The aim was to use the agricultural weed and silica (Si) hyperaccumulator Equisetum arvense as Si fertilizer in plant cultivation. We investigated (1) the Si uptake in various Equisetum species, (2) where Si accumulates in the Equisetum plant, (3) processing methods to release as much Si as possible from dried, ground E. arvense plants and (4) which treatment yields gives the highest uptake of Si in young wheat plants cultivated in soil containing ground E. arvense . The results showed that E. arvense containes 22% Si and was among the best Si accumulators. Equisetum arvense accumulates Si as both soluble and firmly bound fractions. Amorphous silica (SiO 2 ) accumulates in the outer cell walls of epidermis of the entire plant. Regarding the processing method, a longer treatment time, greater concentration of Equisetum , boiling, and the addition of sodium bicarbonate increased the Si availability in ground, dried E. arvense . The addition of untreated, ground, dried E. arvense to the soil, corresponding to 160 kg Si ha -1 , increased the available Si in the soil and the Si uptake in wheat plants by five -fold, compared with the control. Boiling the ground E. arvense increased the Si uptake by 10 times, and the of sodium bicarbonate increased the availability and uptake by 40 times, compared with the control. In conclusion, dried, ground E. arvense can be used as a Si fertilizer as is, after boiling for a slightly better effect, or with sodium bicarbonate (up to a similar amount as the ground material) for best effect.

The potential of arsenic (As) tolerant and sensitive varieties of wheat (Triticum aestivum L.) has yet to be explored despite of alarming situation of arsenic toxicity. To fill this gap, the study aimed to explore the role of antioxidants, phytochelatins, and ascorbate–glutathione for As tolerance in wheat. A total of eight varieties were exposed to different arsenate treatments (0, 1, 5, 10, 50, 100, 200, 500, 1000, 2000, and 10,000 μM) initially to screen effective treatment as well as contrasting varieties via Weibull distribution frequency for further analysis. The Weibull analysis found 200 μM as the most effective treatment in the present study. Selected varieties were analyzed for accumulation of total As and As speciation, oxidative stress (malondialdehyde, hydrogen peroxide), antioxidants (superoxide dismutase, catalase, peroxidase), phytochelatins, and ascorbate–glutathione cycle (glutathione-S-transferase, glutathione reductase, glutathione peroxidase, ascorbate peroxidase). Tolerant varieties showed less accumulation and translocation of total As, arsenate, and arsenite to the shoots compared with sensitive varieties under 200 μM treatment. Low concentration in tolerant varieties correlated with better growth and development response. Tolerant varieties showed higher induction of metabolites (glutathione, phytochelatins) compared to sensitive ones. Furthermore, tolerant varieties showed better performance of antioxidant and ascorbate–glutathione cycle enzymes in response to As exposure. The findings of the present study provided great insight into the wheat tolerance mechanism upon As exposure between contrasting varieties.

We have found that aquatic plants can reduce the content of perfluorinated alkyl substances (PFAS) within a short period of time. The aim of this study was to determine the variation in the uptake of PFAS from contaminated water by various wetland plant species, investigate the effect of biomass on PFAS removal, and determine whether laccases and peroxidases are involved in the removal and degradation of PFAS. Seventeen emergent and one submerged wetland plant species were screened for PFAS uptake from highly contaminated lake water. The screening showed that Eriophorum angustifolium, Carex rostrata, and Elodea canadensis accumulated the highest levels of all PFAS. These species were thereafter used to investigate the effect of biomass on PFAS removal from water and for the enzyme studies. The results showed that the greater the biomass per volume, the greater the PFAS removal effect. The plant-based removal of PFAS from water is mainly due to plant absorption, although degradation also occurs. In the beginning, most of the PFAS accumulated in the roots; over time, more was translocated to the shoots, resulting in a higher concentration in the shoots than in the roots. Most PFAS degradation occurred in the water; the metabolites were thereafter taken up by the plants and were accumulated in the roots and shoots. Both peroxidases and laccases were able to degrade PFAS. We conclude that wetland plants can be used for the purification of PFAS-contaminated water. For effective purification, a high biomass per volume of water is required.

