Are willow trees into Heavy Metal?

A fresh perspective on risk management

The province of Groningen has started a project in Appingedam where risk management of contaminated locations is viewed in a new way. Research is conducted to check if the area, which is polluted with heavy metals, can be managed in a sustainable manner by cultivating willow trees and processing the obtained wood to a sustainable product.

The contaminated location is an old part of a business area of the former strawboard factory ‘De Eendracht’. The intention is to transform this former industrial site into an attractive area for recreational activities, like hiking and cycling. However, a part of the site (about 3 hectares) is contaminated with heavy metals and is not open to the public. To achieve this willow trees have been planted. The dense cultivation of the trees ensures that people can’t access the area, which prevents direct contact with the contamination.

The beauty of willow trees is that they are capable of accumulating or binding the heavy metals, thereby decreasing the risks and cleaning the soil in a natural way. This method of soil remediation by which plants or trees are used to absorb or break down pollution is called phytoremediation.

Do risk management and the creation of a sustainable product go hand in hand?

The province of Groningen desires the answers to several questions during this project. Is it possible to create sustainable added value with willows, which are planted on contaminated soil and does the quality of the soil improve? To obtain the answers the province of Groningen has asked Bioclear earth to monitor the site of ‘De Eendracht’ located in Appingedam for a period of six years. In addition, the municipality wants to know whether it is possible to use willows sustainably.

Update: research shows that willows love heavy metal

After the start of this project in 2016, Bioclear earth conducted monitoring at the contaminated location to evaluate how well the willows are able to extract heavy metals from the soil (phytoextration). In order to do this, we compared the results of the 2018 analyses with those of 2016. The new data show that the willows retain their ability to absorb heavy metals, even though they are older now. The concentration of copper, cadmium and zinc in the willow samples has increased considerably. This means that the willows slowly but surely contribute to cleaning up the (available) heavy metals at the location.

Despite the increase of heavy metals in the willows, the heavy metal pollution in the soil of the location is still relatively high. However, our springtail test (ISQ test) - developed in collaboration with the Free University of Amsterdam - shows that there is no increase of ecological risk for soil life compared to clean soil.

Recycling possiblities for harvested willows
 
In addition, we have investigated how we can use willows sustainably. We have looked at various applications of harvested willows for example as building material, for energy production and for usable chemical compounds.
The next options are the most feasible: 

  • • Using willow as material for garden fencing or mattresses for protection of soil and banks against erosion.
  • • Use as (additional) heating of the office building "De Eendracht" with an aftertreatment of the ashes.

 Even though heavy metals are quite immobile we recommend researching the possible leaching and migration of these metals from the material into the environment, before using the wood for garden fencing or protection mattresses.

Our first findings with this form of phytoremediation are very interesting and can also be useful for other locations in order to create sustainable products in addition to effective risk management.

Do you want to know more about this project, please contact Freek van den Heuvel.

Freek van den Heuvel
Consultant water quality and phytoremediation