Rena: experts on oil dispersants and natural breakdown


Winds now pushing oil onto the Bay of Plenty coast could turn offshore on Thursday, forecasters say. 

State science company NIWA is providing Auckland City Council’s emergency management staff with weather and sea state (currents and waves) forecasts from its EcoConnect forecasting system relevant to the salvage and clean up operation for the grounded container ship Rena.

The  environmental information service forecasts wind, rain and sea conditions, and NIWA Principal Scientist Dr Mike Revell said:

“Our forecasting system EcoConnect indicates that winds over the Tauranga harbour entrance region should peak from the north -north-east at about 35 kmh gusting up to 50 kmh during the early hours of Wednesday morning gradually easing and turning more easterly during the day – onshore winds for Tuesday and Wednesday  with frequent periods of rain. On Thursday and continuing into Friday winds are expected to turn to the westerly quarter – offshore – and reduce to 20 km/h gusting to 30 km/h with the rain clearing”.

All  crew were evacuated by helicopter from the 47,000 tonne container ship Rena on Tuesday as swells of up to 3m pounded it on the Astrolobe Reef, 12 nautical miles off Tauranga.

The ship grounded with about 1700 tonnes of fuel oil aboard, but a Maritime New Zealand (MNZ) spokesman said on Tuesday that between 130 and 350 tonnes  of oil escaped from the ship on Monday night. Fresh oil was seen drifting in a southerly direction down the Bay of Plenty coast.

Pumping of oil from the ship was stopped on Monday  by damage to the oil tender Awanui and the arrival of 3-4m swells and winds of 20-25 knots, but MNZ  later said that there was further damage and flooding at the bow of the  ship overnight. Checks were being made on whether  further oil was leaking from the ship, and if there was  oil in the water, it would be sprayed with dispersant. Oil had been found on beaches from Mount Maunganui to Girven Road and on the southern end of Matakana Island, more oil was also expected at Papamoa and Maketu, and it was “highly likely” that oil would enter Tauranga harbour.

Spraying the oil  at sea has had “inconclusive” results. The chemical used was Corexit 9500 – over 7.5 million litres of that dispersant was used during the response to America’s Deepwater Horizon disaster.

A weather change has meant some of the oil at sea has been pushed to the Bay of Plenty coast, putting more birdlife at risk. Spilled oil spreads quickly: its movement determined by tides and current as well as wind speed and direction. Oil will move at the same speed as the water carrying it and about 3 percent of wind speed, according to experts.

At an earlier spill, in March 1999, near Tutukaka in Northland bilge oil reached the Poor Knights Islands Marine Reserve, but dispersants were also unable to be used because they would make the oil sink to the bottom of the sea. Instead clean-up crews had to scoop up what they could manually and use low pressure spraying of salt water to dislodge oil from rocks. The rest was mopped up by hand, using sorbent cloths, until the prevailing wind eventually moved the slick away.

Physical removal of oil can reduce the damage done, but use of chemicals such as dispersants does not break the oil down into harmless carbon dioxide and water. In the long-term, Bay of Plenty residents may have to rely on micro-organisms such as bacteria to break down those oil residues.

The SMC has set up a Rena Oil Spill resource page which will be updated throughout the next few days as expert information comes to hand.

The SMC rounded up comment from experts on the use of oil dispersants and the ability of marine microbes to break down oil pollutants. Further comments will be added to the SMC website.

University of Southampton lecturer in oceanography Dr Simon Boxall, who has experience of the Erika oil spil on France’s Brittany coast in 1999, and the MV Braer oil spill in the Shetland Islands in 1993, said:
“There is nothing positive about an oil spill, they shouldn’t happen. A ship going aground and spilling its fuel oil is inexcusable.  So far it is a relatively small volume. The stormy weather is both a pro and a con.  The bad news is that it hampers the clean up and access to the stricken vessel.  The good news is that it helps the oil disperse naturally. A good example of this was the Braer spill off the Shetlands … very large volumes dispersed very quickly by heavy storms. Tides and currents will also help.

Microbe activity will act quickly and break the oil that is naturally dispersed in about 4-6 weeks given current temperatures and increasing daylight.  Add to that a team of beach clean-up personnel and the impact of the (estimated) 30 tonnes will be minimal.  There will be some distressing sights of some sea birds killed and of oil on beaches but it will be short-term.
Some experts disagree on the dispersants.   Dispersants do have a role to play but only in a few cases (but) there is a tendency to use them regardless. Contrary to what is coming out they are more harmful than the oil itself and they are NOT less toxic than dishwashing liquid!  Fairy dishwashing liquid doesn’t carry hazchem advice and you don’t wear protective clothing and masks to do the washing up.  In their raw form some dispersants can be very toxic and I believe will do more harm than good.  Most of the Corexit dispersants were banned from use by the UK Government in 1998 for rocky shore areas and can only be used offshore after consultation with govt.,  and if no alternatives are available.  Sweden has a blanket ban on all dispersants in the marine environment.  In this case – with limited knowledge of the region – I’d advise caution on use of dispersants.

