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Critical Review

Integrating dispersants in oil spill response in Arctic and other icy environments Alun Lewis, and Roger C. Prince Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b06463 • Publication Date (Web): 30 Apr 2018 Downloaded from http://pubs.acs.org on May 3, 2018

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Environmental Science & Technology

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Integrating dispersants in oil spill response in Arctic and other icy environments

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Alun Lewis1 and Roger C. Prince*2

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Staines, Middlesex, TW18 2EG, UK [email protected]

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Stonybrook Apiary, Pittstown, NJ 08867, USA [email protected]

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Abstract

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Future oil exploration and marine navigation may well extend into the Arctic Ocean, and

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government agencies and responders need to plan for accidental oil spills. We argue that

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dispersants should play an important role in these plans, since they have substantial logistical

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benefits, work effectively under Arctic conditions, and stimulate the rapid biodegradation of

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spilled oil. They also minimize the risk of surface slicks to birds and mammals, the stranding

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of oil on fragile shorelines and minimize the need for large work crews to be exposed to

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Arctic conditions.

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1. Introduction

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In 2009, the US Geological Survey estimated that the Arctic might house 30% of the world’s

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undiscovered natural gas reserves and 13% of its undiscovered oil, mostly offshore under less

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than 500 m of water1. The decreasing extent and duration of Arctic ice cover suggests that

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extraction of these resources will be increasingly commercially viable2,3. Oil exploration

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activities are most often regulated by national and state authorities that mandate response

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plans for spills and well blow-outs. Subsequent oil production will involve shipping by

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tankers or pipelines, and these too will require planning for the event of a spill229.

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Response plans typically rely on skimming oil as the preferred option, but this is rarely

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successful with large spills in remote areas – despite the massive scale of the response to the

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Deepwater Horizon blow-out for example, much less than 10% of the oil that surfaced was

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collected4, and even less was collected from the water following the spill from the Exxon

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Valdez5. Ice will certainly interfere with skimming operations6. Since biodegradation and

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combustion are the only other processes that remove a majority of the hydrocarbons from the

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biosphere, there has been considerable interest in harnessing these natural processes in oil

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spill response7,8,. The most effective way to stimulate oil biodegradation at sea is to use

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dispersants to facilitate the disruption of the oil slick to tiny droplets. Here we review issues

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to be considered when using this technology in the Arctic and in other cold-water

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environments.

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Arctic regions are characterised by very low air temperatures (winter minima 20 would be produced.

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As their name implies, refined products are commercial products produced in refineries. They

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are typically sold based on physical properties, such as ease of ignition, viscosity or lubricity,

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rather than on chemical composition. Refining begins with distillation, and many streams are

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subsequently treated with catalysts to generate valuable molecules32. Some of the residual

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material is converted to Bunker fuels for ships, and such fuels power almost all large

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commercial vessels33. Bunker fuels are far more viscous than most crude oils, and need

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heating to be pumpable within the ship.

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Crude oils encompass a broad range of viscosities, from close to that of water (a few

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centipoise) to viscous oils that at ambient temperature have the viscosity of peanut butter

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(100,000 cP). Oils with API gravities >20 typically have viscosities27 at ambient temperatures

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of 0°C; they pose a challenge to

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both mechanical recovery and dispersion227.

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The fate and behaviour of oil accidentally released in the Arctic will depend on the

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circumstances of the release and prevailing ice conditions at the time34. Oil released onto the

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sea surface may encounter open water, partial ice cover or total ice coverage depending on

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the season and location. Oil deposited onto near total ice coverage would accumulate on top 5 ACS Paragon Plus Environment

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of the ice and snow. Oil released subsea will rise to the sea surface. If a high level of ice

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coverage is present, a substantial percentage of the oil will be trapped under the ice, and

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potentially become incorporated into the ice as it grows. As oil spreads on the surface of

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water with up to 30% ice coverage, it will drift with the wind at approximately 3.5% of wind

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speed and leave a trail of very thin oil, or sheen, on the sea surface35. As the ice coverage

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exceeds 30%, the oil on the surface between the floes begins to move less independently of

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the surrounding ice36, and at above 50% ice cover the spreading of oil is mostly constrained

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by the ice. The intrinsic properties of crude oils begin to change as soon as they are released

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into the environment, especially on water. As oil spreads on water it loses the lightest

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components by evaporation and begins to incorporate water; both processes gradually

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increase the viscosity and pour point.

