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The macrophytes have the ability accumulating multiple metals/metalloids species from the terrestrial and aquatic environments. The environmental-friendly phytoremediation technologies via these plant species have been applied for non-degradable pollutants removal. The macrophytes derived rhizofiltration is a major and efficient technology for metals/metalloids removal, especially in aquatic environments (e.g. wetland). Comparing with the common metals/metalloids often studied, aquatic U rhizofiltration via macrophytes has been just considered recently. In this study, the field investigation in a U tailing basin wetland showed that the rhizofiltration was crucial for aquatic U retention via Phragmites australis Trin ex Steud. (water to root bioconcentration factor (BCF): 670 to 1556). The aquatic U retention efficiency in aboveground biomass of P. australis was insufficient (BCF: 0.4 to 5.3), comparing with the rhizofiltration. However, the high productivity (1.2 to 1.9 kg•m-2 per growing season) of P. australis still resulted in a notable yearly U accumulation in the areal total aboveground biomass (0.04 to 0.35 mg•m-2 per growing season). It was potentially promoted by the enhanced aquatic U rhizofiltration. The U within aboveground biomass could be released to submerse soil with the degradable or recalcitrant fallen litters. It enhanced the organic carbon supply in rhizosphere together with the root litter, and potential water to root U translocation within mobilized organic compounds. Hence the rhizofiltration stood in the crucial position of the plant-litter-water-soil U recycling in aquatic environment. The results from field investigation and mesocosm experiment further suggested that the Fe plaque (IP) on root surface was crucial for aquatic U rhizofiltration. The IP contained most of root retained U in both environments (proportion of U within IP: 55.8 to 82.6% in field and 66.7 to 86.0% in mesocosm). However, the efficiency of IP assisted aquatic U rhizofiltration was affected by the redox state gradient (-179 to 220 mV) related redox processes. Field investigation suggested that high content of dissolved oxygen (up to 8.2 mg•l-1) was capable to rapidly oxidize soluble Fe(II) as sparingly soluble Fe(III) oxides precipitated in subhydric soil. It consequently limited the aquatic Fe availability for root uptake and precipitation as IP. However, the strong oxidation ability also relatively increased aquatic U(VI) availability incorporated with inorganics and degradable organic matters. It was adverse for controlling the aquatic U concentration (66.7 to 92.0 μg•l-1 in field). On the other hand, it also benefited the U uptake by inner root tissue and upward translocation to aboveground biomass of P. australis. The different inorganic N species also significantly influenced IP assisted aquatic U rhizofiltration. The aquatic NH4+ sustained the reduction and acidification (via nitirification) potential for Fe(III) and U(VI) bioreduction in rhizosphere (-87 to 21 mV in NH4+ cultured mesocosm pots). It improved the root uptake (mainly within IP) of Fe and U (2992.9 to 5010.7 mg•kg-1 Fe and 45.7 to 62.8 mg•kg-1 U in NH4+ cultured root). On the contrary, the NO3- depended strong oxidation ability (23 to 224 mV in NO3- cultured mesocosm pots) inhibited the IP formation and the related aquatic U rhizofiltration efficiency (1568.5 to 2569.5 mg•kg-1 Fe and 26.2 to 49.6 mg•kg-1 U in NO3- cultured root). The aquatic U availability in rhizosphere was also increased via NO3- depended oxidation processes (aquatic U concentration in mesocosm: 1.6 to 589.3 μg•L-1 (NO3-) vs. 1.4 to 58.2 μg•L-1 (NH4+)). The sufficient nitrogen supply is also a significant driving force for high biomass productivity of P. australis. The higher biomass of P. australis increased the U accumulation capacity for root and aboveground tissues. The nitrogen related high biomass accumulation of P. australis also potentially enhanced the share of organic bound U in subhydric soil via plant litters supply. The IP assisted aquatic U rhizofiltration was also affected by the co-existing metals/metalloids in rhizosphere. The field investigation indicated that high As availability (aquatic As/U ratio: 0.7 to 1.6) inhibited the U retention within IP through the competitive absorption, due to its high affinity to IP. The Ca improved the aquatic U(VI) availability by forming the soluble Ca-uranyl-carbonate compounds. The Ca also potentially competed with hydrated Fe(III) oxides within IP by incorporating with U and encourage the U retention within inner root tissue. The P was beneficial for U retention within IP possibly in form of U-Fe-phosphate complexes. However, it was still need to be proofed in further studies. Despite of the biogeochemical conditions