Science: Voyages of an invisible menace: Even an empty ship may carry a dangerous cargo - polluted ballast water. James Curtis reports

Apart from oil spills, the world's shipping fleets carry another, less conspicuous environmental hazard - a danger that presents itself every time an empty cargo ship arrives at port: ballast water.

In November 1991 a strain of cholera was discovered in the ballast water of three ships at ports on the east coast of the United States. The vessels had stopped at ports in South America. In June 1992 a further two ships - also intercepted at eastern US ports - were found to be carrying cholera in their ballast water.

In Australia, scientists examining the ballast water of a Norwegian vessel calling at a Queensland port from Singapore, discovered an organism that could cause botulism in animals and humans. Incidents such as these have prompted the International Maritime Organisation (IMO) to introduce tougher guidelines on ballast water discharges.

All ships use ballast water for stability when sailing unladen. The water is taken aboard at the port of origin and emptied into the harbour when the ship arrives to load its cargo.

However, because ballast is commonly taken on in shallow water, or may occur near a dredging site, a large quantity of silt can also be loaded. This, or the water itself, may harbour aquatic organisms which could be toxic, carry diseases, or assume more dangerous characteristics in alien surroundings.

According to Dr Bill Farnham, of Portsmouth University's marine laboratory, the characteristics of some species in alien environments are often unpredictable. He says: 'A normally innocuous organism can behave quite differently in a new environment.'

In the US, awareness of the problem has been heightened by an infestation of zebra mussels brought to the Great Lakes by European cargo ships. This was 'a disaster', says Steve Thorp, environment officer of the Great Lakes Commission. Since the mollusc's discovery in 1985 it has reproduced rapidly, clogging the intake and discharge pipes of irrigation systems and power plants. The mollusc also harms fish stocks by filtering out essential nutrients in the water. A survey at the National Fisheries Research Centre, Great Lakes, shows it has caused damage costing dollars 5bn (pounds 3.4bn).

In Australia, an outbreak of a toxic alga on the south coast triggered legislation to control ballast water discharges. The dinoflagellate, thought to have been carried aboard Japanese vessels offloading woodchips at Hobart, poisoned shellfish stocks in southern Australia and Tasmania. The algae became so dense in some areas that they caused 'red tides'.

Neil Chambers, marine adviser to the International Chamber of Shipping, says the high volume of coal and iron ore exports from Australian ports makes areas of the coastline vulnerable to contamination. He says 58 million tons of foreign water is discharged annually into Australian waters.

In the UK the Marine Conservation Society is seeking funds to study the hazards of ballast water discharges. It says: 'The introduction of shellfish parasites in ballast water could have a significant impact both upon the native populations and shellfish farmers.'

Scientists at Southampton University discovered a foreign species of tubular worm on pontoons at the city's docks. Other species in the area include the Australasian barnacle and the Far Eastern sea squirt.

The IMO's spokesman, Roger Kohn, says the new measures to deal with ballast water discharges are not mandatory, but he hopes that they will become so. Short-term recommendations include ships exchanging old ballast water for new in mid-ocean, ideally where the depth is 2,000 metres or more. The IMO also suggests that water should be checked against a list of potentially dangerous organisms before a ship leaves port.

For the longer term, it proposes measures such as chemical treatment, oxygen deprivation and ultraviolet light disinfection. Changes to ship design to reduce the volume of ballast required or improve the way it is taken aboard are also under consideration.

Mr Chambers says: 'At this stage it is sensible that the directives should be voluntary because the remedies available are not necessarily the best or most effective.'

He says chemical treatment of ballast water may cause as much environmental damage as some of the organisms themselves. Another solution - heating the water to kill micro-organisms - would be expensive, impractical and time-consuming.

In the short term, Mr Chambers says the most practical solution is to control the problem at source by providing information on the best areas for ships to take on ballast water. This will require the co-operation of port authorities. The issue is being considered by Associated British Ports (ABP) and the European Harbour Masters' Association (EHMA). It is also being monitored by the International Association of Ports and Harbours and the American Association of Port Authorities.

Captain Malcolm Ridge, vice-president of the EHMA and marine adviser to ABP, says ports cannot afford to ignore the issue. He believes that water contamination can cause more long-term problems than oil pollution, because it is not immediately obvious.

It is 'too early' for ports to know exactly what preventive measures they should take, says Capt Ridge. The matter will be raised for the first time at an ABP general meeting this month, and a working group will present its findings to the annual EHMA congress in Marseilles in May.

The author is deputy editor of 'Port Development International'.

