Aqueous Soil Extracts Research Articles

The Problem of Comprehensive Analysis of Organic Agriculture as a Factor of Environmental Safety

Abstract The paper analyses certain aspects of organic agriculture and emphasises the need for an integrated approach in its research. The necessity of using ecologically safe agricultural production as a component of the development of modern civilized states is pointed out in the paper. The method of direct conductometry has been used to study the total mineral composition of plowed soils, which is considered as a component of “green” chemistry methods. The electrical conductivity of aqueous extracts of arable soils, in which mineral and organic fertilizers are applied, is measured. The obtained data vary between 10 and 220 μS. In the paper, for the first time, the regularities of fluctuations of the data of electrical conductivity of aqueous extracts of arable soils, in which various plant cultures had been grown, were revealed and mineral nitrogen fertilizers or organic fertilizers were introduced. Lower data of electrical conductivity are characteristic of plowed soils, in which mineral fertilizers are applied, which indirectly indicates their depletion. The advantage of using organic fertilizers as a necessary component of organic agriculture has been confirmed. It is noted that a promising area of the research is a complete use of an integrated approach to the organic agriculture being farmed in various European countries.

Dynamics of trace metals in the system water – soil – plant – wild rats – tapeworms (Hymenolepis diminuta) in Maglizh area, Bulgaria

BackgroundThe impact of chemical elements on the biosphere is a function of their concentration and chemical form. Elucidation and prognosing of the latters in water basins and soil extracts is of particular significance for the assessment of their bioaccumulation in plants and animals. ObjectivesTrace metals dynamics in the system water – soil–plant–wild rats – Hymenolepis diminuta in two agro-industrial zones (East and West) around Maglizh city, Bulgaria were investigated through experimental studies and thermodynamic modelling of the chemical species. MethodsSamples from surface waters of rivers, their nearby uncultivated soils, meadow uncultivated vegetation (Ranunculus acris and Gramineae) and field rats were collected. In situ measurements and laboratory analyses were performed for the determination of the physico-chemical characteristics and total concentrations of Al, Fe, Mn, Ni, Cu, Zn and Pb. The distribution of their dissolved chemical species in water samples and in the aqueous soil extracts was calculated using a thermodynamic approach. The relationship chemical species - bioaccumulation was discussed. ResultsWaters and soils in the East zone of Maglizh area were found to be more polluted compared to those in the West one, regarding Ni, Mn, Zn, Pb and Cu, while Mn and Cu displayed the highest mobility in West zone soils. Trace metals contents in Ranunculus acris exceed that in Gramineae, since the highest accumulation factors were calculated for Cu and Zn. The highest accumulation in rats was found for Zn followed by Cu, being higher in the West zone. Thermodynamic modelling shows that Mn2+ free ions are dominant in both waters and aqueous soil extracts. Ni2+ and Zn2+ ions followed by metal-organic complexes are dominant in waters of East zone while metal-organic complexes followed by free ions are dominant in waters of West zone and both soil extracts. Metal-organic complexes are dominant for Fe, Cu and Pb in all samples studied, while mainly hydroxy forms (Al(OH)4−) followed by metal-organic complexes are typically for Al depending on pH. ConclusionsExperimentally established bioaccumulation of trace metals in the studied vegetation and rats is a consequence of the total concentration of trace metals in waters and soils, their mobility and chemical species. The dominance of organic complexes of trace metals is a prerequisite for their bioaccumulation in plants. Rats are in direct contact with the soil solution and therefore, of importance is the content of free ions of Mn2+, Ni2+, Zn2+, which are easily absorbed through the skin. The host-helminth system wild rat/H. diminuta could be used as a bioindicator for trace metals pollution.

