Authors: Nina-Nicoleta Lazăr, Mădălina Călmuc, Ștefania-Adelina Milea, Puiu-Lucian Georgescu, Cătălina Iticescu
Categories: Review Article, Food, Fruits, Microplastics, Nanoplastics, Plants, Vegetables
Source: Heliyon
Authors: Nina-Nicoleta Lazăr, Mădălina Călmuc, Ștefania-Adelina Milea, Puiu-Lucian Georgescu, Cătălina Iticescu
Plastics are becoming common environmental pollutants. Plants behave as access routes for plastics in the trophic chain since they can adsorb particles through their roots or on their surfaces. In this review, various methods for sample preparation and analytical methods for plastic isolation and identification from vegetables, fruits, and their seedlings were discussed. The effects that plastic particles have on them were also addressed. All of the studies offer convincing proof that micro and nano plastics already exist in fruits and vegetables, or can easily enter into their seedlings and have a variety of effects. Since most studies have been conducted under strictly controlled conditions using standard plastics, more tests under more environmentally realistic conditions are required to ensure that literature studies are applicable. Also, more fruits and vegetables need to be tested to identify the number of plastics currently there that, when consumed, could harm human health.
Plastics are polymers composed of carbon atoms linked to each other in a chain structure. These are being used in almost every industry due to their low costs and ease to manufacture, water resistance, and high strength proprieties [1]. In the last decades, global plastic production has developed a dizzying amount, reaching approximately 390.7 million tons in 2021 [2]. According to a known European Trade Association, 90% of plastic production in 2021 was fossil-based, and only 10 % was post-consumer recycled and bio-based plastics [2]. While some countries reported lower amounts of plastic produced in 2021, China had a higher production, accounting for almost a third of global plastic production [2]. Even though the globe is currently making efforts to increase plastic recycling, 60% of plastics still end up in the environment [1].
Plastic wastes enter the soil in significant quantities each year without strict laws and regulations on their disposal in most countries [3]. This fact contributes to pollution since plastics are challenging to degrade due to their lightweight and stable chemical characteristics [4]. Although difficult to decompose, abrasion, UV radiation, hydrolysis, and biodegradation create micro (MPs) and nano (NPs) particles with various shapes and textures, including fragments, fibers, pellets, spheres, films, or foams from macro and meso plastics [3]. The most harmful are the particles under 5 mm [5]. Since they have small dimensions and aerodynamic shapes, they can easily move and enter any environment, reaching even into the human body [1,6].
The most identified polymers in the plastic particles from the environment are, polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyamide (PA), and polycarbonate (PC) [7,8]. Understanding the polymer types present in the plastic particles is crucial for pinpointing the origin of pollution. The chemical composition also plays a significant role in the degradation and distribution of MPs and determines their fate in the environment. Hence, a comprehensive understanding of the chemical properties of various MPs is essential to grasp their behavior and devise effective preventive and corrective measures [7,8]. The general sources of MPs and NPs pollution are illustrated in Fig. 1. Shopping bags, food packaging films, toys, containers, pipes, medicine bottles, caps, automotive parts, or chemical fiber clothes are some of the environmental pollution sources [3].Fig. 1The general sources of MPs and NPs pollution.Fig. 1
The estimated amount of plastic particles consumed weekly from food is 5 g/person as stated by Ref. [9]. This is even more concerning given that various studies have already shown that plastics are present in human blood [10,11]. Meat, seafood, vegetables, condiments, and beverages were all reported as contaminated with MP and NPs [6,12]. Oceans, rivers, lakes [13], soil [14], and agricultural lands [15] throughout the world already contain significant amounts of plastics. Due to their small size and abundance in pelagic and benthic habitats, microplastics are ingested by edible aquatic species [6]. Researchers have looked into and discovered MPs in numerous species of fish and seafood from across the globe, this being one of the most researched topics regarding the presence of microplastics in food [16]. Beverages may contain microplastics due to production processes, air pollution, water sources, air quality, or long-term storage in plastic bottles [6]. MP and NP contamination also have an impact on plant growth and development [17]. Various studies have shown that MPs and NPs can be taken up through foliar absorption or transferred to aboveground tissues by plant roots causing physical damage, slowing the development, and increasing oxidative stress [3,18,19]. Additionally, they can accumulate in plants' edible components (leaf, fruit, and stem), representing a great danger to people's intake [13]. Besides, pathogens and other chemical pollutants, including pesticides and heavy metals, can be transported by MPs and NPs, making them even more hazardous [6]. Contaminated water, fertilizer, compost, and soil all have a high potential for introducing MPs and NPs into plant systems [20].
