2019). Their shapes are influenced by the following factors: initial form of the material, time strictly affecting the degradation processes of a material and the conditions/environment in which the material is located (Kwon et al. 2020; Yang, Man, et al. 2022).

Table 2. The categorization of MP based on shape.

Shape name	Abbreviation	Size
Pellet	PT	5–1 mm
Microbead	MBD	1–1 µm
Fragment	FR	5–1 mm
Microfragment	MFR	1–1 µm
Fiber	FB	5–1 mm
Microfibre	MFB	1–1 µm
Film	FI	5–1 mm
Microfilm	MFI	1–1 µm
Foam	FM	5–1 mm
Microfoam	MFM	1–1 µm

Color

The SCS assumes that each MP particle must be assigned a color (Crawford and Quinn 2017) but combinations of colors are allowed (Table 3).

Color is an important factor affecting aquatic organisms. Microplastics found in surface seawater samples and in sediments are usually colorless or white, while multicolored and black ones are less common. Due to the similarity in color, animals may mistake their natural food for MP and ingest it, for example, fish often eat white and transparent plastic fibers. This is the way, MP can enter the food chain and be ingested by humans (Kwon et al. 2020; Yang, Man, et al. 2022).

Table 3. The categorization of MP based on color.

Color	Abbreviation
Any color	ALL
All opaque	AO
All transparent	AT
Amber	AM
Beige	BG
Black	BK
Blue	BL
Brown	BN
Bronze	BZ
Charcoal	CH
Clear	CL
Dark	DK
Gold	GD
Green	GN
Grey	GY
Ivory	IV
Light	LT
Metallic	MT
Olive	OL
Opaque	OP
Orange	OR
Pink	PK
Purple	PR
Red	RD
Silver	SV
Speckled	SP
Tan	TN
Transparent	TP
Turquoise	TQ
Violet	VT
White	WT
Yellow	YL

Routes of exposure to microplastics

The effects of MPs on the human body depend on the routes of exposure. Exposure can occur through the inhalation, the skin contacts and the mucous membrane covering the eye surfaces, or the ingestion of contaminated food (Celebi Sö et al. 2020; Hwang et al. 2020; Yang, Man, et al. 2022).

The inhalation

Airborne MPs can be found around the world (Ebrahimi et al. 2022). Their concentration is known to increase in areas with high population and human activity, especially indoors. Working conditions are also important in the context of respiratory exposure to them. Microplastic deposition and accumulation were confirmed in human lung tissue. The largest number of particles was discovered in the lower part of the lung versus the upper and mid parts. There were identified 12 polymer types in 11 of 13 human lung tissue samples, with the most abundant PP (23%) and PET (18%) (Jenner et al. 2022). It was found that MP may cause respiratory diseases (Jenner et al. 2022; Kumar et al. 2022; Prata 2018). It caused airway and interstitial inflammatory reactions as well as dyspnea (Prata 2018).

The contact by the skin and the mucous membrane of eye

Dermal absorption of MPs may occur through the use of personal care products, and even direct contact with them (e.g. PS) can damage the skin (Hwang et al. 2020).

The mucous membrane covering the eye surfaces is also exposed to MPs from hygiene products. After 48 h of exposure to polystyrene particles on the eye surface of mice resulted in oxidative stress, decreased cell viability, and apoptosis. After 4 weeks, MPs’ (2 µm) deposition was found in the conjunctival sac, and the number of goblet cells in the conjunctival sac of the lower eyelid decreased up to 40% compared to the cells in the control group. In addition, so-called dry eye, ocular surface damage, and conjunctivitis and lacrimal glands were observed (Zhou et al. 2022).

The ingestion of contaminated food

The most common route of exposure to MPs is believed to be through the gastrointestinal tract. They can be ingested involuntarily. It was estimated that people worldwide may consume 0.1–5 g of these particles per week (Senathirajah et al. 2021). After oral exposure to MP, dangerous substances (e.g. polycyclic aromatic hydrocarbon – PAH and polychlorinated biphenyl – PCB) can appear in the gastrointestinal tract (Kumar et al. 2022).

Some MP is excreted from the human body with feces (Luqman et al. 2021; Schwabl et al. 2019; Zhang et al. 2021). Poly(ethylene terephthalate) was the most often identified in these samples. Fecal examinations confirmed that the concentration of PET in infant feces was 10 times higher than in adult samples. Particularly disturbing is the information that MP was also detected in meconium samples (Zhang et al. 2021). As MP was discovered in human feces, it is believed that it can directly affect the microbiota (Lu et al. 2019).

Sources of microplastic

Microplastics constitute the serious problem of global concern. These particles are omnipresent in aquatic and terrestrial environments. Their sources can be everyday objects and contaminated food.

Environment

Considering the problem of MP food contamination is not possible without referring to environmental pollution. Their accumulation has been confirmed in deep seas and oceans, surface and groundwater, soils, coastal sediments, Arctic snow and Antarctic ice, and beaches. Studies on MPs spreading point to wastewater treatment plants as a common source from which they can enter natural waters, groundwater, or terrestrial ecosystems (Zurier and Goddard 2021).

Water reservoirs

The vast majority of marine pollution comes from land, that is, 4.8–12.7 million tons of plastic per year (Haward 2018). It has been found that over 250 000 tons of MP may be floating in the oceans. However, plastic particles concentrations tend to decrease gradually with distance from industrial sources. Their higher amounts are found in urbanized regions with high population density (Talbot and Chang 2022). It is likely that MPs ingested by humans originate from these locations (Kwon et al. 2020; Yang, Man, et al. 2022).

Soil

Microplastics are also found in soil environments (Ren et al. 2022; Tian et al. 2022; Zhang, Kim, et al. 2022). They may affect soil biota including microorganisms (e.g. Proteobacteria). Plastic particles impact the soil bacterial phylogenetic profile (Fajardo et al. 2022). It was found that MP can be transferred from soil to plants and then from plant food to humans (Shi 2021).

Insects

Microplastics can be also carried by organisms, for example, honey bees. The presence of MP attached to the body of bees has been reported. Thirteen synthetic polymers were detected, of which polyesters were the most common, followed by PE and PVC (Edo et al. 2021). Exposure to PS reduced the diversity of bee gut microflora, changed gene expression, was associated with oxidative damage, and detoxification (al Naggar et al. 2021). Microplastic was found in 12% of the honey samples tested (Diaz-Basantes, Conesa, and Fullana 2020; Al Naggar et al. 2021). It was concluded that synthetic particles can be brought into the hive by bees during nectar collection (Liebezeit and Liebezeit 2015; Nowak and Nowak 2021).

Households

Microplastics are ubiquitous not only in environments, but also in households. Nowadays, fabrics, household appliances, disposable or reusable food containers, bottles, jars, cups, caps, and other packaging made of plastic are used intensively. Such objects are usually made of PET, PP, PVC, PS, high-density polyethylene (HDPE), and low-density polyethylene (LDPE) (Geueke, Groh, and Muncke 2018; Hahladakis et al. 2018; Hahladakis and Iacovidou 2018; Lozano et al. 2021).