Soil Aggregates as a Source of Dissolved Organic Carbon to Streams: An Experimental Study on the Effect of Solution Chemistry on Water Extractable Carbon

Over the past two decades, headwater streams of the northern hemisphere have shown increased amounts of dissolved organic carbon (DOC), coinciding with decreased acid deposition. The exact nature of the mechanistic link between precipitation composition and stream water DOC is still widely debated in the literature. We hypothesize that soil aggregates are the main source of stream water DOC and that DOC release is greater in organic rich, riparian soils versus hillslope soils. To test these hypotheses, we collected soils from two main landscape positions (hillslope and riparian zones) from the acid-impacted Sleepers River Research Watershed in northeastern Vermont. We performed aqueous soil extracts with solutions of different ionic strength (IS) and composition to simulate changes in soil solution. We monitored dynamic changes in soil particle size, aggregate architecture and composition, leachate DOC concentrations, dissolved organic matter (DOM) characteristics with fluorescence spectroscopy and trends in bioavailability. In low IS solutions, extractable DOC concentrations were significantly higher, particle size (by laser diffraction) was significantly smaller and organic material was separated from mineral particles in scanning electron microscope observations. Furthermore, higher DOC concentrations were found in Na+ compared to Ca2+ solutions of the same IS. These effects are attributed to aggregate dispersion due to expanding diffuse double layers in decreased IS solutions and to decreased bridging by divalent cations. Landscape position impacted quality but not quantity of released DOC. Overall, these results indicate that soil aggregates might be one important link between Critical Zone inputs (i.e. precipitation) and exports in streams.

The Design and Synthesis of Fluorescent Coumarin Derivatives and Their Study for Cu2+ Sensing with an Application for Aqueous Soil Extracts.

A series of fluorescent coumarin derivatives 2a–e were systematically designed, synthesized and studied for their Cu2+ sensing performance in aqueous media. The sensitivities and selectivities of the on-to-off fluorescent Cu2+ sensing signal were in direct correlation with the relative arrangements of the heteroatoms within the coordinating moieties of these coumarins. Probes 2b and 2d exhibited Cu2+ concentration dependent and selective fluorescence quenching, with linear ranges of 0–80 μM and 0–10 μM, and limits of detection of 0.14 μM and 0.38 μM, respectively. Structural changes of 2b upon Cu2+ coordination were followed by fluorescence titration, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), mass spectrometry, and single crystal X-ray diffraction on the isolated Cu2+-coumarin complex. The results revealed a 1:1 stoichiometry between 2b and Cu2+, and that the essential structural features for Cu2+-selective coordination are the coumarin C=O and a three-bond distance between the amide NH and heterocyclic N. Probe 2b was also used to determine copper (II) levels in aqueous soil extracts, with recovery rates over 80% when compared to the standard soil analysis method: inductively coupled plasma-mass spectrometry (ICP-MS).

Destruction of herbicide atrazine by solar radiation in photo-Fenton system

The efficiency of solar-induced destruction of herbicide atrazine in natural water and aqueous extract from agrogenic and unbroken soil by using photo-Fenton system was studied in this work. 80-90 % atrazine was removed in all water matrices. Using xenon lamp as a solar simulator, the rate of atrazine destruction was found to be higher in aqueous soil extracts than that observed in natural water. However, no significant difference was found between the destruction dynamics in natural water and soil extracts, exposed to natural solar light. This could be attributed to the higher hydroxyl radical exposure under the higher UV irradiance of the Sun.

Spectrophotometric methods for the measurement of soil pH: A reappraisal

The pH of aqueous soil extracts is generally measured potentiometrically by glass electrode (GE). Spectrophotometric methods have also been used till around the '80s, and then they have apparently been abandoned. However, the use of microplates and spectrophotometers able to read absorbance values in them can significantly increase the speed of the data collection (saving analysis time), thus justifying their reappraisal. Three spectrophotometric methods are proposed in this work: a one-indicator (OISM), a separated three-indicator (STISM) and a mixed three-indicator (MTISM) spectrophotometric method. They are based on the addition of one or three colorimetric indicators (methyl red, bromocresol violet, and bromothymol blue) to the aqueous extract. The pH is measured through its absorption properties in the visible region. The analysis of 60 soil samples showed that STISM and MTISM results correlate well with the ones obtained by GE. The STISM method, being more simple and general than the other two methods, is proposed for quick routine analyses. The repeatability, reproducibility and accuracy of STISM (and of GE, for comparison) were evaluated by measuring several times the pH of a series of soil samples and of a certified reference soil. The standard deviations of STISM results were slightly worse than those of GE, whereas the accuracy was slightly better, indicating that STISM and GE have overall similar performances. STISM method is much faster than GE one: the analysis time saving is around 2 min per sample, and it becomes very high when hundreds of samples have to be analysed. It follows that STISM can represent an advantageous alternative to GE for rapid and accurate soil pH measurements.

