Experts explain the harm of PM2.5 to the human body and the resulting fetal defects

PM2.5 refers to particles in the atmosphere with a diameter less than or equal to 2.5 microns, also known as respirable particles. Its diameter is less than 1/20 of the thickness of a human hair. Compared with coarser atmospheric particulate matter, PM2.5 has a smaller particle size, is rich in toxic and harmful substances, stays in the atmosphere for a longer time, and is transported over a longer distance, thus having a greater impact on human health and atmospheric environmental quality.

Causes airway obstruction or inflammation

In late October, Beijing suffered from continuous smog weather. The air was so bad that it was unbearable, but the air quality forecast showed "mild pollution". Environmental experts explained that the reason for this inconsistency is that the official forecast system uses PM10 (particles with a diameter of less than or equal to 10 microns, which can be inhaled) as an evaluation factor.

"It would certainly be a good thing if the authorities could forecast PM2.5 concentrations. Sensitive groups like patients with respiratory diseases could arrange their lives according to the forecast, try to avoid going outdoors, and take protective measures," said Professor Song Weimin from the School of Public Health at Fudan University.

Human beings are like a precision instrument, and every structure is the result of adapting to the environment. Our respiratory system naturally has the ability to block pollutants. Larger pollutants are blocked when passing through the nasal cavity and throat. Even dirt that can enter the trachea and bronchi can be transported out of the respiratory tract with the movement of cilia in the trachea. However, the human body is full of loopholes, and the respiratory system's barrier is powerless against tiny particles.

After passing through the barrier, the tiny particles begin to stir up trouble in the respiratory tract in various forms. One of the most direct ways is that these tiny particles themselves are trapped in the sensitive respiratory tract, causing local obstruction and inflammation. Studies have shown that 75% of particles smaller than 2.5 microns are deposited in the alveoli. We can imagine that if sand gets into the eyes, the eyes will become inflamed. The deep part of the respiratory system is also a sensitive environment. Fine particles that remain in the respiratory system as foreign matter for a long time can also cause inflammation of the respiratory system.

Pathogenic viruses take a ride into the body and cause cancer

In addition to doing bad things themselves, fine particulate matter is like small cars that can freely enter the respiratory system. Other pathogenic substances such as bacteria and viruses take this "ride" to the deep parts of the respiratory system and cause infection.

Don’t think that you can avoid cardiovascular disease as long as you stay away from bad eating habits such as too much fish and meat. Fine particulate matter also has many “ways” to induce cardiovascular disease. For example, fine particles can directly enter the blood and induce the formation of blood clots. Another indirect way is that after fine particulate matter stimulates inflammation in the respiratory tract, the respiratory tract releases cytokines that cause vascular damage and ultimately lead to the formation of blood clots.

Epidemiological surveys have found that polycyclic aromatic hydrocarbons in urban atmospheric particulate matter are associated with the incidence and mortality of lung cancer among residents. In the process of PAHs entering the human body, fine particles play the role of "hitchhiking". Most PAHs in the atmosphere are adsorbed on the surface of particles, especially those with a diameter of less than 5 mm. There are very few PAHs on large particles. That is to say, the more fine particulate matter there is in the air, the more chances we have of being exposed to carcinogens - polycyclic aromatic hydrocarbons.

Affects fetal development and causes defects

There are some more worrying findings. Some reports in recent years have shown that human reproductive capacity is declining significantly, and environmental pollution is considered to be the culprit. A study from northern Bohemia, which looked at pregnant women exposed to high levels of PM2.5, found that high levels of fine particle pollution could affect the development of the fetus. More studies have found that the concentration of atmospheric particulate matter is correlated with increased perinatal and neonatal mortality, low birth weight, intrauterine growth retardation (IURG), and congenital defects.

PM2.5 particles can enter blood vessels through air-blood exchange

Judging from public scientific research data, much of the research on PM2.5 focuses on the lungs.

The researchers started with a toxicology study of the lungs: four groups of rats were exposed to PM2.5 once a day for three consecutive days. After analyzing the lung lavage fluid and lung tissue pathological sections of these rats, it was found that PM2.5 could cause changes in pulmonary vascular permeability, lung cell damage and aggravate oxidative stress damage. In the high-dose exposure group, rats had inflammatory cell infiltration in the lungs and pulmonary septal edema.

An experiment in 2009 collected PM2.5 from the urban atmosphere of Beijing and conducted toxicological studies using the human alveolar epithelial cell line (A549) as a model. In this experiment, different contamination conditions such as 25, 50, 100, and 200 μg/ml were compared and it was found that as the contamination concentration increased, PM2.5 could cause inflammatory damage to these cells.

There are countless academic studies of this kind, but it is difficult for ordinary readers to fully understand them.

"Various evidences show that it is now a consensus that these small particles can damage cells." Wei Fusheng, an academician of the Chinese Academy of Engineering, said that when these small things enter the human body, they generally reach the bronchi and alveoli directly, and can even enter the blood. The carcinogens such as heavy metal oxides or polycyclic aromatic hydrocarbons they adsorb are very harmful.

A study published publicly this year used a nickel mining and smelting area in Gansu as the PM2.5 collection area. Researchers found that in the atmosphere of nickel-polluted areas, the nickel dose in PM2.5 is 65 times that of the experimental control area. Long-term exposure to PM2.5 and high concentrations of nickel will increase damage to cells. The cells tested in this experiment are called "endothelial cells", a group of cells that continuously coat the lining of blood vessels throughout the body. In the researchers' view, the endothelium is not only a barrier between blood and tissues, but its damage and dysfunction are also closely related to the occurrence of many diseases, including hypertension, coronary heart disease, diabetes, chronic renal failure, etc.

Pan Xiaochuan, a professor at the School of Public Health, Peking University Health Science Center, published a paper stating that between 2004 and 2006, when the average daily concentration of PM2.5 at the observation point on the Peking University campus increased, the number of emergency patients with cardiovascular disease at the Peking University Third Hospital, about 4 kilometers away, also increased.

"We used time series analysis to analyze the collected data and found that if the concentration of PM2.5 increases by 10 micrograms per cubic meter, the number of emergency patients with hypertension in the hospital will increase by 8%, and the number of cardiovascular diseases will also increase," said Pan Xiaochuan.

From a group of invisible and intangible small particles to entering the human body, scholars' research direction is becoming clearer and clearer.