Quick! What's the deadliest chemical in tap water? DDT? PCBs? BPA?
Try DNA, says Steve Hrudey, a retired professor of environmental toxicology at the University of Alberta. "That's what a virus is," he says, and it's far more likely to make you sick and dead than anything else that comes out of the tap.
That was one of several lessons a group of about 20 Edmonton area residents learned Wednesday night at the Telus World of Science as part of a free talk on chemical contaminants in water. The talk, organized by the U of A and the science centre, is part of a series of lectures called Toxic Bodies.
People tend to jump to conclusions about risk whenever they hear about a new environmental toxin, many of which seem omnipresent, says Debra Davidson, the talk's organizer.
"All of a sudden, everything looks like a potential source of risk."
These talks are meant to give people a chance to talk to the experts and see which of these toxins they should actually worry about.
Hrudey, a world-renowned expert on drinking water safety best known for his work on the Walkerton tainted water inquiry, says people should worry less about exotic trace contaminants in their water and more about old standbys like E. coli.
"Microbial contamination can kill people," he says, and is still the main threat to water safety.
“Pure” water
About 30 per cent of Canadians drink mostly bottled water, Hrudey says, citing Statistics Canada, and many do so due to a fear of chemical contaminants in tap water.
But if someone says bottled water is somehow more safe and pure, they're lying, he says.
"Bottled water costs you a thousand times more than the stuff that comes out of the tap, and the stuff that comes out of the tap is expensive enough. If you like the convenience of the bottle, fill it up from the tap."
All chemicals are toxic, Hrudey says, and no water is free of chemical contaminants. Even pure rain will have CO2 in it seconds after it forms.
What matters is dosage, he continues. "By and large, it's tough to poison someone through their water with chemical contaminants."
PCBs and DDT, while harmful, are mostly insoluble in water, making it tough to get a dangerous dose of them from your tap. Natural substances like blue-green algae in lakes, on the other hand, can and do kill pets at very low concentrations.
Microorganisms, on the other hand, kill millions of people each year through diseases such as cholera, he says, most of which are spread by improper sanitation and unclean water. "That's what I call unsafe."
That's why he's got a beef with people who fear chlorinated water.
"It was a failure to chlorinate that resulted in people dying in Walkerton," he says, referring to the contaminated water tragedy in that community. His research suggests that many of the contaminated water outbreaks in affluent nations in the last 30 years were also caused by improper chlorination.
Many critics link chlorinated water to rising cancer rates, Hrudey noted. While there have been many studies on this subject, researchers have yet to conclusively show that chlorinated drinking water causes health problems such as cancer. We can't say for sure that it doesn't, he notes, "but the evidence as it's unfolded over the past 35 years is less and less convincing."
The best way to keep drinking water safe is to take an interest in the staff at your local treatment plant, Hrudey says. "If the people who provide [you] with water can't answer simple questions, then I'd start to get concerned."
This lecture series continues Feb. 29 with a talk on pesticides. Visit www.ualberta.ca/ersc for details.
