Long-term soil accumulation of potentially toxic elements and selected organic pollutants through application of recycled phosphorus fertilizers for organic farming conditions

The pollutant input and the risk of contamination by long-term application of recycled P fertilizers (RPFs) in European agricultural soils were estimated by a mass balance approach. Calculations based on literature data were carried out for the potentially toxic elements (PTEs) Cd, Cr, Cu, Ni, Pb, Zn and for the persistent organic pollutants (POPs) PCBs, PAHs and polychlorinated dibenzo-dioxins and -furans. The PTE accumulation estimation during 200 years of fertilizer application, equivalent to 11 kg P ha-1 year-1, the mean P export via harvested products on European stockless organic farms, regarded soil background concentrations and proposed threshold concentrations. For PTEs, inputs were fertilizer application, atmospheric deposition and liming, output processes were leaching and crop harvest. The effect of varying site conditions was assessed by considering two precipitation excess (F) values and two soil pH values. For POPs, fertilizer application and the half-life time were considered. The PTE accumulation risk was low for most RPFs. For the analysed POPs no accumulation was found. The highest accumulation was found for all PTEs at pH 7 and F = 0.1 m year-1, the lowest at pH 5 and F = 0.3 m year-1. A high P concentration in fertilizers resulted in a low PTE flow per unit of P. composts had the highest PTE accumulation risk due to lowest P contents. Struvite, meat and bone meal, digestate of catering waste, ash and biosolids would be better suited as P fertilizers. The use of fertilizers should be regulated based on their pollutant-to-nutrient ratio

Effects of biochar amendment on root traits and contaminant availability of maize plants in a copper and arsenic impacted soil

Biochar has been proposed as a tool to enhance phytostabilisation of contaminated soils but little data are available to illustrate the direct effect on roots in contaminated soils. This work aimed to investigate specific root traits and to assess the effect of biochar amendment on contaminant availability. Amendment with two different types of biochar, pine woodchip and olive tree pruning, was assessed in a rhizobox experiment with maize planted in a soil contaminated with significant levels of copper and arsenic. Amendment was found to significantly improve root traits compared to the control soil, particularly root mass density and root length density. Copper uptake to plants and ammonium sulphate extractable copper was significantly less in the biochar amended soils. Arsenic uptake and extractability varied with type of biochar used but was not considered to be the limiting factor affecting root and shoot development. Root establishment in contaminated soils can be enhanced by biochar amendment but choice of biochar is key to maximising soil improvement and controlling contaminant availability

Editorial: Exploring Plant Rhizosphere, Phyllosphere and Endosphere Microbial Communities to Improve the Management of Polluted Sites

International audienc

Co-localized arsenic speciation and cycling in the rhizosphere of hyperaccumulating ferns

ISSN:1029-7006ISSN:1607-796

Root foraging and avoidance in hyperaccumulator and excluder plants: a rhizotron experiment

Aims: Metal hyperaccumulation is a rare phenomenon described for an increasing number of plant taxa. In this study we investigated the root growth responses of the well-known nickel, zinc, cadmium hyperaccumulator Noccaea caerulescens and of the metal tolerant (non-accumulator) Stellaria media, in order to observe root foraging vs avoidance responses to nickel. Methods: To allow for observations of root growth and foraging preferences, two accessions of Noccaea caerulescens and two accessions of Stellaria media orginating from high nickel and low nickel habitats were grown in rhizotrons with localized nickel enrichment. Results: The root density in the control and nickel-enriched soil areas in the rhizotrons with different N. caerulescens accessions had distinct responses: moderate nickel avoidance was recorded for the non-nickel accession, while a clear foraging response was observed in N. caerulescens from the nickel accession. In contrast, nickel rooting avoidance was observed for both S. media accessions and was more pronounced in the non-nickel accession. Conclusions: This study shows that N. caerulescens originating from different accessions responded differently to soil nickel enrichment, with the nickel accession of N. caerulescens actively foraging for nickel, suggesting a physiological adaptation and demand for this metal. In contrast, a clear nickel avoidance response by a metal tolerant species, S. media, was observed in this study, a phenomenon which has not been previously described; this suggests that root avoidance responses might play a role in the adaptation of metal tolerant species to Ni-rich soils

Increasing the applicability of gentle soil remediation methods : lessons from the Greenland project