The sediments of rivers or harbours have always been considered sinks for numerous heavy metals, pesticides, chemicals and contaminants of anthropogenic origin. The eco-friendly management of contaminated sediment have received attention due to their large-scale presence in harbour areas. Application of bioenergy crop species, such as Salix spp., have shown a strong potential for reducing heavy metals from the contaminated sediment. The aim of this study was to investigate the application of Salix spp. on contaminated dredged sediment and heavy metal accumulation and translocation patterns in different parts of plants. Two Salix cultivars (Wilhelm and Ester; commercially available in Sweden) were cultivated in contaminated sediment for 5 weeks in a field setting. Heavy metals (Cd, Cu, Pb, Ni and Zn) content in different plant parts (root, cutting, shoot and leaves) were analysed by using atomic absorption spectrophotometer (AAS). The result indicated that the root biomass production was negatively affected for both cultivars due to the contaminated sediment medium, even though no morphological symptoms were present. Both Cd and Cu net accumulation were found to be significantly higher in Ester cultivars. The low translocation of heavy metals in Salix spp. hints that accumulated heavy metals are stored in the root parts. Low translocation of heavy metals from contaminated sediments gives a strong potential for using a growth medium to utilize phosphorus (P) in the sediment from a circular economy and bioeconomy perspective.

Contaminant monitoring in biota is important for determining environmental status and to detect or prioritize action on hazardous substances. Predators higher up a food chain are often used for monitoring of contaminants that bioaccumulate. However, it is not always possible to find higher predators that are both abundant and have a wide distribution for national or international contaminant monitoring. Great cormorants (Phalocrocorax carbo) are a widespread and increasingly common top predator of fish in fresh, brackish and salt water. We evaluate the suitability of great cormorant eggs as a matrix for contaminant monitoring by using stable isotopes of carbon, nitrogen and sulfur. Despite the fact that cormorants are migratory, egg isotope values showed a significant separation between five breeding colonies in Sweden (1 fresh water lake, 3 Baltic sites and 1 marine site). This high degree of separation indicates that eggs are primarily produced using local resources (not stored body resources) and that contaminants (mercury concentrations in this study) measured in eggs likely reflect levels in fish prey caught close to the breeding area. Compound specific stable isotope analysis was used to estimate cormorant trophic position (TP) and concentrations of mercury in eggs were positively related to TP. The results show that a multi-isotope approach, combined with good ecological diet knowledge allow for meaningful and comparative interpretation of mercury concentrations in biota and that great cormorant eggs appear a suitable matrix to measure locally derived and maternally transferred contaminants.

In the environment, heavy metals are major stressors for plants, and since plants are immobile, they cannot avoid the stress but must adapt. Therefore, plants may develop avoidance and tolerance mechanisms to reduce susceptibility to metal toxicity. Salix is often found at metal-contaminated sites and, thus, is likely to have evolved mechanisms to adapt with heavy metals.

The aim of this thesis was to identify heavy metal-related traits like tolerance, uptake, accumulation, and root-shoot translocation in Salix and to find potential physiological processes that explain those traits. In addition, Salix’s potential for removing heavy metals from polluted soil, i.e., for phytoremediation, was to be investigated.

About 130 clones of Salix were analysed and characterized regarding tolerance to, uptake of, accumulation, and translocation of cadmium, copper, and zinc. The heredity of these traits, as well as potential tolerance mechanisms such as the induction of phytochelatin production to bind metals, the production of stress-related signalling substances like salicylic acid, antioxidant defence mechanisms, reactions to treatment with nicotinic acid or nicotinamide, preventive uptake or efflux of metals and possible metal-metal interactions, were investigated. Furthermore, the potential for phytoremediation was studied in the field, i.e., in agricultural and industrial polluted soil.