Trace metals pollution of waters and soils in Kardjali region, Bulgaria.

Trace metals pollution of surface waters and their nearby soils in the metallurgically polluted Kardjali region, Bulgaria, were studied. Thermodynamic modeling including the dissolved organic carbon (DOC) was carried out for evaluating the distribution of metal species in waters and soil solutions. Zn was found to be the most widespread pollutant in the water samples, followed by Cu, Mn, and Cd. Geoaccumulation indices of trace metals for the tested soils were calculated, indicating that regarding Al, Fe, Co, Ni, and Cu all soils are "uncontaminated". The most significant soil pollutant was found to be Cd, with all soils being either "extremely contaminated" by this metal or close to the limit, followed by Pb and Zn. The dynamics of trace metal chemical species distribution in surface waters and in the water-soluble soil fractions, as a result of possible spontaneous precipitations, was calculated by applying different thermodynamic models. Regarding Mn, Co, Ni, and Cd in waters and aqueous soil extracts and Zn in aqueous soil extracts, their free ion species prevailed, being more labile and hence toxic for the ecosystem. In the case of Al, Fe, Cu, Cd, and Pb in the waters and aqueous soil extracts and of Zn in waters, stable organic complexes with bidentate bonds, Me(OH)4- or Me(OH)02 prevailed.

Patterns of change in permanganate oxidizable soil organic matter from semiarid drylands reflected by absorbance spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry

Organic matter (OM) oxidized by slightly alkaline KMnO4, termed permanganate-oxidizable carbon (POXC), has recently emerged as a standardized indicator of active, labile carbon within soil quality frameworks. Yet, qualitative information on POXC, particularly in semiarid drylands, is very scarce. The aim of this study was to characterize POXC within three long-term field experiments in Montana, USA: (i) across a wide range of edaphic (e.g., % clay) and management conditions (e.g., cropping intensity) (n = 148); and (ii) to identify the molecular composition of soil OM before and after KMnO4 treatment using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The content of POXC was significantly greater under perennial (382–685 mg/kg) or annual cropping (404–607 mg/kg) than fallow-wheat (359–543 mg/kg) systems. Soil OM changes, however, were equally or better expressed when considering soil organic carbon (SOC) concentration. The occurrence of POXC paralleled SOC (R = 0.87; P < 0.001) and total nitrogen (TN) (R = 0.82; P < 0.001) concentrations, regardless of soil textural differences. The ESI FT-ICR MS analyses of aqueous soil extracts indicated that the KMnO4 reaction oxidized dissolved OM of diverse molecular character. OM molecular composition after KMnO4 treatment was enriched by strongly reduced chemical constituents (O/C < 0.4) at greater condensed aromaticity (AI > 0.67) and hydrogen saturation (aliphatic composition; H/C > 1.5) across all heterogeneous groups (CcHhNnOoSs). Although POXC is a rapid assay widely used for characterizing soil OM dynamics, it may not provide a clear advantage over SOC concentration in semiarid drylands. The view of POXC as a merely labile, simple biodegradable OM fraction needs to be reconsidered.

The effect of hazardous pollutants from coal combustion activity: Phytotoxicity assessment of aqueous soil extracts

Airborne fly ash and related hazardous particles derived from coal combustion contaminate soil and groundwater, negatively affecting ecosystems. The aim of this study was chemical and toxicological evaluation of aqueous extracts of soil collected from the vicinity of a coal-fired Plomin power plant (PPP), using Lemna (Lemna minor L.) bioassay and additional biochemical indicators - photosynthetic pigments, lipid peroxidation, antioxidative enzymes and glutathione. Topsoil samples were collected from distances of 200, 300, 400 and 800 m from the PPP in accordance with the prevailing SW wind direction. Elevated levels of polycyclic aromatic hydrocarbons (up to 15,765 ng L−1) and potentially toxic trace elements were detected in the Plomin soil extracts (PEs) in comparison to control soil extract (CE). Trace elements accumulated in L. minor were mostly in accordance with their concentrations in PEs. The results demonstrate that PEs induced significant growth inhibition and other phytotoxic effects. Those effects can be related to damage caused by increased production of reactive oxygen species and impaired antioxidant levels. The connection among the phytotoxicity, a distribution of analyzed contaminants, and distances from the PPP is clearly established.

