Science and Technology for Canadians

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Summary

Science can help us to take action to improve our health and the environment. Banning DDT in 1972 is considered one of the most important steps in protecting wildlife and people from the effects of pesticides and has set the course for future research into the effects of the chemicals we use.

Transcript of Video

Gillian Deacon
This week on Earth Tones, we're looking at some of the environmental advances that affect our daily lives. Tonight, a development with an unexpectedly negative and lingering impact on earth.

Jay Ingram
At one time, DDT was probably the most commonly used pesticide in North America. By the early '70's, more than one billion kilograms had been released into the environment. DDT was so popular because it's a one size fits all pesticide - kills many different kinds of bugs. But DDT doesn't just kill bugs... it's harmful to all kinds of creatures, especially birds.

Dr. Chip Weseloh
DDT affected the egg shell on birds. Normal eggshells are quite thick. The birds sit on them, then incubate them - but DDT made the egg shells thinner, so when the birds sat on them the eggshell broke, and there were no young produced, so the populations declined.

Jay Ingram
Some bird populations declined more than others. They were more sensitive to DDT's harmful effects.

Dr. Chip Weseloh
Uh... the birds that were affected most by DDT were the ones at the top of the food chain - herring gulls and some of the other fish eating birds, cormorants and brown pelicans - some of the raptors - peregrine falcon in particular. And birds weren't affected equally. Some are much more sensitive than others. The peregrine is very, very sensitive. The double crested cormorant is quite sensitive. The herring gull isn't very sensitive. But the birds at the top of the food chain were the ones that were most affected.

Jay Ingram
That's because DDT is what's called a very persistent chemical. It hangs around in the environment for a long time. For instance, DDT may persist in water for as long as 150 years! It stays in the tissues of all the animals that ingest it. That's why birds at the top of the food chain get a bigger dose. It's called bio-magnification or bio-accumulation.

Dr. Chip Weseloh
... and those are terms that refer to the buildup of a compound as you go up the food chain. DDT, for instance, is in the water and it goes into the small organisms, slightly bigger organisms, and it gets up into the top of the food chain... and by that time it's magnified, where it becomes a greater concentration than it was down at the bottom of the food chain.

Jay Ingram
Birds weren't the only ones beings affected. Mounting evidence of DDT's harmful effects led our government to ban it for most uses in 1969.

Dr. Chip Weseloh
It's not nearly as big a problem as it used to be. Back 10 or 15 or 20 years ago it was a much greater problem because there was more in the atmosphere and more in the environment. It's still bio-accumulating and bio-concentrating, but it's not doing as much as it used to. So the values, the concentrations, are lower now than they used to be, but yes, it's still accumulating.

Jay Ingram
But the news isn't all bad. The ban on DDT has had an effect.

Dr. Chip Weseloh
Oh I think there's lots of cause for optimism. I mean, things are not nearly as bad as they used to be and they're getting better all the time. We have a program going where we've been measuring chemicals in herring gull eggs for 25 years and uh... the levels are much, much less than they used to be. They're about 10 percent of what they were 25 years ago. So they've declined about 90 percent and that's good. I mean, we've made big strides, but we've got a little bit left to go. I mean, eventually we'd like to get to absolutely no chemicals in these birds, and so there's a ways to go. We have to keep working to keep the regulations there and to try and get rid of the bit that's left in the environment.

Earth Tones is produced in co-operation with Environment Canada.