On the list of things you worry about when walking around on a warm summer’s day, road dust is likely not up there with wasps, smog, and bad drivers. But there’s mounting concern it should be.
The European Commission’s Science for Environment released a report stating that laboratory studies suggest short-term exposure to road dust may have serious health effects.
In the simplest sense, road dust is a combination of exhaust, particles from tire and brake wear, dust from unpaved roads or potholes, and pavement dust generated especially by studded tires scraping pavement. You don’t want stuff like asbestos and rubber and fine particular matter in your lungs.
The International Bank for Reconstruction and Development state that long-term exposure to traffic-generated dust “can reasonably be expected to contribute to the 2 million people in low-income countries, who die prematurely every year from exposure to high concentrations of airborne particulates.”
It’s also a considerable cost to our agricultural industry. Road dust emissions cause considerable drops in productivity in farming systems, on account of things like photosynthetic yield loss, increased levels of pest, disease, and weed incidence, dirty produce, and reduced pollination.
What affects crops, naturally affects the environment too. The article, “Effects of road dust on the growth characteristics of Sophora japonica L. seedlings” in the Journal of Environmental Science (Aug 2016) says “road dust causes a series of negative effects on plant physiology.”
So controlling road dust is a challenge. Some cities use sweeper trucks with vacuums, others spray water to keep road dust down, and the trend lately is to use road salts, as they draw moisture from the air and keep the road dust damp and down on the ground.
Here in Newfoundland & Labrador, we have been spending considerable money on the problem of road dust, in part because gravel roads, the worst culprits of road dust, make up almost 18% of the 10,000 kilometres of roads throughout our province.
The Provincial Government recently announced tenders for 1.17 million litres of liquid calcium chloride from Sel Warwick Inc. In 2016, government identified a savings of approximately $250,000 by applying the liquid calcium chloride themselves, using their brine tankers and staff, rather than contracting out the work.
Calcium chloride is a salt that draws moisture from the air, to keep road surfaces constantly damp, which ultimately creates a hard and compact road surface. Sounds great.
Yet the use of calcium chloride isn’t exactly ideal, as road salts do their own corrosive damage to both the natural environment, and our built environment: road salt has destroyed everything from bridges to malls throughout Canada.
If the goal of dust control is to reduce pollution and contamination in our lungs, farms, and built and natural environment, why are we fighting pollutants with pollutants? Road salts contaminate ground water, vegetation, and crops, for example.
There are alternatives, like a lignin and asphalt emulsions, or a product called Dust Stop, with less corrosive effects. But it’s costly, so a lot of governments don’t consider it. Watering roads would even do the trick, but the catch is it must be applied frequently to maintain adequate moisture. In other words, the labour and equipment costs rule it. So calcium chloride it is.