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# Do microplastics affect human immune defenses?

Massimiliano Galluzzi, Michele Lancia, Chunmiao Zheng, Valter Castelvetro,
Eric Lichtfouse

► To cite this version:

Massimiliano Galluzzi, Michele Lancia, Chunmiao Zheng, Valter Castelvetro, Eric Lichtfouse. Do microplastics affect human immune defenses?. Environmental Chemistry Letters, In press, 10.1007/s10311-025-01869-w. http://dx.doi.org/10.1007/s10311-025-01869-w

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# Do microplastics affect human immune defenses?

Massimiliano Galluzzi<fnref n="1" /> ID • Michele Lancia<fnref n="2" />,<fnref n="3" /> ID • Chunmiao Zheng<fnref n="2" />,<fnref n="3" /> ID • Valter Castelvetro<fnref n="4" />,<fnref n="5" /> ID • Eric Lichtfouse<fnref n="6" /> ID

Microplastic pollution has recently raised serious concerns on a global scale, yet their toxic effects are still underexplored. Microplastics, unlike most pollutants, consist of a wide variety of polymers, combined with additives that exhibit varying behaviors when dispersed in the environment. Microplastics can be coated by microbial biofilms and adsorb other pollutants. When microplastics age or aggregate to form larger particles, accurate detection and quantification is limited using current analytical methods. As a consequence, the occurrence of false positives introduces large uncertainties in the analysis of microplastics in the atmosphere, water, and soil. In short, microplastics in the environment are hard to investigate, thus making immuno-toxicity experiments calibrated on environmental observations challenging to carry out. Here, we show that the toxicity of microplastics on the human immune system is higher for small microplastics and nanoplastics, based on evidence from toxicological experiments. By contrast, some plastics such as polyethylene probably display a low toxicity due to their structural similarity with natural polymers such as plant cuticular waxes.

## Microplastics everywhere

The occurrence of microplastics in all ecosystems [1] raises serious environmental concerns, particularly due to their potential harmful effects on the biosphere, including human-kind [2]. Two microplastic categories can be distinguished. Primary microplastics are intentionally incorporated in pharmaceuticals and personal care products to enhance product functionality because they are durable, chemically stable, and able to encapsulate active ingredients [3, 4]. These microplastics can contaminate the environment by escaping treatment in wastewater plants. On the other hand, secondary microplastics originate from plastic waste fragmentation by physical, chemical, and biodegradation processes such as photo-oxidation, thermal exposure, and mechanical forces, thus producing particles smaller than 0.5 mm in size [4, 5]. Increased degradation processes can produce particles below 1 µm in size that are defined as nanoplastics [6].

## Old microplastics adsorb more pollutants

Once released into the environment, both large plastic particles and microplastics are rather resistant to degradation, thus reaching previously uncontaminated environments [7]. For example, the half-lives of 100 µm diameter microplastics

<figure><img src="image_2.png" /></figure>

Michele Lancia
lancia@eitech.edu.cn

Massimiliano Galluzzi
galluzzi@siat.ac.cn

Chunmiao Zheng
zhengcm@sustech.edu.cn

Valter Castelvetro
valter.castelvetro@unipi.it

Eric Lichtfouse
eric.lichtfouse@icloud.com

<footnote n="1">¹ Laboratory of Inflammation and Vaccines, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, Guangdong, China</footnote>

<footnote n="2">² EIT, Eastern Institute of Technology, Eastern Institute for Advanced Studies, Ningbo 315200, Zhejiang, China</footnote>

<footnote n="3">³ State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China</footnote>

<footnote n="4">⁴ Department of Chemistry and Industrial Chemistry, University of Pisa, 56126 Pisa, Italy</footnote>

<footnote n="5">⁵ CISUP - Center for the Integration of Scientific Instruments of the University of Pisa, University of Pisa, 56126 Pisa, Italy</footnote>