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Oil spill response in cold waters may include mechanical recovery with booms and skimmers,

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but will likely rely on in situ burning and dispersants37. Our purpose is to review the latter in

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the context of a potential spill in cold and/or ice-infested waters.

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3. Dispersant effectiveness on spilled oil under Arctic conditions.

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3.1

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Except under the very calmest sea conditions, some spilled oil will disperse into the water

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column as small oil droplets under the influence of waves and other turbulence38. Natural

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dispersion is promoted by increased mixing energy (rougher seas), but resisted by the

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rheology (viscosity and pour point) of the oil, and the oil/water interfacial tension. Natural

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dispersion will initially remove some spilled oil from the sea surface in most sea conditions,

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but soon stops as the oil viscosity increases due to ‘weathering’39. Ice on the sea dampens

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wave action40-42 and will suppress the natural dispersion of oil.

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Natural dispersion can be enhanced by the addition of oil spill dispersants43,44. Dispersants

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are blends of surfactants in solvents and when applied to spilled oil on the sea, the surfactants

Natural dispersion and dispersant use



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in the dispersant orientate at the oil/water interface and lower the oil/water interfacial

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tension45. When mixing energy is applied a high proportion of the oil volume will be

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converted into oil droplets that are small enough to be maintained in the water column by the

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prevailing turbulence225, even if dispersants were applied several days earlier46, or before oil

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was trapped in ice47. The concentration of dispersed oil droplets in water will be rapidly

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diluted to low levels in most sea conditions48-51 and the majority of the dispersed oil will be

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biodegraded promptly (see below).

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While dispersants can be applied with vessels, a major advantage is that they can be applied

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by aircraft52. Initial access to a spill location at the speed of an airplane, and then rapid

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treatment of oil slicks that are spreading over large areas, are important advantages over

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mechanical recovery or vessel application because mechanical recovery has to proceed at the

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speed of vessels. This is particularly important in remote locations; dispersant application is

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far less logistically challenging than mechanical recovery, which requires more personnel and

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equipment. Nevertheless, aircraft use for dispersant application may still be limited by

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weather and the lack of infrastructure in some regions of the Arctic.

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In addition, dispersants are a response option that can treat oil released from a subsea blowout

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at the source53 if the oil cannot be recovered by mechanical means. This is important for

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contingency planning of what is usually the worst-case oil spill scenario for offshore drilling,

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and if implemented has the advantage of treating the oil before it distributes at the surface,

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and immediately enhancing the biodegradation process.

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Removing the spilled oil from the sea surface, or preventing the oil from reaching the sea

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surface by subsea dispersant use, stops the oil from becoming emulsified54 and becoming

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persistent on the sea surface. Emulsified oil will most likely form tarballs55 that may

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eventually drift ashore and persist for years.


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Dispersant effectiveness is most often taken to mean the proportion (percentage) of oil

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dispersed into the water column as the result of dispersant addition. Dispersant effectiveness

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has been studied at sea, in laboratory-scale test methods, and in wave tanks, and a

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comprehensive list of experiments under Arctic conditions is given in Table S1. As discussed

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elsewhere44, dispersant effectiveness at sea can be sub-divided into separate components of

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operational effectiveness (probability of dispersant achieving desired treatment rate in oil),

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chemical effectiveness (proportion of oil dispersed following dispersant addition) and

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hydrodynamic effectiveness (transport and dilution of dispersed oil in the water column).

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Each of these aspects of dispersant effectiveness is influenced by several factors.

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3.2

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A number of large-scale experiments at sea have been conducted over many years49,56 (and

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see Supplementary Materials). Such experiments are very costly, logistically complex, must

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conform to regulatory requirements and are subject to severe restraint by the prevailing

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weather and sea conditions. While it is possible to gain a lot of information about the fate and

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behaviour of spilled oils, and this is extremely useful in calibrating smaller-scale studies, it is

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currently impossible to accurately quantify dispersant effectiveness at sea. Oil dispersed into

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the water column has a very heterogeneous spatial distribution and is rapidly diluted to low

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concentrations. It is therefore not possible to construct a ‘mass balance’ from which the

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dispersant effectiveness at sea can be derived. A variety of monitoring methods, such as the

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SMART (Special Monitoring of Applied Response Technologies)57 protocol, has been

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proposed, but none accurately quantify dispersant effectiveness at sea.

