From Ocean to Brain: A Guide to Microplastics in the Human Body

According to recent research, the average person globally consumes approximately the weight of a credit card each week. Even more alarmingly, scientists have found traces of microplastics in human blood clots, brain tissue, and even the placenta.

How did this happen? Why has this material, once hailed as "the greatest invention of the 20th century," gradually become a hidden threat to our health? And how do they quietly enter our bodies?

Microplastics: Where Do They Come From?

The term "microplastics" first emerged in 2004. Back then, Richard Thompson, a marine ecologist at the University of Plymouth, and his team published a paper in the journal Science, noting that they had discovered large quantities of plastic fragments less than 5 mm in diameter, roughly the size of a grain of rice, in sediments along the UK coast and on the seafloor. This led to the term "microplastics."

The widespread presence of microplastics is directly linked to humanity's continued and excessive use of plastic products and their inappropriate disposal practices. Since 1950, global plastic production has soared from 2 million tons to over 450 million tons in 2020. However, recycling efficiency is extremely low—only 9% of plastic was recycled in 2019. Most went to landfill or incineration, and approximately 22% was discarded into the natural environment. Under the influence of sunlight, wind, and water, these plastics gradually break down and decompose, forming a vast number of microplastics.

▎Three Ways Microplastics Invade the Human Body

Wearing and Washing: Clothing is One Source of Microplastic Release

Compared to natural fibers, synthetic materials such as polyester and nylon are more likely to release microplastics during wear and washing.

A single polyester garment can shed over 1,900 microfibers in a single machine wash. These microfibers are so tiny that they easily pass through washing machine filters and municipal sewage systems, ultimately ending up in natural waterways. It is estimated that approximately 176,500 tons of microplastics from synthetic textiles are released into the environment annually.

Dietary Intake: Vegetables Can Also Absorb Microplastics from the Air

Not only seafood and meat, but vegetables can also carry microplastics. A recent study published in the journal Nature shows that plant leaves can directly absorb and accumulate microplastics from the air, making the atmosphere a key pathway for microplastics to enter crops and ultimately reach human diets.

Even more alarmingly, once microplastics enter an organism, they move extremely quickly. A 2023 animal study showed that ingested microparticles can cross the blood-brain barrier and enter the brain in just two hours.

Drinking Methods: Hidden Risks in Bottled Water, Disposable Paper Cups, and Tea Bags

People who habitually use bottled water, disposable paper cups, or tea bags may be at higher risk for microplastic intake.

According to a study in Environmental Science and Technology, a single nylon or PET tea bag steeped in 95°C water for five minutes can release approximately 11.6 billion plastic particles and 3.1 billion nanoplastics. Another study published in the Journal of Hazardous Materials found that more than 25,000 micron-sized plastic particles were detected in hot drinks poured into disposable paper cups 15 minutes after consumption.

A study published in the Proceedings of the National Academy of Sciences of the United States of America further revealed that each liter of bottled water contained an average of approximately 240,000 detectable plastic particles—especially when the bottle is squeezed or repeatedly opened, which can cause even more particles to be released into the water.

▎The Spread of Microplastics and Health Threats

Currently, most wastewater treatment plants are not equipped with specialized processes to remove microplastics, resulting in some microplastics entering natural waters with their discharge.

From land to sea, microplastics have been found in every corner of the planet—in deep-sea sediments, remote islands, Arctic sea ice, and even Antarctic snow. Microplastics in the environment are ingested by plankton, fish, and shellfish, then accumulated through the food chain and ultimately enter the human body.

Additionally, crops may absorb microplastics from the soil through their roots, transferring them to edible parts. Salt and drinking water have also been found to be carriers of microplastics.

An animal study published by Ningxia Medical University in Ecotoxicology and Environmental Safety suggests that frequent use of single-use plastics may increase the risk of heart failure by 13%. Long-term exposure to these products can alter the composition of gut microbes, triggering inflammation and oxidative stress, leading to myocardial damage and cardiovascular disease.

Furthermore, endocrine disruptors such as bisphenol A (BPA) and phthalates (PAEs), commonly added to plastics, can affect normal hormone function in the human body, further posing a threat to the cardiovascular system.

How to Reduce Microplastic Intake?

1.Avoid direct contact of hot food with plastic bags.

High temperatures can cause plastic to degrade and release microparticles. It is recommended to transfer food to glass or ceramic tableware before eating.

2.Minimize the use of plastic cutting boards.

Studies have shown that microplastics can be shed when cutting vegetables or chopping meat on plastic cutting boards. It is estimated that using polyethylene cutting boards for one year may expose the human body to 14.5 million to 71.9 million microplastic particles.

3.Be cautious when consuming seafood offal.

Microplastics tend to accumulate in the offal of marine life. A study reviewing over 50 papers indicates that shellfish contamination is more severe in Asia. It is recommended to thoroughly wash and cook shellfish before consumption, and to remove the intestines, stomach, and gills.

4.Reduce the use of single-use plastic products, including plastic cups, straws, and takeout containers. Avoid using plastic containers for hot food or drinks to minimize potential exposure.