Phytoextraction of bioavailable metals: pilot trial in the Gothenburg Botanical Garden

Research Project, 2025 – 2027

Gothenburg Botanical Garden - problems and conditions for phytoextraction. The Gothenburg Botanical Garden is centrally located in Gothenburg and in connection with the planning of a new garden facility, a so called forest garden, contamination levels have been detected that just exceed the general guideline values for lead and mercury for sensitive land use (KM). Site-specific guideline values have been developed where the governing risk for lead is the ingestion of soil and for mercury the protection of surface water. The mean concentration of mercury is below the suggested site-specific guideline value, thus lead is the contaminant of concern. Soil sampling and a feasibility study on the potential for phytoextraction have been carried out by Sweco, which shows that the conditions are good: i) the levels of contamination are low to moderate, ii) the contaminants occur in the upper soil layers where the roots of the plants obtain water and nutrients, iii) there are no time restrictions on the use of the area, and iv) the plants can be optimally cared for by the skilled personnel at the Bothanical garden.

Aims and objectives of the project. The overall aim of the project is to increase knowledge, practically and theoretically, about the efficiency and time requirements for phytoextraction as a method for dealing with soil contaminated by low to moderate concentrations of metals, specifically lead, and taking the metal bioavailability into account. The following sub-objectives have been formulated: 1) Design, construct and manage a pilot experiment for phytoextraction of lead using willow (Salix sp.) trees and testing bioinoculation with mycorrhizal fungi in the Gothenburg Botanical Garden. 2) Sampling and analysis of metals in soil, their bioavailability, and uptake in different plant parts. 3) Evaluate the effectiveness of phytoextraction and estimate the expected time needed to reach target concentrations of relevant metals, linked to their bioavailability. 4) Compile practical experiences from the pilot and new knowledge on how to take bioavailability into account when applying phytoextraction. 5) Communicate the results to the industry and academia. 6) Communicate with the public about the ability of plants to cope with pollutants and the importance of soil health and soil functionality to deliver ecosystem services to raise awareness of soil health in line with the EU Commission's proposal for a new soil directive.