Packaging

The popularity of plastic packaging has led researchers to analyze their effects on human health in terms of MP release from various types of food containers (Jadhav et al. 2021). Takeaway containers made from popular polymer materials (PP, PS, PE, and PET) were subjected to investigation (Du, Cai, et al. 2020). Microplastics originated from all the analyzed products, and their quantity ranged from 3 to 29 pieces/container. The highest density was found in PS containers with rough surfaces which easily chipped under the influence of low mechanical force. Therefore, the production of PS-based packaging for food and beverage has been restricted by a decision of the European Parliament in 2021 (Du, Cai, et al. 2020).

Microplastic can enter children’s bodies through pacifiers, toys, contaminated food, and by crawling on carpets and floors made of plastic. One of the primary sources of MP for children is plastic bottles. The release of these contaminants from baby bottles was analyzed (Li et al. 2020). These containers were pre-cleaned and sterilized. After drying under natural conditions, water at 70 °C was poured into the bottles. The average number of MPs per liter of water amounted to 4 million while the maximum was 16.2 million (Li et al. 2020).

Food preparation, cooking, and processing

Microplastics can be introduced into food chain during food preparation, cooking, and processing. It has been estimated that 100–300 MPs/mm are formed on a plastic cutting board during food preparation (Luo et al. 2022). Plastic particles can be also released from the surface of food containers when exposed to microwave or oven heating (Marazuela et al. 2022). The effect of heat treatment of disposable plastic materials on the release of MPs in an aqueous environment was investigated. It was found that soaking in water at approximately 100 °C released 1.07, 1.44, 2.24, and 1.57 million particles/ml from plastic packaging, cups, transparent boxes, and expandable boxes, respectively (Liu, Wang, et al. 2022).

Food with microplastic

Microplastics constitute a potential threat to human health due to their widespread presence in foods we eat. The most common plastic particles found in food are blue-colored and fiber-shaped (Bai et al. 2022).

Sources of MPs for humans can be beverages and foods such as water (Koelmans et al. 2019; Kosuth, Mason, and Wattenberg 2018; Schymanski et al. 2018; Shruti, Pérez-Guevara, and Kutralam-Muniasamy 2020; Vega-Herrera et al. 2022; Wiesheu et al. 2016), tea (Afrin, Rahman, Akbor, et al. 2022; Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020), beer (Diaz-Basantes, Conesa, and Fullana 2020; Kosuth, Mason, and Wattenberg 2018; Lachenmeieret al. 2015; Liebezeit and Liebezeit 2014; Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020; Shruti et al. 2021), wine (Prata et al. 2020), energy drinks (Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020), soft drinks (Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020), animal products, including fish (Karami, Golieskardi, Bin Ho, et al. 2017; Karami et al. 2018; Karthik et al. 2018; O’Connor et al. 2022; Pan et al. 2022; Peters et al. 2018), shellfish (Chinfak et al. 2021; Daniel et al. 2021; Ding et al. 2020; Fernández Severini et al. 2020; Li et al. 2015; Pan et al. 2022), salt (Gündoğdu 2018; Iñiguez, Conesa, and Fullana 2017; Karami, Golieskardi, Choo, et al. 2017; Kosuth, Mason, and Wattenberg 2018; Manimozhi et al. 2022; Yang et al. 2015), sugar (Afrin, Rahman, Hossain, et al. 2022; Liebezeit and Liebezeit 2013) and honey (Liebezeit and Liebezeit 2013), milk (Kutralam-Muniasamy et al. 2020), poultry meat (Kedzierski et al. 2020), plants, including fruits, and vegetables (Oliveri Conti et al. 2020) (Table 4). This chapter will present, in the authors’ opinion, the most interesting examples of foods in which MP is found.

Table 4. Microplastic in food.

Food	Polymer	Size	Quantity/Concentration	Shape	References
Beverages
Water	PE≈PP > PS > PVC > PET	–	1 × 10^-2–108 MPs/m^3	Fragments, fibers, films, foams	(Koelmans et al. 2019)
	–	100–5000 µm	0–61 MPs/dm^3	Fibers	(Schymanski et al. 2018)
	PET, PP, PE, PA	1–500 µm	0–253 MPs/dm^3	Fragments	(Kosuth, Mason, and Wattenberg 2018)
	PBD	7–20 µm	1897 ng/dm^3	–	(Vega-Herrera et al. 2022)
	PI		9143 ng/dm^3
	PET, epoxy resin	100–1000 µm	5 ± 2 to 91 ± 14 MP/dm^3	Fibers	(Shruti, Pérez-Guevara, Kutralam-Muniasamy 2020b)
	Cellulose	–	–	Fibers	(Wiesheu et al. 2016)
Tea	PTFE, PE, PC, PVC, EVA, ABS, cellulose acetate	200.6–220.7 μm	10.9 million grams of MPs/year	Fragments, fibers	(Afrin, Rahman, Akbor, et al. 2022)
	PA, PEA	100–2000 µm	1–6 MPs/dm^3 100% samples	Fibers	(Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020)
Beer	–	100–5000 µm	0–14.3 MPs/kg	Fibers, fragments	(Kosuth, Mason, and Wattenberg 2018)
	–	–	2–79 MPs/dm^3	Fibers	(Liebezeit and Liebezeit 2014)
	–	–	12–109 MPs/dm^3	Fragments
	–	–	2–66 MPs/dm^3	Granules
	PA, PET, PEA	100–3000 µm	0–28 MPs/dm^3 88.9% samples	Fragments, fibers	(Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020)
	–-	–	16 ± 15 MPs/dm^3	Fibers	(Lachenmeier et al. 2015)
			21 ± 16 MPs/dm^3	Fragments
			27 ± 10 MPs/dm^3	Granules
	PE, PS, cellulose	1–5000 µm	10–19 MPs/dm^3	Fibers	(Wiesheu et al. 2016)
	PE, PP, PAM	13.45–1740.24 µm	12–98 MPs/dm^3	Fibers	(Diaz-Basantes, Conesa, and Fullana et al. 2020)
		3.505–202.29 µm	50–920 MPs/dm^3	Fragments
White wine	PE	7–475 µm	< 5857 MPs/dm^3	Fragments, fibers	(Prata et al. 2020)
Energy drinks, soft drinks	PA, ABS, PEA	100–3000 µm	0–7 MPs/dm^3	Fibers	(Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020)
Fish and shellfish
Fish	PP > PE > PS > PET > Nylon-6	–	–	Fragments, filaments, films	(Karami, Golieskardi, Bin Ho, et al. 2017)
	–	–	2.15 × 10⁻ ^8 g MPs/g biota	–	(O’Connor et al. 2022)
	–	–	6.54 × 10⁻ ^8 g MPs/g biota	–
	PP, PET	190–3800 µm	0–3 MPs/brand	Fragments, filaments, films	(Karami et al. 2018)
	–	–	10.1% fishes	Fragments	(Karthik et al. 2018)
	PVC, PET, nylon, silicone, epoxy resin	–	–	Fibers, fragments, spheres	(Peters et al. 2018)
	PS, PSU	< 1000 µm	1.98 ± 1.98 MPs/individual	Fibers	(Pan et al. 2022)
Shellfish	PE, PET, PA	5–5000 µm	4.3–57.2 MPs/individual	Fibers, fragments, pellets	(Li et al. 2015)
	PSU, PET	< 1000 µm	1.88 ± 1.44 MPs/individual	Fibers	(Pan et al. 2022)
	PP, PE, PS	100–200 µm	0.07 ± 0.3 MPs/individual 2.7 ± 12 MPs/kg	Fragments	(Daniel et al. 2021)
	PE, PP, cellulose	–	1.31 MPs/g	Fibers	(Fernández Severini et al. 2020)
	Rayon, PE, PP, PET, nylon	< 1000 µm	–	Fibers	(Chinfak et al. 2021)
	Rayon	100–200 µm	1.2–6.0 MPs/individual 0.8–4.4 MPs/g	Fibers	(Ding et al. 2020)
Spices
Salt	PET, PE, cellophane	<200 µm	7–681 MPs/kg	Fibers, fragments, pellets, sheets	(Yang et al. 2015)
	PE, PP	>149 µm	1–10 MPs/kg	Fragments, filaments, films	(Karami, Golieskardi, Choo, 2017)
	PET, PE, PP	10–3500 µm	50–280 MPs/kg	Fibers	(Iñiguez et al. 2017)
	PE, PP	20–5000 µm	8–102 MPs/kg	Fibers, fragments, films	(Gündoğdu, 2018)
	–	100–5000 µm	46.7–806 MPs/kg	Fibers	(Kosuth, Mason, and Wattenberg 2018
	PE, PP	< 500 µm	42 MPs/l	Fragment, irregular particles	(Manimozhi et al. 2022)
Sugar	–	> 40 µm	217 ± 123 MPs/kg	Fibers	(Liebezeit and Liebezeit 2013)
	ABS, PVC	< 300 μm	343.7 ± 32.08 MPs/kg	Fibers, spherules	(Afrin, Rahman, Akbor, et al. 2022)
Food from terrestrial animals
Honey	–	> 40 µm		Fibers	(Liebezeit and Liebezeit, 2013)
Milk	PES, PSU	< 500 µm	1–14 MPs/dm^3	Fibers	(Kutralam-Muniasamy et al. 2020)
Poultry meat	PS	–	4.0–18.7 MP-XPS/kg	Fibers	(Kedzierski et al. 2020)
Plants
Apple	–	1.56–3.19 µm	52600–307750 MPs/g	–	(Oliveri Conti et al. 2020)
Pear		1.87–2.59 µm	98325–302250 MPs/g
Carrot		1.36–2.00 µm	72175–130500 MPs/g
Broccoli		1.86–2.95 µm	65025–201750 MPs/g
Lettuce		2.18–2.78 µm	26375–75425 MPs/g