Вплив обробітку ґрунту та мінеральних добрив на біологічну активність ґрунту під посівами кукурудзи цукрової

&lt;p&gt;The article is devoted to study of the biological activity of soil under sweet corn crops depending on tillage depth, mineral fertilizers application rate with drip irrigation in the soil-ecological conditions of the Dry Steppe Zone of Ukraine. The plan of the experiment foresaw study of such factors: A — tillage depth (moldboard plowing on 20-22 and 28-30 cm); B — mineral fertilizers application rate (no fertilizers, N&lt;sub&gt;60&lt;/sub&gt;P&lt;sub&gt;60&lt;/sub&gt;, N&lt;sub&gt;120&lt;/sub&gt;P&lt;sub&gt;120&lt;/sub&gt;); C — plants density (35, 50, 65, 80 plants ha&lt;sup&gt;-1&lt;/sup&gt;). We used water of the Ingulets irrigation system for irrigation. The water belongs to II quality class by agronomical criteria of the DSTU 2730-94 and its suitability for irrigation is limited. We studied the soil biological activity on variants with 65 plants ha&lt;sup&gt;-1 &lt;/sup&gt;by the indicies of its respiration rate (method of V.I. Shtatnov) and linen decomposition degree (“application” method). At the same time we have made monitoring of the soil meliorative state depending on the moldboard plowing depth by the toxic salts content, anionic-cationic composition of the aqueous soil extract. The results of the laboratory-field experiments prove that the moldboard plowing depth , mineral fertilizers application rates and soil meliorative state have an influence on its biological activity. The maximum respiration rate, which is used to characterize an activity of the aerobic microflora of the upper soil layers, was at moldboard plowing on depth of 20-22 cm at non-fertilized experimental variant — 250.0 mg СО&lt;sub&gt;2&lt;/sub&gt;/m&lt;sup&gt;2&lt;/sup&gt;×hour. Increase of the tillage depth and mineral fertilizers application rate significantly decreased carbonic acid emission to the athmosphere, which was the minimum of 178.3 mg СО&lt;sub&gt;2&lt;/sub&gt;/m&lt;sup&gt;2&lt;/sup&gt;×h. The maximum linen decomposition degree, which is used to characterize an activity of the cellulose-decomposing soil microflora, was at moldboard plowing depth of 28-30 cm at non-fertilized experimental variant — 58.3%. The tillage depth changed cellulose-decomposing soil microflora activity insignificantly. Mineral fertilizers application at the maximum rate of N&lt;sub&gt;120&lt;/sub&gt;P&lt;sub&gt;120&lt;/sub&gt;decreased cellulose-decomposing soil biota activity 1.7 times comparatively to non-fertilized variant. Higher toxic salts concentration (at 0.006-0.019 %), sodium ions content (at 0.15-0.38 mg-eq/100 g of soil) in the 0-50 cm layer led to decrease of the soil biological activity. We consider, that the best from the agroecological point of view is the variant with moldboard plowing depth of 28-30 cm, mineral fertilizers application rate N&lt;sub&gt;120&lt;/sub&gt;P&lt;sub&gt;120&lt;/sub&gt;.&lt;/p&gt;

The Application of EM38: Determination of Soil Parameters, Selection of Soil Sampling Points and Use in Agriculture and Archaeology.

Fast and accurate assessment of within-field variation is essential for detecting field-wide heterogeneity and contributing to improvements in the management of agricultural lands. The goal of this paper is to provide an overview of field scale characterization by electromagnetic induction, firstly with a focus on the applications of EM38 to salinity, soil texture, water content and soil water turnover, soil types and boundaries, nutrients and N-turnover and soil sampling designs. Furthermore, results concerning special applications in agriculture, horticulture and archaeology are included. In addition to these investigations, this survey also presents a wide range of practical methods for use. Secondly, the effectiveness of conductivity readings for a specific target in a specific locality is determined by the intensity at which soil factors influence these values in relationship to the desired information. The interpretation and utility of apparent electrical conductivity (ECa) readings are highly location- and soil-specific, so soil properties influencing the measurement of ECa must be clearly understood. From the various calibration results, it appears that regression constants for the relationships between ECa, electrical conductivity of aqueous soil extracts (ECe), texture, yield, etc., are not necessarily transferable from one region to another. The modelling of ECa, soil properties, climate and yield are important for identifying the location to which specific utilizations of ECa technology (e.g., ECa−texture relationships) can be appropriately applied. In general, the determination of absolute levels of ECa is frequently not possible, but it appears to be quite a robust method to detect relative differences, both spatially and temporally. Often, the use of ECa is restricted to its application as a covariate or the use of the readings in a relative sense rather than as absolute terms.

