Gardens with remediated soils: hazard mitigation + safe food

Although usually out of our sight, everything in our lives is underpinned by soil our homes, the food we eat, the water we drink. Across all socioeconomic groups and around the world, initiatives for sustainable use of soil, such as urban farming, are on the rise. These approaches to land use often undermine the fact that soils are the most complex natural system, and that their present vulnerability is unprecedented. Land contamination exists in most industrialized countries and is a growing problem in emerging economies. Particularly alarming is the presence of toxic metals, which are persistent in the soil and difficult to remove. As human population and pressure on limited soil resources are continuously growing, more and more metal contaminated land is expected to be put under agricultural production in a delicate balance of needs, social & economic benefits and health risks. We are in contact with soils in our everyday life and this proximity increases the probability that soil pollutants may be carried into the human body. Soil remediation & reuse is a solution, and most EU Member States have made the clean-up and restoration of the land a priority. However, historical excavation to landfill (dig & dump) wastes soil, while soil-sustainable remedial options are currently not applied beyond the scale of pilot, experimental studies. As a consequence, inhabitants can typically not avoid living in contaminated areas. Furthermore, studies of attitudes to soil contamination and remediation show that persons in contact with contaminated soil, such as urban gardeners, often ignore the risk they are exposing themselves too, preferring to focus on the benefits of green, sustainable and local food production. While the increasing demand for food is threatening to reduce health, soil and food quality standards, the problem of soil contamination remains on the margins of scientific debates. Therefore a gentle soil washing technique developed by the University of Ljubljana will be applied on garden soils in Slovenia and in Austria, and together with the AIT Austrian Institute of Technology GmbH soil functionality will be improved and enhanced. The overall aim of this project is to research the environmental, agronomic, social & economic potential of this unique, cost-effective soil remediation technology. The internationally patented technological innovation not only removes Pb and other toxic metals from soil by efficient chemical mean (complexation with strong chelating agent EDTA) but also preserves soil as a natural resource. For farming on reclaimed land experimental gardens will be constructed in Slovenia (Meza Valley) and in Austria (Arnoldstein). Both sites were exposed to Pb mining/smelting and are co-contaminated with Zn and Cd. The combination of the patented washing technique (UNI Ljubljana) and the improving and investigating of soil functionality (AIT) will gain a win-win situation.

The importance of soil conservation and remediation is a central component in the engagement against continuing loss of arable land and are needed to achieve the aims of the new European Green Deal. Sustainable clean up technologies for inorganic contamination are still not yet developed or take decades for completion (e.g. phytoextraction). A promising development is the ReSoil washing technique which uses ethylenediaminetetraacetic acid (EDTA) in a chemical supported soil washing process to extract heavy metals (Cd, Pb, Zn) from contaminated soils. The efficient recycling of the washing solution reduces material input and leaves only traces of stabilized EDTA in the washed soil. In series of outdoor raised bed experiments the remaining risks of the remediated soil and the impact of revitalization measures using organic amendments (Vermicompost and Biochar) were explored. Metal and EDTA concentrations were evaluated in fractions relevant for groundwater safety, food production and gastrointestinal uptake by children. Furthermore, the soil microbial and mesofaunal community and the carbon and nitrogen cycles as fundamental soil function indicators were investigated. This project demonstrated that the soil washing technology has a high potential to improve soils degraded by inorganic contamination. Remediated soil had lower heavy metal concentrations in all fractions and the remediation improved plant growth significantly. The communities of microorganisms and mesofauna exhibited increased activities on the washed soils and the nutrient cycling was enhanced, indicating an improvement in soil health. The Vermicompost/Biochar amendment led to a further increase in microbial activity and plant growth. The shortcomings of the technology were that metal concentrations slightly exceeded Austrian guideline values for garden soils and European food standard limits. Additionally, the mechanical impact of the remediation treatment destroyed the soil structure resulting in a lower water holding capacity, leading to water stress under non irrigated conditions.