Abbreviations: ABS: poly(acrylonitrile-butadiene-styrene); EVA: poly(ethylene-vinyl acetate); PE: polyethylene; PP: polypropylene; PS: polystyrene; PVC: poly(vinyl chloride); PET: poly(ethylene terephthalate); PA: polyamide; PBD: polybutadiene; PI: polyisoprene; PTFE: poly(tetrafluoroethylene); PC: polycarbonate; PEA: poly(ester amide); PAM: polyacrylamide; PSU: polysulfone; PES: polyethersulfone.

Beverages

The largest amount of research that links MP and food topics relates to beverages, in particular water. Microplastics were detected in both bottled (Oßmann et al. 2018; Schymanski et al. 2018) and tap water (Novotna et al. 2019). Plastic microparticles were present in water in the form of fragments and fibers.

Mineral water in PET bottles constitutes an example of the increase of human exposure to MPs. It was found that disposable PET bottles were characterized with MPs concentrations ranging from 0.1 to 1.8 μg/dm³, while for reusable bottles these values increased several times up to 0.6–7.3 μg/dm³ (Oßmann et al. 2018; Schymanski et al. 2018). Therefore, significant amounts of plastic particles were released by food and beverage containers as a result of peeling of their inner surface during washing (both with hot water − 95 °C, and with cold water – with ice added). These treatments were reported to result in the formation of MPs in an average amount of 176 particles/dm³ (Hee, Weston, and Suratman 2022).

Microplastic was also confirmed in water from households (Vega-Herrera et al. 2022) and public places (Shruti, Pérez-Guevara, and Kutralam-Muniasamy 2020). Tap water samples from around the world were tested and 81% of them were contaminated. The average concentration was 5.45 particles/dm³ (Kosuth, Mason, and Wattenberg 2018). In the case of tap water from China, the lowest measured MP count was 440 particles/l. Most of the particles were PE and PP, which were smaller than 50 μm (Tong et al. 2020). The household tap water of the Barcelona Metropolitan Area was also contaminated with PE and PP. These particles had a size of 7–20 μm (Vega-Herrera et al. 2022). In addition, the presence of MP has been confirmed in free public drinking water fountains. Microplastics were detected in all the drinking water samples (42), with an average amounting to 18 MP/dm³. Transparent (69%), blue (24%), and red (7%) fibers, mainly made of PET and epoxy resin, were identified. Most particles had dimensions between 0.1 and 1 mm (Shruti, Pérez-Guevara, and Kutralam-Muniasamy 2020).

The researches on MP content in water are particularly important because it is the basis for many beverages, for example, tea, energy drinks, soft drinks and alcohol. Contaminated water negatively affects their quality, but product packaging is also important. Plastic particles were found to leach from the tea bags. Using electron microscopy, it was stated that a single brewed tea bag releases about 11.6 billion MPs into the water (Hernandez et al. 2019). The same effect was observed after the consumption of hot drinks, such as tea and coffee, from disposable cups (Ranjan, Joseph, and Goel 2021).

Microplastics are present in alcohol, for example, in beer or wine. There are many reports of MP in beer (Diaz-Basantes, Conesa, and Fullana 2020; Lachenmeieret al. 2015; Liebezeit and Liebezeit 2014; Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020; Shruti et al. 2021; Wiesheu et al. 2016) but only one article about the presence of plastic in wine (Prata et al. 2020). In the first case, PE and PET were the most popular, while in the second case PE was the most common. In both cases, these particles were usually fiber-shaped (Diaz-Basantes, Conesa, and Fullana 2020; Kosuth, Mason, and Wattenberg 2018; Lachenmeier et al. 2015; Liebezeit and Liebezeit 2014; Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020; Shruti et al. 2021).

There are also reports of MP being present in other popular beverages, such as energy drinks and soft drinks. Plastic, in the form of fibers, was found in almost 80% of the samples tested, for example, PA, poly(acrylonitrile-butadiene-styrene) – ABS, poly(ester amide) – PEA (Shruti, Pérez-Guevara, Elizalde-Martínez, et al. 2020). These particles originated from textiles and packaging.

