Microplastics suspected to cause Digestive, Reproductive, and Respiratory problems (mice and women)
Effects of Microplastic Exposure on Human Digestive, Reproductive, and Respiratory Health: A Rapid Systematic Review
Environmental Science & Technology https://doi.org/10.1021/acs.est.3c09524
Nicholas ChartresCourtney B. CooperGarret BlandKatherine E. PelchSheiphali A. GandhiAbena BakenRaTracey J. Woodruff
Microplastics are ubiquitous environmental contaminants for which there are documented human exposures, but there is a paucity of research evaluating their impacts on human health. We conducted a rapid systematic review using the “Navigation Guide” systematic review method. We searched four databases in July 2022 and April 2024 with no restriction on the date. We included studies using predefined eligibility criteria that quantitatively examined the association of microplastic exposure with any health outcomes. We amended the eligibility criteria after screening studies and prioritized digestive, reproductive, and respiratory outcomes for further evaluation.
We included
three human observational studies examining reproductive (n = 2) and respiratory (n = 1) outcomes and
28 animal studies examining reproductive (n = 11), respiratory (n = 7), and digestive (n = 10) outcomes.
For reproductive outcomes (sperm quality) and digestive outcomes (immunosuppresion) we rated overall body evidence as “high” quality and concluded microplastic exposure is “suspected” to adversely impact them. For reproductive outcomes (female follicles and reproductive hormones), digestive outcomes (gross or microanatomic colon/small intestine effects, alters cell proliferation and cell death, and chronic inflammation), and respiratory outcomes (pulmonary function, lung injury, chronic inflammation, and oxidative stress) we rated the overall body of evidence as “moderate” quality and concluded microplastic exposure is “suspected” to adversely impact them. We concluded that exposure to microplastics is “unclassifiable” for birth outcomes and gestational age in humans on the basis of the “low” and “very low” quality of the evidence. We concluded that microplastics are “suspected” to harm human reproductive, digestive, and respiratory health , with a suggested link to colon and lung cancer. Future research on microplastics should investigate additional health outcomes impacted by microplastic exposure and identify strategies to reduce exposure.
📄 Download the PDF from VitaminDWiki
DISCUSSION section of PDF
We have identified suspected human health risks from microplastic exposure in three body systems (digestive, reproductive, and respiratory). For reproductive outcomes (sperm quality) and digestive outcomes (immunosuppression) we rated the overall body of evidence as “high" quality and concluded microplastic exposure is “suspected" to adversely impact them based on consistent evidence of adverse health effects and confidence in the association. We downgraded the evidence from “presumed" based on the sample size and number of studies.
For
reproductive outcomes (female follicles and reproductive hormones),
digestive outcomes (gross or microanatomic colon/small intestine effects, alters cell proliferation and cell death, and chronic inflammation),
and respiratory outcomes (pulmonary function, lung injury, chronic inflammation, and oxidative stress)
we rated the overall body of evidence as “moderate" quality and concluded microplastic exposure is “suspected" to adversely impact them based on consistent evidence of adverse health effects and confidence in the association. We concluded that exposure to microplastics is “unclassifiable" for birth outcomes and gestational age in humans based on the “low" and “very low" quality of the evidence.
Given the ubiquity of microplastics and the consistent, growing recognition of their existence in the human body, it is likely that microplastics will impact other body systems, which is a potential area for future research.99 This is a particularly timely given that plastic production is projected to triple by 2060.2
These findings have important implications for policy and research. First, given the indication of harm that we have identified, the need for additional research on the health effects of microplastics should not preclude action. We strongly recommend that regulatory agencies and decision makers can act on limited evidence given that evidence has been shown to grow and get stronger100 and initiate actions to prevent or mitigate human exposure to microplastics. Second, there is opportunity under the U.S. Environmental Protection Agency's Toxic Substances Control Act (TSCA) to consider microplastics as a class or category of chemicals101 in its risk evaluations, which is a key component of identifying health risks for risk management actions. The U.S. Congress gave the U.S. Environmental Protection Agency (EPA) the authority to jointly evaluate any “category of chemical substances",102 defined as “a group of chemical substances the members of which are similar in molecular structure, in physical, chemical, or biological properties, in use, or in mode of entrance into the human body or into the environment, or the members of which are in some other way suitable for classification."103 Microplastics would meet this definition. Additionally, EPA could conduct a cumulative risk assessment based on their draft approach.104
The strengths of this work include the use of established rapid systematic review (rapid review) methods to accelerate the process of performing a full systematic review.38'39 Our rapid review was guided by the Navigation Guide systematic review method,40 which has been implemented to evaluate the health effects of multiple chemical exposures41-43,10S and used by the World Health Organization and International Labor Organization Joint Estimates of the Work-related Burden of Disease and Injury.44 These methods represent a transparent, rigorous, and unbiased approach to gathering the available evidence, evaluating it, and developing actionable statements for decision makers.
