For the past few days, people allergic to certain tree pollens have already been able to feel their first symptoms of the season: nasal congestion, itchy eyes, sneezing. These inconveniences of “hay fever” may seem mild at first glance, but we must not lose sight of the fact that pollen allergies may cause chronic sinusitis or even, in asthmatics, intense attacks.
For experts, this represents a real public health concern. First, because about one in five Quebecers suffers from a pollen allergy, according to the most recent Quebec Population Health Survey, published in 2014. Magalie Canuel, Scientific Advisor to the Department of Environmental Health and toxicology from the National Institute of Public Health of Quebec (INSPQ), adds that it is also because the number of people with allergies and the severity of symptoms are expected to increase over the next few years.
Solutions are emerging to slow the rise in cities, but the lack of data complicates the implementation of concrete actions. “We could help the population by planting fewer allergenic trees in the city, but for that, we would first have to know what people are allergic to,” says Alain Paquette, professor in the Department of Biological Sciences at UQAM, who decided to tackle the problem.
More pollen in the air
The growing season for plants is getting longer due to global warming. Pollen emission therefore begins earlier than before in spring: in 2021, for example, it began three weeks earlier than at the turn of the 2000s. And it continues into autumn for certain plants, including ragweed responsible for many cases of allergy. Few recent data are available, but for this plant species abundant in urban areas, we already knew in 2009 that the growth period had increased by 25 days compared to 1995 in Canada.
However, the upward trend in temperatures in all regions of Quebec favors the dispersal of allergenic plants such as ragweed in northern and eastern Quebec, regions currently less affected by seasonal allergies.
And if there is more and more pollen in the city, it is in particular because of the strong propensity to plant more trees which disseminate pollen than trees which bear fruit, because we want to limit the number of fruits that fall to the ground and that will have to be picked up, emphasizes Alain Paquette.
In addition to increasing the intensity of symptoms, exposure to greater concentrations of pollen and over longer periods would increase the risk of suffering from allergies, which would explain the increase in the prevalence of this problem of health in recent decades.
In great evils the great means
“We know very little about pollen allergies, with the exception of those to ragweed,” explains Alain Paquette. The INSPQ data reveal, however, that tree pollen causes as many allergies as that of this plant. The problem? “We don’t know what tree species people are allergic to or how pollen is dispersed in cities,” he says.
In the spring of 2021, the researcher’s team therefore installed 25 pollen sensors in Montreal with the aim of better understanding during the spring and summer the distribution on the territory of the pollens produced by different species of trees such as birches and alders, already known as major sources of allergies. This year, the researcher and his colleagues recruit allergy sufferers who live or work on the island of Montreal. By completing a questionnaire on their symptoms a few times a week, they will provide valuable data to scientists, who will be able to compare the information collected from city dwellers with the pollen collected from sensors near their homes. The researchers thus intend to determine which tree species have the greatest influence on the health of Montrealers. Such sensors will also be installed this summer in Quebec, Sherbrooke and Chicoutimi.
“The idea of our project, carried out in collaboration with the INSPQ, is to be able to predict which pollens will be present, where, when and in what quantity, summarizes Alain Paquette. We will be able to make recommendations as to the minimum number of sampling stations necessary in a city to properly make these forecasts. Thus, if an alert system is one day put in place, people with allergies will be able to limit the consequences on their health, for example by planning their activities to reduce their exposure to pollen. This data could also be used by doctors to help their patients manage their symptoms.
An inaccurate diagnosis
“If you have ever taken allergy tests, you may have been told that you reacted to maple and birch pollen, for example, relates the biologist. But for a botanist, “maple” doesn’t mean much, it’s not precise enough. Indeed, there are a hundred species of maples in the world, including 10 in Canada.
“It’s not insignificant not to know the species to which you are allergic,” he says. This is because there can be several weeks, even a month, between the dispersal of pollen from the silver maple and that of the pollen from the Norway maple, two of the three most abundant trees in an urban environment. However, a person allergic to one may not be to the other. The pollen grains collected in the sensors will first be observed and counted meticulously under a microscope, which will make it possible to distinguish maple pollen from that of birch, for example. Then, the DNA contained in the pollen samples will be analyzed in order to precisely determine the species from which they come.
Diversify the urban forest
In addition to providing important information on seasonal allergies to the INSPQ and the Ministry of Health, Alain Paquette’s team’s research project will make it possible to make recommendations to municipalities on good practices in terms of management of urban forests. Trees planted in cities, because they are an effective means of combating heat islands, are an essential component of adaptation to climate change. No question, therefore, of planting less to limit allergies. For Alain Paquette, the diversification of tree species will be beneficial for people’s health and that of the ecosystem. A study has also shown that in Vancouver, where the species are almost twice as varied as in Montreal, the prevalence of allergies is much lower. Reducing the proportion of each type of pollen also reduces symptoms, which are generally not triggered by low levels of allergens. “Perhaps we should seriously consider reducing the proportion of trees that are pollinated by the wind,” suggests the researcher. Insect-pollinated species, which are often fruit trees like apple trees, release much less pollen into the air,” he adds.
–
