A case study investigating the effects of EDTA washing and amendments on trace metal-contaminated soil

Trace metals emissions show a sustaining decrease in western Europe since several decades. Sources like leaded fuels have been banned and the use of efficient flue gas cleaning systems have reduced industrial emissions significantly. But trace metal additions are cumulative, and the contamination is permanent. Immobilizing trace metals can be an efficient and cost effective way to prevent groundwater contamination and uptake in the food chain but cannot account for all exposure pathways (e.g. ingestion), while guideline values are only concerned about total concentrations. Soil washing techniques comprise an enormous potential for the efficient and sustainable extraction of trace metals from contaminated soils. The Garden Soil Project is a case study investigating the effect of soil amendments applied after a new ex-situ soil washing procedure (Ethylenediaminetetraacetic acid) from a Cd-, Pb-, Zn-contaminated Cambisol from Arnoldstein, located at a former lead mining and smelting region in Austria.

To investigate the success of the EDTA soil washing and amendment application, an experimental garden was set up at the University Research Center (UFT) in Tulln an der Donau. It encompasses twelve raised beds of 1 m³, filled with three soil variants in four replicates: The contaminated, unwashed soil (U) and two washed variants (W), one amended with 2 %wt biochar and 2 %wt compost (A). The amendments aim to restore soil conditions after the invasive procedure. The success of the trace metal extraction and restoration of the original soil properties is investigated by analyzing vegetable cultivars grown on the soil variants, the physicochemical and microbiological characteristics of the soil in the course of 2 years. First results show a significant reduction in trace metal uptake by different vegetables after washing and an increase in biomass for both washed soil variants W and A. The continuing analysis of trace metals in soil leachates and multiple extractable fractions in soil will allow a more detailed assessment. Furthermore, an ongoing investigation of the carbon and nitrogen cycle, using stable isotopes, will be applied as an indicator for soil functions.