(Photograph omitted)

News
people
Sport
FootballGerman sparks three goals in four minutes at favourite No 10 role
News
Rumer was diagnosed with bipolarity, attention deficit hyperactivity disorder and post-traumatic stress disorder: 'I was convinced it was a misdiagnosis'
peopleHer debut album caused her post-traumatic stress - how will she cope as she releases her third record?
Sport
A long jumper competes in the 80-to-84-year-old age division at the 2007 World Masters Championships
athletics
PROMOTED VIDEO
Sport
Radamel Falcao was forced to withdraw from the World Cup after undergoing surgery
premier leagueExclusive: Reds have agreement with Monaco
Arts and Entertainment
'New Tricks' star Dennis Waterman is departing from the show after he completes filming on two more episodes
tvHe is only remaining member of original cast
Life and Style
Walking tall: unlike some, Donatella Versace showed a strong and vibrant collection
fashionAlexander Fury on the staid Italian clothing industry
Arts and Entertainment
Gregory Porter learnt about his father’s voice at his funeral
music
News
ebooksAn unforgettable anthology of contemporary reportage
Arts and Entertainment
tvHighs and lows of the cast's careers since 2004
Life and Style
Children at the Leytonstone branch of the Homeless Children's Aid and Adoption Society tuck into their harvest festival gifts, in October 1936
food + drinkThe harvest festival is back, but forget cans of tuna and packets of instant mash
Sport
Lewis Hamilton will start the Singapore Grand Prix from pole, with Nico Rosberg second and Daniel Ricciardo third
F1... for floodlit Singapore Grand Prix
New Articles
i100
Life and Style
Couples have been having sex less in 2014, according to a new survey
life
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Volunteer Trustee opportunities now available at The Society for Experimental Biology

Unpaid Voluntary Position : Reach Volunteering: Volunteer your expertise as Tr...

Early Years Educator

£68 - £73 per day + Competitive rates of pay based on experience: Randstad Edu...

Nursery Nurse

£69 - £73 per day + Competitive London rates of pay: Randstad Education Group:...

Primary KS1 NQTs required in Lambeth

£117 - £157 per day + Competitive London rates: Randstad Education Group: * Pr...

Day In a Page

Scottish referendum: The Yes vote was the love that dared speak its name, but it was not to be

Despite the result, this is the end of the status quo

Boyd Tonkin on the fall-out from the Scottish referendum
Manolo Blahnik: The high priest of heels talks flats, Englishness, and why he loves Mary Beard

Manolo Blahnik: Flats, Englishness, and Mary Beard

The shoe designer who has been dubbed 'the patron saint of the stiletto'
The Beatles biographer reveals exclusive original manuscripts of some of the best pop songs ever written

Scrambled eggs and LSD

Behind The Beatles' lyrics - thanks to Hunter Davis's original manuscript copies
'Normcore' fashion: Blending in is the new standing out in latest catwalk non-trend

'Normcore': Blending in is the new standing out

Just when fashion was in grave danger of running out of trends, it only went and invented the non-trend. Rebecca Gonsalves investigates
Dance’s new leading ladies fight back: How female vocalists are now writing their own hits

New leading ladies of dance fight back

How female vocalists are now writing their own hits
Mystery of the Ground Zero wedding photo

A shot in the dark

Mystery of the wedding photo from Ground Zero
His life, the universe and everything

His life, the universe and everything

New biography sheds light on comic genius of Douglas Adams
Save us from small screen superheroes

Save us from small screen superheroes

Shows like Agents of S.H.I.E.L.D are little more than marketing tools
Reach for the skies

Reach for the skies

From pools to football pitches, rooftop living is looking up
These are the 12 best hotel spas in the UK

12 best hotel spas in the UK

Some hotels go all out on facilities; others stand out for the sheer quality of treatments
These Iranian-controlled Shia militias used to specialise in killing American soldiers. Now they are fighting Isis, backed up by US airstrikes

Widespread fear of Isis is producing strange bedfellows

Iranian-controlled Shia militias that used to kill American soldiers are now fighting Isis, helped by US airstrikes
Topshop goes part Athena poster, part last spring Prada

Topshop goes part Athena poster, part last spring Prada

Shoppers don't come to Topshop for the unique
How to make a Lego masterpiece

How to make a Lego masterpiece

Toy breaks out of the nursery and heads for the gallery
Meet the ‘Endies’ – city dwellers who are too poor to have fun

Meet the ‘Endies’ – city dwellers who are too poor to have fun

Urbanites are cursed with an acronym pointing to Employed but No Disposable Income or Savings
Paisley’s decision to make peace with IRA enemies might remind the Arabs of Sadat

Ian Paisley’s decision to make peace with his IRA enemies

His Save Ulster from Sodomy campaign would surely have been supported by many a Sunni imam