Doctor of Philosophy / Department of Agronomy / Gary M. Pierzynski / The bioavailability of Pb and Zn is linked to the solubility of solid phases and other soil chemical characteristics, which is associated with their environmental risk, suggesting that in situ stabilization of these elements can be accomplished by influencing their chemistry. However, more research is needed to investigate the effectiveness of different soil amendments on reducing Pb and Zn bioavailability. A lab study was conducted to evaluate the effects of five different P amendments and time on Pb/Zn speciation in a contaminated soil using synchrotron-based techniques, while a field investigation studied the effects of composted beef manure on plant biomass production and the influence on microbial function, size, and community shifts. In the lab study, the Pb-phosphate mineral plumbogummite was found as an intermediate phase of pyromorphite formation, which has not been documented until now. Additionally, all fluid and granular P sources were able to induce Pb-phosphate formation, but fluid phosphoric acid (PA) was the most effective with time and distance from the treatment. However, acidity from PA increased the prescence of soluble Zn species, which can have negative environmental consequences. Granular phosphate rock (PR) and triple super phosphate (TSP) reacted to generate both Pb- and Zn-phosphates, with TSP being more effective at greater distances than PR. In the field study, compost additions of 269 Mg ha[superscript]1 significantly decreased bioavailable Zn, while increasing estimated available water, plant nutrients, and plant biomass as compared to a contaminated control and low addition of compost (45 Mg ha[superscript]1) over three years. Additionally, compost additions of 269 Mg ha[superscript]1 significantly increased microbial enzyme activities, nitrification, and microbial biomass over the contaminated control through the duration of the study. Increases in microbial activity and biomass are related to increases in total C, available water, and extractable P, while negative relationships were found with electrical conductivity and with bioavailable Zn. The addition of lime or lime plus bentonite with compost did not further reduce metal availability, increase plant biomass, or improve the size or function of microbial communities. High compost additions caused a slight shift in microbial community structure according to phospholipids fatty acid analysis. Increases in the mole percents of both Gram-positive (Gm[superscript]+) and Gram negative (Gm[superscript]-) bacteria were found depending on site. Microbial biomass of Gm[superscript]+, Gm[superscript]-, and fungi were also increased by high compost additions. Results indicate that large additions of compost are needed to increase microbial biomass, improve microbial activity, and re-establish a healthy vegetative community. This study proposes that organic matter and P amendments can be used to stabilize and reduce the bioavailability of heavy metals in soils and mine waste materials, but must be managed carefully and intelligently.

The global soil resources are significantly threatened by pollution. In addition to the existing burden of contaminants in agricultural soils, the increasing anthropogenic input of metal(loid)s, further referred to as trace elements (TE), presents a major public health concern, since it endangers the food security of a rising human population. However, the growing demand for agricultural commodities will increase the pressure on fertile soils. In this context, steering the needed agricultural extensification towards arable TE-contaminated soils (TECS) could protect highly biodiverse or carbon stock land and, thereby, help reach global sustainability targets. The sustainable crop production on TECS requires effective and non-destructive measures to control relevant pollutant linkages. These are offered by gentle remediation options (GRO), the practical adoption of which is scarce across Europe as yet. This study provides different approaches of GRO applied to an agricultural soil in a characteristic post-mining region (Freiberg, Saxony (Germany)) in practical adoption (chapter 2) and under semi-controlled conditions (chapters 3 and 4). Due to severe topsoil contamination by metals (Cd, Pb, and Zn) and As, the pollutant linkages of concern at the study site are food-chain transfer, leaching to the groundwater, and tilling-related dust emissions. The overall aim was to find best management practices for coupling soil remediation with the production of marketable biomass. This was attempted via (i) in situ stabilization, alone (chapter 