Benthic bioaccumulation (Cont.)

a. FDA Action Levels have been established for less than 20 chemicals.

Therefore, risk associated with chemicals for which Action Levels have

not been established cannot be estimated by this approach.

b. FDA Action Levels are based on economic as well as human health

considerations, but do not indicate the potential for adverse impact to

contaminated benthic organisms, or biomagnification and impact to

higher trophic level organisms.

c. There is a lack of toxicity end points that relate body burdens in

invertebrates to toxic effects. For example, measured body burdens of

metals in benthic invertebrates are not well correlated with adverse

effects to the invertebrates since many organisms can store metals in

inert granules or other inactive storage forms. However, USACE has

developed an Environmental Effects Residue Database (ERED),

http://www.wes.army.mil/el/ered. This database compiles and makes

accessible information on tissue concentrations of contaminants that are

associated with adverse ecological effects or, in some cases, with no

adverse effects.

The interpretation of the benthic bioaccumulation bioassays relies on testing

differences between bioaccumulation in the reference sediment and in the

dredged material. This type of testing involves balancing Type I and Type II

errors (Parkhurst 1990; Suter 1993). Ideally, the power of the test (i.e., the

probability of correctly rejecting the null hypothesis, defined as 1-Type II error)

should be used to evaluate the magnitude of the uncertainty in the results. The

magnitude of uncertainty associated with the sediment bioaccumulation test is

ranked moderate given the range of BSAFs in the USACE database. Uncertainty

as to how well the bioassay predicts the bioaccumulation of contaminants could

be easily quantified by comparison of bioaccumulation observed in tests to the

amount of bioaccumulation observed in field validation programs.

Food chain trophic transfer--fish. Trophic transfer and biomagnification

are considered only if bioaccumulation in the dredged material statistically

exceeds bioaccumulation in the reference sediment. The magnitude of

uncertainty is high for estimating biomagnification in fish, since degree of

biomagnification depends upon a thorough knowledge of food chain dynamics in

the ecosystem under consideration (Kidd et al. 1995; Oliver and Niimi 1988).

Uncertainty in model predictions of food chain bioaccumulation can be

quantified by comparison with results from field studies (Scott and Trowbridge

1995). Performing sensitivity analysis of the input parameters for

bioaccumulation models can also provide information on the magnitude of

uncertainty (Burkhard 1998; Iannuzzi et al. 1996).

Food chain trophic transfer--piscivorous birds. Trophic transfer and

biomagnification are considered if bioaccumulation from the dredged material

statistically exceeds bioaccumulation from the reference sediment in the

bioaccumulation test. Risks associated with trophic transfer and biomagnification

of contaminants to higher trophic level organisms can be predicted by using

models or empirically determined biomagnification factors (BMF). For example,

a BMF of 30 was measured for the increase in concentrations of persistent

Chapter 4 Uncertainty in Tiered Evaluation of Dredged Material