Scientists cannot yet name the exact causes of the development of cancer, but there are many risk factors that significantly increase the likelihood of a number of types of tumors. Smoking, physical inactivity, excessive alcohol consumption, obesity – the influence of these factors has long been known. However, until now, no one has associated an increase in cancer incidence with forest fires. In addition to Canadian scientists who shared the results of the world’s first study on this topic in the Lancet.
For Russia, two-thirds of whose territory is covered with forests and where up to 35 thousand forest fires are recorded annually, covering areas up to 3.5 million hectares, this scientific work is especially relevant.
The results of the world’s first study in which researchers assessed the relationship between wildfire exposure and the incidence of several types of cancer (lung cancer, brain cancer, non-Hodgkin’s lymphoma, multiple myeloma and leukemia) are published in the Lancet. These types of cancer were not chosen by chance: the presence of combustion products in the atmosphere also plays a role in their development.
Wildfires release a variety of carcinogenic pollutants that pollute the air, water, ground and inland environments. Forest fires can also pollute soil and water. It is important to note that many wildfire pollutants are known human carcinogens, including polycyclic aromatic hydrocarbons, benzene, formaldehyde, phenols, and heavy metals, suggesting that wildfire exposure may increase a person’s cancer risk. In addition, heavy metals from fires can be deposited in nearby water bodies, accumulate in fish, and can also be found in household dust 3–8 months after a fire. However, some pollutants return to normal concentrations shortly after combustion ceases, while a number of chemicals, including heavy metals and polycyclic aromatic hydrocarbons, tend to persist in the environment for a long time. Thus, exposure to harmful environmental pollutants can continue beyond the period of active combustion through several routes of exposure. This suggests that populations in regions where wildfire frequency is high may have an increased risk of developing cancer.
In particular, high concentrations of environmentally persistent free radicals have been found in charcoal samples that have remained stable for at least five years after fires. Moreover, many heavy metals that are preserved in soil and vegetation become more bioavailable after wildfires due to increased soil erosion and ash dispersion. In addition, violations of exposure limits for nitrates, disinfection by-products and arsenic in surface and groundwater have been observed in areas affected by wildfires.
In the past few years, unprecedented wildfires have devastated many areas around the world. For example, some of the worst wildfire seasons were observed in 2017-18 in western Canada, in 2019-20 in Australia and in 2020 in California (USA). With climate change, forest fires are predicted to become more widespread, severe and prolonged in the future. Prior to this study, however, little was known about the association between wildfire exposure and cancer risk. A team of scientists set out to evaluate the relationship between wildfire exposure to residential areas and the incidence of several types of cancer in Canada.
To this end, a large population-based study was conducted among a representative sample of the Canadian adult population, which was monitored for cancer incidence and mortality from 1996 to 2015. Excluded from the study were residents of large cities (with a population of more than 1-5 million people), recent immigrants, and people under 25 or over 90 years of age. Forest fire impacts were determined based on the area burned within a 20 km or 50 km radius of residence. In total, the analysis included more than 2 million people who were followed for 20 years. During this time, there were approximately 43,000 cases of lung cancer, 3,700 cases of brain cancer, 12,000 cases of non-Hodgkin’s lymphoma, 3,900 cases of multiple myeloma, and 7,700 cases of leukemia.
The scientists concluded that the impact of wildfires was associated with a slight but still increase in the incidence of lung cancer and brain tumors. For example, study participants exposed to a forest fire within a 50 km radius of their residence in the past 10 years had a 4-9% higher incidence of lung cancer than those who were not exposed to fires, and the incidence of brain tumors was 10 % above. A similar situation was among those who lived within a radius of 20 km from the fires.
At the same time, as scientists have established, the impact of fires was not associated with hematological cancers.
There is concern that wildfire pollutants may persist indoors for long periods of time, and several studies have explored this issue. One reported finding concentrations of charcoal in tissue samples collected from homes 3-8 months after a major wildfire in New Mexico. In another study conducted during the wildfire season in Oregon, concentrations of gas-phase polycyclic aromatic hydrocarbons were higher indoors than outdoors, suggesting that these pollutants can persist for a long time once they enter the home. This information will be particularly useful in determining why some cancers (lung cancer and brain cancer) have been associated with proximity to wildfires, while others (hematological cancers) have not. In addition, researchers note that the risk of developing certain types of cancer when exposed to wildfires may increase due to psychological stress.
Long-term exposure to wildfires can increase the risk of lung cancer and brain tumors. Further work is needed to develop long-term wildfire impact estimates that reflect the complex mixture of environmental pollutants released during these events, the researchers conclude.
And although in Russia the majority of forest fires are registered in the taiga, far from settlements, many regions are regularly affected by them. For example, everyone remembers the smog of 2010 in Moscow. About 90% of all fires occur in the Amur Region, Khabarovsk, Krasnoyarsk and Trans-Baikal Territories, the Jewish Autonomous Region.
Source From: MK