Specific Recommendations for Dredged Material Contaminants

Technical Note DOER-C9

November 1999

determine effectiveness of phytoreclamation in reaching reclamation goals. A plant

bioassay procedure (Folsom and Price 1989), which uses a larger volume of soil material

and provides for optimum water management, can incorporate the results of the manufac-

tured soil screening test and be utilized for this purpose. More specifics on a framework

to determine phytoreclamation effectiveness is provided in Price and Lee (1999).

Specific Recommendations for Dredged Material Contaminants:

1. Heavy Metals: Plants can readily accumulate some heavy metals and some plants may

even hyperaccumulate certain metals. The metal-laden plant tissues can be harvested and

properly managed. In some cases, metals can actually be recovered from plants containing

high concentrations (% range) of metals and recycled. The group discussed a number of

known investigations, published and unpublished, where plants have been used for heavy

metal reduction in soils (Table 3). Due to proprietary protection of unpublished informa-

tion, details on some of the items listed are not available. Most of these phytoreclamation

processes for metals involve hyperaccumulation and removal of metal-laden plant tissues.

Plant-assisted reduction of selenium (Se) and Mercury (Hg) includes volatilization through

plant respiration. Brassica juncea has been suggested to hyperaccumulate lead (Pb) after

chelates are added to soil, making the Pb more available. However, when metal chelates

are added to Pb-contaminated soil, migration of chelated lead into surface and groundwater

must be controlled. The group suggested that inactivation of lead through the addition of

phosphate fertilizers and the formation of lead phosphate was a more economic and

environmentally acceptable alternative. Chaney et al. (in preparation) summarizes ap-

proaches and progress in developing commercial phytoextraction systems for these and

other metals using metal hyperaccumulator plants.

In general, the group concluded that, based on the relatively low concentrations of metals

in dredged materials compared to those in mining and industrial sites, the economical

application of phytoreclamation to dredged material may be limited to situations where

heavy metal content of dredged material requires reduction to some lower acceptable

concentration.

2. Petroleum Hydrocarbons: The working group concluded that the application of phyto-

reclamation for reduction of petroleum hydrocarbons may be more feasible than for heavy

metals in dredged material. The use of plants to reduce petroleum hydrocarbons from soil

has been demonstrated on a number of sites using the process of degradation rather than

actual uptake. As shown in Table 4, a number of plant species have been employed for

this process. Most of the species will require a pH near 7.0 for optimum growth and aerobic

conditions to promote a viable and active plant-associated microflora. Fertility levels

would also need to be maintained for the same reasons. Depending on polycyclic aromatic

hydrocarbon (PAH) concentrations and physical conditions of the dredged material,

significant reduction of 3- and 4-ring PAHs can be accomplished in as little as one year.

Larger ring PAHs will degrade more slowly and require more time and possibly a

combination of phytoreclamation and bioreclamation. For total recoverable petroleum

hydrocarbons (TRPH) the same applications apply as for PAHs, and in addition, TRPHs

may require the application of polyacrylamide or PAM.