Based on the collected data it can be concluded that PE, in the form of fibers, is the most common beverage contaminant.

Fish and shellfish

Microplastics are ubiquitous pollutants of aquatic ecosystems and are reported to interact with a wide range of aquatic organisms. Fish and shellfish constitute the popular food matrix in which MP can be found (Gao et al. 2022; Gündogdu et al. 2022; O’Connor et al. 2022).

In Ireland, it is estimated that 73% of deep-sea fish ingest plastic (Eriksen et al. 2014). Fragments of PET are the most commonly found in fish. This situation is a particular problem for commercially important species due to the reduction in yields and resulting in economic losses. Fish accumulate plastic particles in their gut (Bouwmeester, Hollman, and Peters 2015), which is not generally consumed. Therefore, MP found in fish gut cannot be considered a direct threat to human health (Pan et al. 2022). However, plastic particles are able to enter the food chain at higher trophic levels as inedible parts of fish can be used as animal feed ingredients (Bouwmeester, Hollman, and Peters 2015).

A different situation is observed for shellfish. Polyethylene and poly(ethylene terephthalate) microparticles in the form of fibers were the most popular plastic contaminants in these animals (Chinfak et al. 2021; Daniel et al. 2021; Li et al. 2015; Pan et al. 2022). Microplastic was found in bivalves, squids and shrimps, which are filter feeders (Daniel et al. 2021; Li et al. 2015). Bivalve mollusks directly transfer MP to higher trophic levels, because their digestive tract is usually eaten (Farrell and Nelson 2013; Fernández Severini et al. 2020).

Fish and shellfish are consumed globally. However, there are animal species that are consumed regionally, that is, the sea cucumber (Apostichopus japonicus). It is commercially fished or farmed and subsequently consumed in Asian cuisines. The presence of plastic particles in the edible parts of sea cucumber has been confirmed. Microplastic quantity decreased when the analyzed organisms were transferred to clean water. However, trace amounts of MP in their bodies were found for many days after transfer (Mohsen et al. 2022).

Spices

Spices, in particular salt and sugar, can also be a popular source of MP for human. The occurrence of MPs in salt products of various types, for example, commercial brands of table salt, rock salt, and laboratory NaCl was investigated. MP content ranged from 11 to 193, 64, and 253 pcs/kg, respectively. PE in fiber form in such products was most common (Kapukotuwa et al. 2022).

Moreover, sugar from both Europe and Asia were contaminated mostly with MP fibers. However, particles separated from samples from Germany were smaller than the ones from Bangladesh, that is, > 40 μm (Liebezeit and Liebezeit 2013) and <300 μm, respectively (Afrin, Rahman, Hossain, et al. 2022). Poly(acrylonitrile-butadiene-styrene) and poly(vinyl chloride) were most common in European sugar (Liebezeit and Liebezeit 2013). Plastic particles in Asian honey were not identified structurally (Afrin, Rahman, Hossain, et al. 2022).

Food from terrestrial animals

The common group of foods are products derived from terrestrial animals. These can be products made by animals (e.g. honey and milk) as well as animal tissues or organs.

The occurrence of MP in honey and milk was confirmed. In the first case, the plastic particles were of environmental origin, and in the second case, of technological origin. Plastic fibers of a size greater than 40 µm, most likely carried by bees with pollen, were found in honey. This pollution was at a level of 166 MPs/kg (Liebezeit and Liebezeit 2013). In contrast, milk contained particles, mainly polyethersulfone (PES) and polysulfone (PSU) in the form fibers, up to 500 µm. Microplastic contamination of milk resulted from the technological processing, because PES and PSU are commonly used as membrane materials in dairy processes (Kutralam-Muniasamy et al. 2020).

In addition, MP particles can be found in poultry meat. Packaged meat was contaminated in the range from 4.0 to 18.7 MP/kg. Particles were in the form of fibers and were difficult to remove by rinsing. These were PS particles that most likely originated from the packaging (Kedzierski et al. 2020).

In summary, MP contamination in foods of animal origin was the result of the environment contamination as well as technological processing. Microplastic transmission within the animal body was not considered as a possible cause of contamination. This topic is important because MP can transmit to organs (Lu et al. 2018). Unfortunately, the presence of MP in offal has not yet been described.

Plants

Microplastic can penetrate the seeds, roots, culms, leaves and fruits (Dietz and Herth 2011). It can affect the plant growth, development and functioning, including the germination, inhibit roots and leaves growth, the tissue composition (Fajardo et al. 2022). Microplastic impact differs depending on plant species and polymer types (Rillig et al. 2019), and its uptake is inversely proportional to the size (Bosker et al. 2019).

The effect of particles’ shape on plant biomass was investigated. Microplastic in fiber forms increased plant biomass because these particles hold water in the soil. Foams and fragments increased soil aeration and macroporosity, while films decreased soil bulk density (Lozano et al. 2021). Microplastic was able to transfer from plant roots to leaves (Shi 2021). It was found that particles can penetrate rice roots and move to aboveground parts. Plastic accumulation was confirmed in the vascular systems of plant tissues, especially in vascular bundles and leaf veins, and in cell walls and intercellular areas (Liu, Guo, et al. 2022). In addition, MP contamination of agroecosystems reduces food yields (Tian et al. 2022), for example, as a result of PS exposure a reduction in pea (Pisum sativum) yield of more than 30% was observed (Kim et al. 2022).

Microplastic was also detected in fruits and vegetables of edible plants with apples (Malus domestica) and carrots (Daucus carota) as the most polluted. The lettuce (Lactuca sativa) was the least polluted. The plastic particles in fruits and vegetables had 1.56–3.19 µm and 1.36–2.95 µm in size, respectively (Oliveri Conti et al. 2020). It can be concluded that fruits are characterized with a higher MP contamination compared to vegetables. It might be due to the submitted root system, the big vascularization of the pulp, and the tree age (Oliveri Conti et al. 2020). In another research, the accumulation of PE in broccoli and radish sprouts was confirmed. Radish was more affected by MP contamination than broccoli (López et al. 2022).

The effect of polymethylmethacrylate (PMMA) on rapeseed (Brassia campestris L.) was also evaluated, and inhibition of germination rate was observed (Dong et al. 2022). Based on the confirmed MP effects on rapeseed, it is reasonable to investigate the plastic particles content in cooking oil. Attention should be paid to the widespread consumption of rapeseed oil. Unfortunately, such researches are not currently available.

Other

According to Amiri et al. (2022) the route of exposure to MP may be through the gastrointestinal tract, but the source need not be food. Increased exposure to plastic particles has been observed in individuals suffering from geophagy, an eating disorder that involves intentional soil consumption or similar materials. Soil from Hormoz Island (Iran) was found to contain PET, PA, PS, and PP fibers. This is particularly disturbing as it is used to prepare traditional spices, extremely popular in this region, the use of which is both culinary and cultural (Amiri et al. 2022).

