This study investigated the presence and concentration of micro- and nanoplastics (MNPs) in human liver, kidney, and brain tissues obtained from decedents. The researchers found significantly higher MNP concentrations in brain tissue compared to liver and kidney (P < 0.0001, two-way ANOVA). They also observed a significant increase in MNP concentrations in both liver and brain tissues between samples collected in 2016 and 2024 (P-values from Mann-Whitney tests). Furthermore, brain samples from individuals diagnosed with dementia exhibited significantly higher MNP concentrations compared to those without dementia. The predominant polymer type identified in brain tissue was polyethylene (PE).
The study provides compelling evidence for the presence of micro- and nanoplastics (MNPs) in human tissues, including the brain, with significantly higher concentrations found in brain tissue compared to liver and kidney. A notable temporal increase in MNP concentrations was observed between 2016 and 2024, and a strong association was found between MNP accumulation and dementia diagnosis. However, it is crucial to emphasize that the study establishes correlation, not causation, between MNP presence and dementia. The observed association does not prove that MNPs cause or contribute to dementia; other factors related to dementia could influence MNP accumulation, or a common underlying factor could influence both.
The study's practical utility lies in its novel demonstration of MNP presence in human brain tissue and the quantification of MNP concentrations in different organs. This provides a crucial foundation for future research investigating the potential health consequences of MNP exposure, particularly concerning neurological effects. The findings highlight the growing concern of environmental MNP pollution and its potential impact on human health, placing this work in the context of a rapidly evolving field of research.
While the study presents significant findings, uncertainties remain. The mechanisms of MNP uptake, distribution, and clearance in humans are still poorly understood. The study acknowledges the limitations of using decedent tissues and the need for standardized analytical methods. The authors appropriately recommend further research to investigate these mechanisms, explore the potential link between MNP exposure and neurodegenerative diseases, and develop more refined analytical techniques. The guidance provided is cautious and emphasizes the need for more research before drawing definitive conclusions about the health risks of MNPs.
Critical unanswered questions include the specific pathways by which MNPs cross the blood-brain barrier, the long-term effects of chronic MNP exposure on brain health, and whether MNPs play a causal role in the development of dementia or other neurological disorders. While the methodological limitations, such as the use of decedent tissues and the lack of detailed contamination control protocols in the Methods section, do raise some concerns, the use of multiple analytical techniques and the replication of key results across different tissue banks and analytical sites provide some reassurance. However, the lack of detailed contamination control protocols could potentially affect the absolute quantification of MNPs, although the relative comparisons between groups are likely still valid. Further research with more rigorous contamination control is needed to confirm the absolute MNP concentrations.
The abstract clearly presents the central finding: the detection and quantification of MNPs in human tissues, particularly the brain.
The abstract succinctly describes the multi-methodological approach used, enhancing the credibility of the findings.
It concisely summarizes the key results, including differences in MNP composition and concentration across tissues and over time.
The abstract highlights a novel and significant finding regarding MNP accumulation in dementia cases.
The abstract appropriately concludes by emphasizing the broader implications and need for further research.
This high-impact improvement is crucial for placing the study in the context of existing literature and clarifying its novelty. The abstract, as the initial point of contact for most readers, should immediately establish the study's unique contribution.
Implementation: Add a sentence explicitly stating the novelty of the research, such as: "To our knowledge, this is the first study to quantify micro- and nanoplastics in human brain tissue."
This medium-impact change would improve the clarity and completeness of the abstract. While the abstract mentions "complementary methods," it doesn't specify *why* this multi-method approach is crucial. Briefly explaining the limitations of individual methods and the need for a combined approach strengthens the rationale.
Implementation: Add a phrase explaining the need for complementary methods, such as: "...due to the limitations of individual techniques in detecting and characterizing MNPs across a range of sizes and compositions."
This medium-impact change would enhance the abstract's informativeness. While "dementia diagnosis" is mentioned, specifying the *types* of dementia observed would provide valuable context, given the heterogeneity of dementia conditions.
Implementation: Modify the sentence to include the types of dementia, such as: "...in a cohort of decedent brains with documented dementia diagnoses, including Alzheimer's disease and vascular dementia..."
