Environmental Engineering Reference
In-Depth Information
Sediment (Organic Carbon)
Slow
Pore Water
K
oc, rap
Rap
BCF
Deposit-Feeder (Lipid)
Figure 2.2
Conceptual model of distribution of hydrophobic organic chemicals in
sediment. rap = rapidly desorbing compartment; slow = slowly desorbing compart-
ment; K
oc,rap
= partition coefficient between rapidly desorbing compartment and pore
water (l/kg organic carbon); BCF = bioconcentration factor (l/kg lipid). (From Kraaij,
R., Sequestration and Bioavailability of Hydrophobic Chemicals in Sediment, Ph.D.
dissertation, University of Utrecht, Netherlands, http://www.library.uu.nl/digiar-
chief/dip/diss/1960191/inhoud.htm)
studies are especially important. They demonstrate that plant detritus, a
major food source at the base of aquatic food webs, can be the major con-
tributor to recalcitrant compounds' theoretical maximium daily loads, and
K
oc
significantly underestimates the bioaccumulation of recalcitrant com-
pounds from this trophodynamically important geosorbant. In this common
aquatic environmental situation, K
oc
-based environmental risk predictions
(i.e., TBP, EqP, and sediment quality criteria) would not be protective.
K
oc
-derived predictions of bioaccumulation and toxicity of sediments
containing soot (case B in Figure 2.2) have also been shown to be inaccurate.
Socha and Carpenter (1987) compared PAH-contaminated sediments from
two sites within Puget Sound. K
oc
-predicted pore water PAH levels agreed
with empirically determined pore water PAH levels (within a factor of 4) at
a creosote-impacted site. However, no PAH was detected in sediment pore
water from a site impacted by combustion products and natural PAH, even
though detectable levels were predicted using K
oc
. McGroddy and Far-
rington (1995) published similar results on PAH-contaminated sediments in
Boston Harbor. Pore water PAH levels were depleted relative to those pre-
dicted using K
oc
. Variances for individual PAHs varied, but only 0.2 to 5.0%
of K
oc
-predicted phenanthrene was actually measured in sediment pore
water. PAH associated with pyrogenically derived soot particles was sug-
gested as the reason for the discrepancies (McGroddy et al., 1996). Paine et
al. (1996) showed that heavily PAH-contaminated sediments (highest levels
of 10,000 mg/kg and mean levels of 150 mg/kg) from Kitimat Arm, at the
head of Douglas Channel in British Columbia, did not change benthic com-
munity structure, were not toxic to benthic fauna, and generally did not
accumulate in the commercially important Dungeness crab. Most of the PAH
in this sediment originated from the washout of a wet air scrubber from
