Presence of microplastics in human stomachs
November 2024 | ScienceDirect
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Abstract
This study presents the first definitive confirmation of microplastic presence in the human stomach, based on samples from 26 cadavers. 97 microplastic particles were extracted from stomach contents, across all 26 individuals, revealing a universal prevalence of microplastics in the cadavers. Morphological analysis of the extracted particles unveiled distinct shapes, with fibers constituting the majority (52.04 %), followed by fragments (39.80 %) and films (8.16 %). The average quantity of microplastics per individual was calculated to be 9.4 ± 10.4 particles, with an estimated daily intake of microplastics at 32.2 particles per day. These figures are lower than estimates derived from both daily microplastic consumption alone and notably, those calculated from stool analyses. Our study also suggests that the breakdown or transformation of microplastics cannot be ruled out during their passage through the digestive tract. Although the number of microplastics in stomach contents reported in this study was even lower than the daily microplastic intake rates reported in the literature, it provides conclusive evidence for the presence of microplastics in the human stomach and provides important preliminary data in terms of the risks that may arise for human health.
1. Introduction
The escalating production demand and subsequent environmental leakage make plastic pollution a paramount global issue, directly impacting human health as well. By the end of 2019, global plastic production was close to 10 billion tons [1]. Of this total, roughly 10 % underwent recycling, and 14 % underwent incineration, leaving the remaining 76 % in landfills, dumps, or dispersed in the natural environment [2]. A staggering 22 % of all plastics produced globally is estimated to be mismanaged, contributing to environmental leakage [1].
While a significant quantity of plastics is intentionally produced as microplastics for various sectors, the inevitable breakdown of macroplastics into microplastics or nanoplastics is a growing concern. Microplastics (MPs) are defined as plastic particles with sizes ranging from 1 µm to 5 mm [3]. Nanoplastics is used for plastic particles at the nanometer dimension, covering 1–1000 nm (i.e. = <1 µm). Considering a specific weight of 1, the 22 million tons of plastics, previously calculated and reported to have leaked into the environment for the sole year of 2019 [1], results in a staggering outcome—approximately 5×10^26 micro-particles when hypothetically broken down to a size of 100 µm in diameter, posing a significant impact on the world’s ecosystems and eventually to human. To put this into perspective, it is noteworthy that the estimated number of individual live insects at any given time is significantly lower, approximately only 10×10^18 [4].
Whether in the form of macro-, micro-, or nanoplastics, these materials can inadvertently be ingested by a large number of aquatic or terrestrial animals. Consequently, they have been discovered in the stomach contents of a diverse array of terrestrial and aquatic organisms, ranging from earthworms and birds to zooplankton, fish, shellfish, turtles, dolphins, and whales [5], [6], [7], [8], [9].
Micro- or nano plastics also traverse the food web, reaching higher organisms, including humans. Therefore, plastic pollution is recognized not only as a significant environmental threat but also as a critical concern for human health. Recently, heightened attention has been directed towards the matter of human exposure to microplastics, driven by mounting concerns about its potential risks. The measurement of toxic chemicals in the human body, verification of exposure levels, and the implementation of public health protection measures are crucial. However, conducting a risk assessment for micro/nanoplastics is challenging due to the scarcity of data on both toxicological hazards and human exposure [10], [11], [12].
The exposure of humans to plastics, particularly those less than 10 µm in size, has become a prominent concern in this context. Studies conducted to date have primarily assessed human exposure to microplastics through inhalation [13], ingestion, and dermal contact [14]. Human exposure levels to microplastics vary according to age, sex, diet, and lifestyle [15].
Among these routes, ingestion, particularly through the consumption of food, stands out as a prevalent pathway for human exposure to microplastics. Numerous reports have highlighted the presence of microplastics in a wide variety of food items [16]. The research findings suggest a pervasive presence of microplastics across a diverse range of human-consumed food, beverage items, and plastic food packaging [15]. Notable examples include table salts [17], meat products [18], sushi seaweed (nori) [19], rice [20], vegetables, and fruits [21], mussels [22], fish [6], [23], and various beverage products [24].
When inhaled, microplastics, depending on their size, may permeate various organs or tissues by entering the bloodstream through the lungs. Similarly, plastic particles taken up in the intestine could also be transported throughout the body via the bloodstream. The translocation of microplastics through either intestinal absorption or epidermal infiltration, and nanoplastics through blood circulation, has been extensively documented in fish [25], [26]. Hence, the growing number of studies revealing the presence of plastic particles in various human organs is not surprising. The widespread presence of microplastics has been detected in human blood [12] lungs [27], saliva [28], sputum [29], placenta [30], stool [31], [32], [33], liver [34], and urine [35].
The World Health Organization [13] underscores the imperative for enhanced estimations regarding the exposure of the general population to micro/nanoplastics and its co-pollutants through both inhalation and dietary pathways. This data is crucial for understanding the relationship between the human exposure dose of microplastics and their toxic biological effects. The toxic effects of microplastics mainly depend on the physicochemical properties of the particle, the co-existence of organic pollutants, heavy metals that are adsorbed by the particles, and exposed cell types. Potential toxicity mechanism of microplastics includes oxidative stress due to increased intracellular reactive oxygen species (ROS), induced inflammatory response, and disruption of the energy homeostasis and metabolism which could lead to cytotoxicity, genotoxicity, metabolic disorders, and even carcinogenicity [15], [36], [37].
Recent studies have demonstrated adverse health effects due to the presence of micro/nanoplastics in humans. The study conducted by Yan et al. presents findings that indicate a positive correlation between the severity of inflammatory bowel disease (IBD) and the concentration of faecal microplastics [33]. Laboratory tests have demonstrated that microplastics can induce harm to human cells, triggering allergic reactions and even cell death [38]. Nanoplastics have been found to interact with the brain's naturally occurring protein; α-synuclein and resulting in alterations associated with both Parkinson's disease and certain forms of dementia [39]. A potential link between colorectal cancer and microplastic exposure levels has been proposed, based on the analysis of both tumoral colon tissues (TCT) and non-tumoral colon tissues (N-TCT) from patients diagnosed with colorectal adenocarcinoma [40].
Although micro/nano plastics have been identified in various human tissues, organs, fluids (such as blood and milk), and faeces excretion, to our best knowledge, no studies have specifically detected microplastics within human stomach content despite the human gastrointestinal system the primary target of toxic effects of ingested microplastics [37]. While numerous studies have demonstrated the presence of microplastics in a diverse range of food and beverages, their existence and behaviour in the highly acidic (pH = 1.5–2) environment of the human stomach remain unexplored, constituting the primary objectives of the current study.