This low-impact improvement would add a crucial quantitative element to the abstract. Including the range of MNP sizes detected would provide valuable context for understanding the scope of the findings.
Implementation: Add a phrase specifying the size range, such as: "...ranging from 500 µm in diameter down to 1 nm, have increased exponentially..." or "...which present largely as nanoscale shard-like fragments."
This low-impact improvement would provide context for the temporal findings. Specifying the years compared (2016 vs. 2024) would make the abstract more self-contained.
Implementation: Change "the time of death (2016 versus 2024)" to "samples collected in 2016 versus 2024".
The introduction effectively establishes the context by highlighting the increasing environmental concentrations of microplastics and nanoplastics (MNPs) and the associated concerns about human exposure and health.
The introduction clearly states the knowledge gap regarding the tissue distribution and internal dose of MNPs in humans, which is crucial for interpreting controlled exposure studies.
It succinctly summarizes previous research on MNP detection in organs, while also pointing out the limitations of existing methods.
This high-impact improvement is essential to immediately establish the study's unique contribution and justify its significance. The introduction should clearly differentiate this research from prior work, highlighting its novelty to capture the reader's interest and emphasize its importance.
Implementation: Add a sentence explicitly stating the novelty of the research, such as: "This study is the first, to our knowledge, to investigate and quantify MNP presence in human brain tissue, alongside liver and kidney samples."
This medium-impact change would strengthen the introduction by providing a more complete picture of the potential health risks associated with MNPs. While the introduction mentions general health concerns, briefly elaborating on specific potential mechanisms (e.g., oxidative stress, inflammation) would provide stronger justification for the research.
Implementation: Add a sentence or phrase expanding on potential health consequences, such as: "...potential health consequences, including oxidative stress, inflammation, and disruption of cellular processes..."
This low-impact improvement would provide a smoother transition between the problem statement and the study's objective. A concise sentence summarizing the study's aim would enhance the logical flow and clarity of the introduction.
Implementation: Add a sentence clearly stating the study's objective, such as: "Therefore, this study aimed to quantify MNP concentrations in human liver, kidney, and brain tissues to better understand their distribution and potential accumulation patterns."
The Results section clearly presents the core findings, showing significantly higher micro- and nanoplastic (MNP) concentrations in brain tissue compared to liver and kidney, and an increase in MNP concentrations in liver and brain tissues between 2016 and 2024.
The section effectively uses figures and data visualizations (Fig. 1) to support the findings, making the results more accessible and understandable.
The study reports the application of a robust analytical method, pyrolysis gas chromatography–mass spectrometry (Py-GC/MS), which has been validated in other studies, adding credibility to the quantification of MNPs.
The study includes a comparison of MNP concentrations in brain samples from individuals with and without dementia, revealing a significant difference and suggesting a potential area for further research.
The section acknowledges the limitations of visual microscopic methods and justifies the use of Py-GC/MS for detecting smaller nanoplastics.
This high-impact improvement would significantly enhance the clarity and interpretability of the Results section. Currently, the section presents findings primarily focused on *differences* between groups (e.g., 2016 vs. 2024, brain vs. liver/kidney). However, it lacks a clear and concise statement of the *absolute* MNP concentrations found in each tissue type. This omission makes it difficult for readers to grasp the overall magnitude of MNP presence and compare the findings to other studies or exposure scenarios. The Results section is the appropriate place for this information, as it's where the core quantitative data are presented.
Implementation: Add a sentence or short paragraph at the beginning of the Results section summarizing the overall range and central tendency (e.g., median or mean) of MNP concentrations found in each tissue type (brain, liver, kidney). For example: "Across all samples, median MNP concentrations were X µg/g in brain tissue, Y µg/g in liver tissue, and Z µg/g in kidney tissue. The range of concentrations observed was A-B µg/g in brain, C-D µg/g in liver, and E-F µg/g in kidney."
This medium-impact change would improve the completeness and clarity of the Results section. While the section mentions the analysis of samples from different years (2016 and 2024), it doesn't explicitly state the *number* of samples analyzed in each group for each tissue type. This information is crucial for assessing the statistical power and robustness of the comparisons. This belongs in the results section, as it provides context for the quantitative data.
