Transboundary Environmental Issues: China’s Air Pollution and Its Health Effects on the Japanese Population

Transboundary Environmental Issues: China’s Air Pollution and Its Health Effects on the Japanese Population

Foreign Environmental Pollution is Not Someone Else’s Problem

There is currently an increase in respiratory illnesses among the Japanese population, a trend that has become particularly noticeable over the past two years. Perhaps it is more accurate to say that these illnesses have become more prominent rather than simply increasing. The year 2024 was marked by a continuous series of infectious disease outbreaks. While this trend improved in 2025, respiratory illnesses, especially during the summer, have become severe.

In cities like Kawasaki and Yokohama, the occurrence of photochemical smog was an annual event during Japan’s high-growth economic period. Along with Yokkaichi asthma, it was a well-known issue. Environmental measures had eliminated it for a time, but for some years now, photochemical smog warnings have occasionally been issued in Kawasaki. In the summer of 2025, according to people working at Haneda Airport, these warnings in Kawasaki have become a daily occurrence. Not only in Kawasaki, but also in Shinagawa and Ota wards, photochemical smog warnings have been broadcasted multiple times via loudspeakers in the summer of 2025, a fact likely known to local residents.

The situation is reportedly worse in South Korea than in Japan, and even more severe in China. The yellow sand from China’s desertification, along with its environmental and air pollution, rides the westerly winds and affects other countries, making it a serious issue for Japan as well.

During the COVID-19 pandemic and the era of China’s “zero-COVID” policy, while COVID-19 was a concern, it was a relatively good period in terms of other respiratory and infectious diseases. However, once China lifted its zero-COVID policy and restarted its factories, the impact was felt in Japan. Over the past few decades, the number of hay fever sufferers has increased in tandem with China’s economic development, and air purifiers have become commonplace. Yet, many people likely viewed China’s environmental and air pollution as someone else’s problem.

After several years, the “post-COVID” era began, and the zero-COVID policy was lifted. During the pandemic, COVID-19 spread, but thorough public health measures paradoxically reduced the incidence of other infectious diseases. In retrospect, it was a “clean” era. Incidentally, the medical terms “clean” and “unclean” have a different connotation than in general usage, being clearly defined by the presence or absence of pathogens.

2024: A Year Full of Infectious Diseases

In 2024, some form of infectious disease was prevalent throughout the year, regardless of the season. It was considered that the semi-isolated lifestyle during the COVID-19 pandemic reduced exposure to various pathogens, leading to a weakened immune system or a diminished “booster effect” from natural infection and onset. Another theory was that the surge in inbound tourism from all over the world, including the Southern Hemisphere with its opposite seasons, brought various infectious diseases into the country, causing a year-round increase.

In the past, influenza in Japan was often traced back to China, where birds, pigs, and humans coexist. Vaccines were developed by predicting which strains of influenza would arrive from Hong Kong, such as the “Hong Kong flu.” Now, influenza can even break out in the summer. The virus strains are also named things like “Victoria type,” suggesting that influenza outbreaks from various regions with livestock industries, like Australia, can now spread globally due to globalization. This was the general understanding, but the situation in 2025 felt somewhat different.

Changes in Illnesses in 2025

In 2025, the prevalence of various infectious diseases was not as high as in 2024. While summer colds and COVID-19 were still common, the spring and early summer did not see the same level of infectious disease as the previous year. It was thought that society was returning to a pre-COVID state in the “after-COVID” era.

However, a trend that has been present for some time became more pronounced: an increase in unexplained coughs, upper respiratory tract pain, and worsening of respiratory conditions around May, June, and July, even after the hay fever season ended. Summer colds also seemed quite common. While some cases might be attributable to whooping cough, which typically circulates during this period, many cases of persistent cough were not diagnosed as such.

Furthermore, asthma cases increased. I believe there is some connection between asthma, especially pediatric asthma, and panic disorder, and instances of the latter were also observed. The incidence and severity of panic disorder itself seem to have improved in recent years, thanks to work-style reforms and remote work. In urban areas, it is often related to trains, so much so that I would like to call it “train sickness.” Of course, if the cause is clear, it would be diagnosed as agoraphobia or a specific phobia, not panic disorder.

The impact is said to be much more severe in China and in South Korea, which is geographically closer to China. Therefore, it is plausible that these health issues are related to the lifting of China’s zero-COVID policy and the resumption of industrial production and factory operations.

Air and Environmental Pollutants from China

In the long term, there has been a continuous increase in conditions like hay fever in Japan. Owning an air purifier has also become the norm. Here is a rough list of air and environmental pollutants originating from China.

