|
Issue
|
|
Contaminants in dredged material in Confined Disposal Facilities (CDFs)
can move from substrates into food webs because of their contact with
CDF-colonizing or CDF-inhabiting plants and animals, and as such can cause
unacceptable risks outside the CDF. The Corps/EPA Technical Framework
requires exposure-based effects assessments prior to dredging to evaluate
impacts on plants and animals in cases where terrestrial placement is
selected as a disposal alternative. Presently, no specific guidelines
for contaminant residues in plants and animals exist. Moreover, risk assessment
is based on exposure-based effects tests performed on index species, which
may not necessarily give an accurate indication of the fate and effects
of the contaminants in the species actually colonizing or inhabiting the
CDF. The latter situation gives rise to uncertainty in relating the results
of the index-species-based tests to ecosystems developing in CDFs. This
uncertainty should be diminished, and guidance should be developed to
standardize the interpretation of test results in risk assessment aimed
at determining effective long-term management strategies for CDFs. Guidance
is also required to evaluate other beneficial uses for contaminated dredged
material in terrestrial areas.
|
|
Research/Objectives
|
|
An objective of this research is to evaluate exposure-based effects testing
of contaminated soils/sediments of CDFs that will relate the existing
Corps ERDC plant and earthworm bioassay procedures to key ecosystem components
and processes as part of an overall risk assessment. This research is
quantifying the modulation of bioavailability as a function of sediment
characteristics. It is establishing quantitative relationships between
sediment characteristics, concentrations of contaminant species in sediments,
and rates of contaminant bioaccumulation in plants at various relevant
growth stages, and in earthworms at steady-state. These quantitative relationships
are being used to formulate models on contaminant bioavailablity, fates
in food chains, and risk assessment. This research is focusing on upland
areas of CDFs where (a) sites are selected to represent sediment series
characterized by increasing concentrations of metals and organics, (b)
vegetation cover and predominant plant species of these sites are characterized,
and (c) sediment biota of these sites are characterized. This research
is determining biota-to-sediment-accumulation factors of, respectively,
metals and organics in plants and earthworms. Bench-scale work is being
field-verified in cooperation with Corps Districts. The ERDC index plant
and earthworm species are included in the tests. Interpretive guidance
minimizing risks and cost-effective management strategies is being provided.
|
