Markus Puschenreiter, a professor at Vienna’s University of Natural Resources and Life Sciences, says the process, known as “gentle remediation,” involves extracting bacteria from polluted soils and adding them to the roots of trees at a polluted site. “They establish in the rooting zone and support accumulation behavior. They release compounds to mobilize nutrients, but also contaminants.” Willow and poplar are preferred vehicles, as their roots can reach into groundwater.
The goal is to improve the pollutant-remediating potential of the microbes that are already there, says Jaco Vangronsveld, professor at Hasselt University in Belgium. “If those there cannot degrade the pollutant, we can conjugate them with strains that have pathways to break it down. We modified bacteria inside the plants too, to allow them to degrade the compounds that are taken up by the plant, so we have a nice bioreactor.”
In Belgium, Puschenreiter and Vangronsveld tested the process at an old car site that was contaminated with solvents and fuels. Over 6 years, 275 polar trees with pollutant-eating bacteria in the root system were able to remove toluene from the soil.