Digging the root | Are microplastics really as scary as "getting into your brain and chewing your marrow"? The truth may be far from what you think

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"Be careful! Your body may be infiltrated by 'plastic waste'!"

"Scientists Found Microplastics in the Human Brain!"

"Scientists have found microplastics in human blood for the first time, which are not only toxic but also carcinogenic!"

“Plastics are slowly invading your body, starting with the water you drink.”

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When it comes to microplastics, many people are terrified by the various rumors about them on the Internet. So, are these widely circulated claims true insights or over-interpretations?

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Plastic is a widely used synthetic material that can be found everywhere in people's lives. It is completely unnecessary to exaggerate the health hazards of microplastics or even worry about the existing plastic waste in the environment. Of course, it is worth encouraging people to develop good environmental protection habits and reduce unnecessary plastic pollution.

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Jin Yong's novel "The Smiling, Proud Wanderer" describes a magical drug called "Sanshi Nao Shendan" that can be used to control people. The lurking corpse worms in it can drill into the human brain and chew the brain marrow, causing people to go crazy. Since about 2016, online platforms have occasionally appeared articles promoting the hazards of "microplastics". The characteristics of microplastics described in the articles are similar to those of "Sanshi Nao Shendan", causing panic among a considerable number of people.

Since its invention, plastics have been widely used in all aspects of human life. Plastics are the product of science and technology, and also a symbol of human social development and modern civilization. With the widespread use of plastics, people are paying more and more attention to the problems caused by plastics, especially topics related to human health, which often trigger public discussions.

Two facts meet here. First, plastics have been found in almost all ecological environments, from the bottom of the Mariana Trench to the top of Mount Everest. Plastic particles called "microplastics" have been found in animals, and some studies even claim that evidence of plastics has been found in the human body (digestive tract, lungs, blood, placenta, brain, etc.); second, with the improvement of living standards and the development of medical standards, the average life expectancy of human beings continues to increase, and the incidence of aging-related diseases such as cancer, respiratory diseases, cardiovascular diseases, infectious diseases, and inflammatory diseases such as allergies is also increasing.

Creating associations between events is a unique ability that humans have evolved, and creating causal relationships from correlations is a characteristic of the human brain. Once the above two facts meet and are connected, some people naturally conclude that plastic causes various diseases and harms human health.

Of course, there are also research institutions and researchers who search for evidence to support this "conclusion". For example, researchers have studied the toxic effects of plastics on humans and animals from many aspects, including cytotoxicity, immune response, oxidative stress, genetic toxicity, etc. Other researchers have reported many findings that plastics are harmful to health, such as aquatic animals ingesting microplastics, which can lead to changes in gastrointestinal physiology, immune system suppression, and developmental disorders. Some people further deduce that as the food chain is transmitted, these adverse health effects will spread to the entire ecosystem and ultimately endanger human health.

Is this really the case?

Plastic microbeads have long been used in daily chemical products

First, let's take a look at what exactly "microplastics" are that have caused concern and even panic. This term appeared 20 years ago and was proposed by Richard Thompson, a marine scientist at the University of Plymouth in the UK. In 2004, he found a lot of plastic debris the size of rice grains on British beaches, which he called "microplastics." The size of these microplastics is mostly less than 5 mm, so the public and even the scientific community have agreed to call plastics less than 5 mm "microplastics."

From this perspective, microplastics are just a relative concept in terms of size, and this concept has no special meaning in other aspects since its birth. The current understanding of microplastics has gone beyond the scale of the naked eye, and plastic particles of micron or even nanometer size that can be detected by instruments are also collectively referred to as microplastics.

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How are these microplastics produced? Microplastics come from a variety of sources, including decomposed plastic products, resin particles made from plastics as raw materials, etc. These plastic products undergo physical and chemical degradation in nature and become smaller and smaller particles. There is also a kind of processed plastic microbeads, which are closely related to our lives and are a common ingredient in daily chemical products. For example, the tiny plastic particles in some health and beauty products are used as scrubs to remove the stratum corneum of the skin or whiten teeth. The addition of microplastics to daily chemical products has a long history. About 50 years ago, plastic microbeads appeared in personal care products and gradually replaced natural ingredients. There are a large number of products containing plastic microbeads on the market, but most consumers are not aware of it.

These microbeads are too small and are used in beauty products, so their final destination is to be discharged into natural water bodies through the sewage system. After washing your face or brushing your teeth, plastic microbeads are discharged into the environment through the drain pipe. Because the microbeads cannot be removed by the filtration system, they will enter rivers, lakes and oceans and be ingested by fish and other wildlife.

In view of the potential harm of plastic microbeads to the environment, the US President (Obama) signed the Microbead-Free Water Act in 2015 and it was passed by Congress. This act prohibits the production, packaging and sale of cleansing cosmetics containing plastic microbeads in the United States. The act also applies to products such as toothpaste and over-the-counter drugs. However, this act is not established to address consumer safety issues, and there is no evidence that the use of plastic microbeads in cosmetics causes human health problems.

