Effects of Physical/Chemical Amendments and Plant Selection on Phytoreclamation

Technical Note DOER-C3

May 1999

tissue. It utilizes the plant Cyperus esculentus as an indicator crop and can be related to other

crops for heavy-metal uptake (van Driel, Smilde, and van Luit 1985). A test for estuarine

dredged material using Sporobolus virginicus and Spartina alterniflora is described by Lee

et al. (1992a, 1995) and has been used to evaluate contaminant mobility into plants from a

number of saltwater dredged materials. However, for reclaimed saltwater dredged material

to be used beneficially, the soluble salts must be removed, and freshwater plants should be

used in the evaluation. The plant bioassay can be used to determine the potential for plant

growth and uptake of contaminants under simulated field conditions. The plant bioassay test

can be used to determine potential for plant uptake of contaminants by harvesting and analysis

of the plant tissues of the test plant. For purposes of determining effective phytoreclamation

by removal, the total uptake (tissue concentration total plant weight) on a dry weight basis

should be used. Other plant-associated processes (transpiration and plant-associated micro-

bial degradation, etc.) can be determined by comparing preplant and postharvest contaminant

concentrations in the dredged material with a nonvegetated dredged material control.

Effects of Physical/Chemical Amendments and Plant Selection on Phytorecla-

mation. As previously described, the influence of physical and chemical conditions of

dredged material will determine the effectiveness of any phytoreclamation effort. There is

a fine line between availability of nutrients for growth and uptake of contaminants or activity

of other plant-associated processes related to phytoreclamation. Although a contaminant can

be made more or less available through soil amendments, the conditions thus created may

not be favorable to plant growth. The addition of bulking agents, such as sand or organic

matter will not only affect the net concentration of contaminants in a dredged material but

can also affect contaminant uptake by plants. The ability of a particular plant to effectively

remove a particular contaminant from a soil material is dependent on a number of factors

including uptake, total plant biomass, and effects by other contaminants. Some of these issues

are addressed in a study by Price et al. (1997). Plant bioassays were conducted on explosives

contaminated soil to determine the effects of plant selection, soil type, and soil amendments

on uptake of explosives by plants. The soil contained high levels of TNT and RDX at a ratio

of 3 to 1 plus degradation products at trace levels. Although TNT was not found in any of

the plant tissues tested, plant RDX concentrations were significantly increased as soil clay

content was decreased (Figure 7), and the addition of cow manure significantly reduced the

plant RDX concentration in the lower clay soils (Figure 8). Aboveground tissue concentra-

tions of RDX were in the order of lettuce > nutsedge > corn (Figure 9) with lettuce

concentrations as much as 2 orders of magnitude higher. However, as shown in Figure 10,

total RDX removal (concentration dry weight biomass) was in the order of lettuce > corn

> nutsedge. Figure 10 also shows the effects of soil concentration on total uptake. Total

uptake was reduced in the 50.3-mg kg-1 soil as a result of significantly reduced growth. All

plants died in the 667-mg kg-1 soil. The TNT was more likely responsible for the reduction

in plant growth. However, this was not determined.

The plant bioassay procedure (Folsom and Price 1989) can be used to determine effective

use of chemical and physical amendments (lime, chelates, organic wastes, etc.) to alter

contaminant availability and enhance plant uptake or to screen plant species. The selection

of amendments, if needed, should be determined from the physical/chemical characteristic

test results and the intended phytoreclamation process selected. Various plant/soil amend-

ment combinations can be evaluated to determine the optimum combination to reach specific