1. PM2.5 (Particulate Matter 2.5): Fine particles with a diameter of 2.5 μm or less.
2. Yellow Sand-derived Substances: The amount of yellow sand (Asian dust) is increasing due to advancing desertification in China. It can mix with other aerosols and contain heavy metals, as well as adsorb sulfur oxides and nitrogen oxides.
3. Heavy Metals (e.g., Lead, Cadmium, Arsenic): These can travel attached to yellow sand. Lead poisoning is well-known, with historical figures like Chinese emperors, Romans, and Isaac Newton believed to have suffered from it. Cadmium is famous for causing Itai-itai disease. Arsenic is toxic but is sometimes used as a medication for hematologic malignancies.
4. Gaseous Air Pollutants: Photochemical oxidants, sulfur oxides (SOx, such as sulfur dioxide), nitrogen compounds (NOx), volatile organic compounds (VOCs), and ozone (O3). These are known for causing photochemical smog and acid rain. Photochemical reactions in the atmosphere produce ozone and secondary particles (sulfates, nitrates) as photochemical oxidants, which are highly irritating to the respiratory tract. There is also transboundary ozone.
5. Ammonium Salts: Classified under hazardous organic compounds.
6. Hazardous Chemical Substances, Polycyclic Aromatic Hydrocarbons (PAHs): These are carcinogenic.
7. Mercury: Derived from petroleum. Organic mercury is infamous for causing Minamata disease, a form of industrial poisoning.
8. Dioxins: Known as endocrine disruptors and for their mutagenic and carcinogenic properties.
9. Persistent Organic Pollutants (POPs): Hazardous chemicals from previously used pesticides and industrial products like plastics attach to yellow sand particles and travel long distances.
10. Black Carbon: Fine soot particles generated by coal-fired power plants, coal heating, and diesel engines, which also travel across borders.
11. Microplastics and Nanoplastics: An Italian study found microplastics inside atherosclerotic plaques. Uric acid has also been found in these plaques, and hyperuricemia is being studied for its broader pathogenicity, including vascular damage, kidney damage, and cardiac effects, beyond just gout and urinary stones. Rubber and plastic particles from tire wear, textile dust from clothing, and plastic waste degrading outdoors under UV light and weathering break down into fine particles that become airborne.
12. PFAS (e.g., PFOS/PFOA, FTOH): PFAS (Per- and polyfluoroalkyl substances) and FTOH (Fluorotelomer alcohols) also travel long distances in the atmosphere and are deposited on the ground through rain and dry deposition.

Health Effects

The situation in 2024 was obscured by the high prevalence of infectious diseases throughout the year. However, in 2025, from around the end of the cedar and cypress pollen season, there has been a noticeable increase in chronic cough, upper respiratory tract pain, summer colds, and worsening of asthma.

Extreme heat itself is bad for the respiratory system, and there is a term “desert lung” in desert countries. Both excessively high and low humidity put a strain on the respiratory system. The worsening of hay fever and the popularization of air purifiers seem to be correlated with China’s desertification and economic growth. Many people have likely experienced the emergence or exacerbation of these symptoms over the past few decades.

High concentrations of photochemical smog cause irritation to mucous membranes, leading to symptoms like stinging eyes, tearing, sore throat, and coughing. In severe cases, it can cause difficulty breathing, headaches, and nausea. It is thought to cause mucosal irritation, induce or worsen inflammation of the mucous membranes, and disrupt the immune and allergic systems.

Beyond the Respiratory System

Environmental pollutants do more than just damage mucous membranes. As you may have noticed from the list of transboundary pollutants, they include everything from carcinogens to substances related to arteriosclerosis.

Nanoplastics, which are smaller than microplastics, can penetrate mucous membranes into the body and bloodstream. If a substance is small enough and hydrophobic or lipophilic, it can pass directly through cell membranes. Even larger substances may enter cells via endocytosis or through cell membrane proteins. Even without going that far, anyone who has studied or been exposed to public health is likely aware that these substances have various effects on living organisms.

Conclusion

As China’s desertification and industrialization continue to advance, it is expected that health problems will continue to manifest and worsen for the foreseeable future, not only for the Chinese population but also for people in North Korea, South Korea, Taiwan, and Japan, who are affected by the westerly winds.

Furthermore, these pollutants likely have adverse effects on non-human organisms as well. While it may seem presumptuous for someone like me to say so, I believe it is crucial that we strive to protect the global environment.