by the United States government during the Cold War.

The tests were conducted on the Marshall Islands, a remote area of the Pacific Ocean

earmarked for unlimited nuclear destruction.

These are the islands today, which are mostly abandoned.

Though they look like any tropical paradise, these scenic views are tainted with radioactivity.

The radioactivity left behind is so high that you can't move back there,

you can't grow crops there, eat them; you can't drink the water.

So we're talking 70 years later, we can't go back to these sites.

But Ken Buesseler and his research team went back, to measure

just how contaminated this paradise is.

When a nuclear weapon explodes, hundreds of radioactive isotopes are released,

including plutonium-239, which has a half-life of 24,000 years.

And though that rate of decay may seem slow, if you're unfortunate enough to be exposed

to a large amount of this over a lifetime, it could lead to major health problems.

- It's called global fallout.

And the idea was, where did that end up, right?

And the oceans are one place where it ended up.

Is that in the water?

Did it sink to the bottom?

Is it in the marine biota?

So one of the goals of our research trip was to find where the highest levels were

of these radioactive contaminants: plutonium, cesium.

Places we looked were the craters left behind from the hydrogen bombs––that would be

the Mike Test on Enewetak, and Bravo Test on Bikini, 1954.

So these are tests that are thousands of times greater in magnitude and strength,

producing a thousand times more fallout locally and across the globe than the smaller tests.

A challenge that we had to this day is knowing that, if I find plutonium in the lagoon,

in an organism, is it from a particular test?

So we do a lot of what we call fingerprinting: it's a lot like forensics,

as you'd see in a crime scene.

Ken uses radioactive tracers like radium to determine where the plutonium has settled

and if it's leaking from wells, lagoons, or any other groundwater sites.

Ken and his team found that seafloor sediments contributed the most plutonium to the ocean.

This wasn't a complete surprise.

Until atmospheric nuclear testing was banned in 1963, more than 5 tons of plutonium

were dispersed in the atmosphere.

Most of this fell into the oceans and sank,

because plutonium is not readily soluble in seawater.

Cesium was only about two times higher.

Plutonium, within those islands, is about 100 times higher than just outside,

so there has to be a source, 70 years later.

Because of these nuclear tests so long ago, former inhabitants of these islands,

and now their younger generations, may never be able to live there again.

- This is definitely one of those nations that will suffer the most from sea level rise

due to climate change, so they have this double-whammy.

They have the radioactive waste that hasn't allowed them to move home, and now,

they're experiencing the effects of sea level rise and loss of their entire island,

all their atolls, a place to live.

Ken's research here on the Marshall Islands draw parallels to what can be learned

from the Fukushima disaster in 2011.

- One's a nuclear reactor accident, one was an intentional explosion of nuclear weapons, okay.

But still, for the people who live close to these accidents, these high sources,

there's always the question of, "when can I move back?"

"What does that mean in terms of my health and safety?"

It's been frustrating that we run 400+ reactors around the world's oceans

around the edges and inland, and yet we aren't maintaining a cadre of science

to deal with the environmental consequences of doing that.

We live in a radioactive world; we can't get away from it.

So, despite us knowing about levels, what's considered okay or not, for your exposure

through food and air, there's always something that maybe is not considered.

That makes it also very hard to say, when is it okay to move back to certain areas?

And that's the same for Japan, and it will be for Japan for years to come, as it is today,

70 years later in the Marshall Islands.

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