- Laboratory screening trials for candidate plant species
- Evaluation of saprophytic fungi and anaerobic-aerobic bacterial systems
- Pilot-scale phytoremediation demonstration
Unacceptable levels of PCBs, PAHs, and lead were found in soil at a former landfill site in Haiku Valley on Oahu, Hawaii. The U.S. Army Corps of Engineers, Honolulu District, gave Environet the opportunity to use the site to study the potential of indigenous and naturalized saprophytic fungi and plants to reduce levels of those contaminants found in the soil.
This pilot-scale phytoremediation demonstration focused on contaminant removal efficiency, using the most effective plant and fungal species identified during prior greenhouse and laboratory studies. Design issues included plant and fungal growth and maintenance, monitoring of microbial populations in the plant rhizosphere, soil contaminant levels, phytotoxicity, rooting depth, and soil moisture levels.
Prior to the initiation of the pilot-scale demonstration, Environet conducted a biological inventory to identify the types of flora present at the contaminated site. Plants growing in the landfill were sampled and analyzed for PCB, PAH, and heavy metal content. Other preliminary greenhouse and laboratory studies addressed the following:
- Hydroponics of plant uptake of lead.
- PCB surrogate dye degradation.
- Plant uptake of lead and PCBs in soil medium.
- Degradation of PCBs by indigenous saprophytic fungi.
- Anaerobic-aerobic bacteria degradation of PCBs.
Results indicated that three particular species of indigenous saprophytic fungi were very efficient in degrading PCBs and PAHs at up to 70% and 100% respectively. Some indigenous and naturalized plants showed a moderate ability to accumulate lead and other heavy metals, and when adding soil amendments such as EDTA, the level of metals accumulated increased by one to two orders of magnitude.
Phytoremediation offers a promising alternative for cleaning PCB and heavy metal-contaminated soils in Hawaii and other Pacific Islands. If proven to be effective, phytoremediation will provide a less expensive and environmentally-sound method that could potentially replace current conventional approaches.