Elisabeth Eiche

Hazardous concentrations of selenium in soil and groundwater in North-West India

Soil and groundwater samples were collected for bulk elemental analyses in particular for selenium (Se) concentrations from six agricultural sites located in states of Punjab and Haryana in North-West India. Toxic concentrations of Se (45-341 μg L(-1)) were present in groundwater (76 m deep) of Jainpur and Barwa villages in Punjab. Selenium enrichments were also found in top soil layers (0-15 cm) of Jainpur (2.3-11.6 mg kg(-1)) and Barwa (3.1 mg kg(-1)). Mineralogical analyses confirmed silicates and phyllosilicates as main components of these soils, also reflected by the high content of SiO(2) (40-62 wt.%), Al(2)O(3) (9-21 wt.%) and K(2)O (2.2-3.2 wt.%). Prevailing intensive irrigation practices in Punjab with Se enriched groundwater may be the cause of Se accumulation in soils. Sequential extraction revealed >50% Se bioavailability in Jainpur soils. Appearance of selenite was observed in some of the batch assays with soil slurries under reducing conditions. Although safe Se concentrations were found in Hisar, Haryana, yet high levels of As, Mo and U present in groundwater indicated its unsuitability for drinking purposes. Detailed biogeochemical studies of Se in sediments or groundwater of Punjab are not available so far; intensive investigations should be started for better understanding of the problem of Se toxicity.

Increased tolerance to salt stress in OPDA-deficient rice ALLENE OXIDE CYCLASE mutants is linked to an increased ROS-scavenging activity

Highlight The lack of the jasmonic acid precursor 12-oxophytodienoic acid in rice led to increased salt tolerance, which is correlated with an increased ROS-scavenging activity in stress conditions.

Selenium distribution and speciation in plant parts of wheat (Triticum aestivum) and Indian mustard (Brassica juncea) from a seleniferous area of Punjab, India

The concentration, distribution, and speciation of selenium in different parts of wheat and Indian mustard, grown in a seleniferous area in Punjab, were investigated using synchrotron based (XAS) and classical acid digestion and extraction methods. The analyses revealed a high Se enrichment in all investigated plant parts, with Se levels in the range of 133-931 mg/kg (dry weight, dw). Such high Se enrichment is mainly due to the considerable amounts of easily available Se detected in the soil, which are renewed on a yearly basis to some extent via irrigation. Speciation analysis in soil and plants indicated selenate and organic Se as major Se species taken up by plants, with a minor presence of selenite. The analyses also revealed that the highest Se enrichment occurs in the upper plant parts, in agreement with the high uptake rate and mobility of selenate within plants. In both wheat and mustard, highest Se enrichments were found in leaves (387 mg/kg·dw in wheat and 931 mg/kg·dw in mustard). Organic species (dimethylselenide and methylselenocysteine) were found in different parts of both plants, indicating that an active detoxification response to the high Se uptake is taking place through methylation and/or volatilization. The high proportion of selenate in wheat and mustard leaves (47% and 70%, respectively) is the result of the inability of the plant metabolism to completely transform selenate to non-toxic organic forms, if oversupplied. Methylselenocysteine, a common Se species in accumulating plants, was detected in wheat, suggesting that, in the presence of high Se concentration, this plant develops similar response mechanisms to accumulator plants.

Determination of microplastic polyethylene (PE) and polypropylene (PP) in environmental samples using thermal analysis (TGA-DSC)

Microplastics are increasingly detected in the environment and the consequences on water resources and ecosystems are not clear to date. The present study provides a cost-effective and straightforward method to determine the mass concentrations of polymer types using thermal analysis. Characteristic endothermic phase transition temperatures were determined for seven plastic polymer types using TGA-DSC. Based on that, extracts from wastewater samples were analyzed. Results showed that among the studied polymers, only PE and PP could be clearly identified, while the phase transition signals of the other polymers largely overlap each other. Subsequently, calibration curves were run for PE and PP for qualitative measurements. 240 and 1540mg/m(3) of solid material (12µm to 1mm) was extracted from two wastewater effluent samples of a municipal WWTP of which 34% (81mg/m(3)) and 17% (257mg/m(3)) could be assigned to PE, while PP was not detected in any of the samples. The presented application of TGA-DSC provides a complementary or alternative method to FT-IR analyses for the determination of PE and PP in environmental samples.

