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Microbial stowaways: Are ships spreading disease?
Ships are inadvertently carrying trillions of stowaways in their ballast water tanks that could pose a risk to public health, according to newly published research. Get the article here.
When water is pumped out of ballast tanks, it can release disease-causing microbes, said Fred Dobbs, a marine microbial ecologist at Old Dominion University in Virginia.
"This is a very difficult thing to predict," Mr. Dobbs said Wednesday in a telephone interview.
"It isn’t an issue, of course, until the ship discharges its ballast water, and anything that’s lived throughout the course of the voyage will subsequently be dumped into receiving waters."
He was able to track Vibrio cholerae, the bacterium that causes cholera in humans, from an outbreak in Peru to Mobile, Ala.
"We had a pretty good smoking gun argument that ships were transporting these disease organisms from South to North America," said Mr. Dobbs, whose article, titled Ship ballast tanks: how microbes travel the world, appears in the recent edition of Microbiology Today.
Untreated cholera can be deadly.
"The deaths are occurring on the Indian subcontinent, principally, and in South America. There are various estimates between 10,000 and 50,000 people per year that die from the disease."
Other disease-causing microbes in ship ballast tanks, which Mr. Dobbs said are sampled very rarely, include Cryptosporidium parvum and Giardia duodenalis. Both can cause stomach upset. Researchers also found enterovirus in ballast water, which can cause mild respiratory illness and hand, foot and mouth disease.
"We’re playing ecological roulette . . . with transporting all these species everywhere all the time," Mr. Dobbs said.
He stressed there’s been no documented case of disease outbreaks associated with the ballasting activities of ships.
"In particular, in the U.S. and Canada, we’ve got a couple of things working in our favour. No. 1, the water is cool to cold, depending on how far up the coast you are. And we also have very good hygiene. People aren’t washing their clothes and taking drinking water from the same rivers in which there’s sewage pollution."
But ballast water could carry diseases deadly to fish and seabirds, he said.
"Red tide organisms can be transported by ships as well," said Mr. Dobbs, noting agents that cause paralytic shellfish poisoning can also stow away inside ballast tanks.
"That may be as much, if not more, of an issue for us to be considering. The upshot of this is, whether it’s at the U.S., state, Canadian, national or even the international arena, there are a series of standards that are either being proposed or, in fact, are already in force."
Those regulations stipulate what organisms can be discharged with ballast water.
"These are daunting technological and scientific challenges that, arguably, have been made, in some cases, by politicians who don’t appreciate the technical difficulties involved," Mr. Dobbs said.
Ultraviolet radiation and chlorine can be used to treat ballast water, he said. Ultrasound, heat, microwaves and hydrogen peroxide are also proposed fixes.
"There is filtration, which does a great job, but it can only get down to maybe about 25 micrometres, and your garden variety bacterium is one micrometre or less. So filtration isn’t going to get out bacteria."
Ships pump water into and out of ballast tanks to compensate for cargo, increase propulsion efficiency and maximize stability in rough seas.
Mariners are supposed to discharge their ballast water far out to sea, he said. But that can cost time and fuel, an outlay unscrupulous captains might be anxious to avoid. Skippers can also claim an exemption if seas are rough.
"Some shipping companies are very, very good, and others, it’s hard to know whether they’re good or not. If somebody wants to subvert the system, it’s usually possible."