LC–MS/MS Method for Simultaneous Determination of Monoethanol- and Dimethylnitramine in Aqueous Soil Extracts

Monoethanol (MEA)- and dimethyl (DMA)-nitramines are by-products of amine-based post-combustion CO2 capture (PCCC) processing, and are potentially carcinogenic. The compounds are challenging to measure, also with LC–tandem mass spectrometry (MS/MS), attributed to their high polarity and extreme proneness to matrix effects. In contrast to related methods, the MEA- and DMA-nitramines were simultaneously determined in aqueous soil extracts in less than 10 min using a 1 mm × 150 mm Atlantis® T3 (3 µm) C18 column. A mobile phase of water/methanol (90/10, v/v) and 2 mM acetic acid allowed for electrospray ionization (ESI) of both analytes [in contrast to the need for both ESI and atmospheric pressure chemical ionization (APCI) in related methods]. Polarity switching electrospray was required for the simultaneous detection of the analytes, and concentration limits of detection (LODs) in the aqueous soil extracts were ≤5.0 µg L−1 using an injection volume of 20 μL and no prior enrichment step. Matrix effects were compensated for using isotope-labelled internal standards, and satisfactory precision and linearity were obtained (within- and between-day precisions ≤19%, r 2 ≥ 0.995 for concentrations up to 500.0 µg L−1). To avoid signal decrease over time when measuring DMA-nitramine alone, the use of polarity switching was beneficial, in addition to frequent cleaning of the ion transfer capillary. The validated method can be used to determine nitramines in aqueous soil extracts, which is of importance as soil sorption is a determinant of the compounds’ environmental fate.

Agglomeration Determines Effects of Carbonaceous Nanomaterials on Soybean Nodulation, Dinitrogen Fixation Potential, and Growth in Soil.

The potential effects of carbonaceous nanomaterials (CNMs) on agricultural plants are of concern. However, little research has been performed using plants cultivated to maturity in soils contaminated with various CNMs at different concentrations. Here, we grew soybean for 39 days to seed production in soil amended with 0.1, 100, or 1000 mg kg-1 of either multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), or carbon black (CB) and studied plant growth, nodulation, and dinitrogen (N2) fixation potential. Plants in all CNM treatments flowered earlier (producing 60% to 372% more flowers when reproduction started) than the unamended controls. The low MWCNT-treated plants were shorter (by 15%) with slower leaf cover expansion (by 26%) and less final leaf area (by 24%) than the controls. Nodulation and N2 fixation potential appeared negatively impacted by CNMs, with stronger effects at lower CNM concentrations. All CNM treatments reduced the whole-plant N2 fixation potential, with the highest reductions (by over 91%) in the low and medium CB and the low MWCNT treatments. CB and GNPs appeared to accumulate inside nodules as observed by transmission electron microscopy. CNM dispersal in aqueous soil extracts was studied to explain the inverse dose-response relationships, showing that CNMs at higher concentrations were more agglomerated (over 90% CNMs settled as agglomerates >3 μm after 12 h) and therefore proportionally less bioavailable. Overall, our findings suggest that lower concentrations of CNMs in soils could be more impactful to leguminous N2 fixation, owing to greater CNM dispersal and therefore increased bioavailability at lower concentrations.

Fast Ecotoxicity Detection Using Biosensors

The article provides information about a new device, AlgaTox developed in the R&D project sponsored by the Technology Agency (n.TA02030179) and patented in Czech Republic (CZ 305687). Its functionality is based on the use of biosensor, and its main advantage is fast response rate. The toxicity detection is achieved through precise measurement of green algae oxygen production dynamics after their exposure to light of wavelength of 680 nm. Clark sensor with a resolution of 0.05% of the equilibrium oxygen concentrations and stability at a constant pressure and temperature of 0.1% of the equilibrium oxygen concentration at the 24-h measurement is used for the oxygen detection. Laboratory testing of the device has been made using silver nitrate, substance with known inhibitory effect on algae. Real samples of aqueous soil extracts and waste sample from old dried-up industrial tailing pond enriched with insecticide have been also tested. The values of oxygen production inhibition or stimulation determined with the new device in the evaluation of real samples were up to six times higher in comparison with the corresponding values of inhibition (stimulation) of growth rates determined by standard procedure.