Salt adaptation requires efficient fine-tuning of jasmonate signalling.

Understanding the mechanism by which plants sense, signal and respond to salinity stress is of great interest to plant biologists. In stress signalling, often the same molecules are involved in both damage-related and adaptive events. To dissect this complexity, we compared the salinity responses of two grapevine cell lines differing in their salinity tolerance. We followed rapid changes in the cellular content of sodium and calcium, apoplastic alkalinisation and slower responses in the levels of jasmonic acid, its active isoleucine conjugate and abscisic acid, as well as of stilbenes. Differences in timing and sensitivity to either the lanthanoid Gd or exogenous calcium provide evidence for an adaptive role of early sodium uptake through non-selective cation channels acting upstream of Ca2+ and H+ fluxes. We find a correlation of salt sensitivity with unconstrained jasmonate (JA) signalling, whereas salt adaptation correlates with tight control of jasmonic acid and its isoleucine conjugate, accompanied by accumulation of abscisic acid and suppression of stilbenes that trigger defence-related cell death. The data are discussed by a model where efficient fine-tuning of JA signalling determines whether cells will progress towards adaptation or programme cell death.

Geochemical changes in individual sediment grains during sequential arsenic extractions

High concentrations of As in groundwater frequently occur throughout the world. The dissolved concentration, however, is not necessarily determined by the amount of As in the ambient sediment but rather by the partitioning of As between different minerals and the type of fixation. Sequential extractions are commonly applied to determine associations and binding forms of As in sediments. Due to the operational nature of the extracted fractions, however, the results do not provide insight into how and where precisely As is bound within mineral grains and no information about elemental associations or involved mineral phases can be gained. Furthermore, little is known about possible geochemical alterations that actually occur within a single grain during sequential extraction. Therefore, micro-synchrotron X-ray fluorescence analysis was applied to study the micro-scale distribution of As and other elements in single sediment grains. Arsenic was found to be mainly enriched in Fe oxy-hydroxide coatings along with other heavy metals resulting in high correlations. Phosphate leached 34-66% of As from the studied grains. The release of As in this leaching step was accompanied by the disappearance of correlations between As and Fe as well as by a higher Fe/As ratio compared to untreated samples. During the Fe-leaching step the coatings were largely dissolved leading to much lower concentrations of As and Fe. The correlation between As and Fe was preserved only in association with K, indicating the presence of both elements in silicate structures. Several distinctive features were observed such as the release of Fe, Mn and Cr during phosphate leaching as well as the lowering of mean K concentrations due to the Fe-leaching which indicates that not only target mineral phases were dissolved in these extraction steps. The importance of re-precipitation processes during sequential extraction was indicated by a consistently observed increase of the Fe/As ratio from the untreated to the Fe-leached samples.

Tracking Se Assimilation and Speciation through the Rice Plant - Nutrient Competition, Toxicity and Distribution.

Up to 1 billion people are affected by low intakes of the essential nutrient selenium (Se) due to low concentrations in crops. Biofortification of this micronutrient in plants is an attractive way of increasing dietary Se levels. We investigated a promising method of Se biofortification of rice seedlings, as rice is the primary staple for 3 billion people, but naturally contains low Se concentrations. We studied hydroponic Se uptake for 0–2500 ppb Se, potential phyto-toxicological effects of Se and the speciation of Se along the shoots and roots as a function of added Se species, concentrations and other nutrients supplied. We found that rice germinating directly in a Se environment increased plant-Se by factor 2–16, but that nutrient supplementation is required to prevent phyto-toxicity. XANES data showed that selenite uptake mainly resulted in the accumulation of organic Se in roots, but that selenate uptake resulted in accumulation of selenate in the higher part of the shoot, which is an essential requirement for Se to be transported to the grain. The amount of organic Se in the plant was positively correlated with applied Se concentration. Our results indicate that biofortification of seedlings with selenate is a successful method to increase Se levels in rice.