Health impacts

Microplastic can exhibit different types and degrees of toxicity (Lithner, Larsson, and Dave 2011), which depends on the properties of the polymers (and individual mers), the sizes of particles, and shapes (Santana, Moreira, and Turra 2017). Current scientific evidence confirmed that MP concentration, exposure time, the presence of additives used during plastic processing, modification of the particle surface and hydrophobicity are also important (Guerrera et al. 2021).

Poly(vinyl chloride), polystyrene, polyacrylonitrile (PAN), poly(acrylonitrile-co-butadiene-co-styrene) (ABS), and epoxy resin are classified as the most toxic polymers based on monomer toxicity (Yuan, Nag, and Cummins 2022). Greater histological abnormalities have been found in freshwater mussels due to exposure to PVC and PS, compared to PET and PE (Rochman et al. 2017). Monomers, such as vinyl chloride, styrene and chemicals derived from phenolic compounds, for example, alkylphenols, brominated flame retardants, and bisphenol A, are known toxicants. The presence of these substances should be one of the main purposes of MP toxicity evaluation (Kwon et al. 2020; Yang, Man, et al. 2022).

Microplastic can cause acute and chronic toxicity. The toxic effects of MP include: developmental, reproductive and locomotor toxicity, neurotoxicity, immunotoxicity, genotoxicity, and cytotoxicity (Bhagat et al. 2020). The increase in antioxidant defense after exposure to MP indicates that oxidative stress is induced (Du, Xu, et al. 2020; Tagorti and Kaya 2022).

The health effects of MPs depend on their location in the body (Table 5) (Kwon et al. 2020; Yang, Man, et al. 2022). Microplastics have been found inside organisms, on skin and in hair, saliva, and fecal samples (Ebrahimi et al. 2022). Plastic particles can affect human health both indirectly and directly (Kwon et al. 2020; Yang, Man, et al. 2022).

Table 5. Health effects of microplastic.

Organism	Body part/system	MP		Health effects	References
		Type	Size
Scleractinian coral	Immune system	PS	1 μm	The decrease in the immune enzyme (e.g., alkaline phosphatase)	(Tang et al. 2018)
Zebrafish larvae	Bones	PE	20–27 μm	Increase of incidence of skeletal deformities, developmental disorder of caudal fin/scales	(Tarasco et al. 2022)
	Gut			Decrease of goblet cells, enteritis
	Column and tail	PS	10 μm	Body deformation	(de Marco et al. 2022)
	Eyes			Damage of integrity of the visual structure
Zebrafish	Gut	PP	50 ± 26 μm and 200 ± 90 μm	Gut damage, inflammation	(Zhao et al. 2021)
	Gut	PS	5 μm	Gut damage, inflammation, changes in the gut microbiome and tissue metabolic profiles	(Qiao et al. 2019b)
	Gut	PS	0.5 μm	The increase of the volume of mucus, the change in the diversity of microbiota	(Jin et al. 2018)
			50 μm	The increase of the volume of mucus, the change in the diversity of microbiota, inflammation
	Heart	PS	3–12 µm	Decrease of heart frequency of ventricular contraction	(Dimitriadi et al. 2021)
Mice	Raw 264.7 cells (macrophage cells)	PP	20 μm	Cytotoxic effects	(Hwang et al. 2019)
	Raw 264.7 cells (macrophage cells)	PET	191.6 (± 0.9) nm	Inhibition of lysosomal activities, reduction of cellular viability	(Deng et al. 2022)
			1.85 (± 1.02) μm	Proinflammatory response, reduction of cellular viability
	GC-2 cells (spermatocytes)	PS	5 µm	Mitochondrial damage, damage of the mitochondrial genome integrity	(Liu et al. 2022)
	Bone marrow cells	PS	5 µm	Decrease of white blood cell count, hematotoxicity, change of gene expression in bone marrow cells, disturbances in T cell homeostasis pathway, jak/stat pathway and metabolic pathway	(Sun, Xu, et al. 2021)
	Microglial cells of the brain	PS	0.2 and 2 μm	Accumulation in microglial	(Kwon et al. 2022)
	Kidney	PS	0.3 and 0.6 and 4 µm	Histological damage of the kidney, inflammation	(Meng et al. 2022)
Mice	Kidney	PS	2 µm	The histopathological lesions, the higher levels of endoplasmic reticulum stress, inflammatory markers and autophagy-related proteins	(Wang, Lee, et al. 2021)
	Spleen	PMMA	1.4 and 4.6 µm	Spleen enlargement	(Tomazic-Jezic Merritt, and Umbreit 2001)
	Ovaries	PS	0.7918 ± 0.00273 µm	The inflammation of ovaries, induction of inflammation and oxidative stress, the increase of the IL-6 level, the decrease of malondialdehyde (MDA) level, the reduce of the number of antral follicles, the reduction of the quality of oocytes	(Liu et al. 2022)
	Liver	PP	5 µm	The damage of liver structure and function, pyroptosis and ferroptosis, inflammation	(Mu et al. 2022)
	Guts	PE	10–20 µm	Amendments of gut microbiota	(Zaheer et al. 2022)
	Lungs	PS	5 µm	The pulmonary fibrosis	(Li, Zhang, et al. 2022)
Sheep	Red blood cells	PS	< 5 µm	Hemolytic effects	(Hwang et al. 2020)
			6–8 µm	Cytotoxicity
Human	Serum albumin	PVC	5 μm	The destruction of the construction and function of proteins	(Ju et al. 2020)
	Peripheral blood lymphocytes	PE	10–45 µm	Genotoxic effects	(Çobanoğlu et al. 2021)
	Peripheral blood mononuclear cells	PP	20 μm	Cytotoxic effects	(Hwang et al. 2019)
	Microglial HMC-3 cells (macrophage cells)	PS	0.2 and 2 μm	Changes in cellular morphology and immune responses, apoptosis	(W. Kwon et al. 2022)
	Intestinal epithelial Caco-2	PS	0.1 μm	Inhibition of ABC transporter	( Wu et al. 2019)
			5 μm	Mitochondrial depolarization
	Intestinal epithelial Caco-2	PE	6.2 ± 2.0 and 30.5 ± 10.5 μm	Reduction of cell viability	(Gautam et al. 2022)
	Lung epithelial A549 cells
	HaCaT keratinocyte cells (epidermis)			Pro-inflammatory effects
Human	Small intestinal epithelial cell HIEC-6	PS	0.1 and 0.5 and 1.5 μm	The membrane damage	(Zhang et al. 2022)
	Colonic epithelial cell CCD841CoN
	Intestinal CCD-18Co cells	PS	2 μm	The cancer risk, metabolic changes	(Bonanomi et al. 2022)
	Kidney Proximal Tubular Epithelial Cells HK-2	PS	2 µm	The inflammation, higher protein levels of LC3, Beclin 1, mitochondrial protein Bad, higher endoplasmic reticulum stress	(Wang, Lee, et al. 2021)
	Dermal fibroblasts	PS	3 μm	The reduction of viability (40%)	(Hwang et al. 2020)
	Umbilical vein endothelial cells HUVEC	PS	0.5 μm	Cytotoxicity, autophagy	(Lee et al. 2021)

Abbreviations: PS: polystyrene; PE: polyethylene; PP: polypropylene; PET: poly(ethylene terephthalate); PVC: poly(vinyl chloride); PMMA: poly(methyl methacrylate).

