Air pollution constitutes the main environmental risk for public health in the Americas, where around 380,000 premature deaths were attributed to this cause in 2019, according to the Pan American Health Organization (PAHO).[1]
Data from the World Health Organization (WHO) show that almost the entire (99%) of the world’s population is exposed to breathing air with levels of contaminants that are above the limits established in its guidelines on this matter. Among the most dangerous for public health, the United Nations agency highlights: suspended particles smaller than 10 and 2.5 micrometers in diameter (PM10 and P.M.2.5); ozone; nitrogen dioxide; sulfur dioxide and carbon monoxide.[1]
Numerous studies have documented that exposure to polluted air, especially PM10 and P.M.2.5is the main risk factor for the development of respiratory and cardiovascular disorders such as ischemia, myocardial infarction, cerebral infarction and chronic obstructive pulmonary disease.
Regarding deaths due to pollution in outdoor spaces, 80% are attributed to heart disease and stroke, while the remaining 20% correspond to respiratory disorders and cancer.[2]
Furthermore, the burden of morbidity and mortality associated with air pollution, which the WHO classifies as the second most important risk factor for acquiring non-communicable diseases, is exacerbated by increasing industrialization and the effects of climate change (droughts, waves heat, forest fires close to large inhabited areas), which make it much more dangerous for exposed populations, especially minors and the elderly.
Dr. Horacio Riojas Rodríguez, Ph. D.
In this regard, Dr. Horacio Riojas Rodríguez, PhD in public health sciences with an area of concentration in epidemiology and director of Environmental Health of the Center for Population Health Studies of the National Institute of Public Health (INSP), commented to Medscape in Spanish that the most risky contaminants vary in different entities of the country. For example, he explained that in cities like Monterrey, Mexicali and some of Bajío the biggest problems are with high concentrations of PM particles.10.
For its part, for the Metropolitan Area of Mexico City, the main pollutants are PM2.5 and ozone, reported the specialist. In this region, the Metropolitan Air Quality Index (IMECA) with its corresponding modifications has been used since 1982 to monitor the criteria pollutants established by the WHO.
Mexican cities exceed contaminant limits established by the WHO
“Since 2014, various Mexican institutions, including the National Institute of Public Health, have participated in updating air quality standards,” said Dr. Riojas. In the 2019 update, the maximum permissible levels of contaminants were reduced and in the case of particles it was stipulated that these must be reduced every two years so that they approach the WHO criteria.
The specialist added that in 2019 NOM-172 of the Ministry of the Environment was also promulgated at the federal level, which for the first time extended pollutant measurements to all cities in the country, forcing local governments to issue recommendations on the air quality and associated risks.[3]
The most recent change in NOM-172 was made in 2023 and came into force this year, which “speaks of the effort to update the regulations on the matter, although it does not necessarily imply that those (desirable) levels of air quality”, considered Dr. Riojas, who clarified that the concentrations of pollutants in Mexican cities are four times higher than the levels established in the WHO recommendations.[4]
“Almost all Mexican cities are at levels of 20 micrograms of particles per cubic meter, when the WHO guidelines indicate that they should not exceed 5 micrograms. And something similar happens with other pollutants. That is the size of the gap we have to fill,” the specialist acknowledged.
The researcher and his collaborators have found that a reduction in the levels of PM particles10 at 20 micrograms per cubic meter, as well as 0.050 parts per million of ozone (98 micrograms per cubic meter) in the air of the Mexico City Metropolitan Area could prevent 2,300 and 440 deaths per year, respectively. The greatest impact of these pollutants has been seen, according to their study, in people over 65 years of age, as well as in mortality due to cardiopulmonary and cardiovascular disorders.[5]
Various negative effects at a biological level
Octavio Gamaliel Aztatzi Aguilar, Ph. D.
