Asian Scientist Magazine (Aug. 30, 2023) — Microplastics, tiny pieces of once larger plastic items, have been proven to endanger both planetary and human health. These specks of eroded plastic can find their way almost anywhere—in fish, packaged food, the Yangtze River in China and even the human blood.

The particles can undergo further degradation when exposed to natural conditions. Sunlight, heat, wind, and waves introduce further chemical and physical alterations to microplastics, which are then known as weathered microplastics (WMPs), potentially influencing their behavior within biological systems.

In a recent study, published in Environmental research, Korean scientists have found that continuous consumption of these weathered microplastics (WMPs) triggered severe inflammation and toxicity in mouse brains compared to virgin microplastics (VMPs). Their report provides the first step forward in understanding the health consequences of naturally-altered microplastic pollutants.

The team studied polystyrene-derived microplastics due to its significance in modern industries and its frequent occurrence in natural environments. To simulate the weathering process, they exposed the microplastics to seven days of ultraviolet (UV) irradiation and physical stress, emulating the effects of sunlight and waves.

Upon weathering, the microplastics exhibited reduced particle size and molecular weight, a textured surface, yellowing and structural alterations. Given that smaller microplastic particles disperse easier and can be absorbed more readily, the researchers hypothesized that WMPs were likely to be more toxic than their virgin counterparts.

Indeed, mice that received oral administration of WMPs for seven days displayed notably elevated levels of inflammatory proteins compared to the animals consuming VMPs. The researchers also observed an almost five-fold increase in the expression of biological pathways linked to neurodegeneration and cell death in the brains of the mice.

Moreover, further experiments in a human microglial cell line, which play a vital role in regulating inflammatory responses in the brain, also demonstrated a more severe inflammatory response to WMP than to VMP.

“Through proteomics-based analysis, we have, for the first time, identified that plastic leaked into the environment undergoes an accelerated weathering process, transforming it into secondary microplastics that can serve as neurotoxic substances, leading to increased inflammation and cell death in the brain,” said Choi Sungkyun, Head of the Core Protein Resource Center at Daegu Gyeongbuk Institute of Science & Technology (DGIST), who co-led the study.

Growing plastic use could lead to an estimated 12 billion tons of plastic waste being tossed into landfills and natural environments by 2050.

In future work, the researchers intend to carry out more long-term experiments involving a larger mouse population and diverse mouse strains for providing further evidence in support of their hypothesis. They also emphasized the importance for understanding the distribution mechanisms of these microplastics within organ systems.

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Source: Daegu Gyeongbuk Institute of Science & Technology ; Image: Shutterstock