ReviewMicroplastic diagnostics in humans: “The 3Ps” Progress, problems, and prospects
Graphical abstract
Introduction
Plastic pollution is one of the century's major issues for humankind. The intensive production and usage of plastics, along with poor management, has resulted in the indiscriminate disposal of billions of tons of plastic waste into the environment (Jambeck et al., 2015; Geyer et al., 2017). Environmental plastic pollution of various sizes, such as mesoplastics (< 25 mm), microplastics (1 μm - 5 mm), and nanoplastics (< 1 μm), is at the forefront of this situation (Koelmans et al., 2019). Microplastics have been considered as a major environmental threat since they are prevalent in practically all ecosystems (Shahul Hamid et al., 2018; Dusaucy et al., 2021). They are either primary (made to a specified size, such as microbeads) or secondary (derived through physical, chemical, and biological degradation). Due to their small size, they are readily distributed in the environment and have grown ubiquitous enough to be ingested by both aquatic and terrestrial organisms (Wootton et al., 2021; Larue et al., 2021). Microplastics ingested can get incorporated into organs or tissues and convey organic and inorganic pollutants, impairing organisms' survival and reproduction (Guzzetti et al., 2018; Rahman et al., 2021). Additionally, they can penetrate the marine food chain and end up in human-consuming organisms, as there have been reports of microplastic contamination in commercial edible fish (Karbalaei et al., 2019; Akoueson et al., 2020), shrimp (Daniel et al., 2020; Hossain et al., 2020), and bivalves (Cho et al., 2019). Furthermore, microplastics have been detected in a number of human food products such as drinking water (Oßmann, 2021), milk (Kutralam-Muniasamy et al., 2020), soft drinks (Shruti et al., 2020), canned food (Akhbarizadeh et al., 2020), sugar (Afrin et al., 2022), salt (Kosuth et al., 2018), and so on. These findings support the involuntary direct intake of microplastics by humans, which is largely unavoidable. Other routes of microplastic exposure in humans include inhalation and dermal contact (Prata, 2018). As a consequence, we live in an era in which plastics linger in the world's ecosystems, infiltrate the human food chain, and enter the human body.
According to recent estimates, human exposure to microplastics can vary between 74,000 and 121,000 particles per year (Cox et al., 2019). Widespread scientific research is raising concerns about the potential toxicity and effects of microplastics on human health. Animal studies have shown that microplastics as small as 150 μm can cross the cell membrane and translocate into organs, posing a health risk, including oxidative stress, inflammatory effects, various metabolic disorders, and offspring defects (Wright and Kelly, 2017; Rahman et al., 2021). Several investigations into human cell lines have revealed that microplastic exposure causes inflammatory responses, inhibits cell growth, changes in cell morphology, and alterations in gut microbiota (De-la-Torre et al., 2021). Currently, an integrated exposure assessment via biomonitoring studies has become an ever-important goal to better understand the extent of internal exposure of microplastics to humans and assess their real accumulation, fates, and impacts. This has sparked renewed interest in research aimed at characterizing microplastic burdens in human bodies. The first pilot study, conducted by Schwabl et al. (2019), detected and quantified microplastics in human feces samples from people from various countries, demonstrating the likely load of microplastics in the gastrointestinal system as a result of food intake. Ragusa et al. (2021) revealed microplastic contamination in the placenta, implying that microplastics are transferred from the mother to the unborn fetus and constitute a risk to the newborns. Since then, human microplastic research has advanced dramatically, as indicated by the abundance of microplastics investigated in different human biological samples such as colectomy specimens (Ibrahim et al., 2021), saliva (Abbasi and Turner, 2021), sputum (Huang et al., 2022), lung (Amato-Lourenço et al., 2021), liver (Chen et al., 2022), breastmilk (Ragusa et al., 2022), and feces (Zhang et al., 2021a, Zhang et al., 2021b; Ho et al., 2022; Yan et al., 2021). Until recently, the detection of microplastics in blood revealed that microplastics are being transported throughout the body via the circulation (Leslie et al., 2022). These scientific findings received significant attention and impacted people's perceptions and understanding of human internal microplastic exposure.