Accidents in animal experiments vs. difficulties in human research

Professional groups and institutions have been paying attention to the relationship between plastics and the environment. Globally, plastic production has increased year by year, and currently exceeds 300 million tons per year, while the accumulated plastic stock in the environment exceeds 10 billion tons.

Plastic pollution in the ocean accounts for more than half of the plastic pollution on Earth, so early research on the potential harm of plastics began with marine animals. Marine biologists discovered plastic in the stomachs of many seabirds decades ago. As the scope of research expands, the number and types of animals found to have plastic in their bodies have been increasing. With the introduction of the concept of microplastics, there are now almost no animals without plastic in their bodies.

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Based on this phenomenon, a number of microplastic toxicity studies have been conducted in animals. Although some studies have reported the many effects of microplastics on animal physiology, most of these studies are of low quality.

A well-known study comes from Australia, where researchers used a rigorous controlled experimental protocol to observe the effects of microplastics on the development, reproduction, and endocrine function of Japanese quail. The researchers conducted a multi-generation microplastic feeding experiment to examine the toxicological consequences of microplastic ingestion in Japanese quail, including parents and two generations of offspring.

Contrary to the conclusion that plastics are harmful to health, which has long been rooted in many people's minds, this study did not find any evidence that quails fed food containing microplastics in the experiment had long-term toxic effects on mortality, adult weight, organ histology, hormone levels, reproduction, hatching rate and eggshell strength.

In vivo experiments on birds cannot be completely equated with the effects on humans. However, due to factors such as research ethics, verifying the effects of plastic on the human body is much more difficult than animal research. One obvious point is that unlike birds and aquatic organisms, researchers cannot let human subjects actively eat foods with added microplastics. At the same time, population-based observational studies (epidemiological data) are also difficult to draw definite conclusions. In laboratory studies, microplastics have been shown to cause damage to human cells, including allergic reactions and cell death. But even with such studies, it is questionable whether their conclusions can be applied to humans, because different researchers use different microplastics, and are more likely to involve different additives in plastic materials.

So far, no epidemiological studies have documented a link between exposure to microplastics and health effects in a large group of people. Even if such studies exist, they face many problems. For example, areas where plastic products are widely used are often economically developed, and people tend to have better health, which means longer life. Whether it is a longitudinal comparison of the same region over time, or a comparison of people living in different regions during the same period, it is difficult to obtain a correlation between a particular health indicator and microplastics.

Two "microplastics harm health"

Well-known studies are flawed

As plastic products and plastic waste continue to grow on the planet and people become more concerned about their health, a basic question still needs to be answered: What impact does plastic have on human health? If there is harm, to what extent? What evidence exists? To find the answers to these questions, we need to start from the source of the information that "plastic is harmful to health".

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The discovery of microplastics in the viscera of fish and shellfish has caused some people to start to pay attention to the safety of seafood. Especially shellfish products, when we eat shellfish and seafood, we usually eat the viscera together, and the microplastics found in shellfish are mainly in these parts. But shellfish products do not constitute the staple food of most people, and most of them are tasted occasionally. Studies have found that the amount of microplastics that enter the human body through breathing in daily life is far more than the amount ingested from shellfish and seafood. This is because many plastic components in our clothes, home accessories, etc. are constantly falling off and releasing microplastics into the environment.

Subsequently, several studies reported the discovery of microplastics in the human body, mostly concentrated in the lungs and excrement. It is not surprising to find microplastics in the human body (respiratory tract and digestive tract), as almost all components present in the environment and diet can be found in the human respiratory tract or digestive tract.

The news about the health hazards of microplastics started to explode in 2016 and has continued to this day. Following the early news information sources of several large international media, it can be found that the first report on microplastics was an article published in Science magazine in 2016. Due to the influence of the magazine in the scientific community, this article was widely cited in media reports on the possible health hazards of microplastics.

The results of this study claim that when exposed to environmental concentrations of microplastic polystyrene particles, the development of fish will be affected, the hatching rate of fish eggs will be reduced, and the growth rate, feeding preferences and innate behaviors of young fish will be changed. In addition, the olfactory function of individual fish exposed to microplastics is impaired and they lose their olfactory response to predators, thus increasing the chance of being preyed on. The study concluded that microplastics seriously affect the physiological functions of young fish.

As soon as the research paper was published, it caused a huge sensation in the media and also attracted the attention of peers. Soon professional doubts began to emerge, mainly targeting problems with data integrity and analysis methods. In view of this, Science magazine also expressed concern. Uppsala University in Sweden, where the researchers are located, conducted a preliminary investigation in August of that year and believed that there was insufficient evidence to initiate a formal investigation. In the same month, the Swedish Central Ethics Review Board appointed external experts to conduct further investigations. The final investigation concluded that there were problems with the scientific integrity of the two researchers and recommended the recall of the paper. The second year after the article was published, the author took the initiative to ask the magazine to withdraw the paper.