Only a few researchers have investigated MPs and NPs in vegetables and fruits. While most studies focus on the plant's intake of MPs and NPs via roots, leaves, and stems using model plants and the consequences on the plant, few actually analyze the MPs and NPs already found in the fresh vegetables and fruits on the market that people consume every day and may impact consumer's health. Generally, the consumption of fruits and vegetables is associated with a lower risk of diseases due to the high intake of nutrients [21]. According to a 2021 WHO/FAO report, 400 g or more of fruits and vegetables per day are required to sustain good health [22]. But the presence of MPs may lead to harmful effects on the human body instead since they also represent vectors for other pollutants.
In this review, data from research on the uptake and presence of microplastics in fruits and vegetables were gathered, including occurrence, analytical methods, characteristics of MPs, and the potential consequences on biota following MP exposure. The documentary study took place over a period of three to four months by searching on Science Direct platform terms such as “microplastics”, “nanoplastics”, “plastic particles”, “plastics in vegetables”, “plastics in fruits”, “plastics in plants”, “microplastics in food”, “microplastic analysis”. The initial search resulted in 163 945 articles (Fig. 2) for the last 10 years (2014–2023). Further, only the relevant articles were selected by meeting the following (i) studied the presence of micro and nano plastics in vegetables and fruits; (ii) studied the amount of micro and nano plastics in vegetables and fruits; (iii) studied the effect of micro and nano plastics on vegetables and fruits; (iv) studied the pathway of micro and nano plastics entrance in vegetables and fruits. Studies were excluded if treating other food products or edible plants than vegetables or fruits (such as cereals or herbs). Finally, a total of 23 research articles were considered. Information related to the presence and amount of micro and nano plastics in fruits and vegetables is lacking or it is too little, being a topic that has recently come to the attention of researchers. However, this is an emerging topic and is very timely.Fig. 2Number of articles from 2014 to 2023 period resulted for each searched keyword.Fig. 2
The MPs and NPs analysis comprises the following sample collection, processing or treatment, identification, characterization, and quantification (Fig. 3). A critical step in the detection of MPs is sample preparation [23]. There are several different treatments of fruits and vegetables described in the literature. Table 1 presents the methods used by several authors for the analysis of micro and nano plastics in fruits and vegetables.Fig. 3The schematic illustration of consecutive steps involved in the extraction of MPs and NPs from fruits and vegetables.Fig. 3Table 1Methods for the analysis of micro and nano plastics in fruits and vegetables.Table 1SampleCountry of originSample preparation methodIsolation and separation methodIdentification methodReferenceRoots and tubersCarrot (Daucus carota L.)ItalyMineralization with 65% nitric acid at 80 °C, 90 min using a graphite digestion block systemExtraction with dichloromethane by centrifugation at 4000 rpm for 5 minSEM - EDX[24]ChinaPlastic treatment of carrot plants under hydroponic conditions for 1 week–TEM[4]Radish (Raphanus sativus L.)–Plastic treatment of radish plants under hydroponic conditions for 2 weeks–CRM[25]ChinaPlastic treatment of radish seeds under germination conditions for 3 days–CLSM[26]BulbsOnion (Allium cepa L.)ItalyPlastic treatment of onion plants under hydroponic conditions for 72 h–TEM[27]LeafLettuce (Letuca sativa)ItalyMineralization with 65% nitric acid at 80 °C, 90 min using a graphite digestion block systemExtraction with dichloromethane by centrifugation at 4000 rpm for 5 minSEM - EDX[24]ChinaPlastic treatment of lettuce seeds under germination conditions for 7 days–CLSM[26]SeedsPeas (Pisum sativum)KoreaPlastic treatment of pea plants under soil cultivation conditions for 2 months–CLSM[28]FlowersBroccoli (Brassica oleracea italic)ItalyMineralization with 65% nitric acid at 80 °C, 90 min using a graphite digestion block systemExtraction with dichloromethane by centrifugation at 4000 rpm for 5 minSEM - EDX[24]FruitsTomato (Solanum lycopersicum)IndiaPlastic treatment under cultivation on cellulose filter paper–SEM - EDX[29]Apple (Malus domestica)Pear (Pyrus communis)ItalyMineralization with 65% nitric acid at 80 °C, 90 min using a graphite digestion block systemExtraction with dichloromethane by centrifugation at 4000 rpm for 5 minSEM - EDX[24]
