Catalyst: Chemical pollutants toxic to whales

MARK HORSTMAN:

Of all the continents, Antarctica is the coldest, the driest, the highest, the windiest and the brightest. And as the only landmass with hardly any people, you'd expect that it's also the cleanest. For the Southern Hemisphere's population of humpback whales to remain healthy, Antarctica needs to be free of chemical pollution.

DR SUSAN BENGSTON NASH:

The main concern is that the diffused toxic effect it has in just compromising the immune system and, therefore, making the humpback whales more vulnerable to fighting disease.

MARK HORSTMAN:

But new research is revealing that humpback whales are contaminated by toxins that can only come from their staple diet of krill. A few years ago, Susan Bengston Nash analysed several thousand of them to see what they might contain.

DR SUSAN BENGSTON NASH:

We started with krill, krill being the keystone species of the Antarctic, meaning that if you remove the krill you're also effectively removing other species. So it made sense to really start with krill. Find out what's in krill and thereby you can see what predators are exposed to as well.

MARK HORSTMAN:

She found more than 100 different forms of chemicals, known as persistent organic pollutants or 'POPs' for short. They're organochlorine pesticides like DDT… or industrial chemicals like PCBs and dioxins. Many were banned decades ago, but are so long-lived they continue to persist today. The problem is that persistent organic pollutants aren't broken down by water. Instead, they dissolve in the body fat of animals.

DR SUSAN BENGSTON NASH:

They're very lipophilic, so fat-loving. So if they do make it into the food web they can accumulate in our bodies.

MARK HORSTMAN:

But how do these synthetic chemicals end up in remote Antarctica, far away from agriculture and industry? Let's say we dump a load of DDT onto our imaginary planet here. Now, it's long-lived and a volatile chemical. So over decades it evaporates out into the atmosphere. And it only comes back down again when it hits a colder temperature and condenses out of the air. That's how these chemicals move around the world, bouncing from a warm climate down to a colder climate. But, of course, once they're down here it's a one-way trip. There's no going back. That's why persistent organic pollutants end up concentrating at the poles.

DR SUSAN BENGSTON NASH:

Assuming that an air mass has deposited some DDT out of the atmosphere onto the ice, perhaps, then in the summer, when the ice melts, it would either be taken up by herbivores, such as the krill, or else deposited to the sea bed.

MARK HORSTMAN:

And after krill?

DR SUSAN BENGSTON NASH:

After krill you've got everything else in the Antarctic.