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May 29, 2004
BABY TREES WON'T HELP
Air-cleaning capacity of a seedling is tiny compared to trees lost in Red Hill
By James S. Quinn
The Hamilton Spectator
I and others recently published a paper in the publication Science that was reported in national and international media as well as The Hamilton Spectator.
Our team had previously shown increased genetic mutations in the young of mice exposed to air pollution in Hamilton. Our paper showed that filtering the breathable particles out of polluted air by passing it through a High Efficiency Particulate Air (HEPA) filter reduced this genetic damage.
When interviewed by The Hamilton Spectator, I pointed out that breathable particulate has already been associated with lung cancer and asthma. Additionally other research has shown that trees act as pollution filters because the mutation/cancer causing particles in air-pollution would adhere to leaves. Obviously the largest trees produce the greatest benefit.
I pointed out that the removal of 40,000 to 47,000 trees in the Red Hill Valley, combined with the planned highway and its attraction of many diesel trucks will increase the exposure of people to breathable particulate pollution.
As is often the case when the Red Hill Valley Expressway project is in the news, expressway project director Chris Murray was asked for comment. Murray explained that "a 2003 health effects report found no adverse effects due to the loss of trees in the valley."
While Murray 's statement is not technically incorrect, it seems to me to be misleading. In fact, the 2003 health effects report commissioned by the city did not even examine the effect of removing the valley's trees. Furthermore, the report does predict negative health effects on humans from the expressway project.
The city-commissioned RWDI report (2003) on Air Quality Assessment noted short-term improvements from pollution removal by trees including reductions of up to 13 per cent of PM10 (breathable particulate). The report went on to say, "The effects of trees on local air quality have not been quantified for this RHCE study" and did not take the trees into account in their modelling.
Murray also said that "the plan is to replace the trees with seedlings and whips at a ratio of five new trees to each one cut down." There are problems with this plan. They include:
- The 40,000 to 47,000 figure does not include seedlings and saplings. It only counts trees that are more than five centimetres (2 inches) in diameter. It appears that the city doesn't plan to plant any trees of this size. So, by their definition of a tree, the city will plant no trees. It hasn't bothered to count the many additional thousands of seedlings and saplings destroyed that were less than five centimetres in diameter.
- Few of the seedlings and whips will be planted in the valley as the available space will be taken up by asphalt and re-aligned creek bed, therefore most seedlings will have to be planted elsewhere.
- Tree seedlings do not thrive in polluted air, therefore I expect many will die, particularly in areas where they are more needed as air filters.
- The city has already cut down thousands and thousands of trees in the valley and has yet to plant any seedlings to replace them. Indeed, last month, city council struggled desperately to find short-term funding to replace the trees cut down last year along city streets. It was unable to even find money for proper maintenance of street trees in the old city of Hamilton, or for any maintenance at all of the street trees in the suburbs.
- The filtering capacity of a seedling, or a whip (which is a small branch stuck into the ground in hopes that it will root and grow) is miniscule. Residents will have to wait for decades before any surviving seedlings grow into real trees with a filtering capacity approaching what was lost.
Sadly, the expressway project can be described as a massive experiment on the health of people in east Hamilton. I hope medical researchers will monitor this experiment to see the effects of reducing air pollution filtering equipment (trees) and increasing dangerous particulates in the air due to the attraction of diesel trucks and other traffic.
Dr. James S. Quinn is associate professor of biology at McMaster University and a resident of Hamilton.
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