In general, the research from the specialized literature is divided into two studies on MPs already present in fruits and vegetables and studies on the MPs absorption by fruits and vegetables. The most numerous are the studies that analyze the access pathways of MPs in plants. MPs reduce in size with time due to erosion and weathering, becoming easier to be absorbed and having a high impact on plant development, growth, and soil biodiversity [3]. To test that, in order to better understand the path that a plastic particle takes in plants and the negative effects it exerts on it, many studies use hydroponic cultivation, as stated in Table 1. Carrot [4], radish [25], and onion [27] seeds were cultivated under hydroponic conditions, being treated with various MP and NP particle concentrations and dimensions for 3 days to 2 weeks (Table 1). Other researchers tested the MP absorption using the traditional cultivation process under soil conditions. Thus, Gong et al. [26] cultivated lettuce seeds for 7 days and radishes for 3 days in plastic particle-treated soil. Kim et al. [21] cultivated peas seeds in plastic particle-treated soil for a longer period (2 months). Hydroponics represents a cultivating method that provides the calculated resources necessary for plant growth and development [30]. Contrary to conventional agriculture, hydroponics enables total crop nutrition control, employing only the nutrients and water needed by each crop, leading to more effective nutrient regulation and better water management [31]. Since hydroponically produced plants are fed a balanced diet, they are healthier than their soil-grown counterparts [30]. This makes it the ideal approach for understanding how plastic particles reach plants and what kind of effects they have on them.
As mentioned earlier, the sample preparation before MPs analysis is a critical step. For the MP already found in fruits and vegetables, a step that cannot be skipped is the removal of organic and inorganic matter in order to facilitate the isolation and identification of MPs [6]. In general, different acidic, alkaline, or oxidizing solutions are used during digestion to remove the organic matter in food. Given that plant foods are frequently high in cellulose, protein, and lipids, this issue is quite difficult [6]. In terms of fruits and vegetables, Oliveri Conti et al. [24] removed the sample matrices by nitric acid mineralization using a graphite digestion block system (Table 1). The acid digestion method was also reported as being accurate, simple, and rapid for the quantification of PVC from food and food wastes by Lievens et al. [32]. But a tough treatment may lead to MPs degradation and a more difficult subsequent identification [6]. In this sense, many researchers reported color loss and structure change for polyethylene (PE), polypropylene (PP), or polystyrene (PS) during azotic acid or potassium hydroxide digestion [33,34].
The isolation of MPs and NPs comes after the matrix removal as the following important step [35]. Regardless of the sample under study, numerous authors have over the years tested a variety of methodologies. In the specialized literature, flotation and filtration stand out as the most often employed techniques [36]. While floatation involves mixing the digested sample with a floatation media to produce phases separation, filtration using membrane technology involves the mechanism of a pressure difference which causes the liquid to flow through the membrane while the MPs are retained on the surface [36]. However, another method that also stands out in the literature for the isolation of MPs is centrifugation. Oliveri Conti et al. [24] used centrifugation as an isolating method for the MPs and NPs in various fruits and vegetables as stated in Table 1.
Although currently there are a number of methods for the identification and characterization of MP, their counting is still challenging. In the literature, a variety of microscopic and spectroscopic techniques are being used to identify and characterize MPs in terms of colors, shapes, sizes, types, and spectral characteristics [6,37]. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Confocal Laser Scanning Microscopy (CLSM), and Confocal Raman Microscopy (CRM) are the most used microscopic techniques, whereas Fourier-Transform Infrared Spectroscopy is the most used spectroscopic technique [38]. The MPs and NPs particles from fruits and vegetables and their seedlings were analyzed using mostly microscopic techniques as presented in Table 1.
