The International Information Center for Geotechnical Engineers

# Phytoremediation

#### Case histories

##### Heavy Metal and Radinuclide Phytoextraction in Chernobyl (Dushenkov et al., 1999)

In 1986 the nuclear fission plant commonly known as Chernobyl suffered a catastrophic meltdown. Cesium-137 was released as far away as Sweden, but the majority of the fallout occurred immediately north of the reactor site. Most of this pollutant quickly percolated into the sandy topsoil following rainstorms. Twenty different surfactants were used to increase the bioavailability of the cesium. While Indian mustard, corn, peas, artichoke, and sunflower were all used, it was found that only artichokes and sunflowers yielded substantial results. Even so, after only three weeks cesium levels ceased to decrease, and harvesting was prescribed. A modest 0.3% decrease in radioactivity was observed. Dushenkov et al. relied on results from previous studies and treated the lead-laden soil with chelating agents to mobilize it further (Dushenkov et al. 1999). These chelating agents caused a 20-fold increase in the lead uptake levels. Ultimately, incineration was used to reduce the volume of plant waste to less than 10% of its original.

##### Lead Phytoremediation at a New Jersey Brownfield Site (Baylock et al., 1999)

Phytoremediation was used over a 4500 sq ft area outside an abandoned lead-acid battery factory in Trenton, New Jersey. This contaminated site is in close proximity to schools, churches, and residences, and therefore needed to be visually appealing. A portable x-ray fluorescence (XRF) meter was used to quickly inventory the site’s lead levels, while additional samples were sent off-site for more detailed analysis. The metal-accumulating crop “Brassica juncea L. Czern”, also known as Indian mustard was employed to extract lead from the soil. The soil was fertilized and planted with 3.5 in. diameter pots of the mustard plant. EDTA was applied at varying rates to assess its affect on lead solubility and resulting plant uptake. Soil moisture was tracked with four sensors, and irrigation was provided with overhead sprinklers. Each growing cycle took 6 weeks, plants were harvested by cutting them at ground level, the site was rototilled, and three growth cycles could occur in one growing season. Although multiple growing season treatments were used for an overall 13% reduction in lead levels, 72% of the planted area was treated to below the EPA direct contact criteria of 400 ppm in one growing season.

Figure 2. Results of New Jersey Phytoremediation Project, Baylock et al. (1999)

##### OneSITE Wastewater Treatment Plant in Woodburn, Oregon (Zadrow , 1999)

Ten thousand poplar trees “populous trichocarpa deltoides” were planted over a ten acre abandoned sludge lagoon in an attempt to stabilize the waste and open over 400 acres for a treatment buffer. This buffer is currently working as an alternative to releasing over 5 million gallons of untreated wastewater to a small seasonal stream. The ten acre pilot plot was aimed at preventing the construction of a $2.5 million storage lagoon. EPA awarded$250,000 for the initial planting of poplar trees, which grow twice as fast as pine species and can be sold to the lumber industry every 10 years.  After the $2.5 million dollar tree planting project is implemented over all 300 acres, the municipality estimates the income of$800,000 every ten years upon harvesting of the trees.