in rhizosphere, the aboveground transpiration of P. australis also affected the IP formation and related aquatic U rhizofiltration. The higher transpiration rate (TR) of P. australis (3.3±1.2 mm•d-1 in field, 4.5±2.0 mm•d-1 (NH4+)/5.0±2.2 mm•d-1(NO3-) in mesocosm) increased the aquatic nutrient/non-essential elements availability for root uptake. For this reason, the aquatic U rhizofiltration of P. australis (21.8±3.1 mg•kg-1 in field, 62.1±1.0 mg•kg-1 (NH4+)/47.6±1.8 mg•kg-1 (NO3-) in mesocosm) was enhanced under higher TR. The higher TR also promoted the formation of IP and its U retention capacity. Furthermore, the U translocation from root to above ground biomass (mainly in leaves) of P. australis was also enhanced under higher TR. It was potentially benefited by the increased transpirational pull and root uptake of other active mediator (e.g. Ca). The effect of transpiration was also coupled with the different N species on IP assisted aquatic U rhizofiltration. The higher TR depended strong root uptake and assimilation of N increased the biomass accumulation of P. australis. Furthermore, the higher TR also potentially increased the share of root in biomass partition of P. australis. Consequently, the stronger transpiration resulted in the higher aquatic U accumulation in area related root biomass (up to 84.0±3.6 mg•m-2 (NH4+) and 86.4±5.8 mg•m-2 (NO3-) U per season in mesocosm). In conclusion, it was possible for eutrophic P. australis stands to retain the aquatic U via rhizofiltration. The IP on root surface was a crucial mediator contributing the aquatic U rhizofiltration, especially in iron rich milieu. The efficiency of IP assisted aquatic U rhizofiltration could be further improved under suitable environmental conditions. In this study, these conditions might include: i) reductive rhizosphere environment with active reducers (e.g. NH4+) encouraging Fe(II) generation for IP formation and U retention within it; ii) limited competitive elements (e.g. As and Ca) co-existed with Fe and U in rhizosphere; iii) sufficient nutrients (e.g. N) supply and related high biomass productivity of plant; iv) strong transpiration effect improved the nutrient assimilation of root and also the aquatic U/Fe availability for root uptake. By adjusting these conditions (also include other potential factors not discussed in this study), an effective rhizofiltration technology was supposed to be applied for aquatic U removal.

The macrophytes have the ability accumulating multiple metals/metalloids species from the terrestrial and aquatic environments. The environmental-friendly phytoremediation technologies via these plant species have been applied for non-degradable pollutants removal. The macrophytes derived rhizofiltration is a major and efficient technology for metals/metalloids removal, especially in aquatic environments (e.g. wetland). Comparing with the common metals/metalloids often studied, aquatic U rhizofiltration via macrophytes has been just considered recently. In this study, the field investigation in a U tailing basin wetland showed that the rhizofiltration was crucial for aquatic U retention via Phragmites australis Trin ex Steud. (water to root bioconcentration factor (BCF): 670 to 1556). The aquatic U retention efficiency in aboveground biomass of P. australis was insufficient (BCF: 0.4 to 5.3), comparing with the rhizofiltration. However, the high productivity (1.2 to 1.9 kg•m-2 per growing season) of P. australis still resulted in a notable yearly U accumulation in the areal total aboveground biomass (0.04 to 0.35 mg•m-2 per growing season). It was potentially promoted by the enhanced aquatic U rhizofiltration. The U within aboveground biomass could be released to submerse soil with the degradable or recalcitrant fallen litters. It enhanced the organic carbon supply in rhizosphere together with the root litter, and potential water to root U translocation within mobilized organic compounds. Hence the rhizofiltration stood in the crucial position of the plant-litter-water-soil U recycling in aquatic environment. The results from field investigation and mesocosm experiment further suggested that the Fe plaque (IP) on root surface was crucial for aquatic U rhizofiltration. The IP contained most of root retained U in both environments (proportion of U within IP: 55.8 to 82.6% in field and 66.7 to 86.0% in mesocosm). However, the efficiency of IP assisted aquatic U rhizofiltration was affected by the redox state gradient (-179 to 220 mV) related redox processes. Field investigation suggested that high content of dissolved oxygen (up to 8.2 mg•l-1) was capable to rapidly oxidize soluble Fe(II) as sparingly soluble Fe(III) oxides precipitated in subhydric soil. It consequently limited the aquatic Fe availability for root uptake and precipitation as IP. However, the