From the Laboratory to the Field: Modeling Contaminant Fate and Transport on Plants Growing in Phytoremediation Systems

From the laboratory to the field: Modeling contaminant fate and transport in plants growing in phytoremediation systems

Gayathri Gopalakrishnan, M. Cristina Negri*, Paul L. Benda and John Quinn, Argonne National Laboratory

Phytoremediation or contaminant removal using plants has been deployed at multiple sites to remediate contaminated soil and groundwater. Research has shown that trees are low-cost, rapid and relatively simple to use monitoring systems as well as inexpensive alternatives to traditional pump-and-treat systems (Vroblesky et al 1999, Struckhoff et al 2005, Gopalakrishnan et al 2008). However, a better understanding of the mechanisms governing the fate and transport of chemicals in plants is required to accurately predict the performance of phytoremediation systems.

Plant uptake models have been developed based on direct absorption of the chemical into the root in combination with microbial degradation, followed by contaminant translocation in the transpiration stream (xylem), sorption in the plant tissue and transpiration by the leaves or diffusion out of the tree (Trapp and McFarlane, 1995; Burken and Schnoor, 1998; Ma and Burken, 2004). These models have been developed for ideal conditions that match those in the laboratory, which are approximations of field conditions. Comparison of field data with model results has indicated that model parameters such as the diffusion coefficient obtained in the field are 2-100 times greater than laboratory results (Ma and Burken 2004, Gopalakrishnan et al 2008).

This study investigates the scale effect on model parameters such as sap flow rate and diffusion coefficient as a result of differences in plant sizes, for example between hydroponic plants in the laboratory and large trees in the field. These results are then evaluated using existing models for contaminant fate and transport in plants at a phytoremediation site at Argonne National Laboratory to determine system performance as related to contaminant remediation and hydraulic control.