Microplastics are everywhere, including being found to enter our bodies through cavities exposed to the outside world. Two new studies have further examined the effect of microplastics on our health, with one finding that they cause brain inflammation and the second finding them in the heart, a completely enclosed organ.
Although small, at less than 5 mm (0.2 in) wide, microplastics have gained big notoriety of late, being found everywhere in the world, from the summits of Mount Everest to the depths of the ocean. So it’s hardly surprising that microplastics have also made their way into our internal organs.
Two recent studies have investigated microplastics in organs and the effects they might have. The first, undertaken by researchers at South Korea’s Daegu Gyeongbuk Institute of Science and Technology (DGIST), examined the effect of ingested weathered microplastics on the brains of rats. The second, by the Capital Medical University in Beijing, China, looked at microplastics found in the heart and bloodstream before and after surgery.
The DGIST study concerned the toxicity of weathered microplastics, which have undergone natural degradation after exposure to ultraviolet (UV) light and wind. With previous studies showing that microplastics can enter the tissues of living organisms, including humans, the researchers wanted to see whether they produced harmful effects on the brain.
Weathering caused by sunlight, air, heat, rain and wind alters the physical and chemical properties of microplastics. UV light, for example, causes a reaction that produces free radicals and promotes the fragmentation of the plastic into smaller particles called secondary microplastics. However, the precise biological effects of weathered microplastics are poorly understood.
The researchers artificially created secondary microplastics by replicating the process of natural weathering, subjecting crushed microplastics to UV light and physical impact for seven days. They then orally administered the weathered microplastics, measuring 100 micrometers or less, to rats once a day for seven days. Another group of rats were fed unweathered microplastics.
They found that, compared to the control group, the rats fed weathered microplastics showed a significant increase in the expression of inflammatory proteins associated with neurodegeneration and cell death, as well as a decrease in pro-inflammatory proteins in the external brain tissue. After conducting experiments using a human microglial cell line, the cells that regulate brain inflammation, the researchers found that the weathered microplastics stimulated the microglia to activate an inflammatory response.
The researchers say their findings suggest that weathered microplastics are more toxic than unweathered ones.
“Through proteomics-based analysis, we have, for the first time, identified that plastic leaked into the environment undergoes an accelerated weathering process, transforming into secondary microplastics that can serve as neurotoxic substances, leading to increased inflammation and cell death in the brain,” said Seong-Kyoon Choi, corresponding author of the study. “The implications of microplastics’ harmfulness are particularly alarming, as secondary microplastics exposed in natural environments induce a more severe inflammatory response in the brain.”
The DGIST study demonstrates that microplastics can produce harmful effects when ingested, but can microplastics make their way to our innermost organs, such as the heart, which is not directly exposed to the environment? The Capital Medical University study shows that the answer to that question is ‘yes.’
In this study, researchers collected heart samples from 15 people during heart surgery, in addition to pre- and postoperative blood samples from seven of the participants. Analyzing the samples using laser direct infrared imaging, they found microplastics in the heart and surrounding tissues.
Microplastics were not found in all tissue samples, but nine types were found across five types of heart tissue, measuring between 20 and 500 micrometers in width. Nine types of microplastics were also detected in pre- and postoperative blood samples.
The plastics found were polyethylene (PE), polyethylene terephthalate (PET), polyurethane (PU), polyvinyl chloride (PVC), polycarbonate (PC), polypropylene (PP), polyamine (PA), polystyrene (PS), and poly(methyl methacrylate) (PMMA). PET was the most prevalent (77%) in tissue samples. The most prevalent plastics in blood samples were PA (49%) and PET (22%).
Tens to thousands of individual microplastic pieces were observed in most tissue samples, though amounts and plastic types varied across participants. All of the blood samples – pre- and post-surgery – contained plastic particles of diverse types, but after surgery, their average size decreased.
The researchers say their study provides preliminary evidence that microplastics can accumulate in the heart despite being enclosed in the chest cavity. They say it also shows that an overlooked path of microplastic exposure, especially the larger particles, is invasive medical procedures, which may permit direct access to the bloodstream and tissues.
Further studies are needed to investigate how microparticles enter the heart tissues and their potential effects on long-term prognosis following heart surgery.
The study about weathered microplastics and brain inflammation was published in the journal Environmental Research, while the study about microplastics in the heart was published in the journal Environmental Science & Technology.
Sources: DGIST via Asia Research News, Capital Medical University via American Chemical Society