strong oxidation ability also relatively increased aquatic U(VI) availability incorporated with inorganics and degradable organic matters. It was adverse for controlling the aquatic U concentration (66.7 to 92.0 μg•l-1 in field). On the other hand, it also benefited the U uptake by inner root tissue and upward translocation to aboveground biomass of P. australis. The different inorganic N species also significantly influenced IP assisted aquatic U rhizofiltration. The aquatic NH4+ sustained the reduction and acidification (via nitirification) potential for Fe(III) and U(VI) bioreduction in rhizosphere (-87 to 21 mV in NH4+ cultured mesocosm pots). It improved the root uptake (mainly within IP) of Fe and U (2992.9 to 5010.7 mg•kg-1 Fe and 45.7 to 62.8 mg•kg-1 U in NH4+ cultured root). On the contrary, the NO3- depended strong oxidation ability (23 to 224 mV in NO3- cultured mesocosm pots) inhibited the IP formation and the related aquatic U rhizofiltration efficiency (1568.5 to 2569.5 mg•kg-1 Fe and 26.2 to 49.6 mg•kg-1 U in NO3- cultured root). The aquatic U availability in rhizosphere was also increased via NO3- depended oxidation processes (aquatic U concentration in mesocosm: 1.6 to 589.3 μg•L-1 (NO3-) vs. 1.4 to 58.2 μg•L-1 (NH4+)). The sufficient nitrogen supply is also a significant driving force for high biomass productivity of P. australis. The higher biomass of P. australis increased the U accumulation capacity for root and aboveground tissues. The nitrogen related high biomass accumulation of P. australis also potentially enhanced the share of organic bound U in subhydric soil via plant litters supply. The IP assisted aquatic U rhizofiltration was also affected by the co-existing metals/metalloids in rhizosphere. The field investigation indicated that high As availability (aquatic As/U ratio: 0.7 to 1.6) inhibited the U retention within IP through the competitive absorption, due to its high affinity to IP. The Ca improved the aquatic U(VI) availability by forming the soluble Ca-uranyl-carbonate compounds. The Ca also potentially competed with hydrated Fe(III) oxides within IP by incorporating with U and encourage the U retention within inner root tissue. The P was beneficial for U retention within IP possibly in form of U-Fe-phosphate complexes. However, it was still need to be proofed in further studies. Despite of the biogeochemical conditions in rhizosphere, the aboveground transpiration of P. australis also affected the IP formation and related aquatic U rhizofiltration. The higher transpiration rate (TR) of P. australis (3.3±1.2 mm•d-1 in field, 4.5±2.0 mm•d-1 (NH4+)/5.0±2.2 mm•d-1(NO3-) in mesocosm) increased the aquatic nutrient/non-essential elements availability for root uptake. For this reason, the aquatic U rhizofiltration of P. australis (21.8±3.1 mg•kg-1 in field, 62.1±1.0 mg•kg-1 (NH4+)/47.6±1.8 mg•kg-1 (NO3-) in mesocosm) was enhanced under higher TR. The higher TR also promoted the formation of IP and its U retention capacity. Furthermore, the U translocation from root to above ground biomass (mainly in leaves) of P. australis was also enhanced under higher TR. It was potentially benefited by the increased transpirational pull and root uptake of other active mediator (e.g. Ca). The effect of transpiration was also coupled with the different N species on IP assisted aquatic U rhizofiltration. The higher TR depended strong root uptake and assimilation of N increased the biomass accumulation of P. australis. Furthermore, the higher TR also potentially increased the share of root in biomass partition of P. australis. Consequently, the stronger transpiration resulted in the higher aquatic U accumulation in area related root biomass (up to 84.0±3.6 mg•m-2 (NH4+) and 86.4±5.8 mg•m-2 (NO3-) U per season in mesocosm). In conclusion, it was possible for eutrophic P. australis stands to retain the aquatic U via rhizofiltration. The IP on root surface was a crucial mediator contributing the aquatic U rhizofiltration, especially in iron rich milieu. The efficiency of IP assisted aquatic U rhizofiltration could be further improved under suitable environmental conditions. In this study, these conditions might include: i) reductive rhizosphere environment with active reducers (e.g. NH4+) encouraging Fe(II) generation for IP formation and U retention within it; ii) limited competitive elements (e.g. As and Ca) co-existed with Fe and U in rhizosphere; iii) sufficient nutrients (e.g. N) supply and related high biomass productivity of plant; iv) strong transpiration effect improved the nutrient assimilation of root and also the aquatic U/Fe availability for root uptake. By adjusting these conditions (also include other potential factors not discussed in this study), an effective rhizofiltration technology was supposed to be applied for aquatic U removal.

