Nitrogen gas could help solve ballast water pollution problem

A team of scientists from the US and Japan have discovered that a novel method for combating ship ballast corrosion could also help prevent a common pollution problem – that of spreading invasive species around the world in the ballast water of ships.

When nitrogen gas is bubbled through ballast water in ships’ tanks, it removes the oxygen, killing most aquatic organisms and preventing the oxidation that causes the tanks to corrode.

“It’s a rare win-win treatment that addresses a serious environmental problem and offers a cost-saving for the shipping industry,” marine ecologist Mario Tamburri of the Monterey Bay Aquarium Research Institute, one of the researchers who carried out the study, is reported as saying in The Scientist.

The research team discovered that the larvae of three species well-known for their tendency to invade new habitats, the European green crab, the zebra mussel, and the Australian tubeworm, died after three days following the treatment. However, some microbial species, including anaerobic bacteria and those with cyst stages in their life-cycles can survive the treatment, the scientists have found. “But for animals and plants, it’s going to be very effective,” said Tamburri. And, until international law mandates total mortality of ballast water organisms, it’s a great place to start.”

Ballast water, which is taken on by ships that are not fully laden in order to give them stability and is then ejected prior to arrival at a port, has been found to cause considerable damage to habitats by inadvertently introducing alien species, many of which can out-compete native species (see related story). One such example is that of European zebra mussels introduced to the US, which have carpeted the Mississippi River bed, even clogging pipes.

According to the US Environmental Protection Agency, more than 10,000 marine species each day around the world are being transported in ballast. Alien species are also known to have caused 70% of the native aquatic species extinctions in the last century.

The research was also carried out by scientists from the Elkhorn Slough National Estuarine Research Reserve in California and Sumitomo Heavy Industries in Japan.

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