Acute Toxicity of Bismuth to the Earthworm &amp;lt;i&amp;gt;Eisenia andrei&amp;lt;/i&amp;gt;

Bismuth (Bi) is increasingly used in several industrial applications including the production of alloys, drugs, cosmetics and munitions formulations. However, little information is available on the environmental fate and ecotoxicological effects of Bi. The present study describes 14 days acute toxicity of Bi, added as Bi citrate to a natural sandy soil, to the adult earthworm Eisenia andrei. Total measured Bi concentrations were 298.0, 399.5, 431.0, and 469.5 mg Bi/kg dry soil. Data indicates that Bi was toxic to Eisenia andrei, as determined by LC50 and LOEC, i.e., 416.0 and 399.5 mg Bi/kg dry soil, respectively. At 14 days in the presence of Eisenia andrei the bioaccessible fraction of Bi in soil, as determined in KNO3 aqueous soil extracts, increased by a factor ranging from 1.6 to 30.0 compared to those measured at the beginning of experiment. Moreover, this study shows that an increase in pH caused by the presence of earthworm in soil was accompanied by increase in Bi bioaccessibility and consequently toxicity. For example, when Bi bioaccessibility increased from 0.262 to 7.516 mg Bi/kg dry soil, the mortality rate increased from 0 to 79%. Assuming that there were at least two routes by which Eisania andrei enhanced Bi bioaccessibility; one route was guided by the mobility, the biochemical (mucus) and the biological (bacteria) interactions of Eisenia andrei with soil constituents, and the other route was marked by the death of earthworms and the release of the accumulated Bi from the carcass.

Potential application of immunoassays for simple, rapid and quantitative detections of phytoavailable neonicotinoid insecticides in cropland soils

This study evaluated the applicability of commercially available kit-based enzyme-linked immunosorbent assay (ELISA) to simple, quick, and quantitative detection for three water-extractable (phytoavailable) neonicotinoid insecticides: dinotefuran, clothianidin, and imidacloprid in soils. ELISA showed excellent analytical sensitivity for determination, but with cross-reaction to structurally related neonicotinoid analogues, which might produce false positives. To analyze insecticides in soil samples of diverse physicochemical properties, they were extracted with water. The aqueous soil extracts were assayed directly with ELISA. No matrix interference was observed without additional dilution with water. Recovery experiments for the insecticides from aqueous soil extracts spiked at 2–10 ng/mL showed good accuracy (72–126%) and precision (<16%). Kit-based ELISAs were used to estimate soil–water distribution coefficients (Kd). Values estimated using this method showed positive correlation between organic carbon contents in soil and those for evaluated insecticides. Results indicate that the evaluated kit-based ELISA has applicability for simple, quick, and reliable detection of phytoavailable insecticides in soils and for estimating Kd values in soil.

Robust analysis of underivatized free amino acids in soil by hydrophilic interaction liquid chromatography coupled with electrospray tandem mass spectrometry

Amino acids are an important and highly dynamic fraction of organic N in soils and their determination in soil without derivatization is challenging due to the difficulties in separation and detection of trace amounts of these polar analytes. In the present work, we developed an analytical method to quantify 20 free amino acids in aqueous soil extracts without derivatization. The method employed hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC–MS/MS) technique combined with a cation exchange solid phase extraction (SPE). Four stable isotope labelled amino acids were used as internal standards to improve the method performance. Good separation of 20 underivatized amino acids was achieved within 12min. The limit of detection (LODs) and limit of quantification (LOQs) were in the range of 13–384ngg−1 and 43–1267ngg−1 (dry soil basis), respectively. The results showed that overall recoveries with high precision were obtained for the extracted free amino acids from ten different soils. The overall recoveries of 18 amino acids were similar for the ten soils used, which differed substantially in organic C content and in other properties as soil texture and pH. For most of the amino acids, the average recoveries from soil extracts were between 74% and 117%, with the exception of Met (31%), Pro (52%) and Arg (68%). Variability was within acceptable limits (relative standard deviations were between 4% and 13%), with the exception of Met (relative standard deviation=90%) and Arg (relative standard deviation=53%). Thus the proposed method with high throughout and high analyte specificity shows great promise for consistent analysis of free amino acids extracted from soils and offers new horizons for the analysis of amino acids in terrestrial and aquatic ecosystem.

