Corresponding author : David Steffy PhD, Professor, Department of Physical and Earth Sciences, Jacksonville State University, Jacksonville, Alabama, USA, E-mail: dsteffy@jsu.edu
Received: June 12, 2012 Accepted: June 13, 2012 Published: June 15, 2012 doi:10.4172/jhhe.1000e101
Should dispersants be sprayed on an oil spill to relieve the
impact of the spill on an aquatic environment? The major release of
crude oil to the Gulf of Mexico during the summer of 2010 caused
the reemergence of this controversy. Between April 20 and July 15,
2010, approximately 686,000 metric tons of crude oil was accidently
released from the British Petroleum (BP) Deep Horizon well located
in the Gulf of Mexico [1]. The damaged well head released between
1,670 to 2,670 metric tons of crude oil per day [2]. BP sprayed over
4,670 metric tons of chemical dispersants on the sea surface and
injected 2,600 metric tons at the well head to alleviate the spread of
crude oil slicks in the Gulf of Mexico [3]. The resulting concentration
of the dispersants as it was incorporated in the marine system was
not controllable. The spray results in dispersants being delivered at
various concentrations throughout the surface and the upper water
column.
According to the National Research Council (NRC) [4] guidelines,
dispersants should be used “When containment and recovery are not
possible, practical, or sufficient, the application of dispersants may
help to break up the oil slick prior to contact with sensitive habitats
and resources.” Furthermore, pre-approved use of dispersants is
based on geographic zone, distance to shore, water depth, and other
mitigating factors deemed important by on-scene coordinator [4]. In
an open marine environment, the dispersant and its delivery system
should be aerially sprayed as droplets 600-1,000 nm in size on the
visible oil slick, and wave action would incorporate the dispersant
vertically throughout the slick.
The dispersant’s effectiveness is dependent upon the composition
of the crude oil, sea energy (wave height), amount of dispersant
applied, type of dispersant used, state of oil weathering temperature,
and salinity of the water. The effectiveness is the percent of oil
dispersed to the amount of oil that remains in the oil slick [5]. The NRC [4] states that the first three of the variables stated above have the
most impact on dispersion. As the crude oil slick becomes weathered,
its dispersible nature should lessen.
Four questions arise from this process: (1) How does the
surfactant capability change as the concentration changes during
its incorporation in the water column? (2) How does the surfactant
capability change as the temperature changes?; (3) How does the
chemistry of salt water influence this surfactant capability?; and
(4) Does the surfactant acting over wide range of concentrations
generate oil droplets small enough so that there is no coalescence of
the droplets with time?
There are problems associated with the use of surfactants. As the
surfactant spreads and approaches the coastline, the salinity of the
marine system changes to a brackish one and eventually to a freshwater
system. Does a change in salinity alter the surfactant capability? Also,
Li [6] stated that a critically small diameter of oil droplet of about
10 micrometers needs to be reached in dispersed oil so that the oil
droplets due not coalesce thereby negating the dispersant activity.
Surfactants must be acceptable environmentally. Clearly,
surfactant selection is a multifaceted issue, although guidelines for
proper selection are readily available [7,8].
Li Z (2011) Monitoring dispersed oil droplets size distribution at the Gulf of Mexico Deepwater Horizon spill site. International Oil Spill Conference 2011 Program Book. Portland.
Li Z (2011) Monitoring dispersed oil droplets size distribution at the Gulf of Mexico Deepwater Horizon spill site. International Oil Spill Conference 2011 Program Book. Portland.
