Plants can break down persistent pollutants.
Liu J, D Hu, G Jiang and JL Schnoor. 2009. In vivo biotransformation of 3,3’,4,4’-tetrachlorbiphenyl by whole plants – poplars and switchgrass. Environmental Science and Technology doi: 10.1021/es901244h.
The enzymes in the roots of a poplar tree can alter the chemical structure of a common type of PCB pollutant, rendering it less harmful than the original chemical.
Prior laboratory studies found plant cells were able to modify the long-lived pollutants. These new results confirm that at least one type of living plant can do the same. The results are a first step in determining if plants would be a valuable tool in cleaning up contaminated sites.
Polychlorinated biphenyls (PCBs) are a group of persistent environmental contaminants that have been linked to cancer, reproductive defects, nervous system damage and many other types of problems. Although PCBs have not been produced in the United States for more than 30 years, they are very resistant to breakdown and still persist in the environment. Different varieties of PCBs can have widely different properties and toxicities.
Their long-lived nature has resulted in a legacy of contaminated land and water sites across the US. While the PCB-contaminated waterways – such as the Hudson River – are better known to the public, there are close to 300 sites with PCB-contaminated soils on the Environmental Protection Agency's National Priority List of Superfund sites.
A team of scientists from the Chinese Academy of Sciences and the University of Iowa evaluated the ability of poplar trees and a type of switchgrass to chemically modify or metabolize a common PCB, CB77. The poplars changed CB77 in several ways, including removing the chlorine atoms from the molecule. These modifications potentially turn CB77 into less harmful forms. Switchgrass was less able to modify CB77.
Enzymes in the tree roots changed the chemical structure of the PCB. Enzymes are molecules that modify, make or break down chemicals in a similar manner in all life – from plants to bacteria to insects to people.
The plants in the study were grown hydroponically - that is, with their roots suspended in nutrient solution and not in soil. Growing them in water eliminates other sources of chemical modifiers, such as bacteria in the soil and on the plant roots.
The new findings hold promise for using plants as a way to help clean the soil in PCB-contaminated sites. Many more questions still need to be answered. Future research will likely focus on the ability of plants to metabolize other forms of PCBs typically found in contaminated soils, the extent plants can remove PCBs from soil and whether plant-based modifications of PCBs produce only less harmful forms of PCBs.
