MADELEINE BRAND, host:

There are some dangerous, not boring, stowaways traveling on ships that transport goods around the world: tiny organisms. They live in the water deep in a ship's hold and in the course of their international travels, these microbes are causing havoc across the globe.

NPR's Jon Hamilton reports on efforts to stop them.

(Soundbite of engine)

JON HAMILTON: The stowaways begin their voyage in the dark, far below decks when someone opens a valve.

Dr. MARIO TAMBURRI (Researcher, University of Maryland; Director, Maritime Environmental Resource Center): There it goes. There's the water starting to fill.

(Soundbite of ballast water)

HAMILTON: Mario Tamburri, a researcher from the University of Maryland is shinning his flashlight into a ballast tank on the Cape Washington, a 700-foot ship moored in Baltimore harbor. Water from the Chesapeake Bay is flooding the tank.

Dr. TAMBURRI: The tank itself is about 650 cubic meters. It's enormous.

HAMILTON: The size of a large swimming pool. And there's another one on the other side of the ship. The tanks allow large vessels to remain stable with different cargo loads. But they also mean a ship from Baltimore maybe carrying millions of gallons of local water to Singapore or Dubai, and Tamburri says that water may contain billions of microscopic eggs or larvae from local sea creatures.

Dr. TAMBURRI: Even though lots of organisms die on those voyages anyway, it only takes a few that survive, you know, two weeks going across a major ocean and they can establish themselves and establish a new population.

Dr. ANDREW HUDSON (Water Expert, United Nations Development Program): Once they are established, they are virtually impossible to eradicate.

HAMILTON: Andrew Hudson advises the United Nations Development Program on international water problems. He says, most species don't do well in a new place, but the ones that can survive are often so adaptable they take over. Zebra mussels from Russia, for example, have clogged the intake pipes of power plants and water treatment facilities along many U.S. rivers. That costs billions of dollars each year. And invasive species coming from U.S. waters can cause even bigger problems. One example: a comb jellyfish that has found its way to the Black and Caspian Seas. Hudson says the jellyfish is devouring tiny offspring from a fish called the kilka.

Dr. HUDSON: And the kilka fishery has in effect collapsed. And we've seen very moving footage of Iranian fishermen who've basically lost their livelihoods because of the collapse of the kilka fishery just due to this invasive.

HAMILTON: Countries including the U.S. have tried to control the problem by requiring incoming ships to flush their ballast tanks in the open ocean. But that hasn't done the trick. So governments are preparing to impose tougher standards on ballast water. In response, several companies have developed systems to kill organisms in ballast tanks. Hudson says these systems need to be affordable and meet two other criteria.

Dr. HUDSON: They have to be highly effective in terms of drastically reducing the proportion of living organisms in that water, number one. Number two, if they use chemicals, they need to ensure that the water that's released is free of any kind of toxic chemicals that would impact on ecosystems as well.

HAMILTON: Independent scientists need to test the systems to make sure they work as advertised.

(Soundbite of ballast water)

HAMILTON: And that's what Mario Tamburri and his team are doing on the bottom deck of the Cape Washington. It's a space big enough for full-court basketball, but designed to carry things like tanks and Humvees and helicopters.

Dr. TAMBURRI: And it's been completely transformed into essentially a research lab for looking at how well ballast water treatment systems work to remove organisms in that water. And so we have a variety of pipes and tanks and areas for looking under a microscope and sensors and a whole suite of instruments.

HAMILTON: Tamburri points to a pipe coming from the ship's engine room.

Dr. TAMBURRI: Water comes through that first 8-inch valve, and then it's split in two ways. Half the water goes into a control tank, which means it's untreated, just natural ballast water. And half the water goes through a treatment system and the one we're looking at over the next few weeks is a system that chlorinates the water and filters the water to remove the organisms.

(Soundbite of ballast water)

HAMILTON: A ship couldn't easily carry enough chlorine to get the job done. So they make it using electricity, which can produce chlorine from the salt in sea water. The chlorine is potent at first, but breaks down and becomes harmless during the voyage. Researchers won't know how well this system works, though, until they compare samples from the treated ballast tank with samples from the other control tank.

Dr. TAMBURRI: And the idea is that after five days, the treated should have very close to nothing alive in there. And the controlled should still have very high numbers, similar to what we brought on a ship originally.

HAMILTON: Chlorine is just one approach to the ballast water problem. Companies are also trying to zap the stowaways with heat, ultraviolet light, ozone and nitrogen. John Hamilton, NPR News.

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