9.3.1 Tier II - Prescreen Evaluation of Field Plant Tissue

1. Information is sufficient to reach a decision without further evaluation.

This is the case if there are no reasonable, potentially complete exposure

routes, or all potentially complete routes clearly involve such minimal

potential exposure as to pose negligible risk of any effects, to ROC

populations outside the CDF. No further evaluation of plant

bioaccumulation is necessary.

2. Information is not sufficient to reach a decision regarding plant

bioaccumulation. This is the case if there are potentially complete

exposure routes that may pose a potential risk to ROC populations outside

the CDF.

9.3 Tier II Prediction of Plant Bioaccumulation

Potential

9.3.1 Tier II - Prescreen Evaluation of Field Plant Tissue

Tier II provides a prescreening procedure that may be used in situations where

(1) a CDF has historically received only dredged material from the project being

evaluated, (2) there is reason to believe contaminant-related characteristics of the

dredged material have not changed since the last placement of this material in the

CDF, and (3) plants of the same species are established on the CDF and on nearby

naturally occurring habitats that reflect environmental conditions that would have

existed in the vicinity of the CDF if dredged material had never been placed there,

but all other influences on environmental quality at the site had occurred. Under

these circumstances, the same species of plants from the CDF and the similar

nearby habitats may be sampled and analyzed for COC and their COC

concentrations compared. If the COC concentrations in the plants from the

dredged material do not statistically exceed the concentrations in the plants from

the nearby habitats, this indicates that bioavailability of the COC from the dredged

material is not greater than in surrounding habitat and there is no need for further

evaluation. Other results indicate that further evaluation in Tiers II or III should

be considered.

9.3.2 DTPA Procedure for Prediction of Plant Bioaccumulation

Potential

A simplified tool for the prediction of plant bioaccumulation of metals by

plants is the extraction of metals from sediment using diethylenetriamine-

pentaacetic acid (DTPA). The DTPA extraction procedure is described by Lee et

al. (1978) and Folsom, Lee, and Bates (1981). The DTPA procedure has been

used in a number of studies to successfully predict plant bioaccumulation from

dredged material placed in terrestrial (wetland and upland) environments (Lee,

Folsom, and Engler 1982; Lee, Folsom, and Bates 1983; U.S. Army Engineer

Waterways Experiment Station1987) and compared well with actual

concentrations of metals in leaves of bioassay plants. Sediment from the proposed

dredging project is extracted using the DTPA procedure in both the wet and air-

dried conditions to represent wetland and terrestrial conditions in a CDF.

Reference soil is also subjected to the DTPA extraction for comparison. The

DTPA procedure can be applied directly to freshwater dredged material. For

upland conditions, plant growth in dredged material from saltwater environments

9-7

Chapter 9

Plant Bioaccumulation