Oil spill dispersant article

tests quite often conclude that dispersing oil
makes it more capable of causing toxic effects
because the oil (and the partially water-soluble
chemical compounds from the oil) become
much more available to the test organisms.
The potential for causing toxic effects to
marine life is greater if dispersants are used,
than if they are not. However, the dispersed oil
concentrations needed to cause effects in the
tests, and the time of exposure required to
cause these effects, are normally much higher
and more prolonged than occurs at sea when
dispersants are used.
Even within a standardised toxicity test methodology
there are many variables:
Test organism
The oil concentration and period of exposure
required to cause effects depends on the test
organism used. Amphipods (very small shrimplike
creatures) are particularly sensitive to dispersed
oil. Other marine creatures are much
less sensitive.
Observed effect
Sub-lethal effects, rather than lethality, have
often been used as toxic effect indicators.
Even lower degrees of exposure will cause
no observable effects and the NOEC (No
Observable Effects Concentration) can be
determined for a particular period of exposure.
Interpreting toxicity data can be diffi cult. The
results cannot be directly ‘translated’ into
effects that could be caused at sea without
taking into account the exposure levels that
will occur at sea.
Realistic exposure levels
Experience from both experimental fi eld trials
and dispersant operations at real spills have
shown that dispersed oil will quickly be
diluted into the sea. The oil in water con
centration rapidly drops from a maximum of
30-50 ppm just below the spill short time
after treatment, to concentrations of