Implementation: Include the sample sizes (n values) for each group (2016 and 2024) and each tissue type (brain, liver, kidney) directly in the text, not just in the figure legend. For example: "Liver samples from 2016 (n=X) and 2024 (n=Y) were analyzed..."
This medium-impact improvement would enhance the clarity and flow of the Results section. The section jumps between different comparisons (tissue types, time points, dementia status) without clear transitions or a logical organizational structure. This makes it difficult for the reader to follow the progression of findings. Improving the organization would make the results easier to understand and interpret. The results section should have a logical flow.
Implementation: Organize the Results section into subsections with clear headings that reflect the different comparisons being made. For example: * "MNP Concentrations in Different Tissue Types" * "Temporal Trends in MNP Concentrations" * "MNP Concentrations in Dementia vs. Non-Dementia Brain Samples"
This low-impact improvement would enhance the clarity of the Results section. While the section mentions "12 different polymers," it doesn't list them all in the main text. Listing these polymers would provide a more complete picture of the MNP composition and allow for easier comparison with other studies. This is relevant to the results as it provides context for the data.
Implementation: List the 12 different polymers analyzed in the main text of the Results section, not just in the figure legend or methods. For example: "The analysis included 12 different polymers: polyethylene (PE), polypropylene (PP), ..."
This low-impact improvement would add clarity. The section mentions "orthogonal methods" but doesn't explicitly name them in the Results. While they are likely detailed in the Methods, briefly mentioning them here would provide context for the Py-GC/MS results. This is relevant to the results as it reinforces the robustness of the findings.
Implementation: Briefly mention the orthogonal methods used alongside Py-GC/MS in the Results section. For example: "Consistent with the Py-GC/MS findings, analysis using [orthogonal method 1] and [orthogonal method 2] also showed..."
Fig. 1 | Overview of total MNP concentrations from all decedent samples from liver, kidney and brain. a, Microplastic concentrations in liver, kidney and brain decedent human samples (n = 20–28 separate participants for each timepoint; Supplementary Table 1) from the UNM OMI. Data are shown on a log10 scale, with the bar representing the group median value and 95% confidence interval. Orange-colored symbols in the 2016 brain samples were analyzed independently at Oklahoma State University. P values from Mann-Whitney tests (two-sided) indicate significant differences in samples from the same organ between 2016 and 2024 (with more comprehensive statistical treatments in Supplementary Methods-Statistical analysis). Brain MNP concentrations were significantly higher than liver and kidney, analyzed by two-way ANOVA (P < 0.0001). b, Overall distribution of 12 different polymers suggests a greater accumulation of PE in the brain relative to liver or kidney (average shown per group; see Extended Data Fig. 1 for individual data). c, PE (which was in the highest abundance and consistently had the highest confidence spectra) concentrations in all organs followed similar trends compared to total plastics (also represented as group median value and
Fig. 2 | Visualization of putative plastics in the brain. a, b, Polarization wave microscopy (a, black arrows indicate refractory inclusions; inset is a digital magnification for clarity) and SEM (b, visual fields are 15.4 and 20.1 µm wide) were used to scan sections of brain from decedent human samples. c, Large (>1 µm) inclusions were not observed; additional polarization wave examples are highlighted (white arrows highlight submicron refractory inclusions). Resolution limitations of these technologies drove the use of TEM to examine the extracts from the pellets used for Py-GC/MS. d, Example TEM images resolved
The Discussion effectively connects the study's findings back to the broader context of increasing environmental MNP concentrations and the potential implications for human health.
The section acknowledges the limitations of the study, such as the lack of standardized analytical methods and the potential for contamination, which adds to the scientific rigor and transparency.
The Discussion highlights the novelty of the findings, particularly the detection of MNPs in human brain tissue and the higher concentrations observed in dementia cases.
The section discusses potential mechanisms of MNP uptake and distribution, drawing on insights from other organisms and suggesting possible pathways in humans.
The section appropriately emphasizes that the findings regarding dementia are associative and do not establish causality, maintaining scientific accuracy and avoiding overinterpretation.
This high-impact improvement would significantly enhance the Discussion's depth and impact by placing the current findings within the context of existing literature on MNP exposure and potential health effects. The Discussion section's purpose is to interpret the results in a broader scientific context. Currently, the Discussion makes limited references to other studies, primarily focusing on methodological comparisons. A more thorough comparison with existing research would strengthen the study's conclusions and highlight its contribution to the field.