Soil suppressiveness by organic amendment to Fusarium disease in cucumber: effect on pathogen and host

Soil suppressiveness to Fusarium wilt and crown rot disease, caused by Fusarium oxysporum f. sp. radicis-cucumerinum in cucumber, develops following the incorporation of wild rocket (Diplotaxis tenuifolia (L.) DC.) crop residues, manifested as reduction in disease incidence. We studied mechanisms that might be involved in disease suppression. Exposure of nonamended-nonsuppressive soil to volatile organic compounds generated from wild rocket decomposing in the soil induced soil suppressiveness to Fusarium disease in nonamended soil. Similarly, a crude aqueous soil extract from wild rocket-amended (suppressive) soil induced suppressiveness to Fusarium disease when cucumber seedlings were transplanted into nonsuppressive soil amended with this soil extract. Suppressive soils did not show any effect on F. oxysporum f. sp. radicis-cucumerinum macroconidial germination, mycelium growth or new chlamydospore production. Root colonization with Fusarium spp. was suppressed in inoculated plants after 6 days, but not after 3 days. No evidence for induced resistance was found when plants were first grown in suppressive soil followed by inoculation and transplanting in nonsuppressive soil, or when plants were inoculated with Botrytis cinerea. Findings suggest that the microorganisms perpetuate the mechanisms of suppressiveness following the introduction of organic amendments, and that this occurs in the root zone.

Methodological issues about techniques for the spiking of standard OECD soil with nanoparticles: evidence of different behaviours

The aim of this study is to investigate at what extent the results of standard nanoparticle (NP) toxicity testing methodologies are affected by the different exposure procedures on soil organisms. In this view, differences in physicochemical properties of ZnO NPs (<100 nm), ZnO bulk (<200 nm) and ionic Zinc (ZnCl2) and their ecotoxicological potential toward Lepidium sativum were investigated with respect to three different spiking methods. Results show that the spiking procedures give homogeneous distribution of the testing nanomaterial in soil but the physicochemical and ecotoxicological properties of the testing species differ according to the spiking procedure. Dry spiking produced the highest ZnO solubility whereas spiking through dispersions of ZnO in water and in aqueous soil extracts produced the lowest. At the same time, the ecotoxic effects showed different trends with regard to the spiking route. The need for a definition of agreed methods concerning the NP spiking procedures is, therefore, urgent.

Fate of the insecticidal Cry1Ab protein of GM crops in two agricultural soils as revealed by ¹⁴C-tracer studies.

Insecticidal delta-endotoxins of Bacillus thuringiensis are among the most abundant recombinant proteins released by genetically modified (GM) crops into agricultural soils worldwide. However, there is still controversy about their degradation and accumulation in soils. In this study, (14)C-labelled Cry1Ab protein was applied to soil microcosms at two concentrations (14 and 50 μg g(-1) soil) to quantify the mineralization of Cry1Ab, its incorporation into the soil microbial biomass, and its persistence in two soils which strongly differed in their texture but not in silt or pH. Furthermore, ELISA was used to quantify Cry1Ab and its potential immunoreactive breakdown products in aqueous soil extracts. In both soils, (14)CO2-production was initially very high and then declined during a total monitoring period of up to 135 days. A total of 16 to 23 % of the (14)C activity was incorporated after 29 to 37 days into the soil microbial biomass, indicating that Cry1Ab protein was utilized by microorganisms as a growth substrate. Adsorption in the clay-rich soil was the most important factor limiting microbial degradation; as indicated by higher degradation rates in the more sandy soil, extremely low concentrations of immunoreactive Cry1Ab molecules in the soils' aqueous extracts and a higher amount of (14)C activity bound to the soil with more clay. Ecological risk assessments of Bt-crops should therefore consider that the very low concentrations of extractable Cry1Ab do not reflect the actual elimination of the protein from soils but that, on the other hand, desorbed proteins mineralize quickly due to efficient microbial degradation.