Arsenic Mobilization from Historically Contaminated Mining Soils in a Continuously Operated Bioreactor: Implications for Risk Assessment

Concentrations of soil arsenic (As) in the vicinity of the former Złoty Stok gold mine (Lower Silesia, southwest Poland) exceed 1000 μg g(-1) in the area, posing an inherent threat to neighboring bodies of water. This study investigated continuous As mobilization under reducing conditions for more than 3 months. In particular, the capacity of autochthonic microflora that live on natural organic matter as the sole carbon/electron source for mobilizing As was assessed. A biphasic mobilization of As was observed. In the first two months, As mobilization was mainly conferred by Mn dissolution despite the prevalence of Fe (0.1 wt % vs 5.4 for Mn and Fe, respectively) as indicated by multiple regression analysis. Thereafter, the sudden increase in aqueous As[III] (up to 2400 μg L(-1)) was attributed to an almost quintupling of the autochthonic dissimilatory As-reducing community (quantitative polymerase chain reaction). The aqueous speciation influenced by microbial activity led to a reduction of solid phase As species (X-ray absorption fine structure spectroscopy) and a change in the elemental composition of As hotspots (micro X-ray fluorescence mapping). The depletion of most natural dissolved organic matter and the fact that an extensive mobilization of As[III] occurred after two months raises concerns about the long-term stability of historically As-contaminated sites.

Different forms of osmotic stress evoke qualitatively different responses in rice

Drought, salinity and alkalinity are distinct forms of osmotic stress with serious impacts on rice productivity. We investigated, for a salt-sensitive rice cultivar, the response to osmotically equivalent doses of these stresses. Drought, experimentally mimicked by mannitol (single factor: osmotic stress), salinity (two factors: osmotic stress and ion toxicity), and alkalinity (three factors: osmotic stress, ion toxicity, and depletion of nutrients and protons) produced different profiles of adaptive and damage responses, both locally (in the root) as well as systemically (in the shoot). The combination of several stress factors was not necessarily additive, and we even observed cases of mitigation, when two (salinity), or three stressors (alkalinity) were compared to the single stressor (drought). The response to combinations of individual stress factors is therefore not a mere addition of the partial stress responses, but rather represents a new quality of response. We interpret this finding in a model, where the output to signaling molecules is not determined by their abundance per se, but qualitatively depends on their adequate integration into an adaptive signaling network. This output generates a systemic signal that will determine the quality of the shoot response to local concentrations of ions.

Characterization of recharge and flow behaviour of different water sources in Gunung Kidul and its impact on water quality based on hydrochemical and physico-chemical monitoring

Karst aquifers are important water resources but highly vulnerable due to their heterogeneous and complex characteristics. Various hydrological aspects (recharge, flow behaviour) have to be known in detail to develop a sustainable concept for water collection, distribution and treatment. In the karst area of Gunung Sewu (Java, Indonesia) such a concept was to be implemented within a German–Indonesian joint IWRM project. The basic hydrogeological conditions and water quality aspects were characterized on a regional scale through hydrochemical monitoring of springs, wells, subsurface and surface rivers. More detailed information about the recharge, flow and storage behaviour was obtained from high resolution monitoring of T, EC and discharge in one large underground river system. The water quality is well below any guideline values with regard to inorganic pollutants during dry season. During rainy season, dissolved Al concentrations are frequently above the Indonesian guideline value. Slow matrix flow is the most important recharge component during dry season, thus assuring the year-round water availability in the subsurface karst. During rainy season, quick infiltration of the surface water is a dominant recharge component. Rapid response of discharge, T and EC to heavy rain suggests the presence of point recharge that feeds a highly karstfied conduit system with fast conduit flow and short transit time of water. The strong variations in discharge and hydrochemistry are particularly challenging for technical water usage and treatment facilities. Piston flow is indicated to be the third important flow component and is induced by heavy rainfall.