By Anna Tomczak, Department of Health Sciences, Carleton University
It seems like we, as a society, are constantly being warned against disease-causing products, whether it be the dangers of BPA found in our water bottles or the associated risks of getting vaccinated. Rarely are these “findings” of danger found to be true. In fact, such warnings tend to create more public disorder than the alleged dangerous products themselves. Recently however, studies have indicated that what was previously considered as “safe” levels of fine particulate matter (PM2.5), may actually be associated with an increased risk of adverse health effects.
Fine particulate matter consists of airborne particles found in polluted air, resulting from chemical reactions in the atmosphere and through fuel combustion. Exposure to this particulate matter has observable effects on human health, and it has been identified as one of the top 10 health risks worldwide. Long-term exposure to PM2.5 has been specifically linked to increased risk of cardiovascular disease, diabetes, hypertension, and non-accidental mortality. In 2013, fine particulate matter was declared a human carcinogen by the International Agency for Research on Cancer due to findings of increased risks of lung cancer reported in several epidemiological studies Alarmingly, more studies are finding that concentrations of fine particulate matter at levels less than 10 µg/m3 have a direct association on the risk of both cardiovascular disease and non-accidental mortality. These findings have important public health implications as these levels of pollution are common in most Canadian cities.
Findings from a recent paper provide more evidence that these low levels of air pollution are affecting Canadians’ health. Villeneuve et al. (2015), conducted a study looking at long-term exposure to fine particulate matter air pollution and mortality among Canadian women. The study followed 89,835 healthy women between the ages of 40 and 59 for 25 years. They grouped women according to their exposure to PM2.5 at their homes, and compared mortality rates across different levels of pollution. They were able to adjust their comparisons for other risk factors that are associated with mortality such as smoking, obesity and other characteristics, They assigned air pollution exposures by taking satellite-based measures of PM2.5 between the years 1998 and 2006 and linked these to participants postal codes. They were able to determine which women died, and their cause of death by linking participants’ information to the Canadian Mortality Database
As with any study looking to define a relationship between an exposure and an outcome, outside factors that may play a role in explaining the outcome must be considered and controlled for. Building off of previous studies, where socio-demographic and occupational characteristics were analyzed with regards to PM2.5 exposure and mortality, Villeneuve et al., looked to expand the already existing knowledge through the analysis of four additional factors: smoking, obesity, place of birth and whether the participants had moved within 5 years of the initial recruitment. Furthermore, dose-response models were created to better understand how the concentration of PM2.5 relates to mortality.
This is great, but what does this all mean? Are we in danger or not? The study revealed several key findings that shed the impact of fine particulate matter on daily life.
Residential PM2.5 Concentration
Using the satellite-based surface readings of PM2.5 and the residential postal codes of the participants, the median exposure to PM2.5 across all participants was determined to be 9.1µg/m3, which is considered to be a fairly low concentration.
Are Low Concentrations of PM2.5 Dangerous?
Unlike the tales of the dangers of BPA in water bottles, low doses of fine particulate matter do in fact increase the risk of cardiovascular disease, specifically ischemic heart disease and nonaccidental mortality. Villeneuve et al estimated that an increase of 10 µg/m3 of PM2.5 increases the risk of ischemic heart disease and non-accidental mortality by 30% and 15%, respectively. Considering that such low doses were thought to be safe is shocking! Even after adjusting for the socio-demographic, occupational and risk factors, these results remain the same, indicating that these mortalities can be explained by the exposure to fine particulate matter. These results were further confirmed by the dose-response model that indicated a linear trend between PM2.5 concentration and ischemic heart disease mortality, where an increase in exposure leads to an increase in risk of mortality. The findings of this study are very similar to risk estimates obtained from a separate Canadian cohort study that was done using census data.
Another Reason to Stay in Shape
Interestingly, and maybe not so surprisingly, obesity was found to play a role in modifying the relationship between exposure to PM2.5 and mortality by cardiovascular disease. Associations between PM2.5 and mortality were found to be stronger for obese women compared to nonobese women. This suggests that women who are more obese may be more susceptible to the harmful effects from long term exposure to air pollution.
Was I Born in the Wrong Country?
Luckily, where you are born does not have an effect on the risk estimates of mortality outcomes. Women who were born outside of Canada had no observable disadvantage or advantage compared to those born in Canada. Similarly, having moved in the first five years of the study also did not have an effect on the risk estimates.
This study adds to the findings of recent studies showing mortality impacts at air pollution levels commonly observed in Canadian cities. Additionally it expanded this knowledge by identifying obesity as an important modifier in this relationship. It becomes quite evident that even low concentrations of fine particulate matter can have a visible impact on human health. Having these new insights on the influences of fine particulate matter at very low levels begs the question of what can be done to lower pollution levels, and how low can we go. Because low concentrations of PM2.5 have an observable influence on human health, new policies may need to be put into place to help protect the population.
These findings are yet another indication that the pollution we help create, whether it be through our reliance on industrial processes, or our own driving habits, has a significant impact on our health. It is important to remember that even though that paper mill down the street may seem harmless, it can be quite dangerous.
Villeneuve, P. J., Weichenthal, S. A., Crouse, D., Miller, A. B., To, T., Martin, R. V., . . . Burnett, R. T. (2015). Long-term Exposure to Fine Particulate Matter Air Pollution and Mortality Among Canadian Women. Epidemiology. doi: 10.1097/EDE.0000000000000294
Ontario Ministry of the Environment and Climate Change. (2010). Fine Particulate Matter. Retrieved from: http://www.airqualityontario.com/science/pollutants/particulates.php
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