Step 4: Specify contaminants of concern (Cont.)

d. Criteria for protection of humans from consumption of water and

organisms.

Those compounds which meet WQC and are neither bioaccumulatable nor act

synergistically with other compounds will be screened out as COCs. The risk

assessment can screen out compounds which do or may bioaccumulate if their Tier

II analyses of TBP in the dredged sediments is less than the TBP calculated for

reference sediments. If the TBP for the dredged sediment is greater than the TBP for

reference sediments according to Tier II protocols, then the decision to retain or

screen out the COC depends on the results of Tier III testing.

Summary of Tier III evaluations. Tier III assesses the impact of contaminants in

the dredged material on appropriate sensitive organisms to determine if there is a

potential for the dredged material to have an unacceptable impact. This tier uses

water-column and whole sediment toxicity bioassays and bioaccumulation tests.

Water-column toxicity bioassays assess the effects of sediment-associated

contaminants on water-column organisms. Water-column toxicity tests must be used

when WQC are not available or when synergistic effects are suspected. If the

concentrations of dissolved plus suspended contaminants do not exceed 0.01 of the

acutely toxic concentrations, the dredged material complies with water-column

toxicity criteria. If the concentration exceeds 0.01 of the acutely toxic

concentrations, the dredged material does not comply.

Whole sediment bioassays assess the effects of sediment-associated

contaminants on benthic organisms. If bioassay organism mortality is statistically

greater than in the reference sediment and exceeds mortality in the reference

sediment by at least 10 percent (or a value that is in accordance with approved

testing methods), the dredged material does not meet the limiting permissible

concentration for benthic toxicity.

Tier III benthic bioaccumulation tests determine bioavailability through 28-day

exposure tests. Bioaccumulation potential has to be in compliance with regulations

before a dredged material can be considered acceptable for ocean dumping. Tier III

includes comparing concentrations of COCs in tissues of benthic organisms after a

28-day exposure period to Food and Drug Administration (FDA) Action Levels. It

is considered unacceptable if the concentration of contaminants in any test species

exceeds FDA action levels.

If tissue contaminant concentrations are less than FDA action levels or if no

FDA levels are available, they must be compared to contaminant concentrations in

tissues of 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 reference sediment, then the

dredged material complies with bioaccumulation regulations. If the concentrations

of COCs in organisms exposed to dredged material exceed those of organisms

exposed to reference sediment, Tier III provides eight factors to consider to

determine compliance.

Application of Tier III results to selection of contaminants of concern. The

selection of COCs for the risk assessment uses the Tier III bioaccumulation test

Chapter 2 Problem Formulation