HALIFAX: A report on the Arrow oil spill says the local environment has recovered and the wreck should remain.
A report in the Marine Pollution Bulletin entitled “Reflecting on an anniversary, The 1970 Arrow oil spill in Chedabucto Bay, Nova Scotia, Canada” by Kenneth Lee, in ecosystem science with Fisheries and Oceans Canada, Peter G. Wells, with Dalhousie University’s International Ocean Institute and Donald G. Gordon, of the Bedford Institute of Oceanography, reviewed the state of the environment in Richmond and Guysborough counties in the wake of the wreck of the Arrow oil tanker, which ran aground on Cerberus Rock on February 4, 1970.
Under charter at the time to Imperial Oil, the Arrow was approaching the former Nova Scotia Pulp and Paper Mill in Point Tupper after a voyage from Aruba, carrying 10 million litres of oil.
The vessel struck the rock amid severe weather and gale force winds, and while it seemed there was no threat of leakage at first, bad weather continued to batter the Arrow.
Four days later, the wreck of the Liberian registered oil tanker broke in two pieces, resulting in the spill of millions of gallons of thick Bunker C Crude Oil into Chedabucto Bay, and the stern sinking in deeper water.
Subsequent attempts in the following days to remove the cargo were unsuccessful, nor were attempts to recover the stern. In all, about 10,330 tonnes of fuel were spilled, coating 75 miles of shoreline with thick black sludge killing wildlife and threatening the fishery. It remains the largest spill on Canada’s East Coast.
According to the recently released report, a significant fraction of residual oil still remains in Black Duck Cove in Guysborough County, a site that received no remedial activities.
“It is not hard to find these oil deposits as they are not buried very deeply,” Wells told The Reporter. “Turn over rocks and shovel down, and oil bubbles up.”
The report declared that the ecosystem “largely recovered” from the spill and the local fishery is “robust,” even pointing out that Black Duck Cove is a now a small day-use provincial park.
“It’s on the way to recovery, rather than say fully recovered,” Lee noted. “The oil that remains at Black Duck Cove, most of the oil is actually buried quite deep.”
The report said the results of detailed chemical analysis and biological tests showed that oil in the surface layers – which had undergone significant biodegradation and photo oxidation – was of low aquatic toxicity and habitat recovery was evident from the amount of diversity.
“There’s some parts of the oil that do not degrade; they’re going to be there for a long time,” Lee noted. “The fact of the matter is some of these very high-weight molecular compounds like those aren’t very toxic because the molecules, large organisms can’t take them in. Part of the oil is equivalent to an asphalt highway and that’s why you see black rocks coating some of the spots.”
Lee said oil that is deep in the sediments is almost as toxic as that which spilled from the Arrow because of a lack of oxygen that allows bacteria to cause degradation.
“That oil is buried quite deep and to go and try and clean that oil, you would do more environmental damage than just leaving it there,” Lee said. “If you’re going to go in and bring trucks and dig up the whole beach to try and get at that oil which is at a deeper level, you’re going to cause more long-term environmental damage than if you left it alone.”
Wells said what is left of the most acutely toxic fractions of the oil, although minimal in heavy oils like Bunker C, can still impact the environment.
“The remaining oil, in places such as Duck Cove, is composed of heavier hydrocarbon molecules, less acutely toxic but still biologically available to burying animals and hence can be taken up by them, especially filter feeders such as mussels and clams, and contaminate their flesh,” Wells explained. “These compounds can also cause other effects, especially to reproduction, if taken up and residing in the gonads. If this oil remains buried, the risks of contamination are low or negligible.”
And while the impacts on species like sea birds can be damaging and long-term, Wells said the effects of oil spills in coastal environments tend to be short-term.
“Previously oiled coastal marine environments have been shown to recover, with little sign of persistent uptake of oil components, contamination of tissues, and subsequent effects.”
Lee explained that spills cause the most damage when oil comes to near-shore coastal waters where biological activity is higher, rather than remaining at sea where chemical dispersants and other clean-up techniques can be used.
Shoreline cleanup of the oil spill was a long, difficult process in 1970 which pioneered many clean-up techniques, like the “Slick Licker,” used in later tanker disasters.
The final retrieval of oil from the Arrow was completed on April 11, 1970 and some of the oil was removed and placed at sites on Isle Madame and eastern Richmond County.
Wells said he and the other authors believe the wreck of the Arrow should remain in Chedabucto Bay, because like the oil that leaked from the tanker, moving it will do more harm than good.
“We [the authors] think it is best not to disturb the remaining oil in the hull, as: a) it cannot be easily removed without bringing up the whole hull; b) that oil will not pose significant threats to marine organisms if exposure does not occur; and c) disturbing the hull further may release some of the oil, causing contamination of local organisms.”
As an example, Lee pointed out that during the clean-up of oil which spilled from the wreck of the Exxon Valdez in Alaska, 30 years ago, crews used high-pressure hoses to clean oil from rocky shorelines and beaches which washed away and killed organisms. He believes the oil should be allowed to further degrade naturally, a belief based on recent scientific findings based on DNA and RNA analysis.
On the 45th anniversary of the spill, the Canadian Coast Guard had to act fast to contain a leak from the wreckage.
After oil was first spotted around Cerberus Rock in September of 2015, and a Transport Canada aircraft flying over Chedabucto Bay confirmed the finding, Canadian Coast Guard crews worked quickly to determine the source of the leak then contain what was in the water.
Oil escaped from the wrecked tanker through a 12–foot crack in one of the submerged tanks. The Coast Guard said the vessel had shifted at some point, creating the breach.
Although the vessel was pumped out in 1970, the Coast Guard said residual oil or clingage remained in the tanks.
The report notes that underwater inspections by divers in 2015 confirmed that oil was leaking from the stern section. To address concerns over environmental impacts, the Coast Guard implemented a response operation that removed over 30,000 litres of heavy residual oil and Environment Climate Change Canada implemented a Shoreline Clean-Up and Assessment Technique survey of Chedabucto Bay that included analysis for the presence of petroleum-related hydrocarbons on the shoreline. Oil samples from within the hull of the sunken tanker did not show significant weathering.
Once crews patched the crack, they pumped out the oil that floated to the surface, then checked the rest of the wreckage to see if other cracks appeared, while containing and removing oil from the water. Pumping operations began on October 22 and crews worked until November to clean up the oil.
“It’s not that the Government of Canada is walking away from it,” Lee stated. “The Canadian Coast Guard and the Government of Canada are always flying over those sites looking in case something occurs, and if there is another seep, they feel is in danger, there’s no doubt about it, they’ll go back and try to recover that oil and solve the problem.”
The report confirmed that the stern section of the Arrow’s hull still lies on the seabed off Cerberus Rock.