The results showed a significant variation in all the analysed traits for all metals. The correlations between the traits were that all traits had high heredity was high for all traits. Phytochelatins were not found. The activity of ascorbate peroxidase, guaiacol peroxidase, and superoxide dismutase increased in response to metal treatments with no differences between tolerant and sensitive clones. Catalase activity decreased in response to all heavy metals examined. Salicylic acid levels were not affected by heavy metals. Glutathione levels increased to Cu and Zn treatments but not to Cd. Lipid peroxidation (measured as thiobarbituric acid-reactive materials) increased the response to all treatments, more in roots of tolerant clones and in shoots of sensitive clones. Nicotinic acid and nicotinamide treatments decreased the toxic effects of heavy metals in sensitive, but not tolerant clones. 

Zinc net uptake increased in the presence of Cu and Cd in all clones, while Cd uptake was not affected by interactions with Cu or Zn. Net uptake of Cu decreased in the presence of Cd and Zn in highly tolerant clones. Cd uptake was lower in sensitive low-accumulating and higher in tolerant high-accumulating clones. Zn uptake did not differ between clones. Leakage was similar in untreated and pre-treated plants for Zn and Cd but faster in tolerant low accumulators of Cd and in tolerant high accumulators of Zn. Salix plants from polluted areas showed high accumulation in root and low translocation to shoots, combined with higher internal tolerance than clones from unpolluted sites. 

Salix cultivation led to significant soil decontamination from heavy metals and organic pollutants already after two years. After ten years of Salix cultivation, contaminant levels had decreased by 20% to 87%, depending on the contaminant. In agricultural soil, wheat cultivated after four years of Salix had up to 33% lower Cd levels in the grains, and Cd levels in the soil were reduced by up to 27%.

These results show that Salix has no dominant mechanisms for the heavy metal-related traits investigated. In any case, the ability of Salix to accumulate high levels of heavy metals can be used in phytoremediation

In our previous work, we used Salix viminalis in the field to decontaminate agricultural soils containing cadmium. Our aim in the current study was to determine whether S. viminalis could decrease the levels of heavy metals, arsenic, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in industrial soil at a former workshop site. The site was planted with S. viminalis cuttings in July 2003. Soil samples were collected yearly from 2005 to 2015 and analysed for heavy metals, arsenic, PCBs and PAHs. The results showed that 21% of chromium, 30% of arsenic, 54% of cadmium, 61% of zinc, 62% of copper, 63% of lead, 87% of nickel, 53% of PCBs and up to 73% of PAHs were removed from the soil after 10 years of S. viminalis treatment. After just 1 year of Salix cultivation, a significant decrease was observed in most of the contaminants in the soil. The reduction in contaminants was linear at first but slowed down after a few years. The number of years prior to a slow-down in rate of removal differed between the contaminants. This study concludes that S. viminalis can be used for the phytoremediation of contaminated industrial soil and that the rate of decontamination differs between substances.

This study evaluated the effects of salicylic acid (SA), beeswax waste extract (BWE) and licorice extract (LE) as novel biostimulants, on drought-induced oxidative stress on sesame. The treatments consisted of three drought stress conditions (full irrigation, 90 % field capacity (FC); moderate stress, 60 % FC; and severe stress, 30 % FC) together with four exogenous foliar applications (control, water; LE, 5000 ppm; BWE, 2000 ppm; and SA, 1.5 mM). Plants subjected to drought stress displayed significant reduction in plant height, leaf area index, biological and seed yield, chlorophyll a and b content, quantum efficiency of photosystem II (Fv/Fm), net photosynthetic rate (P-n), stomatal conductance (g(s)), transpiration (T-r) and water use efficiency (WUE). Drought stress stimulated Malondialdehyde (MDA), proline, protein and carotenoid contents, and catalase (CAT), ascorbate peroxidase (APX), Guaiacol peroxidase (GPX) and glutathione reductase (GR) activity, while the exogenous foliar application of substances mitigated the oxidative damages. The alleviated effect of BWE on drought stress was more effective than those of LE and SA. In conclusion, it could be recommended that the application of the natural substances may lead to overcoming the negative effects of drought stress by regulating osmoprotectants content and antioxidant defense system, increasing mineral nutrients in plant organs and adjusting photosynthesis systems; consequently, contributing to improving the sesame productivity.