What is really worth paying attention to is the discovery of microplastics in the blood, and there are even reports claiming that microplastics have been found in the brain and placenta.

A study published in 2022 conducted a quantitative analysis of microplastics in whole blood donated by 22 healthy people and found that microplastics were present in the blood of 17 people. The study used gas chromatography/mass spectrometry to test whole blood samples from healthy blood donors and quantified plastic particles larger than 700nm, and found that the average concentration of plastic particles in the blood was 1.6 µg/ml.

Why has this work attracted attention? This is related to the particularity of the blood system. The digestive system and respiratory system are the "external environment" of the human body, which constantly exchanges substances with the outside world through breathing and eating. It is not surprising to detect microplastics in these two systems. But the blood system is different, it belongs to the "internal environment" of the human body.

Here we need to introduce a concept called " bioavailability ", which is an important concept in drug development. It refers to how much of a drug can enter the blood when it is administered orally or through other non-intravenous injection methods. This is the prerequisite for most drugs to work. This concept also applies to toxic substances. The detection of microplastics in the blood means that they are bioavailable, that is, they can be absorbed by human blood.

This study seems to provide new evidence of the presence of microplastics in human blood. However, based on the data and analysis methods, this conclusion is uncertain. After the article was published, an industry expert raised a number of questions about the study, believing that the conclusions drawn from the study were more based on a patchwork of evidence based on assumptions rather than on the research data itself. There are many problems with the acquisition of its research data, such as external contamination; in addition, there are also many problems with its analysis methods. Finally, it is also necessary to point out that this study has not been verified by peers so far.

There is no definitive evidence that microplastics are harmful to health

Even if microplastics are indeed detected in human blood, does it mean that they are harmful to health? Still no. It may not be difficult to find a correlation between microplastic intake and a certain health indicator, but it is very difficult to establish a causal relationship. One reason is that we are exposed to many types of chemicals in our daily lives, and plastics are not necessarily special among them. There are many different types of plastics themselves, and with other added ingredients in plastic products, there are thousands of types of chemicals involved.

Compared with the known risks posed by heavy metals or other industrial pollutants, the health risks of microplastics, even if they exist, are likely to be small (after all, plastics themselves are not clearly toxic). This does not mean that there is no need to pay attention to the health risks of microplastics. The hazards of such industrial pollutants can be believed (even if they are speculative or suspected), but it is not right to create panic by fabricating and spreading rumors. If such issues are not scientifically understood and treated, it is easy to have panic similar to the application of genetically modified technology. Although the objects of panic are different, the essence of panic is the same.

A few years ago, due to widespread concern about microplastics, the World Health Organization (WHO) specifically reviewed the health risks of microplastics and formed the first summary report on the impact of microplastics on humans. The core content of the report is that microplastics are everywhere, including in the ocean, fresh water, drinking water, food and air, but no clear evidence has been found that it poses a risk to human health.

Plastics are indispensable in modern life. It is necessary for government agencies and professional groups to restrict and limit the use of plastic products through policies, regulations and guidelines. As mentioned above, the United States passed legislation in 2015 to restrict the use of plastic microbeads in daily chemical products, and many local governments in the United States have also introduced some "plastic bans." For example, New Jersey, where I live, began to implement a bill last year to prohibit all supermarkets from providing plastic packaging bags to shoppers.

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As consumers, we don’t have to worry about the health risks of plastics for the time being. This doesn’t mean that we don’t need to care about the plastic problem. The plastic problem goes far beyond the impact on human health. As a part of the earth, each of us has an obligation to maintain environmental safety. There are many things we can do to control the pollution of plastics to the environment, such as drinking direct drinking water at home, only carrying bottled water when going out, and not throwing away empty plastic bottles when hiking.

Excessive concern and worry about unknown problems will not help solve any of your own health problems. Why don't we start from the known and clear direction? Quitting smoking, limiting alcohol, reducing sugar and salt, and exercising regularly are all things that everyone can do.

Author: Wang Chenguang, PhD in Biology, former professor of Peking Union Medical College

Reviewer: Dr. Li Changqing, a practicing physician in the United States

References:

Richard C Thompson et al. Lost at sea: where is all the plastic? Science. Science. 2004 May 7;304(5672):838.

Oona M Lönnstedt et al. Environmentally relevant concentrations of microplastic particles influence larval fish ecology. Science. 2016 Jun 3;352(6290):1213-6.

Lauren Roman et al. Is plastic ingestion in birds as toxic as we think? Insights from a plastic feeding experiment. Sci Total Environ. 2019 May 15; 665:660-667.

Heather A Leslie et al. Discovery and quantification of plastic particle pollution in human blood. Environ Int. 2022 May; 163:107199.

https://news.un.org/en/story/2019/08/1044661

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