Oliveri Conti et al. [24] used SEM with an energy dispersive X-ray detector (EDX) to detect the presence of plastic particles in carrots, lettuce, broccoli, apple, and pear. Sahasa et al. [29] also used SEM-EDX to monitor the adhesion of microplastics to the surface of tomato roots. SEM provides images of a sample by scanning its surface using a focused beam of electrons [23]. It has a clear and high resolution, analyzing particles of 0.5–4 nm, but according to Jung et al. [9], brings the disadvantages of being expensive, long time-consuming, and lacking information on the type of polymer. The attachment of an EDX can provide some details about the elemental composition of the plastic particles [23]. Dong et al. [4] and Giorgetti et al. [27] used TEM to analyze the plastic particles from carrot and onion seedlings. TEM provides images by transmitting a beam of electrons with energies (higher than in SEM) that penetrate the material [9,39]. It has a high resolution for particles under 1 nm [9]. All SEM and TEM microscopes generate a highly focused electron beam that impacts the sample inside a vacuum chamber. SEM microscopes, however, are designed primarily to examine material surfaces, whereas TEM microscopes are designed primarily to examine the internal structure of specimens [39].
Gong et al. [26] analyzed the MPs from radishes and lettuce using the CLSM technique. Kim et al. [28] also used CLSM to investigate the accumulation of MPs in peas seedlings. The structural characteristics of cells and the location of specific structures inside those cells in fixed tissue can be studied by CLSM by using the fluorescence excitation principle [40]. Tympa et al. [25] followed the absorption of plastic particles by radish seedlings using CRM. Raman spectroscopy and confocal microscopy are combined in CRM, allowing the observation of molecular data of a specific sample area [41]. It offers data on the depth and hidden structures of thin samples, has a high spatial resolution, and enables the acquisition of depth profiles in three-dimensional thin structures [42].
The first line of defense for plants against herbivore attacks, unwanted air exchange, and water loss is their leaves. Due to their stomata's size, which is roughly 25 mm long and 3–10 mm wide, they can absorb plastic particles as small as 5 nm through lipophilic and hydrophilic pathways [3]. Nevertheless, the majority of studies on the uptake of MPs by plants have focused on the root system since they can directly interact. The MPs adhere well to the surfaces of the roots since they have a wide surface area and produce exudates, being able to access also the stems, leaves, and other above-ground organs [3].
The primary criterion for classifying plastic particles is their size. EFSA (European Food Safety Authority) defined microplastics as fragments having 0.1 μm to 5 mm in diameter, while every particle under those sizes is considered nanoplastics [43]. This classification has since been utilized in every research. Although, spherical particles are more suitable for this classification compared to the irregular shape [3]. The form of MP particles in the environment is frequently irregular. For instance, pellets, films, and fragments constitute most of the MP forms in agricultural soil [3]. Another important criterion for characterizing plastic particles is their chemical composition (which affects their distribution, degradation, and environmental fate), as well as their electrical charge (which affects their absorption by the plants) [3]. Table 2 presents the main paths identified in the literature through which MPs and NPs of various sizes end up in fruits, vegetables, and their seedlings.Table 2Characteristics of the micro and nano plastics found in fruits and vegetables.Table 2SamplePolymers' typeShape and size of plasticsLocation in plantReferenceRoots and tubersCarrot (Daucus carota L.)Not specified1.36–2.00 μmPeeled vegetable[24]PS>1 μm50–150 nmRootsRoots and leaves[4]Radish (Raphanus sativus L.)ABSPowder, 0.3–2 μmRoots[25]PSSpheres, 100 nmRoots[26]BulbsOnion (Allium cepa L.)PSIrregular shapes20–190 nmRoots[27]LeafLettuce (Letuca sativa)Not specifiedPS2.18–2.78 μmWhole vegetable[24]Spheres, 100 nmRoots[26]SeedsPeas (Pisum sativum)PSMicrospheres0.02 μm average diameterStem and roots[28]FlowersBroccoli (Brassica oleracea italic)Not specified1.86–2.95 μmWhole vegetable[24]FruitsTomato (Solanum lycopersicum)Apple (Malus domestica)Pear (Pyrus communis)PEIrregular shapes60 μmIrregular shapes<500 μm1.56–3.19 μm1.87–2.59 μmRoots and shoots[29]PPRoots[44]Not specifiedPeeled fruit[24]
Following carrot cultivation in the hydroponic environment under single microplastic pollution conditions, Dong et al. [4] observed large-sized PS exceeding 1 μm in the roots and 50–150 nm in the leaves (Table 2).
