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Key benefits of dispersant use
Case study: use of dispersants for Deepwater Horizon incident
More information about dispersants
Dispersant was used initially in the response, but application was officially suspended on Thursday 13 October. Aerial dispersant applications began on Thursday 6 October after preliminary tests showed it to be effective.
Dispersant operations continued, with on-going reviews of efficacy for the next week. Many of the results were inconclusive, and a decision was made to halt aerial application of dispersant.
Why did MNZ use Corexit 9500?
MNZ has tested a range of pre-assessed and approved dispersants on the oil. Of these, Corexit 9500 was identified as the most effective.
Because the properties of heavy fuel oils change very quickly at sea, effectiveness is expected to be variable. Initial field trials on fresh oil were promising, although dispersion of weathered oil (oil that has been at sea exposed to the elements) is unlikely to be effective.
The dispersant Corexit 9500 was tested onsite on Thursday morning and then deployed aerially on Thursday afteroon. Initial assessments were that the dispersant had not been as effective as anticipated. MPRS believed the dispersant was working, but was simply be taking longer than normal to take effect.
Dispersants are chemicals (similar to dishwashing detergents) that help remove oil from the sea surface by breaking oil slicks into small droplets. The small droplets are then dispersed and diluted into the underlying seawater by wave action. Naturally occurring oil degrading bacteria quickly use the oil droplets as a food source.
Modern dispersants have a low toxicity (about eight times less toxic than dishwashing detergents). All dispersants used in New Zealand are tested against established international criteria to assess their suitability for use and their environmental impacts.
Corexit 9500 is the world's most heavily scrutinised and studied dispersant, and it has been repeatedly shown in independent studies to be appropriate for use in marine oil spills.
The impact, effectiveness and viability of using a dispersant is carefully considered before its use, and all applications are carefully monitored, documented and assessed.
The method used to apply a dispersant depends on the size and location of the oil in the water and the available resources. Dispersant application most commonly involves spraying from surface vessels or aerial application by small fixed wing aircraft or helicopters.
Residents living near Tauranga's beaches have been needlessly worried by an anonymous leaflet dropped in local letterboxes suggesting that many people have become ill due to dispersant used in the early oil spill operations nearly a month ago.
Maritime New Zealand (MNZ) trialled the dispersant Corexit on heavy fuel oil spilled from the Rena in the earliest days of the response but discontinued the trial after three days because the results showed the dispersant was not effective in the prevailing conditions. There are no plans to resume using dispersant in the Rena oil spill response.
Dr Jim Miller, the Medical Officer of Health for Toi Te Ora - Public Health said that there had been no reports of anyone suffering illness that could be attributed to the use of dispersant.
MNZ Principal Environmental Advisor Paul Vorwerk said that Corexit had been through a full approval process before being cleared for use in New Zealand, and was extensively used overseas.
About 3100 litres (3 cubic metres) of the dispersant had been used in the Bay of Plenty, which has an estimated 5.4 trillion cubic metres of water, so the dilution factor was significant, Dr Vorwerk said. "To put it in context, if the dispersant diluted through only one fifth of the water in the Bay, it would be equivalent to pouring one 10-litre bucket of dispersant into three million Olympic swimming pools, each of which contains 1.1 million litres of water."
The dispersant had been used according to the NZ Guidelines for Dispersant Use, under controlled conditions several km offshore from the mainland and not within 200m of Motiti Island and the Astrolabe reef.
The effects of Corexit were studied extensively following its use in the Deep Water Horizon oil spill response in the Gulf of Mexico and showed that its components broke down in between 7-28 days and that the potential for it to bio-accumulate and persist in seafood was low.
Sorbents are materials that attract and hold oils. Most sorbents rely on oil being absorbed into them, like a sponge, but others rely on the oil adhering to the sorbent material.
Sorbents can be in the form of booms, pillows, pads or snares. They are generally made from polypropylene or polyethylene and can be wrung out and reused.
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Source: Safe Seas Clean Seas – issue 33, September 2010
In April this year, a blow-out on the Deepwater Horizon rig in the Gulf of Mexico caused what is thought to be the largest marine oil spill in the history of the petroleum industry.
The ensuing clean-up has been one of the largest oil spill response operations ever undertaken, involving more than 3,700 vessels, 75 aircraft and more than 700,000 metres of boom.
At the time of publication, more than 14,300 people had worked on the response, including professional oil spill responders drawn from New Zealand and around the world.
MNZ General Manager Monitoring and Response Bruce Anderson says the Deepwater Horizon operation is a clear illustration of the worldwide nature of oil spill response.
Spill Response Technician Chris Moore (left) and MPRS
Equipment Technician Scott Read during dispersant
application
from an L-382 Hercules, one of four
Hercules
used for this purpose
after the Deepwater
Horizon blow-out.
“A response of this magnitude requires global cooperation, as no one country has this level of resource to hand,” says Bruce. “Quite apart from the physical equipment, the expertise is held by only a small number of people dotted around the world. What we've seen happen in the United States is those people coming together to work collaboratively to solve the problem.”
Among the experts a number of New Zealanders have been invited to assist their US colleagues - including nine from MNZ and one from Auckland Regional Council (ARC).
Bruce says those deployed from MNZ brought a range of skills and capabilities to the response. Six staff were sent from the Marine Pollution Response Service (MPRS) in Auckland: Group Manager Nick Quinn, Planning and Training Manager Rob Service, Operations Manager Neil Rowarth, Response Planning Officer Dayne Maxwell and equipment technicians Scott Read (who went twice) and Mark Cavanagh. All are oil spill response experts, with strengths in different fields.
Also deployed were MNZ's Maritime Security and Incident Response Group Manager Renny vanderVelde, Environmental Analyst Alison Lane and Safety Auditor Christiaan Moss.
Dispersant is applied to an area of the spill.
Mick Courtnell, an ARC staff member from the harbourmaster's office, also joined the response. Mick is a member of the National Response Team, New Zealand's pool of oil spill response personnel who are initially called out in the event of an oil spill.
Bruce says the deployment of New Zealand personnel to assist an international spill response has many benefits for this country. “It's an opportunity for them to get their hands dirty - to use their skills and expertise and work alongside other experts in their field.
“We have had people on board vessels monitoring the oil plume, spraying dispersant from aircraft, working in command centres, liaising with beach clean-up teams, and providing technical advice,” he says.
“When they come back to New Zealand, they bring what they've learnt back and share it with the oil spill response community here.”
“They also, of course, contribute a lot to the response - the expertise we have in New Zealand is held in high regard throughout the world, and the ongoing requests for our assistance reflect that. Universally, the feedback I have received has been that our people have been a credit to themselves and New Zealand.”
Oil spill response is an area Bruce says demands a collaborative approach. “I think a lot of people have been watching what's going on in the Gulf and worrying that we don't have the resources for that scale of response here. But the truth of the matter is - no one does. The United States had to call on its global colleagues for assistance, and so would we.
"The important thing is to have the resources and capability to respond in that critical first 36 hours. And the fact is, there are people throughout New Zealand who work really hard all year round to ensure that we do have those resources and that capability.”
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For more information about the regulation of dispersant use in New Zealand, see the link below:
Marine Protection Rules Part 132: Dispersants & Demulsifiers [PDF:75Kb, 16 pages]
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