If contaminants (oil, BTEX, VOCl, metals, cyanides, ...) are taken up by the plant, they are degraded to harmless products and/or stored in the plant tissues.

Unfortunately, planting trees does not guarantee effective soil and/or groundwater remediation. Control and monitoring by humans is necessary.

Firstly, natural phytoremediation depends on the type of plant, but also on the present micro-organisms. If degradation is insufficient and increased concentrations of pollutants are present in the soil, phytotoxicity may occur, causing the plant to show poor growth, become ill or even die.

Secondly, if volatile organic compounds are present, they can be volatilized by the leaves (evapotranspiration).

Both obstacles are overcome by enriching the appropriate plant-associated microorganisms. Endophytic bacteria, which live naturally within the plant, if 'equipped' with the appropriate degradation mechanisms, help plants to survive in situations with elevated levels of toxic pollutants and increase the capacity of the plants to degrade these pollutants and thus to remove them from the environment.

The enrichment of these benefactors in the plant therefore optimizes the phytoremediation process.