4.1) or combined with phytoexclusion (chapter 2), (ii) labile TE phytoextraction (chapter 3), and (iii) (aided) phytostabilization (chapter 4.2). Soil remediation by GRO was assessed with scientifically established (DGT, soil solution; chapter 4.1) and/or legally relevant chemical soil extractions (NH4NO3-solution; chapters 2 to 4) and pH measurements. Additionally, earthworms served as ecotoxicological endpoints (chapter 4.1). Initial soils, earthworms, vegetative and generative biomass produced from each approach, as well as the investigated soil additives, including fertilizers, were microwave-assisted chemically digested (HNO3, H2O2, aqua regia) prior to analysis. All environmental samples were analyzed for TE by inductively coupled plasma mass spectrometry (ICP-MS). Nutrient concentrations in soil additives and selected plant samples were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). The measured TE concentrations were evaluated against applicable European and/or national thresholds. At field (chapter 2), the repeated fertilization with superphosphate and/or lime marl basically attenuated the chemical TE availability over a three years crop rotation of Brassica napus, Triticum aestivum, and Hordeum vulgare. In turn, the simultaneous phytoexclusion by low-accumulating cultivars (LAC) effectively decreased the Cd concentrations in cereal grains (by averagely 21 % in wheat and 39 % in barley). However, straw metals´ accumulation or grain As uptake partly revealed opposing trends among LAC and high-accumulating cultivars (HAC). As investigated under semi-controlled conditions (chapter 3), a sunflower (Helianthus annuus L. mutant inbred line M7 (R3B-F-U/R13M10A; test series R13F-MP)), modified towards enhanced labile TE phytoextraction by chemical mutagenesis, proved less advantageous as pre-crop for winter wheat (Triticum aestivum L. cv. Tiger) than the regionally common winter oilseed rape (Brassica napus L. cv. Lorenz). This resulted from soil alkalinization by rape, whereas sunflower mobilized more TE than it depleted from the rhizosphere. Within in situ stabilization approaches under semi-controlled conditions, a Fe- /Al-rich drinking water treatment residue (WTR), soil-applied at a rate of 1 % (m/m) prior to cultivation of wheat (Triticum aestivum L. cv. Tiger; chapter 4.1) or Szarvasi-1 (Elymus elongatus subsp. ponticus cv. Szarvasi-1; chapter 4.2), decreased the chemical availability of As, Cd, and Pb by up to 77 % , 46 %, and 61 %, respectively. Thereby, it immobilized these hazardous TE increasingly effective over time and better than a Mn-rich WTR or lime marl. The bioassays with wheat and earthworms (Dendrobaena veneta L.) showed, however, that the habitat function for biocenoses benefited more from the Fe-/Al-rich WTR when it was applied at a lower application rate (0.5 % m/m). This resulted from dose-dependent P fixation and TE entries induced by the WTR, to which Szarvasi-1 appeared insensitive. Unlike As, the availability of Cd and Zn to biota in amended soils could not be predicted by any of the applied chemical methods due to endpoint-specific binding of competing cations to the biotic ligand (plant roots, earthworm tissue), and a preferential translocation of Zn over Cd in planta. Among all studied plants, the perennials Szarvasi-1 and cup plant (Silphium perfoliatum L.; chapter 4.2) best excluded the present mixture of TE in shoots, whereby the latter exhibited growth depression. However, only grain biomass of barley and rape, and partly of low-accumulating wheat, produced at the study site presented legally compliant animal feed based on European limit values for Cd and As. Given the investigated measures´ restricted efficacy to assure forage safety, a land-use change e.g. towards the perennial Szarvasi-1, which provides a continuous plant cover at low tillage and input requirements, possibly accompanied by the monitored reuse of an Fe- /Al-rich WTR, could most promisingly control all above-stated pollutant linkages. Revenues could be generated from energy conversion or valorization in the fibrous material sector. The waste recycling of WTR in TECS, though promising, requires proper characterization, eventual process optimization, and further studies regarding long-term stability to ensure legal compliance and environmental safety. Future research and breeding efforts regarding low Cd cultivars in particular could greatly contribute to safe food or forage production at the majority of moderately contaminated sites.:Table of contents Danksagung VI Abstract VII Zusammenfassung X List of Figures XIV List of Tables XVIII Abbreviations XXII 1 Introduction 1 1.1 The contamination of