The Davis Strait - DCE - Nationalt Center for Miljø og Energi

week period after the Exxon Valdez spill was 1.59 ppb, at a depth of 5 m.
This is well below levels considered to be acutely toxic to marine fauna
(Short & Harris 1996).
SINTEF (Johansen et al. 2003) reviewed available standardised toxicity studies
and found acute toxicity down to 0.9 mg oil /l (0.9 ppm or 900 ppb) and
applied a safety factor of 10 to reach a PNEC (Predicted No Effect Concentration)
of 90 ppb oil for 96-hour exposure. This is based on fresh oil which
leaks a dissolvable fraction, most toxic for eggs and larvae. Weathered oil
will be less toxic.
The concentrations of oil in the waters at the Deepwater Horizon blowout in
the Mexican Gulf in 2010 published to date were > 50 µg/l (50 ppb) BTEX
(benzene, toluene, ethylbenzene and xylene, constituting only a fraction of
the oil) measured in a subsea plume of oil 16 km from the well site (Camilli
et al. 2010) and total PAH concentrations up to 189 µg/l near the well site
(Diercks et al. 2010). The latter study found PAH concentrations associated
with acute toxicity in discrete depth layers between 1000 and 1400 m extending
at least as far as 13 km from the wellhead.
Water-soluble components (WSC) could leak from oil encapsulated in ice.
Controlled field experiments with oil encapsulated in first-year ice for up to
5 months have been performed in Svalbard, Norway (Faksness & Brandvik
2005). The results show that the concentration of water-soluble components
in the ice decreases with ice depth, but that the components could be quantified
even in the bottom ice core. A concentration gradient as a function of
time was also observed, indicating migration of water-soluble components
through the porous ice and out into the water through the brine channels.
The concentration of water-soluble components in the bottom 20 cm ice core
was reduced from 30 ppb to 6 ppb in the experimental period. Although the
concentrations were low, exposure time was long (nearly four months). This
might indicate that the ice fauna are exposed to a substantial dose of toxic
water-soluble components and at least in laboratory experiments with seaice
amphipods sublethal effects have been demonstrated (Camus & S. 2007,
Olsen et al. 2008). Leakage of water-soluble components to the ice is of special
interest due to the high bioavailability to marine organisms, relevant
both in connection with accidental oil spills and release of produced water.
11.2 Oil spill impacts on the environment
There are generally two types of effects from oil in the marine environment:
physical contact (e.g. with bird plumage and fish eggs) and intoxication
from ingestion, inhalation and contact. Contact gives acute effects, while intoxication
can give both acute and long-term (sublethal) effects.
Table 11.2.1 gives an overview of potential impacts from a large oil spill.
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