Gentle remediation options (GRO) include various and in general plant-based options to remediate trace element contaminated soils (TECS) at low cost and without significant negative effects for the environment. Although GRO comprise very innovative and efficient technologies, they are still not widely used as practical site solution due to several hindrance reasons. Greenland has been launched on January 1 2011 to address several issues: - Sustainable management adapted to TECS and deployment of GRO at field scale; - Valorisation of plant biomass produced on trace element (TE) -contaminated sites; - Harmonization of methods to assess the bioavailability of TE and development of a tool set to monitor the sustainability of GRO; - Improving GRO through plant selection and modifications in soil TE bioavailability; - Appraisal of current GRO practice, and development of implementation guidance and decision support frameworks. Various current gaps / shortfalls in GRO application and development, i.e. lack of rigorous large-scale applications of GRO, variability in methods used for analysis and appraisal, potential for increasing the efficiency of GRO through biotechnology, technologies for biomass valorization and their uncertainty, bestpractice guidances for the application of GRO at field scale, including appraisal of the various options available and their uncertainty, methods for monitoring, development and evaluation of a decision support tool (DST) focused on GRO, which can be integrated into existing, well-established and utilized DSTs / decision-frameworks, etc. are addressed. The overall aim of GREENLAND is to make GRO fit for purpose, which will substantially contribute to improvement of soil quality and ecosystem services on the local level (land owners, communities), but also at the European level. In addition to that, the use of biomass produced on GRO-treated contaminated land will contribute to socio-economic development at the local level and help to fulfil the increasing demand for biomass use in raw material and energy production all over Europe while avoiding the competition for food production and land change use. During the first 3 years of Greenland, major achievements have been reached in all workpackages. The field experiments have been successfully maintained, in spite of partly challenging conditions, e.g. severe drought periods. Several biomass valorisation options were tested. Based on test results, literature overview and ongoing interviews with biomass processing enterprises, a list of feasible options is prepared. Suitable indicators of gentle remediation progress and success were identified in a comprehensive ring test on soil samples from field trials. The results obtained so far were summarized and submitted for publication. A second ring test will confirm the preliminary results. To enhance the efficiency of GRO, several plantassociated bacterial strains and combinations of soil amendments were evaluated. For bringing GRO into practical application, a decision support system has been published, along with valuable information on stakeholder engagement and empowerment. A technical guideline, which will be available at the end of Greenland, is now prepared

Bacterial Communities Associated with Flowering Plants of the Ni Hyperaccumulator Thlaspi goesingense

Thlaspi goesingense is able to hyperaccumulate extremely high concentrations of Ni when grown in ultramafic soils. Recently it has been shown that rhizosphere bacteria may increase the heavy metal concentrations in hyperaccumulator plants significantly, whereas the role of endophytes has not been investigated yet. In this study the rhizosphere and shoot-associated (endophytic) bacteria colonizing T. goesingense were characterized in detail by using both cultivation and cultivation-independent techniques. Bacteria were identified by 16S rRNA sequence analysis, and isolates were further characterized regarding characteristics that may be relevant for a beneficial plant-microbe interaction—Ni tolerance, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore production. In the rhizosphere a high percentage of bacteria belonging to the Holophaga/Acidobacterium division and α-Proteobacteria were found. In addition, high-G+C gram-positive bacteria, Verrucomicrobia, and microbes of the Cytophaga/Flexibacter/Bacteroides division colonized the rhizosphere. The community structure of shoot-associated bacteria was highly different. The majority of clones affiliated with the Proteobacteria, but also bacteria belonging to the Cytophaga/Flexibacter/Bacteroides division, the Holophaga/Acidobacterium division, and the low-G+C gram-positive bacteria, were frequently found. A high number of highly related Sphingomonas 16S rRNA gene sequences were detected, which were also obtained by the cultivation of endophytes. Rhizosphere isolates belonged mainly to the genera Methylobacterium, Rhodococcus, and Okibacterium, whereas the majority of endophytes showed high levels of similarity to Methylobacterium mesophilicum. Additionally, Sphingomonas spp. were abundant. Isolates were resistant to Ni concentrations between 5 and 12 mM; however, endophytes generally tolerated higher Ni levels than rhizosphere bacteria. Almost all bacteria were able to produce siderophores. Various strains, particularly endophytes, were able to grow on ACC as the sole nitrogen source

Gentle soil remediation of trace element-contaminated soils - success stories from the greenland project

Contamination of soils with trace elements (TE) is worldwide still one of the major environmental problems. Conventional technologies for soil remediation are usually very expensive and may negatively affect or destroy soil structure and functions. Phytoremediation technologies, however, include a set of gentle remediation options (GRO) which are approaches based on plants and associated microbes as well as soil amendments for remediating trace element-contaminated soils at low cost and without significant negative effects for the environment. The main technologies are phytoextraction, in situ immobilization and assisted phytostabilization. Although GRO comprise very innovative and efficient technologies, they are still not widely used as practical site solution due to several reasons of hindrance. Although major progress has been achieved on the lab scale, success stories obtained in the field are still limited, in particular regarding the long-term efficiency. Also, the issue of valorization of the potentially contaminated plant biomass has insufficiently been addressed so far. Furthermore, additional development is needed regarding the adequate determination of end-points of GRO. Finally, the application of GRO as practical site solution may be hindered by legal frameworks and by insufficient knowledge of the decision makers. Long term and large-scale field experiments may provide data required for the overall assessment of GRO efficiency, effectiveness and sustainability. Therefore, the EU-FP7-project “Gentle remediation of trace element-contaminated land – GREENLAND; www.greenland-project.eu) with 17 partners from 11 countries has been launched on January 1 2011 to address these issues and to make GRO ready for use as practical site solution