Environmental Engineering Reference
In-Depth Information
desorb the particular contaminant and is used to calculate sequestration
energy (Talley et al., 2002), which is a measure of how tightly the particular
recalcitrant compound is bound to the sediment.
In the first use of thermal desorption data to infer biological availability
of sediment-bound recalcitrant compounds, dredged material from the Mil-
waukee Harbor confined disposal facility was studied. It was characterized
by many factors, including bulk particle quality, PAH levels, sequestration
levels (by TD-MS), the rapidly desorbed fraction (using Tenax beads), and
two measures of bioavailability — earthworm uptake and microbial biodeg-
radation potential (Talley et al., 2002; Ringelberg et al., 2001). The silt/clay
low-density fraction constituted 95% of the dry weight of the dredged
material and contained less than 40% of the Soxhlet-extractable PAH. The
majority of this fraction's PAHs were biodegradable by microorganisms and
could be taken up by earthworms. The higher-density coal-derived fraction
constituted 5% of the dredged material dry mass, but more than 60% of the
PAH. The PAH from this fraction did not readily desorb onto Tenax and was
not available to microbes or earthworms. Recalcitrant compounds in the
slowly desorbing, less biologically available fraction were characterized by
higher desorption energies.
These first results suggest that practical bioremediation could be
expected to remove the rapidly desorbing fraction (approximately 50% of
the Soxhlet-extractable PAH for this CDF material) from whole sediment.
This is consistent with the results of a biotreatability study performed on
the material (Myers et al., 2002) and with results for Amsterdam Harbor
sediment (Cornelissen et al., 1998). Additionally, both Talley's and Myers's
results suggest that the residual tightly bound PAH (approximately 50
mg/kg or 50% of the solvent-extractable PAH) may not present nearly as
much risk for bioaccumulation and toxicity as one would infer from the
total Soxhlet-extractable PAH level. The slow or negligible rate of desorp-
tion curtails uptake and can enable biodegradation of whatever is slowly
desorbed.
In summary, TD-MS can be a very useful analytical tool for rapid char-
acterization of contaminated sediments. It enables rapid determination of
the types and levels of recalcitrant compounds present in sediment and the
energy with which they are bound. This information can provide a basis for
predicting the bioavailability of sediment-bound recalcitrant compounds
and, subsequently, bioaccumulation (Talley and Larson, 2001). Most impor-
tantly, TD-MS is the basis for the current development of several direct
sampling techniques that will enable field-portable recalcitrant compound
analysis in near real time (Wise, 1998; Palmer et al., 2000; EPA, 2002). This
capability will fundamentally change the approach we use to survey envi-
ronmental chemical contamination (Crumbling et al., 2001).