Radish was treated as well with micro and nanoparticles under hydroponic conditions. Tympa et al. [25] found acrylonitrile butadiene styrene (ABS) particles of 0.3–2 μm in the roots of radish seedlings, while Gong et al. [26] observed PS particles of 10 nm in the radish roots as well after hydroponic cultivation. PS particles were reported also in other plants (Table 2). Giorgetti et al. [27] found irregular shape particles of 20–1190 nm in the roots of onion seedlings, while Gong et al. [26] reported spheres of 100 nm in the roots of lettuce seedlings. In addition, Kim et al. [28] reported PS microspheres having 0.02 μm average diameter in the stems and roots of peas seedlings. In addition, PE of 60 μm having irregular shapes were reported by Sahasa et al. [29] and PP smaller than 500 μm were reported by Shorobi et al. [44] in tomato roots and shoots (Table 2).
While most researches followed the particle's path in plants, Oliveri Conti et al. [24] analyzed the particles already found in fruits and vegetables (Table 2). Thus, they reported plastics with sizes between 1.36 and 2.00 μm in peeled carrot, 2.18 and 2.78 μm in whole lettuce, 1.86 and 2.95 μm in broccoli, 1.56 and 3.19 μm in peeled apple, and 1.87 and 2.59 μm in peeled pear. Carrots were the most contaminated vegetable, whilst apples were the most plastic-contaminated fruit samples. The lettuce had the largest MPs in size, whereas the carrot samples contained the smallest particles [24].
Several investigations have focused on the cellular and physiological effects of plastic particles on fruits and vegetable seedlings. Table 3 presents the main effects of MPs and NPs on various plants investigated by many researchers.Table 3Effects of micro and nano plastics on fruits and vegetables.Table 3SampleEffectReferenceRoots and tubersCarrot (Daucus carota L.)Deformation of cell walls, texture modification; reduction of roots and leaves biomass[4]Radish (Raphanus sativus L.)Reduction of root and shoot length;[45]Cherry radish (Raphanus sativus L. var*. radculus pers.)Inhibition of shoot fresh weight, root fresh weight; reduction of leaf number;[46]BulbsOnion (Allium cepa L.)Cytotoxicity, genotoxicity, and oxidative damages;[27]LeafLettuce (Letuca sativa L.)Inhibition of plant growth, reduction of nutritional quality; oxidative stress induced;[47](Lactuca sativa* L. var. ramosa Hort)Inhibition of growth and photosynthesis; Stimulation of ROS accumulation;[48](Lactuca sativa L. cv. ‘Red Sails’)Enhanced DBP toxicity, but reduced DBP content; inhibition root growth and viability; reduction of soluble protein and sugar content; increasing vitamin C content; cell damage;[49]SeedsPeas (Pisum sativum)Negative effects on reproductive and nutritional factors;[28]Lentils (Lens culinaris)Inhibition of germination and seedlings growth; cell membrane damage of seedlings[50]Soybeans (Glycine max)Inhibition of germination viability, plant growth (in height, culm diameter, leaf area, and biomass production);[51]Common bean (Phaseolus vulgaris L.)Significant impact on root nodules;[52]FruitsCucumber (Cucumis sativus)Inhibition of plants' growth; chlorophyll and sugar metabolism;[53]Pumpkin (Curcubita pepo L.)Reduction of roots and shoots biomass, leaf size, chlorophyll content, photosynthetic efficiency, micro- and macro-elements;[54]Tomato (Lycopersicon esculentum L.)Reduction of seed germination percentage, germination index, root growth, physiological and biochemical activities;[55]Inhibition of germination and seedling emergence; Inhibition of root and shoot growth;[29]Inhibition of germination and root growth;[44]Strawberry (Fragaria x ananassa Duch)Reduction of plant height, stem diameter, and number of inflorescences; Decrease of fruits' total number and weight;[56]Reduction of plant biomass, root volume, and surface area; favors the accumulation of heavy metals;[57]
A significant number of investigations suggested that plant development is negatively affected by plastic particles. Initially, negative influences on plant germination were observed by many authors. De Silva et al. [50] noted that PE microspheres, having concentrations of 50 mg/L and 100 mg/L and diameters ranging from 740 to 4990 nm, significantly reduced the viability of lentil seed germination (Table 3). Inhibitory effects on the germination percentage of tomato seeds were also reported by Shi et al. [55] when average particle sizes (52–368 μm) of PS, PE, and PP with irregular shapes and concentrations of 10–1000 mg/L were used in the tests. The inhibitory effect in this investigation also increased with the microparticle concentration [55]. The same effect on tomato seeds was reported also by Sahasa et al. [29] when concentrations between 0.25 and 1 % of PE particles were used. According to Li et al. [51], adding plastic debris had a substantial impact also on the soybean germination viability and was inversely correlated with increasing plastic concentrations from 0.1 to 1%.
