Many potentially deadly stowaways are traveling around the world aboard thousands of vessels. Microorganisms such as cholera and ecoli are getting a free ride in the ballast water of ships. This heightens the potential for spreading harmful diseases from port to port. Two US researchers have developed a solution to the problem, which involves 'zapping' the bugs with ultra violet light. The method uses a lamp that emits UV rays to kill the disease-causing bacteria and other microorganisms found in the water.

Tests carried out with a prototype have shown that it is effective in killing many bacteria. The prototype of the device is Plexiglas chamber 30 centimetres high, filled with half a litre of water. The Plexiglas blocks the UV rays, preventing them from escaping. A tube shaped UV lamp is placed in a protective sleeve, which is inserted into the chamber. The lamp is turned on anywhere from a few seconds up to a few minutes. The treatment length depends on the target microorganisms. Low doses of the light prevent the cells from replicating, at higher doses they are killed. The method could be applied in a number of other areas, say researchers, such as processing drinking water or sewage treatment. The next phase of development will involve the device being built to cater for larger amounts of water, more conducive to the amounts of ballast found in a ships' hull.

The creation of the lamp and chamber follows research carried out last year in the US Smithsonian Environmental Research Centre. The ballast water of commercial vessels arriving in Chesapeake Bay on the US East Coast was tested and found to contain billions of microbes, some disease-causing. Each litre of water taken from the hull had about a billion bacteria as well as seven billion virus-causing particles. Cholera-causing bacteria were detected in all 15 ships examined. In the US alone more than 79 million tonnes of ballast water is dumped into the sea each year.