Environmental Engineering Reference
In-Depth Information
compounds' exposure potential in the context of microbial degradation and
the sorbant quality of sediment organic carbon; and introduces the practical
utility of thermal desorption mass spectrometry with respect to identification
and quantification of recalcitrant compounds, measuring recalcitrant com-
pounds' release energy, and the compatibility of the development of
field-portable direct-sampling analytical technologies.
2.2
Bioavailability of recalcitrant compounds and
environmental risk assessment
The Clean Water Act (Section 404 of PL 92-500) and the Marine Protection,
Research, and Sanctuaries Act (also known as the Ocean Dumping Act,
Section 103 of PL 92-532) require that sediment-associated contaminants be
evaluated for their ability to accumulate in biota. Jointly, the U.S. Army Corps
of Engineers (USACE) and the U.S. Environmental Protection Agency (EPA)
adopted a tiered system to evaluate this bioaccumulation potential (
Imple-
mentation Manual for Section 103
Green Book
, and
Implementation
Manual for Section 404
, a.k.a.
Inland Manual
). Definitive bioaccumulation tests
require that three different organisms be exposed to sediment for 28 days
and then the recalcitrant compounds' body burdens determined using stan-
dard analytical techniques. From a practical perspective, it is not feasible to
test all sediments and dredged material the USACE must manage. It is also
apparent that noncontaminated sediments do not warrant bioaccumulation
testing, and some sediments are so contaminated that bioaccumulation is a
foregone conclusion. The EPA/USACE testing manuals describe a screening
level protocol termed
thermodynamic bioaccumulation potential
(TBP) (McFar-
land, 1995). TBP has been widely used in tier 2 evaluations to exclude from
further testing sediments from both extremes of the contamination level
continuum.
TBP predicts the partitioning behavior of recalcitrant compounds
between sediment organic carbon and benthic organism lipid. TBP is based
on a thermodynamic model (Mackay, 1982) of the environment as a system
composed of various compartments where contaminants have come to equi-
librium though passive processes. At equilibrium, fugacity (i.e., escaping
tendency) is equal in all sorptive and solution phases (Mackay, 1991). On
the basis of fugacity, it is possible to predict the equilibrium distribution of
a nonpolar contaminant between any two phases. The two most relevant
phases with respect to the bioaccumulation of recalcitrant compounds from
contaminated sediment are sediment organic matter and organism lipid.
The sorption of recalcitrant compounds to sediments has been simply
but elegantly described. Karickhoff et al. (1979) combined thermodynamic
theory (i.e., fugacity) (Mackay, 1979) with empirical correlations to derive a
systematic procedure for predicting contaminant sediment sorptive behav-
ior. In spite of the “high degree of variability and complexity in sediment
composition and large number of potential sorptive interactions,” Karickhoff
, a.k.a. the
