PHYTO RESEARCH CASE STUDY:
Project Name : Etobicoke Field Site (Ficko et al, 2010) (Ficko et al, 2011) (Whitfield et al, 2007) (Whitfield et al, 2008)
Location: Etobicoke, Canada (outside Toronto)
Institution/ Scientists: Royal Military College of Canada, Queens University – Barbara A. Zeeb, Sarah A. Ficko, Allison Rutter
Date installed: Studies ongoing since 2004
Plant species installed: Cucurbita pepo ssp pepo ‘Howden’ (Pumpkin), Carex normalis (Sedge) and Festuca arundinacea (Tall Fescue)
Amendments: NPK Fertilizer, Rototilling
Contaminant: PCB’s (Aroclors 1254/1260) @ 37ug/g
Target Media & Depth: Soils, top 60 centimeters (2 feet)
This Field Site is a former electric transformer manufacturing facility located in the town of Etobicoke just outside Toronto, Canada. Approximately 9,000 tons of PCB contaminated soil are located at the site and have been secured with an asphalt cap. Groundwater flowing through the contaminated soil is treated with an on-site wastewater treatment facility before being discharged into the city sewer system. An area of asphalt was excavated and converted into a phyto research study plot.
Studies on the site first started with field trials to see if various PCB accumulating species that were identified in green house studies might accumulate PCBs in field conditions including Cucurbita pepo ssp pepo ‘Howden’ (Pumpkin), Carex normalis (Sedge) and Festuca arundinacea (Tall Fescue) (Whitfield et al. 2007). Further studies focused on different Pumpkin planting methods including the use of a trellis system and planting in potting soil (Whitfield 2008). This study showed the importance of the pumpkin root structure (adventitious root system) in the uptake of PCB’s and also revealed that increased planting density might be counterproductive to overall PCB uptake. The study still showed however that although this particular subspecies of pumpkin can take up more PCBs than other plants, they likely do not take up enough to be useful at highly contaminated sites.
Further investigations have utilized a unique method to identify additional PCB extracting species by analyzing weedy species that naturally colonized the bed edge of planting plots used in previous studies. A 2010 study by Sarah Ficko et al. revealed 27 natural plant colonizers of the PCB contaminated soil. When analyzed for PCB concentrations within their tissues, it was found that 17 of the species accumulated PCB’s at levels similar to or greater than previously identified PCB accumulator Pumpkin. Three of the species, Solidago canadensis (Canada Goldenrod), Chyrsanthemum leucanthemum (Ox-eye Daisy) and Rumex crispus (Curly Dock), were further tested at the site (Ficko et al. 2011). They were found to have a greater extraction capacity than the pumpkin. However, further research is needed to identify the specific mechanism of PCB extraction within the identified weed species as well as optimize the planting density and methods of harvest. These studies reveal the importance of identifying natural colonizers of contaminated sites to advance knowledge of species capable of contaminant extraction, as well as identifying commercially viable species for phytoextraction. Phytoextraction of PCBs is still being investigated in scientific field trials, and research over time will show if it may be viable for future field-scale remediation. Field scale remediation of areas of low PCB soil concentration may be viable in the future if the time of remediation is flexible (i.e. it may take many years).
Cucumbers, Tall Fescue and Sedge were planted on an old electric transformer site contaminated with PCBs to test for extraction potential. Spontaneous vegetation emerged on the edges of the plot, and those species were also tested for extraction. Of the 27 plant colinizers, 17 native invador ‘weeds’ were found to extract greater amount of PCBs than the original test species. These species are currently being tested on other sites. Phytoremediation potentail for PCBs has not yet been verified, and plants are not viable means for field extraction at this time.