<footnote n="6">⁶ State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, Shaanxi, China</footnote>
of thermoplastic polyurethane and polyamide-6 in temperate
climate conditions are 73 and 147 years, respectively [8].
Microplastics adsorb minerals, organic matter, microorgan-
isms, and various pollutants, due to their surface properties,
and can act as carriers of these contaminants [9–13]. This
adsorption capacity is even increased by the aging processes
that weather the microplastic surface and develop nanomet-
ric cracks and wrinkles, resulting in an increase in surface
roughness [14]. Unfortunately, wastewater treatment plants
are poorly effective in removing microplastics from sewage
effluents; therefore regulatory actions have been prompted
in several countries to restrict the use of microplastics in
rinse-off cosmetics [15].

Microplastics in water, air, and soil

The concentration of microplastic pollution in waters is het-
erogeneous, reaching 100,000 items per liter in wastewater
plant effluents [16], but is negligible in large groundwater
systems [17, 18]. In agriculture, the intensive use of sewage
sludge and plastic mulching has led to microplastic levels
reaching up to 10,000 items per kg of soil [19], with poten-
tial risks to soil fertility [20]. In the atmosphere, indoor envi-
ronments exhibit fallout levels ranging from 1200 to 11,130
items m⁻²d⁻¹ [21, 22], exceeding outdoor concentrations
of 118 to 602 items m⁻²d⁻¹ [23, 24]. This highlights the
substantial role of household dust and synthetic textiles as
a domestic source of microplastic pollution [25]. Investiga-
tions of water, soil, and atmosphere report microplastic sizes
ranging between 10 and 500 µm [26], yet this data may be
underestimated due to the limits of detection of light-based
spectroscopy methods [27].

Microplastics in humans

Numerous studies have found microplastics in the organs
and tissues of wildlife [28] and humans [29, 30], raising con-
cerns about their potential accumulation in the human body
and associated health risks [31]. A summary of recent data
about detection and quantification of microplastic in human
fluids and tissues is presented in Table S1. Toxicity studies
have focused on the effects of microplastics on the human
immune system [32]. Microplastics were found able to alter
inflammatory responses, induce oxidative stress, and disrupt
gut microbiota homeostasis, potentially leading to immune
dysfunction [33]. Nonetheless, most existing data originates
from experimental in vivo models such as mice or in vitro
cultured cell lines, and uses spherical pristine microplastics
of a single polymer type with uniform size. When exposure

levels are calibrated on environmental data with averaged
concentrations and size of microplastics ranging from 10 to
500 µm (Fig. 1), experiments generally report a low inflam-
mation or toxicity [34–36]. By contrast, studies using similar
concentrations calibrated on environmental data but using
much smaller microplastics from 0.5 to 5 µm in size, consist-
ently report inflammation and toxicity in both in vivo and
in vitro conditions [36–40]. In this case, the probability of
interaction between biointerfaces and the total surface of
microplastics far exceeds real-world exposure levels. Data
from recent literature about the effects of microplastics on
in vitro and in vivo models are presented in Table S2.

Experiments performed under controlled conditions pro-
vide mechanistic insights into microplastic effects, but fail
to capture the complexity of human exposure to microplas-
tics for several reasons. First, nanoplastics are not taken into
account because standard spectroscopic techniques have a
spatial resolution limit of approximately 10 µm [26]. Sec-
ond, microplastics in the environment are highly heteroge-
neous with different sizes, shapes, chemical compositions,
and weathering. Third, in the environment, the surface of
microplastics can be coated with organics, minerals, and
biofilms that might induce or enhance antibiotic resistance
in pathogens [41]. Moreover, key aspects of human expo-
sure remain poorly understood, such as the real exposure of
microplastics, the microplastics fraction that successfully
crosses epithelial barriers, and the extent to which these par-
ticles enter the blood circulation [29]. As a consequence, it
is not known whether microplastics hamper human immune

<figure><img src="image_3.png" /><figcaption>**Fig. 1** Top: microplastics modeled in size and mass according to environmental observations show limited effects with immune cells, leading to low inflammation and toxicity. Bottom: in contrast, experiments using smaller microplastics, including nanoplastics, show stronger interaction and uptake by immune system cells, triggering inflammation, tissue damage, and functionality impairment</figcaption></figure>
defenses or whether they are eliminated like the common particulate matter that the immune system is well equipped to handle, as discussed in the following section.