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3.3

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In the absence of the ability to quantitatively determine dispersant effectiveness at sea, many

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tests have been devised to measure dispersant effectiveness in the laboratory58, including the

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Warren Spring Laboratory (WSL) LR 448 Rotating Flask method59, Mackay-Nadeau-

Dispersant effectiveness at sea

Dispersant effectiveness in the laboratory



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Steelman (MNS) method60, Swirling Flask Test (SFT)61, Baffled Swirling Flask Test (BFT)62

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and the Institut Français du Pétrole (IFP)63 dilution method. These test methods only assess

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the chemical effectiveness aspect of dispersion, the proportion of oil dispersed by dispersant

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addition, and are typically used or proposed to assess dispersant effectiveness for regulatory

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purposes in various countries. An important misconception is that dispersant effectiveness

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tests used for regulatory listing accurately predict field performance. Regulatory tests

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normally use methods and test oils that will produce a mid-range effectiveness such as 45%64,

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60%65 or 75%66 so that the relative performance of dispersants, under the conditions

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employed in the test method, can be discriminated. These tests do not predict dispersant

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effectiveness in the field, or even in large wave tanks, where effectiveness is routinely >90%,

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even at 1°C 60. The apparent dispersant effectiveness in any method depends on several

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factors, including the intensity of the mixing action (which varies greatly between the

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methods), the reduction in oil/water interfacial tension achieved by dispersant addition

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(dependant on dispersant composition and treatment rate), and the resistance to dispersion

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caused by the flow properties (rheology, including viscosity and pour point) of the oil tested,

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under the conditions of the test. A major disadvantage of laboratory methods is that it is not

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possible to scale the results to predict dispersant performance at sea. In part, this is because

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laboratory tests do not include the operational and hydrodynamic elements of dispersant

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effectiveness at sea, especially the enormous potential dilution available at sea. There have

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been attempts to measure the energy dissipation rates in some laboratory test methods67 to

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provide a more fundamental basis for comparisons between different methods, but these have

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yet to be conclusive, and comparisons between apparent effectiveness in the laboratory and at

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sea remain elusive.

221

3.4

Dispersant effectiveness in wave tanks


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The use of wave tanks of various sizes addresses some of the artificialities of laboratory scale

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testing. The waves produced in a wave tank can be well-characterized and they produce a

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dispersion mechanism that resembles dispersion of oil at sea more closely than the mixing in

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the various laboratory tests. Experimental parameters can be controlled in a way that is not

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possible at sea and, being a closed system, oil that is not dispersed can be recovered to

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provide a quantitative estimate of dispersant effectiveness. The effectiveness of ‘good’

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dispersants in wave tank experiments is much higher than in laboratory tests, routinely

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>90%68,69.

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3.5

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Arctic conditions, in the context of dispersant effectiveness, refers to low surface water

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temperatures near 0°C, the possible presence of ice, and as a more minor effect, water

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salinities transiently differing from temperate oceans.

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The effect of low water temperature

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The low water temperatures of the Arctic gave rise to concerns that dispersants would be

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inherently less effective than in temperate climes because the lower water temperature would

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increase oil viscosity. This concern has proved to be unjustified in most cases. In general, low

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viscosity oils can be dispersed easily while higher viscosity oils are more difficult to disperse,

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but there is no linear decrease of dispersant effectiveness with oil viscosity. Instead, the

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dispersant effectiveness is approximately constant until a high viscosity value is reached at

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which the dispersant effectiveness drops. In the late 1970s it was considered that an oil

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viscosity of higher than 2,000 cP (equivalent to liquid honey at room temperature) would be

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the limit for dispersant effectiveness70, but subsequent studies71-73 have shown that modern

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dispersants can disperse some weathered and emulsified oils with a significantly higher

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viscosity of 20,000 cP or more (equivalent to chocolate syrup at room temperature). A single

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viscosity value is an inadequate description of the flow behaviour (rheology) as almost all

Dispersant effectiveness in Arctic conditions



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‘weathered’ oils, and all emulsified oils, exhibit non-Newtonian flow behaviour, and

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weathering varies within a floating slick. Nevertheless, the concept of a generally-applicable

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‘limiting’ oil viscosity for effective dispersion persists in dispersant effectiveness studies74,75.

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To aid contingency planning for oil spill response, some ‘rules of thumb’ have evolved, and it

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is considered unlikely that dispersant will be effective on ‘weathered’ oils that have a

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viscosity of more than 10,000 cP or a pour point (the temperature at which it just flows228) of

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5-10°C above sea temperature227. As oil viscosity increases with the time the spilled oil is on

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the sea surface, the decrease in likely dispersant-effectiveness can be expressed as a time

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“window of opportunity” for dispersant use76.