Negative impacts of micro and nano plastic particles on plants’ root and shoot length after seeds germination are commonly observed (Table 3). The root and shoot length of lentil seedlings was inhibited to varying degrees as the PE concentration increased [50]. Shi et al. [55] reported that both root length and fresh weight of tomato seedlings were reduced by microplastics under PS, PE, and PP exposure conditions. Roots and shoots growth inhibition of tomato plantlets were also reported by Sahasa et al. [29] and Shorobi et al. [44]. After being exposed to 50 mg/L PS particles with sizes ranging from 10 to 700 nm, cucumber plantlets' biomass was reported to have decreased by Li et al. [53]. Carrot roots and leaves lost biomass when PS concentration from the growing environment increased from 10 to 20 mg/L, according to Dong et al. [4]. In two of their studies, Gao et al. [48,49] reported growth inhibition in two lettuce plantlet varieties by MPs of various concentrations.
Pumpkin plants responded differently depending on the type and concentration of the four microplastics that were tested, including PE, polyvinyl chloride (PVC), PP, and polyethylene terephthalate (PET) [54]. PVC was found to be the most harmful material and PE was the least hazardous after tests using amounts of plastic particles ranging from 0.02 to 0.1%. Reduced biomass in the roots and shoots, as well as changes in leaf size, were all associated with microplastic toxicity as Colzi et al. [54] declared. Soybean plants’ height and culm were inhibited by different concentrations of plastic residues in PE treatments as proved by Li et al. [51]. Additionally, they noted that the PE addition considerably reduced the leaf area of soybeans, particularly at the maximum addition level of 1%. Contrarily, Meng et al. [52] found that the application of various concentrations of low-density polyethylene (LDPE) to bean plants had no significant impact on shoot, root, and fruit biomass or pod number when compared to the control treatment. However, LDPE showed significant impacts on specific root nodules, representing a potential threat to plant growth (Table 3).
Kim et al. [58] also reported no significant impact on peas growth and development after the treatment with PS particles of an 0.02 mm average diameter and a concentration of 20 mg/kg. Yet, they observed complex toxicity over the reproductive factors. Singh & Kumar [45] went further and tested the combined effect of nano plastic particles contaminated with zinc oxide and copper oxide on radish seedlings. They noticed the reduction of root and shoot length and fresh weight as compared to the control when the concentration of contaminants increased from 10 to 1000 mg/kg. In a distinct radish investigation, Cui et al. [46] found that while 2% PA and PP soil contamination had minimal effects on cherry radish growth over the 30 days of cultivation, 2% PVC significantly impacted it. Also, after PVC exposure the shoot and root fresh weight, and leaf number drastically decreased in comparison to the control.
Plant height, biomass, root volume, and stem diameter were significantly affected by both single and combined applications of HDPE of 2–5 mm in a concentration of 0.5 g/kg and Cu nanoparticles [57]. Usually, the root length decrease may be due to the accumulation of plastic particles on the seed capsule and root surface blocking the absorption and uptake of nutrients and water [15].
In general, plant reactions differ depending on the amount of microplastic present, with some situations showing a dose-dependent effect. Nevertheless, not all plants are significantly impacted by microplastics in terms of growth.