## Do microplastics represent an immunological risk?

Do microplastics behave or not like common environmental particulate matter? The answer to this question is essential to evaluate the immune system response. Indeed, throughout human history, exposure to various particulate matter such as volcanic ash, mineral dust, and combustion by-products has shaped the evolution of immune defenses [42]. Specifically, the immune system has developed sophisticated protective mechanisms, including mucociliary clearance in the respiratory tract and phagocytic scavenging in tissues, to eliminate non-biological intrusions. Unlike pathogenic microbes that develop strategies for evading immune detection and replicate within the body, microplastics are relatively inert and incapable of deploying an elusion mechanism, making them less problematic in immunological terms. Moreover, the molecular structure and properties of some microplastics, such as polyethylene, are similar to those of natural polymers like plant cuticular waxes [43]. Therefore, the toxicity of such microplastics is likely to be low because living organisms have evolved to metabolize these compounds. Whereas other synthetic polymers that are structurally different from natural polymers are expected to induce more toxicity, yet these aspects have been poorly studied [44].

## Bio-corona

Environmental microplastics aggregate and adsorb other contaminants and agents, further modifying their physicochemical properties. In particular, a biofilm or 'bio-corona' [45], which is a dynamic layer of proteins, lipids, and other organic molecules, can coat the microplastic surface before entering the body. The bio-corona may contain pathogens or toxins, thus altering the influence of microplastics on the immune system [10]. As a consequence, in vitro studies must incorporate biological fluids to mimic the formation of a bio-corona. Notably, the interaction with the immune system largely depends on a such bio-corona, which drives the recognition versus the lack of recognition by the immune cells and the subsequent immune reaction. This immune reaction can be ignorance or tolerance, recognition and elimination/encapsulation, or, in rare cases, a pathological inflammatory response [46].

## Chemical additives

The role of plastic chemical additives in microplastic toxicity is poorly known. This is important because, in many cases, the adverse effects of microplastics do not originate from the polymers, but from the leaching of chemical additives such the metallic polymerization catalysts. Plastics commonly contain many compounds such as stabilizers, plasticizers, and flame retardants, many of which exhibit endocrine-disrupting and cytotoxic properties [47]. In addition, many small organic molecules are continuously generated by environmental photo-oxidation of the polymer, further contributing to the complexity of the toxicity profile [48]. Therefore, there is a need for investigations on environmentally relevant and aged microplastics to decipher the various toxicity contributions.

## Nanoplastics

Another overlooked factor in experimental studies is the microplastic size. In particular, nanoplastics are more numerous than microplastics, pervasive, and capable of crossing biological barriers [48]. Conducting experiments with nanoplastics is challenging and represents a frontier in analytical research. Nanoplastics are difficult to detect, as their size falls below the resolution limits of standard spectroscopic techniques [27]. Characterizing nanoplastics is prone to producing false negatives, due to the capacity of these fragments to form large hetero-aggregates. In addition, the techniques to detect nanoplastics require a complex sample pretreatment, which is often incompatible with the analysis of macroscopic samples from environmental or biological origins [49].

**Supplementary Information** The online version contains supplementary material available at https://doi.org/10.1007/s10311-025-01869-w.

**Funding** The authors acknowledge the National Key R&D Program of China (Grants No. 2023YFE0117000 and No. 2024YFE0104500), the Italian Ministry of Foreign Affairs and International Cooperation (Grant No. CN24GR04), the National Natural Science Foundation of China (Grants No. T2350610283 and No. 82261138630), the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2024A1515012508), the Youth Innovation Promotion Association of the Chinese Academy of Sciences (Grant No. 2022363), the Bill and Melinda Gates Foundation (Grant No. INV-059115), and the Alliance of International Science Organizations (Grant No. ANSO-CR-KP-2022-01).

