3.6 Seafloor Compartment Functions
51
Equilibrium Partitioning Theory (EqP) is used to determine exposure to sedimentdwelling organisms (Schwartz et al. 1990; Di Toro et al. 1991; EPA 2008). With input
of THC in sediment from oil drift modelling in kg/m
2 , ERA Acute first calculates the
concentration of THC (C THC ) in the sediment in ppb, using mixing depth, dry density
and water content of the soft substrate type, and then calculates the partitioning of
THC between sediment-bound (THC sed ) and bioavailable interstitial water (THC IW )using inputs of octanol-water coefficients (K OW ) and total organic carbon (TOC)
to calculate organic carbon/water partition (K OC ). The concentration in IW (C IW )
determines exposure to infauna.
C THC,sed ,cell,sim
mg
kg
=
THC sed ,cell,sim
kg
m 2
× 10 6
mg
g
×
1
BDepth(m) × (1 − WatC)
DryDens
kg
m 3
where:
• Mixing depth (BDepth): Depth of bioturbated layer in m (meters). Used to derive
THC concentrations in sediments from THC/m
2
• WatC: Water content of sediment = porosity (void volume) (given as Volume
fraction 0–1 where 1 = 100%)
• DryDens: Density of dry weight fraction of sediment.
Log 10 K OC = 0.00028 + 0.983 × (Log 10 K OW )(Di Toro et al.1991)
where
• TOC: Concentration of TOC in habitat, is sediment (as fraction) = foc
The concentration of THC in the sediment interstitial water is calculated as:
THC IW,cell,sim = THC sed,cell,sim /(foc × Koc) (derived from EPA 2008 and Di Toro
et al. 1991).
For deposit feeders that ingest sediment particles, partitioning between THC sed
and exposure in gut water (THC Ing ) is determined using calculated bioconcentration
factors (BCF) to determine Biota-to Sediment Accumulation factors (BSAF) (Kraaij
et al. 2002; (Klif) Klima- og forurensningsdirektoratet 2011).
BSAF = BCF/(K oc × f oc )
where: Log BCF = 0.85 × Log K OW − 0.70
(See more information how this is used in Stephansen et al. 2015). The calculated exposure concentration THC IW or THC Ing is entered into the SSD-curve by
Nilsen et al. (2006) to calculate plet IW and plet Ing . For epifauna, e.g. corals or
51
Equilibrium Partitioning Theory (EqP) is used to determine exposure to sedimentdwelling organisms (Schwartz et al. 1990; Di Toro et al. 1991; EPA 2008). With input
of THC in sediment from oil drift modelling in kg/m
2 , ERA Acute first calculates the
concentration of THC (C THC ) in the sediment in ppb, using mixing depth, dry density
and water content of the soft substrate type, and then calculates the partitioning of
THC between sediment-bound (THC sed ) and bioavailable interstitial water (THC IW )using inputs of octanol-water coefficients (K OW ) and total organic carbon (TOC)
to calculate organic carbon/water partition (K OC ). The concentration in IW (C IW )
determines exposure to infauna.
C THC,sed ,cell,sim
mg
kg
=
THC sed ,cell,sim
kg
m 2
× 10 6
mg
g
×
1
BDepth(m) × (1 − WatC)
DryDens
kg
m 3
where:
• Mixing depth (BDepth): Depth of bioturbated layer in m (meters). Used to derive
THC concentrations in sediments from THC/m
2
• WatC: Water content of sediment = porosity (void volume) (given as Volume
fraction 0–1 where 1 = 100%)
• DryDens: Density of dry weight fraction of sediment.
Log 10 K OC = 0.00028 + 0.983 × (Log 10 K OW )(Di Toro et al.1991)
where
• TOC: Concentration of TOC in habitat, is sediment (as fraction) = foc
The concentration of THC in the sediment interstitial water is calculated as:
THC IW,cell,sim = THC sed,cell,sim /(foc × Koc) (derived from EPA 2008 and Di Toro
et al. 1991).
For deposit feeders that ingest sediment particles, partitioning between THC sed
and exposure in gut water (THC Ing ) is determined using calculated bioconcentration
factors (BCF) to determine Biota-to Sediment Accumulation factors (BSAF) (Kraaij
et al. 2002; (Klif) Klima- og forurensningsdirektoratet 2011).
BSAF = BCF/(K oc × f oc )
where: Log BCF = 0.85 × Log K OW − 0.70
(See more information how this is used in Stephansen et al. 2015). The calculated exposure concentration THC IW or THC Ing is entered into the SSD-curve by
Nilsen et al. (2006) to calculate plet IW and plet Ing . For epifauna, e.g. corals or