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A consolidated body of work, built up over many years, shows that low water temperatures

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do not preclude dispersant effectiveness. Early work used laboratory-scale methods with

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water temperatures of 0°C and 20°C to assess the effectiveness of different dispersants77-80.

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The lower water temperature caused higher oil viscosity, but did not result in significant

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changes in the measured dispersant effectiveness; the oil viscosity was not limiting dispersant

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effectiveness. Tests using a small wave tank in the 1980’s81 also concluded that dispersion of

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crude oils with water temperatures of 0°C was feasible, and subsequent wave tank

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experiments showed that Hibernia crude oil (API Gravity 35°) can be dispersed in cold water

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(0°C and 1°C) until the oil has lost ~10% by evaporation. Further studies68,82,83 with a wider

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range of crude oils indicate that dispersant effectiveness can be >90% with water

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temperatures of 0°C to 2°C. Oils with viscosities of 3,000 cP or less were dispersed with a

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very high level of effectiveness, although this decreased to ~50% for oils with viscosities of

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10,610 and 18,690 cP. Cold-water tests conducted at OHMSETT in 201684 with four

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dispersants showed a range of dispersant effectiveness, and some achieved high levels of

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effectiveness.

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The effect of ice


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Studies on the effect of the presence of ice on dispersant effectiveness using laboratory test

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methods also began in the early 1980s, but results with different protocols were inconsistent.

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The presence of ice in the MNS test85 caused a reduction in dispersant effectiveness because

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the ice caused total damping of the air-induced waves. Similarly, tests with the oscillating

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hoop method 86 resulted in reduction of dispersant effectiveness with up to 50% ice coverage.

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Yet testing in a laboratory-scale wave tank with a paddle-board wave generator87 suggested

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that the presence of ice caused higher dispersant effectiveness than when ice was absent.

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Tests were conducted outdoors in the Canadian winter in a wave tank with broken ice of

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different types to resolve the ambiguity88. Low energy wave activity caused extensive

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dispersion (>90%) of crude oil treated with dispersant when broken ice was present, but not

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in a lead created between two ice sheets. Dispersant effectiveness tests with cold water and

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brash ice were also conducted at OHMSETT89. The oils tested were Chayvo crude oil from

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Sakhalin (API gravity 35.5°) and Hibernia crude oil (35°) and the dispersant was Corexit

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9527. Three-meter diameter boomed areas of oil and ice were subjected to long period, non-

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breaking, low waves. Very low energy waves (15 cm height, 6 s period) did not cause

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dispersion of oil in ice-free conditions, but as a mixture of blocks and small fragments of ice

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was added to the cold water, higher ice concentrations consistently produced higher

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dispersant effectiveness. A similarly extensive study using a meso-scale flume with varying

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amounts of ice was conducted to determine the weathering and dispersibility of weathering

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Statfjord crude oil (API gravity 39.4°) under simulated Arctic conditions90. Weathering of oil

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was slower in Arctic conditions than at higher water temperatures with no ice present. It

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seems the low water temperature led to a higher oil viscosity and slower spreading, and the

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presence of ice further restricted the spreading of the oil so that the oil layer on the sea

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surface was thicker than it would have been at higher temperatures. This resulted in slower

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evaporative loss of volatile oil components, less water-in-oil emulsification, and the time



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“window of opportunity” for effective dispersant use was thereby increased. The limited

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mixing energy available due to wave damping in high ice coverage becomes the limiting

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factor for dispersant effectiveness, and additional mixing energy would need to be applied

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after dispersant application to achieve maximal dispersion of the oil, perhaps by propeller

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wash from icebreakers or support vessels91 if these are available.

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Dispersant effectiveness at sea with ice

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The findings of the laboratory and wave tank studies with regard to the ‘weathering’ of oils

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and dispersant effectiveness in Arctic conditions have been confirmed by measurements and

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observations at sea92,93. For example, dispersants were successful in dispersing five different

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oils (API gravity 23.7-43.3°) in the marginal ice zone of the Barents Sea with ice coverage of

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70-90%. Even after six days the oils were dispersible with Corexit 9500, providing agitation

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was supplied by the water-jet thrusters of small boats; less than 10% of the oil remained on

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the sea surface after dispersant treatment93, compared to the majority of oil remaining in the

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untreated slicks.

