We are focusing on lead (Pb), nickel (Ni), chromium (Cr), polychlorinated biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH) because these contaminants represent the most important known or suspected risks in the slough sediments. A key part of assessing risks is to know how these contaminants are distributed between sediment solids and the pore water contained in the sediments. In the screening level risk assessment (SLRA) it was necessary in most instances to estimate this distribution of contaminants from studies done at other sites. These prior studies provided only approximations of distribution factors. While this was fully appropriate for the SLRA, and represented the best available information at that time, it is highly desirable to improve these estimates by direct measurements using actual Columbia Slough sediments. Parametrix, Inc. is currently collecting samples from Buffalo Slough that they will use for such direct measurements. Our work will provide vital (and complementary) additional information.
Our project will directly identify the rates at which target
contaminants distribute among the sediment, the sediment pore water,
and the fine particles (colloids) suspended within the pore water.
This will be of direct use to Parametrix and BES in refining the risk
assessments they currently are preparing as part of the focused
remedial investigation. The results will also be used to improve
modeling of the movement of sediment-associated contaminants, a
project currently being performed at Portland State University
(PSU). Finally, the results will also be useful in guiding the
actions taken during the subsequent feasibility studies and in the
sediment restoration program. This project will achieve its goals
through tasks in the following areas:
2.1. Equilibrium Distribution of Contaminants in Sediments
Determine the equilibrium adsorption/partitioning parameters for Pb,
Ni, PCB, and PAH in slough sediments. These parameters will
complement the direct measurements of apparent contaminant
partitioning being carried out by Parametrix and will allow us to
model contaminant behavior over a wide range of conditions. Our
results will enhance the generality of the Parametrix findings.
Collectively the data will be used to define the availability of toxic
chemicals to organisms in the sediments, a factor critical to the risk
assessment. The data we obtain is also crucial to understanding the
movement of sediment- associated contaminants in the slough.
As a subset of this task, we will measure the chemical form of
chromium in selected slough sediments. We suspect that chromium in
the sediments actually is in a relatively harmless form (trivalent
Cr); if this is true, the risks from Cr are very small and this
element need not be considered in future restoration plans.
2.2. Role of Non-Settleable Colloids and the Impact on Toxicity Estimates
Quantify the amounts and behavior of fine, nonsettling particles
(colloids) in the desorption, transport and availability of Pb, Ni,
PCB, and PAH. This colloidal material can bind significant amounts of
pollutants. These colloid- bound pollutants may appear to be in
solution, but are typically much less bioavailable than chemicals that
are truly in solution. Better knowledge of these colloids will
further improve risk assessments and will also be of great importance
in understanding how sediment-associated contaminants move through the
slough.
2.3. Rates at Which Contaminants are Taken Up and Released by Sediments
Measure the rates of adsorption (uptake) and desorption (release) of
Pb, Ni, PCB, and PAH under chemical conditions typical of the Columbia
Slough. Knowing the rates at which chemicals are taken up or released
from sediments is essential to accurate modeling of the transport of
sediment contaminants, as in the companion modeling work being
performed by PSU.
2.4. Fugacity Modeling of the Distribution of Contaminants among Air,
Water, Fish, and Sediments
Couple fugacity modeling with our findings on pore water chemistry to
forecast the distribution and availability of hydrophobic organic
compounds like PCB. "Fugacity" is a measure of the tendency of
a contaminant to "flee" from one phase to another (such as from
water into fish tissues). Fugacity modeling is a valuable tool for
understanding how contaminants migrate into fish tissues or escape
into the air, and thus is helpful for both risk and transport
assessments.