Implementation: Incorporate a more comprehensive discussion of relevant literature on MNP exposure, tissue distribution, and potential health effects (especially neurological effects). Compare and contrast the current findings with those of other studies, highlighting areas of agreement, disagreement, and novelty. For example: "Our findings of PE predominance in the brain are consistent with [citation] who reported... However, our observation of higher MNP concentrations in dementia cases contrasts with [citation] who found... This discrepancy may be due to..."
This medium-impact improvement would strengthen the Discussion by providing a more balanced perspective on the study's limitations. The Discussion section should critically evaluate the study's strengths and weaknesses. While the Discussion acknowledges some limitations (e.g., lack of standardized methods), it could be more explicit about potential biases or confounding factors that might influence the results. This is crucial for a balanced interpretation of the findings.
Implementation: Expand the discussion of limitations to include potential biases or confounding factors, such as: * The use of decedent tissues, which may not fully reflect MNP distribution in living individuals. * The potential for postmortem changes in MNP distribution or degradation. * The limited demographic information available for the samples, which restricts the ability to control for potential confounders. For example: "It is important to acknowledge that the use of decedent tissues may introduce certain biases. Postmortem changes in tissue integrity or MNP distribution cannot be entirely ruled out..."
This medium-impact change would enhance the Discussion by providing a more concrete and actionable roadmap for future research. The Discussion section should outline future research directions. While the Discussion mentions the need for further research, it could be more specific about the types of studies needed to address the remaining knowledge gaps. This would provide a clearer direction for the field.
Implementation: Provide more specific recommendations for future research, such as: * Studies investigating the mechanisms of MNP uptake and transport across the blood-brain barrier. * Longitudinal studies examining the relationship between MNP exposure and neurological outcomes in living individuals. * Research to develop and validate standardized methods for MNP detection and quantification in human tissues. * Studies exploring the potential role of MNP exposure in the pathogenesis of specific neurodegenerative diseases. For example: "Future research should focus on elucidating the mechanisms by which MNPs cross the blood-brain barrier. Longitudinal studies with well-defined cohorts are needed to investigate the potential link between chronic MNP exposure and the development of neurodegenerative diseases..."
This low-impact improvement would improve the clarity and flow of the Discussion. The section jumps between different topics (limitations, mechanisms, future research) without clear transitions or a strong unifying narrative. A more organized structure would enhance readability and strengthen the overall argument.
Implementation: Organize the Discussion into subsections with clear headings that reflect the different themes being addressed. For example: * "Comparison with Existing Literature" * "Potential Mechanisms of MNP Uptake and Distribution" * "Limitations of the Current Study" * "Future Research Directions" * "Conclusions"
This low-impact improvement would add nuance to the discussion of potential MNP accumulation mechanisms. The Discussion mentions lipid ingestion as a potential pathway, but it could briefly discuss other possibilities, such as inhalation or uptake through the olfactory system, to provide a more complete picture.
Implementation: Briefly mention other potential routes of MNP exposure and uptake into the brain, such as inhalation and subsequent translocation via the olfactory nerve. For example: "In addition to ingestion, inhalation of airborne MNPs may represent another route of exposure. Studies have suggested that inhaled nanoparticles can reach the brain via the olfactory nerve [citation]..."
The Methods section clearly describes the source of human tissue samples, including the use of a consistent collection protocol and the inclusion of samples from multiple repositories.
The section provides a concise overview of the Py-GC/MS method used for detecting polymer solids, referencing detailed supplementary methods for further information.
The section clearly states the specific polymers included in the microplastics-CaCO3 standard used for comparison in the Py-GC/MS analysis.
The section mentions the software used for identifying polymer spectra, adding to the transparency and reproducibility of the analysis.
The section briefly mentions the data normalization step, which is crucial for accurate quantification of MNP concentrations.
This high-impact improvement would greatly enhance the study's methodological rigor and transparency. The Methods section is the appropriate location for this level of detail. Currently, the Methods section provides a general overview of the tissue collection protocol but lacks crucial details about the *specific* procedures used to ensure consistency and minimize contamination. This omission undermines the reliability of the findings, as variations in tissue handling could significantly impact MNP measurements. Providing a detailed, step-by-step protocol is essential for reproducibility and allows other researchers to critically evaluate the methods.
