Environmental Engineering Reference
In-Depth Information
has been characterized as hard or glassy. Glassy organic matter strongly
binds recalcitrant compounds (Brannon et al., 1998) and is characterized by
slow mass transfer rates and nonlinear adsorption kinetics (Haitzer et al.,
1999; LeBoeuf and Weber, 2000). Kerogen is another organic matter fraction
that has undergone diagenic alterations that has been shown to have non-
linear recalcitrant compounds' sorption isotherms and high capacity to bind
recalcitrant compounds (Song et al., 2002). Little is known about the distri-
bution of kerogen in surface sediments in the context of sequestering recal-
citrant compounds. A portion of kerogen and other organic material can
also be dissolved in pore water in a form that is not removed by filtration
(Gauthier et al., 1987) and thus greatly affects the pore water recalcitrant
compound concentrations and mechanisms of recalcitrant compounds' bio-
accumulation.
This emerging technical information on the sorption behavior of recal-
citrant compounds with respect to the quality of sediment organic carbon
can directly affect the USACE management of dredged materials.
Soxhlet-extractable PAH levels in dredged material from a confined disposal
facility at Milwaukee Harbor (Table 2.1) averaged 115 mg/kg, but only 46
mg/kg (i.e., less than half) was readily biologically available for either micro-
bial degradation (Ringelberg et al., 2001) or bioaccumulation in earthworms
(Talley et al., 2002). The empirically determined BSAF for total PAH accu-
mulation from Milwaukee Harbor-dredged material into the earthworm
(
Eisenia fetida
) was 0.08. Five percent of the dry weight mass of Milwaukee
Harbor-dredged material was coal/coke. Sixty percent of the total extractable
PAHs were associated with this coal/coke fraction, and almost none of it
was biologically available. As a consequence, the potential for bioremedia-
tion to reduce the total extractable PAH from this dredged material is limited
(Myers et al., 2002).
2.6 K
oc
-based predictions
Appropriate use and informed interpretation of the data derived from
screening tools are essential for effective sediment management. Sediments
have been described in which K
oc
-based predictions of bioaccumulation and
toxicity have been inaccurate. Thus, the universal application of K
oc
-based
predictions without reasoned judgment in interpretating the resulting pre-
dictions can lead to both significant under- and overassessments of environ-
mental risk. Karickhoff's “justifiable simplification” will be an even more
useful screening tool when its limits of applicability are more fully under-
stood and appreciated. The environmental distribution and relative abun-
dance of organic matter that sequesters recalcitrant compounds in sediment,
and the fate of recalcitrant compounds when desorbed from this material,
are currently not known but warrant further study. To gain this perspective,
we present and discuss additional tests and environmental parameters that
will improve assessments of recalcitrant compound bioaccumulation poten-
tial from sediments.