agricultural soils with trace elements - a global challenge to be tackled at local scale 1 1.2 The study site 5 1.3 Objectives 7 1.4 Structure of the thesis 8 2 Field assessment of conventional fertilizers and cultivars of annual plants 11 2.1 Management of trace element-contaminated agricultural land by in situ stabilization combined with phytoexclusion over a three years crop rotation 11 3 Exploring pre-crop effects of annual oilseeds 37 3.1 Trace elements bioavailability to winter wheat (Triticum aestivum L.) grown subsequent to high biomass plants in a greenhouse study 37 4 The potentials of drinking water treatment residues and/or perennialplants 53 4.1 Trace elements bioavailability to Triticum aestivum and Dendrobaena veneta in a multielement-contaminated agricultural soil amended with drinking water treatment residues 53 4.2 (Aided) phytostabilization of trace elements using cup plant (Silphium perfoliatum L.), or tall wheatgrass (Elymus elongatus subsp. ponticus cv. Szarvasi-1) and soilapplied drinking water treatment residues 77 5 Synthesis 91 5.1 The potential of crop management practices to mitigate food chain transfer of trace elements 91 5.2 The in situ stabilization efficacy under differential experimental conditions 96 6 Future perspectives 101 References 104 List of publications 121 Erklärung 123

Le phytomanagement de matrices contaminées en métaux couple leur réhabilitation écologique avec la production de biomasses végétales pour la bioéconomie. Un front de science est d’identifier des assemblages végétaux et d’optimiser leur production, aidée ou non par l’ajout d’amendements. Le phytomanagement de deux sols, l’un contaminé en Cu, l’autre en Cd, Pb et Zn, a été testé en conditions contrôlées. L’emploi conjoint de biochar et de grenaille d’acier diminue la phytotoxicité des 2 sols. En pots, sur 2 ans, cette combinaison d’amendements séquestre du carbone, diminue la phytotoxicité du sol contaminé en Cu et produit une biomasse d’Arundo donax L. et de Populus nigra L. non contaminée, utilisable par le secteur de l’énergie. Ces modalités de culture et d’amendement ont été installées pour un suivi à long terme sur le site contaminé en Cu. Parallèlement, en microcosmes, parmi 4 macrophytes utilisées en zone humide construite (CW) pour décontaminer des matrices aqueuses (i.e. Arundo donax L., Cyperus eragrostis Lam., Iris pseudacorus L. et Phalaris arundinacea L.), A. donax est la mieux adaptée pour fournir des racines à forte concentration en Cu utilisables pour produire un écocatalyseur riche en Cu. Le phytomanagement d’un effluent de bouillie bordelaise (EB, 69 μM Cu) par A. donax a été testé en CW pilote. Il est décontaminé en 48h, sa concentration en Cu respectant la réglementation du rejet d’effluent en réseau d'assainissement. Cependant, après un cycle de circulation, la concentration en Cu des racines d’A. donax (623 ± 140 mg Cu kg-1) est inférieure aux besoins de l’éco-catalyse, et le cycle serait à répéter pour atteindre les 1000 mg Cu kg-1 requis. / The phytomanagement of metal-contaminated matrices (soils and water) combines their ecological remediation and the production of non-food crops for the bioeconomy. One science frontier is to identify plant assemblage and to optimize their biomass production, aided or not by amendment addition and cultural practices. A Cu-contaminated soil and a Cd/Pb/Zn-contaminated one were phytomanaged in controlled conditions. The combination of biochar and iron grit reduced the phytotoxicity in both soils. In a 2-year pot experiment, this amendment combination decreased the phytotoxicity of the Cu-contaminated soil, enhanced soil C sequestration and produced an uncontaminated biomass of Arundo donax L. and Populus nigra L. adapted for bioenergy production. These combinations of culture and amendment are tested in field trial at the Cu-contaminated site. In parallel, in microcosm experiment, out of 4 macrophytes commonly used in constructed wetlands (CW) to clean up aqueous matrices (i.e. Arundo donax L., Cyperus eragrostis Lam., Iris pseudacorus L. and Phalaris arundinacea L.), A. donax was the best adapted to produce a high Cu-rich root mat potentially usable as Cu-ecocatalyst. Clean up of a Bordeaux mixture effluent (BME, 69 μM Cu) by A. donax was tested in a pilot-scale CW. The BME was decontaminated in 48 hours, its Cu concentration being in compliance for indirect discharge of chemical industry effluents. However, after one BME circulation cycle, root Cu concentration of A. donax roots (623 ± 140 mg kg-1) was lower than threshold value for Cu-ecocatalysts (1000 mg kg-1) and successive treatments must be repeated to achieve required Cu concentration.