## Declarations

**Conflict of interest** The authors declare no conflict of interest. EL declares that he is Chief Editor of Environmental Chemistry Letters.
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## Do microplastics affect human immune defenses?

Massimiliano Galluzzi, Michele Lancia, Chunmiao Zheng, Valter Castelvetro, Eric Lichtfouse

Table S1 summarizes recent findings from studies investigating microplastic detection in human body fluids and tissues. The data focus on common physical quantities such as mass concentration and size. Assuming microplastics homogeneous and with a spherical geometry, absolute number of microplastics in fluids and tissues (N) is assessed with the following formula:

$$N = \frac{c_m}{\rho_P \frac{4}{3} n^{\frac{d}{2}} \left(\frac{d}{2}\right)^{\frac{3}{2}}} \quad \text{Eq. S1}$$

Where N is the absolute number of microplastics per mL or g, C<sub>m</sub> is the mass concentration, ρ<sub>P</sub> is the average density of microplastics (assuming 1.2 g/cm<sup>3</sup>), d is the diameter.

Table S2 presents results from immunological/biological investigations of the effects of microplastics using *in vitro* / *in vivo* laboratory models. We provide the same physical quantities such as concentration, size and absolute number, plus the time Δt describing the interaction with cells or the total administration time in animals.

**Table S1.** Literature results on the detection and quantification of microplastics in human fluids and human tissues. Table entries show the location in fluid or tissue with respective mass concentration (C<sub>m</sub>) expressed in µg/mL for fluids or µg/g for tissues, typical size (d, diameter), absolute number per mL or g, main methodology of analysis, reference, and comments. In italics we present extrapolations using Eq. S1 and spherical geometry. Notes: <sup>a</sup> if size is not provided, the lower size limit is considered, <sup>b</sup> for N assessment purposes, fibers are assumed cylindrical, <sup>c</sup> for N assessment purposes, average size are considered. Abbreviations: MP: microplastic. µFTIR: micro Fourier transform infrared spectroscopy; PyGCMS: pyrolysis gas chromatography mass spectrometry; LDIR: laser direct infrared; NR: Nile Red staining; PWM: polarized wave microscopy; SEM-EDX: scanning electron microscopy with X-ray diffraction elemental analysis, TEM: transmission electron microscopy.

