This is scientific American 62nd Science. I'm Julia Rosen. Got a minute?

The Mariana trench is the deepest spot in the world's oceans. Only three humans have ventured into the trench in submersibles, but plenty of our

pollution has made the voyage to the bottom of the sea. A new study finds that critters

living more than six miles below the ocean surface contain high levels of harmful

compounds like polychlorinated bifenals or PCBs and flame retardants.

But an important thing is if you're at the deepest place in the world there's no

where else to go.

Alan Jameson, a marine ecologist at Newcastle University in the UK.

You can't be dispersed horizontally, you can't go back up.

So for every nanogram of pollutant that's gone into the deep seas there's no mechanism to put it back

again.

So of course the valleys are going to be high because it's only a one-way traffic, right?

Jameson and his colleagues used robotic traps to collect deep sea amphipods living in the most remote parts of the oceans.

These creatures look a bit like shrimp and they're well adapted to their extreme environment, he says.

The deep sea ones are incredible scavengers.

This is why they thrive in the deep sea,

because it's a low food environment

where most of their food comes from dead carcasses raining from the surface or particulates coming down.

So everything from an organic particle to a dead whale is fair game to an anaphropod. The food that floats down to the ocean bottom carries man-made contaminants, including

PCBs, which entered the surface ocean from rivers and coastlines.

Companies stopped manufacturing these chemicals in the 1970s after they were found to be dangerous,

but they don't break down easily, so they're still swirling around in the oceans and working their way down to the sea floor,

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