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The effect of salinity variation

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The salinity of Arctic seawater can be lower than standard open ocean salinity (~35 ppt or

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psu) due to extensive freshwater from the Mackenzie River delta into the Canadian Beaufort

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Sea and the Ob and Yenisey rivers into the Kara Sea94 (which can also deliver large amounts

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of suspended sediments). The temperature and salinity in the very top layer of a calm sea (a

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few centimetres) also varies as ice cover forms and melts; salt is expelled from ice into the

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water during freeze-up and low salinity water is released into the sea when the ice melts,

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although such discrepancies are usually eliminated with any wave action. Laboratory testing

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under simulated Baltic Sea conditions95 with low salinities concluded that different

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dispersants varied in their effectiveness, and similar results have been found in other

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studies96,97. Most dispersants have been formulated to be most effective at salinities above


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20ppt, and their performance is slightly reduced in brackish water, but oil spill dispersants

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that are effective in low salinity and fresh water can be readily formulated98, if required.

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4. Toxicity of dispersants and dispersed oil

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Dispersants were first used on a large scale in the response to the 1967 Torrey Canyon

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disaster. While the products were judged successful at sea, dispersants and degreasing agents

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were also applied directly to oiled shorelines, and flame-throwers99 were used as part of

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shoreline clean-up. There were relatively persistent ecological effects from such treatment100,

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and this precedent-setting event has challenged perceptions about dispersant use ever since43.

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It led to development of new dispersant formulations101 with minimal acute toxicity45 and

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restrictions on where dispersants are applied (i.e., not on shorelines). Further there has been a

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revolution in understanding acute and chronic toxicity tests102-104. Modern dispersants are

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typically formulated from chemicals already used as food additives and/or cosmetics105, and

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they have acute toxicities106,107,218 (LC50 values for 48 - 96 hour exposures of tens to hundreds

335

of ppm) essentially equivalent to common shampoos and dish cleaners106,108 (including those

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used to clean oiled sea-birds109). Standard aerial application of dispersants219 (47 l/ha) hitting

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water with no oil would result in a transient concentration of dispersant in the top meter of

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seawater of ~5ppm. When it successfully disperses oil, however, there will be a many fold

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higher concentration of oil in the water.

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The acute toxicity of oil and dispersed oil falls in a range of LC50 values (48-96 hour

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exposure) of 2 to 50 ppm102104, and Arctic species are no more sensitive than their temperate

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cousins111,112. Studies reporting that dispersed oil is more acutely toxic than an undispersed

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slick are the result of reporting nominal concentrations, and when toxicity test results are

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based on measured oil concentrations in the water, dispersant-treated oil is no more toxic than

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physically dispersed oil; the components in the oil drive the toxicity and dispersants do not

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cause a synergistic effect110. Thus, as with all toxicants, it is ‘the dose (concentration x time



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of exposure) that makes the poison’113, and the potential for acute effects rests on exposure to

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more than a few ppm oil or dispersant for some time.

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To understand the potential for acute toxic effects after application, we need to know the

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concentration of dispersed oil in a dispersing plume, and how this changes with time. The

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concentration immediately after dispersion could be several hundred ppm114, but dilution and

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diffusion rapidly reduce the concentration to around 1 ppm within a few hours as the plume

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increases in volume. It is worth noting that without this dilution, the droplets would

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eventually aggregate, as they do in laboratory vessels, and re-form a floating slick – it is the

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turbulence and enormous dilution available in the sea that makes dispersion a viable

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technology114. Once dispersion has occurred, coalescence becomes less and less likely as the

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droplets dilute and have fewer collisions. Whether the surfactants remain with the droplets

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once they have formed, or diffuse away, has no influence on the fate of the oil. Dilution

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continues, of course, but most field trials failed to find oil after several hours. In any case we

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can expect that oil concentrations continue to fall as time proceeds, and it is noteworthy that

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despite the ongoing release of oil into the Gulf of Mexico from the tragic Deepwater Horizon

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blowout, the vast majority (84%) of the >20,000 water samples taken had oil concentrations

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below 1 ppb115, even though sampling was biased towards locations where oil was expected

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based on winds and currents.

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We can thus conclude that oil dispersion – whether by natural wave action or enhanced by

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dispersants - will likely have a very local and short duration toxic influence on the indigenous

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meiofauna and flora – small and developing fish, copepods, algae etc. – but that the volume

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impacted is likely only the first meter or so beneath the dispersed slick, and only for a short

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time. Measured concentrations of dispersed oil in the deepwater ‘plume’ from the Deepwater

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Horizon wellhead were all less than 1 ppm oil, and most were much lower115, so again the

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acute toxicity was likely low.


