Some of those bombs are known to contain wartime chemicals such as mustard gas, choking agents and blistering agents, and they have begun to leak.

Canada and other nations commonly dumped unused weapons at sea or in harbours as they approached home base, but the practice stopped in 1975 after NATO studies presented in Helsinki in 1972 showed chemicals will likely leak, potentially harming marine life and human health.

Some of the most cluttered and dangerous deposits of bombs in these parts are corroding in soft silt at the bottom of the Bedford Basin and Halifax Harbour, in the centre of the province’Äôs most densely populated region.

There are more than 3,000 military munitions sites off Nova Scotia, in rich fishing areas or near Sable Island, where explorations for natural gas are ongoing.

There are also sites between Cape Breton and Newfoundland at which the United States, under a $100-million deal, dumped an unknown amount of weapons and other military material, including vehicles, from its bases in Stephenville and Argentia after the Second World War.

Mr. Long, a principal in Decommissioning Consulting Services of Ontario, says a cleanup will be unavoidable in the near future.

"It’Äôs a worldwide epidemic," he said of the dangers lurking in most oceans.

Aging bombs can be easily triggered by minor underwater pressure ’Äî the "equivalent to the tap of a pencil," he said, noting that seismic blasts used by companies exploring for gas generate much greater pressure than that.

"We’Äôve been lucky," he said.

"Blindly conducting seismic has the potential to damage soft-skinned chemical weapons that could leach out into the environment. Most likely, these agents are releasing into the environment already from seismic research being conducted off Nova Scotia."

An accidental drop of an anchor by an unsuspecting boater in the Bedford Basin, for example, could also set off a series of explosions like the one in 1945, when a munitions depot caught fire in the area. Boaters are still not permitted to drop anchor due to the vast amount of unexploded munitions.

But Mr. Long says a fishing net could also easily pull triggers off unexploded bombs, something many snow-crab fishermen fear happening off the coast of Cape Breton.

In 2003, the Department of National Defence began a five-year, $10-million study to explore 50 munitions sites, some on land, to determine risks. Once that study is completed, the military is expected to develop an action plan if needed.

Until that’Äôs done, Mr. Long doesn’Äôt expect any cleanup to be ordered, given Canada’Äôs priorities in the ongoing war on terror overseas, but it’Äôs not stopping him and others from getting locals trained for future demolition.

Just last Wednesday, Eskasoni First Nation signed an agreement to train local people to use Department of Defence bomb-disposal methods, because there’Äôs a large munitions site immediately off the reserve in Bras d’ÄôOr Lake.

The pilot project will include environmental and hazardous materials management and methods to clean up unexploded ordnance on land and at sea.

Tuma Young, the band’Äôs chief executive officer, said Eskasoni signed a partnership with Mr. Long’Äôs company in hopes of providing new skills and, eventually, jobs.

"We can clean up these sites and provide our people with employment," Mr. Young said. "Eskasoni used to be a bombing range. . . . They used to test bombs here. We found a few munitions.

"We have to take a long term view on this . . . but these areas, we’Äôre already fishing in them. There’Äôs a danger of nets hooking, so we got to keep one eye on the problem and one eye on the future."

In 1999, two bombs, one weighing 110 kilograms, were pulled out of silt in shallow waters during a construction project in Bedford.

The Canadian navy determined that alloy plugs on the bomb had corroded and the explosives had dropped out, but 400 people still had to be evacuated.

Explosives were scattered all over the harbour after the Halifax Explosion in 1917 and again when a munitions depot caught fire and exploded in 1945. As well, Second World War munitions have been washing ashore for years at the mouth of the harbour from the Clare Lilly, a British ship that ran aground in 1942 just off Portuguese Cove.

"In the last couple of years we’Äôre really starting to see a lot of different-coloured lobsters ’Äî blue ones, red ones ’Äî coming out of the water. In a lot of areas of the world where chemical weapons are found, you find different colours of species of animals," said Mr. Long, who now lives in Sydney.

"It’Äôs also been in our experience that these different sites are where some of the highest rates of cancer are as well."

A NATO study presented at the Helsinki Convention in 1992 showed underwater discharge of chemical weapons at sea can attack the photosynthesis of plankton and affect the hatching rates of crustaceans.

But dangers are not limited to the sea.

Mr. Long’Äôs de-mining company, using a high powered metal detector, found dozens of unexploded munitions ’Äî some partly buried ’Äî metres away from several Halifax highways last year. He retrieved and detonated or dismantled them all.

"We have to clean up these sites," he said, but he acknowledged that politics and military priorities will play a factor in deciding when that will happen.

His company has extensively de-mined areas of Bosnia and Afghanistan and helped India restore fresh-water supplies when the 2004 tsunami in Asia lifted landmines out of the ground near wells.

Halifax served as a main launching point for Allied convoys headed overseas during both world wars, and the harbour contains more unexploded bombs than any other place in North America, according to the military.

Explosives were never cleaned up, but because the harbour is so deep the military has said they don’Äôt pose a big threat unless they are disturbed.

Sonar and remote submersibles are being used in the federal study to determine the types of bombs involved and what should be done with them.

It’Äôs unknown when the results will be released.