Implementation: Provide a detailed, step-by-step protocol for tissue collection, including: * Specific anatomical locations from which tissues were sampled (beyond just "frontal cortex"). * Instruments used for tissue dissection and handling (e.g., type of scalpel, forceps). * Detailed description of the containers used for tissue storage (material, size, cleaning procedures). * Specific steps taken to minimize contamination during collection and handling (e.g., use of gloves, sterile instruments, clean room environment). * Duration and conditions of tissue storage before processing. Example: "Brain tissue samples (approximately 1 cm³) were obtained from the left superior frontal gyrus using a sterile, disposable stainless steel scalpel and PTFE-coated forceps. Samples were immediately placed in pre-cleaned, 50 mL polypropylene containers filled with 10% neutral buffered formalin..."
This high-impact improvement is crucial for ensuring the reproducibility and validity of the study's findings. The Methods section is the appropriate place to detail these critical steps. The current Methods section describes the chemical digestion and ultracentrifugation steps but lacks crucial details about the *specific* procedures and quality control measures used to prevent and monitor contamination. This omission raises concerns about the potential for external MNP contamination to influence the results. A detailed description of contamination control measures is essential for demonstrating the rigor of the study.
Implementation: Provide a detailed description of the contamination control procedures, including: * Specific measures taken to prevent contamination during sample processing (e.g., use of laminar flow hood, filtered solutions, pre-cleaned glassware). * Detailed description of blank samples used (e.g., reagent blanks, procedural blanks) and their processing. * Frequency of blank sample analysis and acceptance criteria for blank contamination levels. * Specific steps taken to clean and prepare glassware and equipment. * Details of any air filtration or environmental monitoring used in the laboratory. Example: "All sample preparation steps were performed in a Class 100 laminar flow hood. Reagents were filtered through 0.2 µm PTFE filters before use. Glassware was thoroughly cleaned with [detergent], rinsed with ultrapure water, and baked at [temperature] for [duration]. Procedural blanks (containing all reagents but no tissue) were processed alongside each batch of samples..."
This medium-impact improvement would enhance the clarity and reproducibility of the Py-GC/MS analysis. The Methods section should provide all necessary details. While the Methods section mentions Py-GC/MS, it lacks specific details about the *instrument parameters* used. This omission makes it difficult for other researchers to replicate the analysis and compare their findings. Providing these details is standard practice in scientific publications and enhances the study's transparency.
Implementation: Provide specific details about the Py-GC/MS instrument parameters, including: * Make and model of the Py-GC/MS instrument. * Pyrolysis temperature and duration. * GC column type and dimensions. * GC oven temperature program. * Carrier gas and flow rate. * MS detector type and settings (e.g., scan range, ionization mode). Example: "Py-GC/MS analysis was performed using a [Make and Model] instrument equipped with a [Pyrolyzer Model] pyrolyzer. Pyrolysis was conducted at [temperature] for [duration]. The GC separation was performed using a [Column Type] column ([dimensions]) with a [Carrier Gas] carrier gas at a flow rate of [flow rate]..."
This medium-impact improvement would improve the clarity and completeness of the Methods section. It is important to specify how data were handled. The Methods section mentions that the resulting data were normalized to the original sample weight, but it doesn't specify the *units* used for the sample weight. This ambiguity could lead to confusion and inconsistencies in data interpretation. Specifying the units is a simple but important detail that enhances the clarity and reproducibility of the study.
Implementation: Specify the units used for the original sample weight in the data normalization step. Example: "The resulting data were normalized to the original sample weight (in grams) to render a mass concentration (µg g-1)."
This low-impact improvement would enhance the completeness of the Methods section. It is important to fully describe the methods used. While the section mentions that limited demographic data were available, it doesn't explicitly state whether *cause of death* was recorded for all participants or only a subset. Clarifying this point would provide a more complete picture of the available data and potential limitations.
Implementation: Clarify whether cause of death was recorded for all participants or only a subset. Example: "Limited demographic data (age, sex, race/ethnicity, cause of death [recorded for all participants], and date of death) were available..."