Benthic ecosystems have come under intense pressure, due to eutrophication-driven oxygen decline and industrial metal contamination. One of the most toxic metals is Cadmium (Cd), which is lethal to many aquatic organisms already at low concentrations. Denitrification by facultative anaerobic microorganisms is an essential process to transform, but also to remove, excess nitrate in eutrophied systems. Cd has been shown to decrease denitrification and sequester free sulfide, which is available when oxygen is scarce and generally inhibits complete denitrification (i.e. N2O to N2). In polluted sediments, an interaction between oxygen and Cd may influence denitrification and this relationship has not been studied. For example, in the Baltic Sea some sediments are double exposed to both Cd and hypoxia. In this study, we examined how the double exposure of Cd and fluctuations in oxygen affects denitrification in Baltic Sea sediment. Results show that oxygen largely regulated N2O and N2 production after 21 days of exposure to Cd (ranging from 0 to 500 μg/L, 5 different treatments, measured by the isotope pairing technique (IPT)). In the high Cd treatment (500 μg/L) the variation in N2 production increased compared to the other treatments. Increases in N2 production are suggested to be an effect of 1) enhanced nitrification that increases NO3− availability thus stimulating denitrification, and 2) Cd successfully sequestrating sulfide (yielding CdS), which allows for full denitrification to N2. The in situ field sediment contained initially high Cd concentrations in the pore water (∼10 μg/L) and microbial communities might already have been adapted to metal stress, making the effect of low Cd levels negligible. Here we show that high levels of cadmium pollution might increase N2 production and influence nitrogen cycling in marine sediments.

Cadmium (Cd) can stress plants by affecting various physiological functions. Cd stress-response mechanisms were investigated in two genotypes of domesticated safflower (Carthamus tinctorius) and a population of wild safflower (Carthamus oxycantous) to explore potential differences in tolerance mechanisms of these species. A hydroponic experiment was conducted with 6-day-old safflower plants. Genotypes AC-Sterling (tolerant) and Saffire (semi-tolerant) from C. tinctorius, and Arak (sensitive) a population from C. oxycantouswere subjected to three concentrations of Cd (i.e., 0, 1, and 20 mu M CdCl2). Genotypic differences were detected in Cdtolerance index, Cd concentration in shoots and roots, Cd translocation to shoots, Cd bound to cell walls, superoxide dismutase (SOD) activity, lipid peroxidation, and phytochelatins accumulation in safflower plants upon exposure to CdCl2. Results indicate that genotypic differences were more obvious in the presence of low (i.e., 1 mu M) rather than high (i.e., 20 mu M) CdCl2 concentrations. Comparing genotypes, root and shoot Cd accumulation was highest in the semi-tolerant genotype. Cadmium translocation to shoots was increased with increasing tolerance. The percentage of Cd bound to root cell walls was higher in the tolerant genotype, but only with low CdCl2 addition. Furthermore, in the tolerant genotype, SOD activity was lowest in both roots and shoots with low CdCl2 addition but highest with high CdCl2 addition, while the opposite was found for phytochelatins. Lipid peroxidation was decreased with Cd tolerance at both CdCl2 concentrations. We conclude that safflower relies mainly on binding Cd to the cell walls and the formation of phytochelatins in root and shoot tissues, in order to handle the Cd stress, evidenced by lessening Cd-induced lipid peroxidation.