Nature did a lovely job of Braer and very little human intervention took place (no dispersants).  The Erika involved substantial mechanical beach clean up but we did a study 5 months after the spill and levels of hydrocarbons on the beaches of France that had been impacted were below background levels (and in fact were better than one or two control beaches). The Rena spill needs containment as first priority, booming where possible to contain the marine based oil.  Beach clean-up will be important and the oil breaks down more slowly on the beach than at sea.  At sea, nature will disperse and break the oil down very quickly, without use of chemicals”.

CSIRO research scientist Professor Nic Bax, who leads the Biodiversity  Hub at the University of Tasmania,  said:

“Responding to oil spills is a very complex, high pressure situation requiring decisions to be made based on whatever data are available at the time. One of the difficulties in assessing the environmental impacts of oil spills is the lack of environmental baselines against which to measure the changes. Hydrocarbons impact the environment and plants and animals through several different pathways – physically through smothering or the external oiling of birds and marine mammals, and chemically through the toxicity of the compounds entering the animal itself causing different levels of short and long-term poisoning. The most visible impact of oil spill is through smothering and this is often the one that gets most attention. The chemical impacts are harder to quantify being less visible, although tainting in commercial species (or the perception of tainting) can have immediate commercial impacts”.

“While the impacts of oil spills are visually alarming with high local impact, far more oil enters the global oceans through other mechanisms.   Local environmental impacts of oil spills will continue after the obvious tarry oil has been removed or dispersed. This is at least in part because some oil seems to usually remain hidden at depth in the sediments. The time this oil remains depends on the environment, with cold, low energy environments being the slowest to recover”.

“Dispersants when applied on reasonably fresh oil can disperse the oil though the water column. Dispersants do not change the amount of oil but they redistribute it. They can be used to alter the parts of the environment that are affected from surface creatures and sensitive shorelines to the water column and bottom creatures. Where they are used in deep water and high energy environments they also serve to spread the oil over a wider area (or volume),  diluting it and reducing its immediate impact. Dispersants used to be quite toxic but now are considered to be much less toxic than the oil itself, so the main environmental decision regarding their use is determining where the oil will have least harm i.e. concentrated at the surface and on sensitive shorelines, or dispersed through the water column. There does not seem to be much evidence to indicate that dispersing oil leads to greater uptake by organisms, although this would be very hard to measure”.

“It seems that oil will eventually be broken down by natural processes including microbial activity. Microbial activity may be especially important after oil has entered habitats such as sub-surface sediments where physical weathering can no longer occur. It seems to be a long-term process as oil has been detected in sediments a decade after oil spills have occurred. The more volatile components of the oil are typically considered to be the most toxic, but they are also the components that will boil off or evaporate most rapidly. Typically heavier crudes hang around longer are harder to disperse and have a greater visual and aesthetic impact. Evaporation of the oil will be increased in warmer temperatures thus reducing impacts. Dispersion in the water column will be increased in high energy environments (such as high wave action) which will dilute the oil … reducing its local impact”.

“In low energy environments,  there is little opportunity for physical processes to operate. Areas of high tidal energy will again serve to spread and dilute the oil, but may make it harder to prevent the oil reaching sensitive areas. Spilt oil that remains at the surface will gradually be dispersed by natural physical processes at least in high energy environments. Oil that reaches low energy environments or gets buried in sediments may persist for several years”.

Professor Ravi Naidu, Managing director of the Co-operative Research Centre For Contamination Assessment And Remediation Of The Environment, in South Australia, comments:

“This spill could impact on the sensitive aquatic environment and life cycle of the marine ecosystem. The oil  will not disappear quickly… it will be in the aquatic environment for a while. There are volatile hydrocarbons in the oil which will disperse but the oil which is not removed will continue to have an effect. There will be some natural remediation by microbes in the coastal environment, but it may be found that these are not as active as they are in warmer tropical waters. Oil which is bound to organic matter in the sediments may be the easiest to break down – the wave action will be an advantage.”

Marine ecologist Associate Professor Mark Costello, at Auckland University’s Leigh Marine Laboratory, comments:

“[Effectiveness of the microbes] seems to depend on what type of oil it is, and what type of environment it is, as the physical environment breaks it into smaller pieces. Dispersants, like a lot of detergents, will kill animals and plants as well. Some of the new ones may be safer, but I don’t know how safe they are.

“You do get natural oil and gas leaks in various parts of the world. The marine microbes which break down oil slicks seem to be pretty cosmopolitan and they break down lumps of oil in other places.

“I know people have sprayed nutrients such as nitrogen on beaches to try and speed up the growth of bacteria that would help degrade the oil – but as far as I know this has been experimental and it’s not yet clear whether it has any effect in degrading the oil faster. The nutrients could have their own knock-on effect”.