Microplastics research in the human body is currently ongoing and limited to a few regions around the world, but it is rapidly evolving, with more studies expected to emerge in the near future. Despite the fact that there is no universally accepted definition of methodological approaches, various approaches for isolating and characterization of microplastics have sprung up in recent years. As of now, a major part of the attention in the literature is focused on the detailed negative consequences of microplastics on humans. To the best of our knowledge, the topic of microplastics investigation in the human body has not been systematically reviewed and introduced to a broad audience, although it is recently gaining huge attention in the microplastic scientific community. Moreover, understanding and leveraging the details of the recent advances is crucial to reliable assessment and provides an intriguing route forward to widening development. Given the growing interest in the topic, the primary goal of this systematic review of the literature is to provide the research community with a timely overview of microplastics in human biological samples in order to better understand current progress, identify challenges, and forecast future prospects. The review is divided into three parts. The first part includes the development of new approaches to sampling, isolating, detecting, and characterization of microplastics, combined with the contamination prevention measures that have recently been established. The second part describes a summary of the microplastics' abundance and characteristics documented in the human body. Following this, the third section analyzes current challenges and provides potential solutions based on our findings. Taking it all together, this review will be valuable to both specialists and novices as it offers tools to comprehend and employ in future investigations.
Section snippets
Literature search strategy
In this review paper, all peer-reviewed articles that investigated microplastics in human biological samples were searched in the Pubmed/Medline, Scopus, and Web of Science databases, with no publication year restrictions, and all relevant articles were retrieved on August 1, 2022. The search terms used were microplastics and/or any of the following keywords: human, blood, placenta, saliva, colon, hair, liver, kidney, lungs, sputum, feces, and breast milk. The search resulted in 4114 records
Search results: where is the field right now?
The very first publication of microplastics in human biological samples appeared in 2019. Nonetheless, the selected studies demonstrate a significant advancement in microplastic research on human biological materials, with 80 % of the studies published between 2021 and 2022 (Fig. 1a). The articles considered for this study were separated to determine the kind of human biological sample tested for microplastics. The large number of studies (85 %) selected focused on assessing microplastics in a
Initial steps
Designing human biomonitoring studies of microplastics involves several steps, which are separated and given in the following section.
Sampling methods
In general, there are two methods for collecting human biological samples: invasive and non-invasive. While blood, BALF, and tissues from the kidney, spleen, lung, and liver must be obtained in an invasive manner, samples from saliva, hair, skin, and hands were readily available and easily collected in the noninvasive procedure. They are obtained either at the clinic or hospital with the assistance of allied health professionals or from the participants themselves. In general, the sample
Quality assurance and quality control
Since potential airborne contamination is a major concern in microplastics research, the following measures were taken during laboratory experiments in all of the publications reviewed as shown in Fig. 4 and Supplementary Material Table S4: (i) cotton lab gowns and latex gloves were worn during laboratory work, (ii) all liquid reagents and media were filtered prior to use, (iii) when not in use, samples were covered with a glass lid or aluminum foil, (iv) workplace and each apparatus were
Microplastic abundance and characteristics: a baseline understanding
Until date, evidence of microplastics has been found in 15 human biological components (Fig. 5). The prevalence of microplastics varied greatly among the biological parts studied, with no microplastic particles found in the kidney. A prevalence of 100 % was reported majorly in 13 samples, while a low prevalence of microplastics (40–60 %) was observed in feces (Supplementary Material Table S5). On looking into the levels of microplastics, the following mean concentrations were reported in
A road lined with challenges and crucial tips to get there
The most recent advancements in microplastic extraction and detection procedures have allowed scientists to undertake a variety of studies on human biological samples from all around the world. Nonetheless, any researcher intending to conduct similar biomonitoring studies should be aware of the current limitations and challenges in order to move ahead and obtain more representative and robust data.
Cross-contamination of samples is one of the potential issues currently, and a significant one for
Conclusions and future outlook
Converging evidence points to human exposure to microplastics through various food chains and inhalation, suggesting potential health risks. This review has done its best to provide a concise summary as well as an early view of recent breakthroughs on microplastics in human biological samples. Recent knowledge can help to improve understanding of the application of many microplastic screening methods, together with data on microplastic abundance from individuals over the age of 18 from Europe
CRediT authorship contribution statement
V.C. Shruti - Conceptualization, Methodology, Data curation, Writing - original draft; Gurusamy Kutralam-Munaisamy - Conceptualization, Methodology, Data curation, Writing - original draft; Fermín Pérez-Guevara - Methodology, Conceptualization, Supervision, Priyadarsi D Roy - Methodology, Conceptualization, Supervision. All authors contributed to the article and approved the submitted version.
Declaration of competing interest
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.
Acknowledgements
VCS gratefully acknowledges financial support from DGAPA-UNAM postdoctoral fellowship program, Instituto de Geología, Universidad Nacional Autónoma de México.
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