We applied the key characteristics approach,S1'S3'S6 an approach that is in alignment with the State of California's current efforts to advance methods using biological and mechanistic data to understand human health harms from exposure to chemicals.106 For the digestive and respiratory outcomes, we utilized the key characteristics of carcinogens.
For reproductive health outcomes , we utilized the key characteristics of reproductive toxicity.S1,S6 We used the concept of key characteristics to identify mechanisms indicative of cancer or reproductive toxicity.S1'S3'S6'81 Using this approach, the greater the number of key characteristics identified, the more likely the exposure (microplastics) was linked to these adverse health outcomes. We prioritized the evidence most useful for understanding the impacts of microplastic exposure on human health and reported significant findings on the basis of statistical relevance. We conducted a sensitivity analysis to test the robustness of our results when including only one type of microplastic and only one study result per outcome in the synthesis.
We extrapolated microplastic exposure concentrations in rodent studies to the predicted exposure concentrations in humans. We converted all microplastic concentrations (which were reported in a variety of ways, including micrograms per liter, micrograms, milligrams per kilogram, micrograms per gram, and milligrams per day) to particles per liter for water or particles per gram for food. Assuming an approximate daily consumption rate of S mL of water and S g of food for each rodent, a daily microplastic consumption rate was estimated unless specified otherwise.107 To convert the units from mass to particles, we assumed a spherical shape and density of each plastic polymer under standard conditions (1.0S g/cm3 for polystyrene and 0.96 g/cm3 for polyethylene).108
For microplastic sizes between S and 1S0 um, the range of daily microplastic intake for exposed rodent experiments is approximately 7-70 000 microplastic particles, which is in range with the estimated daily microplastic intake for humans (~422 particles per day).109 For smaller microplastic sizes such as 0.0S-0.S nm, the range of daily exposure concentrations was approximately 7 X 106 to 8.02 X 1011, which could be higher than estimated human exposure concentrations but can still be informative for human health effects.
There were both methodological limitations and evidence base limitations of this review. Although the methods we employed were extremely rigorous, we recognize the possibility for increased human error, particularly in our screening and risk of bias assessment methods in which one person was screened/evaluated and another verified, which would be conducted in duplicate in a full systematic review. We also did not evaluate all outcomes reported in the included studies, nor did we consider all body systems that may be impacted by microplastic exposure. We further recognize that we were addressing only rodent studies and that the inclusion of other species (such as zebrafish) would make our findings more robust. Additionally, the use of p values to identify if there was a significant harmful difference between the control and most exposed group is likely to underestimate the number of outcomes where microplastic exposure leads to changes between these groups. However, we avoided placing increased weight on statistical significance, which does not address biological significance or the magnitude of the effect observed.
Despite the growing body of evidence linking microplastics to adverse health outcomes, limitations in the evidence base remain. The studies in our rapid review are limited to primary microplastics of only three polymer types (polystyrene, polyethylene, and polypropylene) and one source of secondary microplastics (tire wear particles). The shape and size of microplastics evaluated in the included studies were also very homogeneous (generally spherically shaped). The variety of microplastics in terms of polymer types, sizes, and shapes is much greater and may differentially impact health but has not been studied in chronic rodent systems.110 We also could not account for additives in the plastics or the effects of microplastics degraded from sources like fabrics given the lack of studies on these topics. We could also not consider aggregate or cumulative exposures to microplastics and other environmental contaminants. We also did not consider the biological contaminants that may attach to microplastics,111 which may impact how other environmental chemicals or other biological contaminants enter the human body. Our study was also limited by the study population; only one study each evaluated sensitive life stages (e.g., child development), exacerbation by other stressors (e.g., poverty and food scarcity), or disease or genetic status (e.g., only healthy homogeneous rodents evaluated). Thus, we could not evaluate cumulative impacts of microplastic exposure.
There is a potential for publication biases. It is possible that studies showing null effects of microplastic exposure were either not accepted or submitted for publication or that other important end points in the included studies were either not measured or not reported. We additionally found limited human studies, which could reflect a lack of appropriate resource allocation to address the challenges of conducting epidemiological studies, or that this is a nascent area of research and that the follow-up time required to show the relationship between microplastics and human health effects has not been sufficient for these studies to be published. As this was a rapid review, we did not contact the authors for missing data.
Given these limitations, it is likely our conclusions underestimate the true health impacts of microplastic exposure. Importantly, these limitations highlight that there are clear opportunities for future research, including (1) epidemiological studies and standardizing analytical methods investigating the health impacts of microplastic exposure, (2) other health outcomes impacted by microplastic exposure, and (3) evaluating the impact of microplastic exposure for susceptible human populations due to their developmental stage or other socioenvironmental stressors. Finally, research should focus on identifying, and then evaluating, strategies for mitigating or preventing exposures to microplastics.
VitaminDWiki -Microplastics causing problems in humans, etc. (Vitamin D can help) - many studies
VitaminDWiki – Interactions with Vitamin D contains
{include}