<table><thead><tr><th>Human body location</th><th>Concentration C<sub>m</sub></th><th>Size d</th><th>Number N</th><th>Method</th><th>Ref.</th><th>Comments</th></tr></thead><tbody><tr><td>Blood</td><td>1.6 µg/mL</td><td><sup>a</sup>>0.7 µm</td><td>7.4*10<sup>6</sup><br>MP/mL</td><td>PyGCMS</td><td>1</td><td>Published work has received a comment paper<sup>2</sup></td></tr><tr><td>Blood</td><td>0.7 µg/mL</td><td>93 µm</td><td>4.3 MP/mL</td><td>µFTIR</td><td>3</td><td>Possible cross-contamination suggested by the occurrence of large fragments<sup>4</sup></td></tr><tr><td>Sputum</td><td>3.1 µg/mL</td><td>74 µm</td><td>12 MP/mL</td><td>LDIR</td><td>5</td><td></td></tr><tr><td>Alveolar fluid</td><td>0.005 µg/mL</td><td><sup>b</sup>1730<br>µm</td><td>0.01<br>MP/mL</td><td>µFTIR<br>SEM-EDX</td><td>6</td><td>Possible cross-contamination suggested by the occurrence of large fragments</td></tr><tr><td>Breast milk</td><td>0.5 µg/mL</td><td><sup>c</sup> 35 µm</td><td>20 MP/mL</td><td>LDIR</td><td>7</td><td></td></tr><tr><td>Brain</td><td>4760 µg/g</td><td>0.15 µm</td><td>2.8*10<sup>11</sup><br>MP/g</td><td>PyGCMS<br>TEM</td><td>8</td><td>Probable overestimation due to fat rich tissue<sup>4,9</sup>; TEM has large uncertainties in microplastic detection</td></tr><tr><td>Liver</td><td>465 µg/g</td><td>3 µm</td><td>2.74*10<sup>7</sup><br>MP/g</td><td>PyGCMS<br>PWM</td><td>8</td><td>PWM has large uncertainties in microplastic detection</td></tr><tr><td>Liver</td><td>0.002 µg/g</td><td>9.8 µm</td><td>3.2 MP/g</td><td>µRaman, NR</td><td>10</td><td></td></tr><tr><td>Placenta</td><td>0.45 µg/g</td><td><sup>c</sup> 35 µm</td><td>18 MP/g</td><td>LDIR</td><td>7</td><td></td></tr><tr><td>Placenta</td><td>0.027 µg/g</td><td>20.3 µm</td><td>2.7 MP/g</td><td>LDIR</td><td>11</td><td></td></tr><tr><td>Lung</td><td>0.03 µg/g</td><td>40 µm</td><td>0.7 MP/g</td><td>µFTIR</td><td>12</td><td></td></tr><tr><td>Colon</td><td>9.8 µg/g</td><td><sup>b</sup>1100<br>µm</td><td>28.1 MP/g</td><td>µFTIR</td><td>13</td><td>Possible cross-contamination suggested by the occurrence of large fragments</td></tr><tr><td>Vein tissue</td><td>6.9 µg/g</td><td>90 µm</td><td>15 MP/g</td><td>µFTIR</td><td>14</td><td></td></tr><tr><td>Feces</td><td>10 µg/g</td><td>200 µm</td><td>2 MP/g</td><td>µFTIR</td><td>15</td><td></td></tr><tr><td>Feces</td><td>0.7 µg/g</td><td><sup>c</sup> 35 µm</td><td>27 MP/g</td><td>LDIR</td><td>7</td><td></td></tr><tr><td>Feces</td><td>280 µg/g</td><td>400 µm</td><td>7 MP/g</td><td>µFTIR</td><td>16</td><td></td></tr><tr><td>Feces</td><td>58 µg/g</td><td>150 µm</td><td>28 MP/g</td><td>µRaman</td><td>17</td><td></td></tr></tbody></table>
<table><caption>**Table S2.** Literature results of immunological and toxicological studies of microplastics interacting with living cells/tissue. Table entries show the biological system used and mass concentration (C<sub>m</sub>) expressed in µg/mL for *in vitro* cell cultures, or µg/g/day for daily concentrations during administration. Values of size (d, diameter), absolute number (N) per mL or g/day, description including material, status and interaction time, reference, and comments are reported. In italics, we present extrapolations using Eq. S1 and spherical geometry. Notes: <sup>c</sup> daily concentration of administration normalized on mice weight (23 g), <sup>d</sup> daily concentration of administration normalized on 7 days chick weight (100 g) and daily water intake (300 mL). Abbreviations: PS: polystyrene, HDPE: high-density polyethylene, PE: polyethylene, PMMA: polymethyl methacrylate, CaCo-2 Colorectal adenocarcinoma cells, HMC3: human microglial clone 3 cells; GC: granulosa cells; ROS: Reactive Oxygen Species.