Precipitation over coal fly ash surfaces raises concerns about potential downstream impacts of dissolved selenium (Se) on aquatic ecosystems. Detention ponds hold runoff until aqueous Se concentrations meet water quality regulations: within 10 days, 90% of runoff must be discharged and cannot exceed 11.8 μg Se L-1 (ppb). Constructed wetland (CW) phytoremediation is a potential treatment option to meet these regulations. This research was conducted to 1.) Assess the potential of native southeastern aquatic macrophytes for Se tolerance and removal efficiency compared to unplanted (UNP) detention ponds; 2.) Evaluate seasonal influence on Se removal in CWs over four, weekly flood-discharge cycles; and 3.) Determine the effect of temperature on aqueous Se removal. Monoculture CW microcosms (110 L) were flooded six days with 500 or 1000 ppb Se, as selenite (SeO32-) or selenate (SeO42-) evaluating five plant species for Se tolerance. Seasonal evaluations were conducted with cattail (Typha angustifolia L.; CAT) and duckweed (Lemna minor L.; DWD) over four weekly flood-discharge cycles at 16 or 32 ppb SeO42--Se. Cattail, DWD, or UNP volatilization chambers (VCs) flooded with a 3 L solution at 35 ppb SeO42--Se were evaluated under 12 h photoperiod at either 20 or 30°C. All experiments contained a zero Se control. Water, plant, and soil total Se concentrations were determined by inductively coupled plasma-mass spectroscopy (ICP-MS) and analyzed with PROC GLM (SAS EG 7.1) at α=0.05. Cattail and DWD were selected for further evaluation with SeO42--Se. The greatest aqueous Se removal was observed in the summer (73%), followed by the fall (42%) and spring (41%), compared to winter (18%). Temperature was strongly correlated with Se removal (0.65, P<0.0001). Except for summer, after two flood-discharge cycles, CAT and DWD improved aqueous Se removal compared to UNP controls. Volatilization chamber data indicated greater Se removal at 30 (69%) compared to 20°C (54%). At 30°C, DWD decreased aqueous Se concentrations below 11.8 ppb Se within 10 days. Given their efficacy and abundance, CAT and DWD are deemed suitable species for phytoremediation in CWs supplied with Se-impacted waters.

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.

Det här arbetet ger en orientering i växters olika förmågor att rehabilitera miljöskador och belyser möjligheten att använda växternas essentiella och varierande förmågor i miljöarbetet. De ämnen som har skadlig inverkan på miljön kallas för miljögifter. Både globalt och i Sverige har omloppet av många miljögifter ökat markant de senaste århundradet. Växter kan användas för att rena förorenad mark. De olika processerna när växter renar mark, vatten och luft från föroreningar samlas under begreppet fytoremediering. Det finns olika metoder och reningsprocesser inom fytoremediering. Växter kan dels ta upp och lagra föroreningar, bryta ned dem till ofarliga beståndsdelar samt förhindra så att de inte sprider sig ut i ekosystemet. I det här examensarbetet har föroreningssituation vid järnvägsstationen i Ockelbo använts som exempel för att konkretisera fytoremediering till en specifik plats. En beskrivning av de till platsen relaterade föroreningarna arsenik, bly, kadmium, kvicksilver, koppar, zink, PAH (polycykliska aromatiska kolväten) och olja presenteras tillsammans med aktuella fytoremedieringsmetoder och grödor för respektive förorening. Som slutsats bedöms fytoremediering vara möjligt för järnvägsstationen i Ockelbo. Fördelar och nackdelar med fytoremediering på stationen lyfts fram och möjliga parallella användningsområden medan fytoremedieringen pågår diskuteras. Vidare diskussion förs kring fytoremediering, miljöfrågor och rådande regelverk och logistik i Sverige. Arbetet innefattar ett förslag till utformning av fytoremediering på stationsområdet. Förslaget inkluderar ett växtval av olika fytoremedieringsgrödor lämpliga för platsen.