Indirect health impacts

Indirect health impacts of MP is due to the fact that their surfaces provide an ideal environment for pathogens to grow, thus, making them carriers of biological contaminants. In addition, plastics can transport chemical pollutants.

Pathogens on MP surface

Pathogens that can form specific layers on the surface of MP are fungi, bacteria, and protozoa. Microplastics create a favorable environment for microorganisms as they bind water and nutrients. The pathogens can cause, for example, dysbiosis, which reduces host immunity and promotes infections (Kwon et al. 2020; Yang, Man, et al. 2022).

Pathogenic fungi accumulate on the surface of MPs, grow and multiply but also become resistant to temperature and sunlight (Gkoutselis et al. 2021). The surface of plastic particles can be covered with slimy layers of sediment or biofilm that allow pathogens to adhere, mutate and exchange DNA (the collection of exogenous DNA) (Mehrabi et al. 2011). Microplastics can also serve as carriers for antibiotic-resistant bacteria. Some bacterial strains living in biofilms increase antibiotic resistance by up to 30-fold (Pham, Clark, and Li 2021).

The adhesion of pathogens to the MP surface mainly depends on the type and shape of the particles. Microsized PE spheres and polyester fibers were found to be carriers for protozoa Toxoplasma gondii, Cryptosporidium parvum, and Giardia enterica which cause parasitic diseases in humans and animals. Interestingly, larger numbers of parasites adhere to the surface of microfibers than to microspheres (Zhang, Kim, et al. 2022).

Microplastic as a carrier of chemical pollutants

Microplastic affects the absorption and release of chemical contaminants as well as the transport of substances such as additives (e.g. tetrabromobisphenol A – TBBPA), heavy metals (e.g. Mn, Zn, As, Cr, Cu, Pb, and Ni), organic pollutants (e.g. PCB), medicines (e.g. methylene blue), and pesticides (e.g. carbendazim – KAR, dipterex – DIP, diflubenzuron – DIF, malathion – MAL, difenoconazole – DIFE, imidacloprid – IMD, buprofezin – BPF, and difenoconazole – DFZ). It can exacerbate the harmful effects of contaminants (Chen et al. 2017; Rainieri et al. 2018; Rainieri and Barranco 2019; Rochman et al. 2013).

Heavy metals

Once released into the aquatic environment, the MP surface can be colonized by biofilm which can also increase the adsorption of contaminants. Polystyrene particles of approximately 75 μm and 4000 μm, on which a biofilm of freshwater fungus Acremonium strictums had formed, were investigated. The biofilm increased heavy metal adsorption on MP and particle size played a key role in this process as well as biofilm colonization. It was found that particles of about 75 μm can carry more biofilm on their surface than those with a size of 4000 μm. There are more functional groups on the surface of the former MPs compared to the latter, which promotes electrostatic interactions and chemical association of heavy metals. The 75 μm particles show a greater capacity for Cu adsorption and Cr(VI) reduction, which may be associated with functional groups in the biofilm (Wu et al. 2022).

Microplastics act as carriers of heavy metals. Metal ions are adsorbed on the surface or adjacent layers, mainly through electrostatic interactions and complexation (Kinigopoulou et al. 2022). Adsorbed metals can diffuse into the solutions in which they are present. Significant release of Mn, Zn, As, Cr, Cu, and Ni from the MP surface in NaCl solution and Mn, Zn, As, Cr, Cu, Pb, and Ni in gastrointestinal solutions was found (Chen et al. 2022).

There was also analyzed the transfer of Cu and Pb from MP (polyamide 12 – PA12 and polylactide – PLA) into catfish organisms Clarias gariepinus, which are a major food source in Southeast Asia. Fish were reared for three months and exposed to seven different feed combinations supplemented with plastics and metals. At monthly intervals, fish gills, intestines, liver and edible muscle were analyzed for Cu and Pb. It was found that PLA carried higher amounts of metals compared to PA12. The highest metal concentrations were observed in gills, followed by liver, intestines, and edible muscles of fish (Jang et al. 2022).

Pesticides

The affinity and release of harmful substances vary depending on the type and concentration of both plastic and other contaminants as well as the degradation of MPs surface. Due to their small size, large specific surface area, and hydrophobicity, plastic particles are ideal carriers of hydrophobic substances such as pesticides, for example, KAR, DIP, DIF, MAL, DIFE. These substances are adsorbed in the following order DIF > DIFE > MAL > KAR > DIP. It was found that MPs can increase the harmfulness of pesticides through their adsorption and desorption. The adsorption kinetics and isotherm studies indicate that surface interactions as well as mass transfer and intramolecular diffusion are involved in the adsorption process. Therefore, the contaminants’ adsorption process is determined by both physical factors and chemical interactions. In contrast, thermodynamic studies show that pesticides’ adsorption is a spontaneous and exothermic process (Li et al. 2021; Wang, Gao, et al. 2022).

The presence of polyethylene MP can significantly prolong the half-lives of pesticides in water, for example, the half-life of terbuthylazine increases from 31.8 days to 45.2 days in the presence of 10 μg/dm³ MP (Wang, Gao, et al. 2022). High pH, low salinity, and elevated temperature promote the adsorption of pesticides such as IMD, BPF, DFZ. The adsorption capacity of the mentioned substances on PE was as follows: DFZ > BPF > IMD, (Li et al. 2021).

Other chemicals

Microplastic also enhances TBBPA accumulation in a commercial mussel species (Tegillarca granosa). It is dangerous because TBBPA is considered an endocrine disruptor and an immunotoxic agent (Zhang, Kim, et al. 2022). Similar observations were made in studies performed on zebra fish and sea bass (Granby et al. 2018). Higher concentrations of PCB and brominated flame retardants – BFR were detected in the muscle tissue of fish fed pellets containing a combination of contaminants and MP compared to those with feed containing only contaminants without plastic particles (Granby et al. 2018).

In addition, the impact of PS at 3 mg/dm³, phenanthrene (PHE) 0.2 mg/dm³ and a combination of both parameters was tested on zebra fish. The interaction of MP and PHE boosted oxidative damage, stimulated immune response, and changed microbial composition (Xu et al. 2021).