</caption><thead><tr><th>Cell/tissue type</th><th>Concentration C<sub>m</sub></th><th>Size d</th><th>Number N</th><th>Material / Description</th><th>Ref</th><th>Effect/comment</th></tr></thead><tbody><tr><td>Vascular smooth muscle cells</td><td>1000 µg/mL</td><td>550 µm</td><td>10<sup>7</sup> MP/mL</td><td>PS, HDPE, pristine and aged, Δt = 168h</td><td>18</td><td>Particles do not internalize. The leaching of chemical compounds after degradation causes inflammation. ROS generation is observed.</td></tr><tr><td>CaCo-2</td><td>100 - 1000 µg/mL</td><td>85 µm</td><td>300 - 3000 MP/mL</td><td>PE, pristine spherical, Δt = 48h</td><td>19</td><td>Moderate toxicity at high concentration, low to negligible toxicity at low concentration.</td></tr><tr><td>Liver organoids</td><td>0.25 - 25 µg/mL</td><td>1 µm</td><td>10<sup>5</sup> - 10<sup>7</sup> MP/mL</td><td>PS, pristine spherical, Δt = 48h</td><td>20</td><td>ROS generation, oxidative stress and inflammation response at medium to high concentration, lipotoxicity at low concentration</td></tr><tr><td>Immune cells from donors</td><td>1-100 µg/mL</td><td>0.06 - 1 µm</td><td>10<sup>6</sup> - 10<sup>8</sup> MP/mL</td><td>PS, PMMA, pristine, spherical, Δt = 72h</td><td>21</td><td>At high concentrations, inflammation is downregulated, but ROS and toxicity is assessed. Negligible effects at low concentration.</td></tr><tr><td>HMC3 Microglia</td><td>1, 5, 10 µg/mL</td><td>0.2 µm<br>2 µm<br>10 µm</td><td>10<sup>7</sup> - 10<sup>9</sup> MP/mL<br>10<sup>4</sup> - 10<sup>6</sup> MP/mL<br>10<sup>2</sup> - 10<sup>4</sup> MP/mL</td><td>PS, pristine spherical, Δt = 24h</td><td>22</td><td>10 µm spheres in size have negligible effects. 0.2 to 2 µm spheres in size cause microglia activation and apoptosis.</td></tr><tr><td>Cardiomyocyte organoids</td><td>0.025 - 2.5 µg/mL</td><td>1 µm</td><td>10<sup>4</sup> - 10<sup>6</sup> MP/mL</td><td>PS, pristine spherical, Δt = 72h</td><td>23</td><td>Cardiotoxicity increases with concentration.</td></tr><tr><td>Mice, lung</td><td>0.3 - 0.6 µg/g/day<sup>d</sup></td><td>1 µm</td><td>10<sup>6</sup> MP/g/day</td><td>PS, pristine spherical, Δt = 4 weeks</td><td>23</td><td>Microplastics are administered by inhalation. Cardiotoxicity is observed.</td></tr><tr><td>Mice, gut</td><td>0.26 - 26 µg/g/day</td><td>80 µm</td><td>0.8 - 80 MP/g/day</td><td>PE, pristine spherical, Δt = 5 weeks</td><td>24</td><td>Oral administration. Intestine inflammation is observed only for the highest concentration group due to intestinal dysbacteriosis.</td></tr><tr><td>Chicken liver, macrophages</td><td>3-300 µg/g/day<sup>e</sup></td><td>5 µm</td><td>10<sup>4</sup> - 10<sup>6</sup> MP/g/day</td><td>PS, pristine spherical, Δt = 6 weeks</td><td>25</td><td>Oral administration. Mitochondrial damage, persistent autophagy, and lysosome activation in macrophages are observed. Liver inflammation is reported.</td></tr><tr><td>GCs cells</td><td>1 - 25 µg/mL</td><td>0.5 µm</td><td>10<sup>7</sup> - 10<sup>8</sup> MP/mL</td><td>PS, pristine spherical</td><td>26</td><td>Granulosa cells apoptosis is observed.</td></tr><tr><td>Mice ovary</td><td>0.08 - 8 µg/g/day</td><td>0.5 µm</td><td>10<sup>6</sup> - 10<sup>8</sup> MP/g/day</td><td>PS, pristine spherical, Δt = 13 weeks</td><td>26</td><td>Fibrosis, decrease of ovarian cells capacity is observed.</td></tr></tbody></table>

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