Table 1. Types of Phytoreclamation Technology for Metal-Contaminated Soil Materials: Advantages and Disadvantages (U.S. Environmental Protection Agency (EPA) 1996

Technical Note DOER-C3

May 1999

Table 1

Types of Phytoreclamation Technology for Metal-Contaminated Soil Materials:

Advantages and Disadvantages (U.S. Environmental Protection Agency (EPA)

1996)

Type of Phytoreclamation

Advantages

Disadvantages

Phytoextraction by trees

High biomass production

Potential for offsite migration and leaf

transportation of metals to soil surface

Potential for metal recovery

Metals are concentrated in plant biomass

and must be disposed of eventually

Phytoextraction by grasses

High accumulation

Low biomass production and slow growth

rate

Potential for metal recovery

Metals are concentrated in plant biomass

and must be disposed of eventually

Phytoextraction by crops

High biomass and increased

Potential threat to the food chain through

growth rate

ingestion by herbivores

Metals are concentrated in plant biomass

and must be disposed of eventually

Phytostabilization

No placement of contaminated

Remaining liability issues, including

biomass required

maintenance for indefinite period of time

(containment rather than removal)

Rhizofiltration

Readily absorbs metals

Applicable for treatment of water only

Potential for metal recovery

Metals are concentrated in plant biomass

and must be disposed of eventually

humus rich topsoil. In Stafford et al. (1991), earthworms were not shown to accumulate significant

amounts of cadmium from nonforested dredged material in the Times Beach, New York, CPF.

However, earthworms in the leaf-littered dredged material beneath volunteer cottonwood trees had

significantly elevated cadmium levels, indicating potential transfer to higher levels of the food

chain. These types of situations must be considered in the screening and selection process and, if

necessary, management strategies developed to minimize risks to the ecosystem. Control of

cottonwood trees and replacement with trees, such as red oak, that minimize uptake of metals would

be appropriate in the above example.

The processes and considerations for phytoreclamation of dredged material are complicated. A

simple, fast-screening tool is currently not available. However, a protocol to determine if phytore-

clamation of dredged material would be successful is now being developed. Each dredged material

will require that site/application-specific considerations and physical/chemical characteristics be

evaluated. In some cases, contaminated, freshwater dredged material may be phytoreclaimed soon

after dewatering with little to no modification. In other cases, modifications such as reduction in

soluble salts or chemical amendments may be necessary to enhance plant growth or increase the

plant availability of a given contaminant.

The plant pathways and phytoreclamation processes for each contaminant class are shown in

Table 2, and, as indicated by question marks, some of these processes are not fully understood.