Microplastics released into the environment are degraded by mechanical abrasion and exposure to ultraviolet radiation. In a study by Hüffer, Weniger, and Hofmann (2018), HDPE and PP were subjected to accelerated aging under atmospheric conditions using ultraviolet irradiation with or without hydrogen peroxide. The adsorption of two model contaminants, PHE, and methylene blue, was evaluated. Physical and chemical characterization of the particles showed that aging led to significant surface oxidation and micro-crack formation (Hüffer, Weniger, and Hofmann 2018). The affinity of PHE and methylene blue for MP was stronger in this case compared to the degraded materials versus the undegraded materials. Microplastic oxidation can increase the adsorption of organic pollutants (Bhagat et al. 2022).

It can be concluded that MP increased the uptake of harmful compounds by organisms. The adsorption of organic contaminants is higher on particles subjected to accelerated degradation processes than on original ones. It was found that PE adsorbs more organic compounds (e.g. PCBs) than other plastics (e.g. PP and PVC) (Teuten et al. 2009). Among the most common mechanisms of sorption of organic contaminants on MP can be listed as hydrophobic interaction, followed by electrostatic interactions (e.g. Van Der Waalsa), hydrogen bonding, halogen bonding, and π–π interactions (Li et al. 2021). Therefore, the increase of the potential food safety hazards can be observed (Kwon et al. 2020; Yang, Man, et al. 2022).

Direct health impacts

Direct health impacts of MP concern the exposure to MP related to the type of polymer, size, and shape of the particles and the presence of additives used at the plastic processing stage. When analyzing the effects of plastics on human health, monomers such as vinyl chloride and styrene deserve particular attention. Some authors suggest that the presence of these substances should be one of the main targets of research evaluating the influence of MP on human health (Sánchez et al. 2022). Besides polymers, MPs also contain chemicals, intentionally added during the production of plastics, which can cross the intestinal barrier (Sánchez et al. 2022). The presence of additives used in plastics processing is often overlooked. This approach is inappropriate as the processing of poly(vinyl chloride) requires plasticizers, including phthalates, or phthalic esters, which can constitute up to 50% of the mass. They affect the hormone balance, increase the risk of allergies, and cause infertility problems (Rana et al. 2020). Microplastic can affect not only the body but also the psyche of the test organisms.

Aquatic animals

The consumption of MP may have adverse effects on aquatic organisms (Dimitriadi et al. 2021; Jin et al. 2018; de Marco et al. 2022; Qiao et al. 2019b; Tang et al. 2018; Tarasco et al. 2022; Zhao et al. 2021). Different species of fish (e.g. zebrafish) are often used in in vivo studies of, for example, intestinal diseases (Dimitriadi et al. 2021; Jin et al. 2018; de Marco et al. 2022; Qiao et al. 2019a; Tang et al. 2018; Tarasco et al. 2022; Zhao et al. 2021).

When taken orally, MPs can end up in the stomach. The predominant polymer (65%) found in the stomach of the flathead grey mullet is PE (Avio, Gorbi, and Regoli 2015). Microplastics can be absorbed through the gastrointestinal tract and transported to other parts of the body in different species of fish, both saltwater and freshwater (Guerrera et al. 2021). They can cross the intestinal barrier and reach organs such as the liver in commercial fish species Mugil cephalus (Avio, Gorbi, and Regoli 2015). Microplastic with a diameter of 5 μm accumulates in the fish gills, liver, and intestines, whereas the one with a diameter of 20 μm only in the gills and intestines. Microplastic can also affect physiological processes (Li, Chen et al. 2022). It can induce local inflammation in tissues and organs of animals (Hwang et al. 2020), lipid accumulation in the liver (Ebrahimi et al. 2022; Lu et al. 2016; Yin et al. 2021), intestinal dysbiosis, inflammatory bowel disease and the changes of the intestinal microflora in zebrafish (Souza-Silva et al. 2022). High intake of plastics may reduce the absorption of ingested food, thus, leading to reduced energy intake, which may have further consequences for the growth, or development of organisms (Ruthsatz et al. 2022), and fertility, such as in copepods (Lee et al. 2013). The rate of MP excretion is also important (Santana, Moreira, and Turra 2017) because contaminants can be metabolized by organisms and, thus, adversely affect their functioning (Gray 2002).

Polystyrene particles significantly increase superoxide dismutase and catalase activities in zebrafish. Metabolomic analysis suggests that MP induces changes in metabolic profiles in fish liver and disrupts lipid and energy metabolism (Lu et al. 2016). Similar studies on zebrafish exposure to polystyrene MP were performed using 5 μm microspheres (50 μg/dm³ and 500 μg/dm³). After 21 days of testing, there were observed changes in enzyme biomarkers and significant histological shifts associated with inflammation and oxidative stress. Significant changes in the gut microbiome and gut metabolic profiles in zebrafish were also identified. The study by Qiao et al. (2019a) provided evidence that exposure to MP can cause intestinal damage (Qiao et al. 2019a). In another study by Jin et al. (2018), male zebrafish was exposed to PS of 0.5 and 50 µm for 14 days (100 and 1000 μg/dm³). As a result, gut mucus volume increased, microflora dysbiosis and inflammation in the gut of adult zebrafish were observed. In addition, 0.5 µm MPs caused an increase in IL1α, IL1β and IFN mRNA and protein levels in the gut (Jin et al. 2018).

Furthermore, in addition to the digestive system, the immune system is also exposed to significant MP effects. The immune system recognizes the enemy in plastic particles, reacts violently at first, and then weakens (Santana, Moreira, and Turra 2017). Acute exposure to MP resulted in immune system impairment, such as in the scleractinian coral Pocillopora damicornis. A significant decrease in alkaline phosphatase enzyme was observed (Tang et al. 2018).

Terrestrial animals

Terrestrial mammals constitute a popular model organism used during analyses of the health effects of MP (Deng et al. 2022; Hwang et al. 2019; Kwon et al. 2022; Li, Chen,, et al. 2022; Liu, Zhuan, et al. 2022; Liu, Hou, et al. 2022; Meng et al. 2022; Mu et al. 2022; Sun, Chen, et al. 2021; Sun, Xu, et al. 2021; Tomazic-Jezic, Merritt, and Umbreit 2001; Wang, Zhao, et al. 2021; Zaheer et al. 2022).

Polystyrene particles with diameters of 0.46 and 1 µm affected red blood cells (RBCs) and caused hemolysis. Red blood cells of sheep were used in this study, because their structure and function are similar to human (Hwang et al. 2020). Microplastic with sizes from 0.1 µm to 10 µm was found in rabbits’ lymph, from 30 to 40 µm in rodents’ lymph (Yuan, Nag, and Cummins 2022), whereas PVC microparticles of 5–100 µm in the portal vein of dogs (Volkheimer 1975).

Microplastics can cross the blood-brain barrier and it was observed in a study conducted on mice. Researchers orally administered plastic particles up to 2 µm in diameter to mice for 7 days. It was found that MPs accumulated in microglia cells accompanying neurons and deteriorated their ability to multiply. This resulted in apoptosis, changes in immune response and inflammatory reactions (Kwon et al. 2022). As a mouse is a common mammal model, the findings presented and the health risks of MP to animals should not be ignored.