Plastic fragments in plants have the potential to cause damage to cells and interfere with intracellular molecules [3]. For instance, exposure to PS, PE, and PP reduced soluble sugar content in tomato plants as Shi et al. [55] demonstrated. With the increase of microplastic concentration, the soluble sugar content in plants decreased gradually. A similar pattern was found in analyses of soluble protein content. Generally, the soluble protein content was more sensitive than the soluble sugar content when exposed to microplastics [55]. Reduced chlorophyll content and photosynthetic efficiency in pumpkin plants, were all associated with microplastic toxicity when four microplastics were tested [54]. After being exposed to 50 mg/L PS particles with sizes ranging from 10 to 700 nm, cucumbers’ chlorophyll and sugar metabolism were reported to have decreased by Li et al. [53]. Emerging contaminants are a direct threat not only to the flora and fauna present but also to human health [45]. Moreover, PS particles promoted protein and amino acid content in harvested beans according to Kim et al. [58]. Serious cytotoxicity, genotoxicity, and oxidative damage were discovered when onion seeds were germinated for 72 h with PS microspheres at concentrations of 0.01–1.0 g/L [27]. A foliar exposure of lettuce plantlets to PS led to reduced chlorophyll and carotenoid contents, induced significant oxidative stress, and weakened the antioxidant defense system in lettuce leaves [47]. Cell membrane damage was induced by the PEMPs at the highest concentrations in lentil seedlings [50]. Although PE particles caused the reduction of soluble protein and sugar content, leading to cell damage, they increased the vitamin C content in lettuce plantlets, according to Gao et al. [49].
Inducing oxidative damage and inhibiting photosynthesis may result from plastic particles accumulating in cell wall pores and obstructing water and nutrients as they pass through leaf capillaries. Moreover, various functional groups on plastic surfaces can attract other hazardous chemicals. Furthermore, by releasing pollutants that have been swollen onto their surfaces, plastics could directly cause phytotoxicity [59].
All these studies are evidencing that fruits and vegetables are other significant access routes for plastic particles into the human body. Micro and nanoplastics are potentially dangerous and may cause a number of health issues, such as oxidative stress, immunological disorders, and an increased risk of cancer for humans [60]. In addition, other dangerous microorganisms might be transported by plastic particles [61,62]. The most recent studies on the environmental end-life of microplastics demonstrate unequivocally that people will continue to consume plastic particles [1]. As long as the worldwide regulation does not impose strict and clear rules regarding their production, use, and recycling [63], plastics will end up in the soil, plants, fruits, and vegetables, and, implicitly, in the human body.
The current state of plastic particle detection in plants reveals a lack of standardized techniques. A significant number of existing methods heavily depend on subjective visual inspection, introducing the possibility of inconsistent results. There is a critical need for the advancement of reliable and precise detection and quantification methods. These methods should possess the capability to identify and measure plastics in various edible plants, with a particular emphasis on fresh fruits and vegetables. Establishing standardized procedures for the systematic collection, fractionation, characterization, and quantification of polymer particles in food, becomes imperative in meeting this demand. In addition, MPs and NPs transport from edible plants into the food chain must be studied along with the corresponding ecological and health impacts.
Plastic pollution is an increasing global concern since plastics have persisted in the environment for hundreds of years. Through the food chain, which is considered the most important among many other environmental sources, humans are frequently exposed to microplastics. In the literature, most studies focus on the plastic particles in fish and seafood, but they lack information about plastics' presence in fruits and vegetables since their consumption is recommended due to the health benefits they can provide. Numerous techniques can be utilized for the separation and identification of plastic particles in fruits, vegetables, and their plantlets, but there is a need for developing a more precise method in terms of quantification. Plant roots are the main paths through which micro and nano particles of various types of plastics can enter into plants, howbeit leaves are also access ways. In general, particles under 3 μm penetrated the plant tissues taken in the literature studies, inhibiting plant growing, inducing oxidative stress, and unbalancing the nutrients report. The short periods that have been the focus of the majority of experiments in the literature are not conclusive since the majority of plants spend several months during the agricultural season being exposed to MPs. Therefore, extensive experimental investigations under long-term and realistic outdoor conditions are required. In addition, few studies actually examine the MPs and NPs already present in the fresh vegetables and fruits on the market that people consume every day which may have an impact on consumers’ health. Knowing the amount of plastic contained in the edible fruits and vegetables that end up on consumers' plates is therefore necessary.
This work was supported by the project "DINAMIC", financed by the Romanian Ministry of Research and Innovation, Contract no. 12PFE/2021.
Data will be made available on request.
Nina-Nicoleta Lazăr: Writing – original draft, Methodology, Investigation, Data curation, Conceptualization. Mădălina Călmuc: Writing – original draft, Methodology, Investigation, Data curation, Conceptualization. Ștefania-Adelina Milea: Writing – review & editing, Data curation. Puiu-Lucian Georgescu: Visualization, Supervision, Resources, Project administration, Funding acquisition. Cătălina Iticescu: Visualization, Supervision, Project administration, Funding acquisition.
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.