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Chronic effects of dispersant-facilitated dispersed oil are more difficult to predict, not least

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because there have been few studies at the dilutions that occur in the sea, and in any case

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biodegradation removes dispersed oil and dispersant quite promptly (see below). The

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dispersants used in the Deepwater Horizon response show neither androgen- nor estrogen-

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receptor activity116, and their components have been in widespread commercial use for so

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long that unexpected chronic effects seem unlikely. The widespread use of dioctyl

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sulfosuccinate in commerce, for example, led Hayworth and Clement117 to conclude that the

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trace amounts of this compound in nearshore waters in the Gulf of Mexico came from

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terrestrial sources rather than dispersant applications. Chronic effects of the hydrocarbons

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themselves undoubtedly include the initiation of detoxification mechanisms, such as the

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potential induction of cytochrome P450s118,119. Since hydrocarbons have been part of the

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biosphere for millions of years, such responses may simply indicate a healthy response to

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environmental exposures.

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This is not to say that oils spill have no adverse environmental impacts – of course they do,

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and there has been a wealth of work curated by NOAA on research following the Deepwater

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Horizon tragedy120. Responders and responsible parties will debate how extensive these

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effects are, or will be in a different location, and these discussions in turn will inform Net

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Environmental Benefit Assessments in the Arctic. Fodrie et al.121 point out that there is a

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discrepancy between consistently negative impacts on individual organisms in the laboratory,

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and the absence of measurable negative impacts among populations of estuarine fishes

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exposed to oil. A recent paper considering the risk to Arctic cod populations in the Beaufort

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Sea suggests that even very large spills are unlikely to have a detectable population effect122.

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5. Oil and dispersant biodegradation under Arctic conditions

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The biodegradation of oil has been studied for almost a century123 and by 1941 it was clear

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that marine microorganisms were able to degrade a long list of hydrocarbons: ‘gasoline,



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kerosene, lubricating oils, crude oils,…’124. There has been enormous progress since then,

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and the biodegradation pathways of most of the broad classes of hydrocarbons are reasonably

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well understood in aerobic environments125-130. Aerobic biodegradation in seawater is

400

remarkably extensive, with the essentially complete disappearance of nearly all the

401

hydrocarbons in a few weeks at dilutions that reflect environmental concentrations of

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dispersed oil131. The slowest to degrade are cyclic saturated hydrocarbons such as the

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hopanes and steranes131, and the asphaltenes and resins that are the pigments of petroleum.

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There is some evidence that the latter components are at least partially biodegradable132-135,

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but the biodegradation of road asphalt is very slow, even with canine nutrient amendments.

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The biodegradation of hopanes and steranes is known136,137,131, but their environmental

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persistence is such that Ourisson138 concluded that there was of the order of “1011-12 tonnes in

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the biosphere, which is as much or more than the total mass of organic carbon in all living

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organisms.” Once the majority of the hydrocarbons have been degraded131,200, the residue is a

410

tar-like material rather akin to road tar – a non-oily solid that probably amounts to no more

411

than 15% of an oil with API gravity >20°. In small quantities, as the remainder from the

412

biodegradation of small oil droplets, the residue is difficult to distinguish from humic and

413

fulvic substances in sediments139. We note in passing that the polycyclic aromatic

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hydrocarbons of most toxicological concern222 (e.g. benzo[a]pyrene, 5-methylchrysene, etc.)

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are pyrogenic, and are not found beyond miniscule amounts in crude oils27.

416

The rate of biodegradation has been the subject of much confusion for many years, with

417

estimates of half-lives in the environment ranging from days to years140. A major

418

confounding factor in understanding biodegradation is the insolubility of most hydrocarbons

419

– for example decane is only soluble to 49 ppb, and longer alkanes are even less soluble141,

420

while the solubility maximum for phenanthrene in seawater is 710 ppb142 and of

421

perhydrophenanthrene (its fully saturated form) is 20 ppb141. Thus almost all the components


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of a dispersed oil are present as a separate phase, oil droplets, in seawater, and microbial

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attack is restricted to the surface of the oil at the oil-water interface. The surface area is

424

maximized with the smallest droplets, and as expected Brakstad et al.142 have shown that oil

425

droplets of 10µm diameter are degraded subtly faster than those of 30µm under identical

426

conditions. A major goal of modern dispersant application is thus to facilitate the generation

427

of the smallest possible droplets. When oil is dispersed as dilute droplets of 1km) shoreline led to measurable oil concentrations on the shore of only 1-2ppm215.

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Page 1 of 58 ACS Paragon Plus Environment ... - ACS Publications

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