The health effects of MPs are related to their size. Particles smaller than 20 μm can penetrate organs in mammalian bodies (Lusher, Hollman, and Mendoza-Hill 2017). Polystyrene accumulation was observed in the kidney and liver of mice. Male mice orally exposed to 1000 μg PS/dm³ for 5 weeks were characterized by decreased body and liver weights, as well as the number of lipids (Lu et al. 2018). In addition, there was observed a phagocytosis in mouse macrophages as a result of exposure to 1.4 µm and 6.4 µm polymethylmethacrylate (PMMA) and 1.2, 5.2, and 12.5 µm PS particles (Tomazic-Jezic, Merritt, and Umbreit 2001). Particles below 150 μm in size can induce systemic exposure, be absorbed by living organisms, migrate through the intestinal wall, and reach lymph nodes (Lusher, Hollman, and Mendoza-Hill 2017). Particles larger than 150 μm are not absorbed but can cause local inflammatory effects (Presence of Microplastics and Nanoplastics in Food, with Particular Focus on Seafood 2016; Yuan, Nag, and Cummins 2022).

Currently, it is thought that environmental factors may be one of the causes of autism spectrum disorder (ASD) development (Gaugler et al. 2014). It is the group of etiologically distinct conditions that led to similar behavioral manifestations. Prenatal and postnatal exposures to PE lead to ASD-like traits in a mouse model (e.g. problems in social interactions). In addition, this contact resulted in gut microbiome amendments, the alteration of glucose metabolism, and the increase of the expression of EGR-1 and AGR genes. This is particularly important because ASD patients have gastrointestinal disorders. Moreover, mutations in EGR-1 have been linked to ASD (Zaheer et al. 2022). However, further research is needed to establish a link between the presence of MP in the body and autism.

Humans

There are few studies in the literature on the effects of MP on humans (Bonanomi et al. 2022; Çobanoğlu et al. 2021; Gautam et al. 2022; Hwang et al. 2019, 2020; Ju et al. 2020; Kwon et al. 2022; Lee et al. 2021; Wang, Zhao, et al. 2021; Wu et al. 2019; Zhang, Kim, et al. 2022). Most analyses have been conducted on human cells, such as peripheral blood mononuclear cells (Çobanoğlu et al. 2021; Hwang et al. 2019), umbilical vein endothelial cells HUVEC (Lee et al. 2021), HaCaT keratinocyte cells (Gautam et al. 2022), dermal fibroblasts (Hwang et al. 2020), lung epithelial A549 cells (Hwang et al. 2020), microglial HMC-3 cells (Kwon et al. 2022), kidney proximal tubular epithelial cells HK-2 (Wang, Zhao, et al. 2021), cells of intestinal epithelial Caco-2 (Gautam et al. 2022; Wu et al. 2019), small intestinal epithelial cells HIEC-6 (Zhang, Kim, et al. 2022), colonic epithelial cell CCD841CoN (Zhang, Kim, et al. 2022) and intestinal CCD-18Co cells (Bonanomi et al. 2022). Cells exposed to MP experience cell death three times faster than when exposed to other foreign bodies. The rate of their regeneration also decreases significantly as a result of this contact (Nienke Vrisekoop van UMC Utrecht onderzoekt gevaren van microplastics 2019). Zhang, Kim, et al. (2022) found that MP damages cell membranes ( Zhang, Kim, et al. 2022). The particles with sizes of 0.–5 µm were more likely to induce cell apoptosis after short-term exposure, compared to MPs with sizes less than 0.2 µm (Banerjee et al. 2022).

The presence of MP in human body fluids has been also confirmed. Some of blood samples contained up to three types of plastics, approximately 50% of the samples contained PET, approx. 30% – PS, and approx. 25% – PE. It is particularly important as it shows that MPs are present in the bloodstream and can penetrate organs via this route (Leslie et al. 2022).

In the body, MP releases toxic substances (e.g. TBBPA, styrene, vinyl chloride) that can cause various diseases, including cancer (Bonanomi et al. 2022). Polysytrene in the form of MP induces an immune response and stimulates the production of cytokines and chemokines. Interleukin-6 (IL-6) secretion also increases after contact with PS particles (diameter ˂3 µm, concentration = 500 µg/cm³) (Hwang et al. 2020). Long-term exposure of HepG2 liver cells to functionalized PS resulted in increased levels of interleukin-8 (IL-8), a key pro-inflammatory cytokine (Banerjee et al. 2022).

Nanoplastic

Plastic particles can acquire toxic properties with decreasing size (Stock et al. 2022). Particles smaller than MP with a size between 1 and 100 nm are called nanoplastic (NP), which is characterized by a high toxicity. This is caused by its very small particle sizes and large specific surface area. In the intestine, NP causes stronger inflammation and oxidative stress than MP. Nanoplastic can enter tissues, whereas MP is often blocked and cannot fully exert its toxic effects (Lusher, Hollman, and Mendoza-Hill 2017).

The studies showed that the harmfulness of plastic depended on particle size, surface functionalization, exposure time and dose. It was found that 50 nm PS induced apaptosis to SNU-1 human gastric epithelial cells. A higher apoptosis rate was observed with aminated particles compared to carboxylated or non-functionalized particles (Banerjee, Billey, and Shelver 2021).

In addition, NP destroys the cell membrane integrity of gametes and causes toxic effects on progeny as it is transferred across the placenta in a mice. Administration of PS during gestation produced a negative impact on fetuses and led to anxiety-like behaviors of progenies. Additionally, these particles caused apoptosis in neuronal cell lines, oxidative damage, and inhibited γ-aminobutyric acid synthesis in a brain (Yang, Zhu, et al. 2022).

It can be concluded that NP induces higher toxicity including reproductive and neurotoxicity than MP (Yin et al. 2021). Thus, the monitoring of the level and harmfulness of these particles is particularly important.

Conclusions

Microplastic is a ubiquitous contaminant that can be found in air, water, and soil. The most common route of exposure to MP is believed to be through the gastrointestinal tract. It poses a significant threat to human health due to its widespread occurrence in food. In addition, MP carries pollutants and microbial pathogens into living organisms. It can be accumulated in the body, induce inflammation, and have adverse effects on the immune, endocrine, reproductive and digestive systems. Exposure to MP is associated with a risk of oxidative stress, changes in cell division and viability, DNA damage, immune responses, metabolic disruption, intestinal dysbiosis, increased risk of cancer, respiratory, and neurodegenerative diseases. Microplastic can affect both the body and the psyche of the test organisms. It is supposed that plastic particles may be one of the causes of ASD.

Unfortunately, gaps in analytical methodologies make a comprehensive understanding of MP problem difficult. The standardization of requirements and the implementation of uniform experimental procedures for plastic particles are essential to ensure proper food quality. It will allow the real assessment of health risks associated with the presence of MP in food products.

Disclosure statement

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.

Funding

The author(s) reported there is no funding associated with the work featured in this article.