“The PMs2.5 are more associated with deaths of people who suffer from respiratory diseases, but the range of possibilities of generating damage includes cardiovascular, cerebral, reproductive and endocrine alterations of the metabolism in terms of insulin resistance and diabetes,” said Octavio Gamaliel Aztatzi Aguilar. , master and doctor in Toxicology Sciences, researcher at the Department of Toxicology of the Center for Research and Advanced Studies (CINVESTAV) of the National Polytechnic Institute.
Poor air quality can also be associated with different types of cancer, as various studies have documented, recalled the CINVESTAV specialist. However, he clarified, “we must not lose sight of the fact that there are other factors in the population that can determine whether or not someone is more susceptible to suffering from it, such as lifestyle or diet.”
Aztatzi Aguilar, who is head of Laboratory 26 of Inhalation and Integrative Toxicology of the CINVESTAV Department of Toxicology, pointed out that there is no safe level of exposure, since any of the contaminants can cause negative effects at a biological level. Thus, when a pathogenic agent such as the tuberculosis bacillus or SARS-CoV-2 appears, exposed people become much more vulnerable to contagion.
“Exposure to particulate matter and other pollutants also contributes to making us more susceptible to contracting respiratory tract infections, not only SARS-CoV-2 infections, but others such as influenza or tuberculosis,” added Aztatzi Aguilar, also a member of the Scientific Committee. and Air Quality Surveillance Technician in Mexico City.
Most research on the effects of air pollutants has focused precisely on evaluating cardiorespiratory symptoms, airway inflammation, and damage to lung function. However, the toxicologist reiterated, the inflammatory response in the airways can extend to other organs, causing genetic, biochemical, physiological and tissue alterations.
The effects of endotoxins
The CINVESTAV specialist explained that PM2.5 They contain a component called endotoxin ─from biological decomposition, mainly from bacteria, and which is not regulated in environmental air quality standards─, which can cause damage beyond the cardiopulmonary system, especially kidney function.
These types of effects have been clinically documented in various studies. One of them, carried out by experts from the Division of Nephrology and Hypertension of the Department of Medicine at Stony Brook University, in New York, United States, found that elevated concentrations of endotoxin in the blood of critically ill patients were associated with a worse performance of kidney function and longer hospital stays.[6]
In animal models, Aztatzi Aguilar and his collaborators have observed that endotoxin can induce acute and chronic changes in kidney function. “These are due to the modulation of cellular responses: they start from the lung and contribute to the deterioration of other structures and organs such as the heart. And indirectly, respiratory alterations lead to the deterioration of the cardiovascular system, which tries to compensate for these modifications in the pathway. pulmonary disease, raising blood pressure, which can generate renal hemodynamic changes.[7]
Aztatzi Aguilar recognized that to modify environmental standards so that they include endotoxin monitoring, more epidemiological evidence and multicenter studies are required. For this reason, he warned of the need to study the speciation of particulate material, since it is a very heterogeneous and complex mixture of organic and inorganic molecules.
“There is a component of polluting particles generated by industrial activity or automobiles, but there are also other sources specific to each region or atmospheric dust, which would be present even if combustion vehicles were not circulating. It is known, for example, that vegetation releases certain natural compounds that can also contribute to the generation of ozone,” explained the specialist.
For this reason, he stressed the need to more rigorously evaluate certain components of particulate matter, since with current criteria based on environmental standards only total quantities of particles per volume of air are reported, without discerning, for example, that there may be a high concentration of toxic metals in a relatively small space.
“Monitoring other components of particulate matter could help us explain the phenomena that occur in our (Mexican) population and thus implement actions that correct or mitigate the emission of this type of pollutants,” suggested Aztzazi Aguilar. Likewise, she considered it essential to raise awareness among the population and medical personnel who deal with health problems associated with air pollution.
“This is one of the challenges we have, for example, in Mexico City with recent environmental contingencies: people are not going to die in the streets due to air pollution, but we must understand that this phenomenon generates acute or chronic effects and that the consequences of exposure to the liver, heart or pancreas can occur long after inhalation of the contaminant.”
Dr. Riojas Rodríguez, Ph. D. and Aztatzi Aguilar, Ph. D. have declared that they have no relevant financial conflicts of interest.