Benthic bioaccumulation (Cont.)

The bioaccumulation potential must be demonstrated to be in compliance with

the regulations before a dredged material can be considered to be acceptable for

placement in an unrestricted open-water disposal site.

Concentrations of contaminants in organisms should reach steady state by the

end of the standard test (e.g., 28-day tests for organic contaminants). Where it is

desirable to estimate the steady-state concentration of neutral organic

contaminants, a correction can be made to estimate the concentration at steady

state. Steady-state concentrations of contaminants are compared in Tier III to

applicable Food and Drug Administration (FDA) Action or Tolerance Levels for

Poisonous or Deleterious Substances in Fish and Shellfish for Human Food.

Tissue contaminant concentrations measured in the bioassay that are

statistically lower than FDA Action levels, or for which there are no levels, are

compared to tissue concentrations for organisms similarly exposed to reference

sediment. If tissue concentrations of COCs in organisms exposed to dredged

material do not statistically exceed those of organisms exposed to the reference

sediment, the dredged material is predicted not to result in unacceptable

bioaccumulation of contaminants in benthic invertebrates (although benthic

toxicity must be considered). If tissue concentrations of COCs in organisms

exposed to the dredged material do statistically exceed those of organisms

exposed to reference sediments, the final determination of compliance is assessed

by consideration of the following factors:

a. Number of species in which bioaccumulation from the dredged material

is statistically greater than bioaccumulation from the reference material.

b. Number of contaminants for which bioaccumulation from the dredged

material is statistically greater than bioaccumulation from the reference

material.

c. Magnitude by which bioaccumulation from the dredged material exceeds

bioaccumulation from the reference material.

d. Toxicological importance of the contaminants whose bioaccumulation

from the dredged material statistically exceeds that from the reference

material.

e. Phylogenetic diversity of the species in which bioaccumulation from the

dredged material statistically exceeds bioaccumulation from the

reference material.

f. Propensity for the contaminants with statistically significant

bioaccumulation to biomagnify within aquatic food webs.

g. Magnitude by which contaminants whose bioaccumulation from the

dredged material exceeds that from the reference material also exceed the

concentrations found in comparable species living near the proposed site.

Uncertainties associated with benthic bioaccumulation bioassays include the

following:

Chapter 4 Uncertainty in Tiered Evaluation of Dredged Material