Solution Extraction Methods Research Articles

Integrated effects of water conditions and aging on chromium speciation and availability in two paddy soils spiked with hexavalent chromium

ABSTRACT Indoor incubation experiment was conducted under flooding (FD), 100% field capacity (100% FC), and alternating wetting and drying (AWD) conditions for 90 days using Guangdong (GD) and Jiangxi (JX) paddy soils spiked with hexavalent chromium [Cr(VI)]. The chromium speciation and availability were investigated usingsequential extraction, diethylene triamine pentaacetic acid (DTPA) leaching, and alkali solution extraction methods. The concentrations of Cr(VI), acid-extractable Cr and DTPA-Cr were reduced by 72%–89%, 48%–81%, and 42%–98%, respectively, at 90 d compared with 1 d. The sequence for acid-extractable Cr and DTPA-Cr concentrations was 100% FC>AWD>FD. While, it was AWD>100% FC>FD for Cr(VI) concentrations. Acid-extractable Cr, DTPA-Cr, and Cr(VI) concentrations in JX soil were higher compared with GD soil. The changes of DTPA-Cr concentrations were well fitted by Elovich kinetic model. These findings revealed water management and aging greatly affected chromium speciation and availability, having potential implications for sustainable agriculture and human health.

Comparison of solution extraction methods for estimating electrical conductivity in soils with contrasting mineralogical assemblages and textures

Characterization of the soil solution is of fundamental importance for monitoring plant nutrient availability, environmental contamination, and evaluation of salt-affected soils. Due to the diversity of methodologies adopted in various parts of the world, comparison of the most common extraction methods in different types of soils is warranted. This study compared the efficiency of five soil solution extraction methods for five soils with different mineralogical assemblages and textures with the most commonly used saturated paste extract method. The extraction methods compared were: centrifugation, porous extractor capsules, and soil–water extracts (soil:water ratio of 1:2, 1:5, or 1:10). The soil types evaluated were: Regosol, Luvisol, Gleysol, Nitisol and Ferrosol in the soil surface and subsurface horizons. Linear regression equations were developed that allowed accurate estimation of electrical conductivity of the saturated paste extract (ECse). Ten equations were developed for the porous capsule method, eight were developed for the centrifugation method (with the exception of the Regosol with 900 g k−1 of total sand, which was not suitable for this method due to the high sand content), and 30 equations were developed for the soil–water extract method (at each of the soil:water ratios tested). The diversity of equations developed for soils with different mineralogical assemblages and textures should assist growers and extension workers who need to know the soil electrical conductivity for making soil management decisions.

Lead was mobilized in acid silty clay loam paddy soil with potassium dihydrogen phosphate (KDP) amendment

The immobilization effectiveness between Pb and phosphorus in soil varies with soil types. To clarify the effect of phosphate on the availability of Pb in agricultural soil, a culture experiment with three types of paddy soil was performed with potassium dihydrogen phosphate (KDP) added. EDTA, DGT and in-situ solution extraction methods were used to represent different available Pb content. Results showed that the concentration of EDTA-Pb in HN soil was slightly elevated after exogenous KDP added. The supplement of 300 mg/kg KDP significantly increased the content of soluble Pb in both acid silty clay loam soil and neutral silty loam soil (increased by 104.65% and 65.12%, respectively). However, there was no significant influence of KDP on the concentration of DGT extracted Pb. XANES results showed that Pb(OH)2, PbHPO4, humic acid-Pb and GSH-Pb were the major speciation of Pb in soil colloids. The proportion of Pb(OH)2 and humic acid-bounded Pb in soil colloids were elevated after exogenous KDP added. Our results indicated that there was a mobilization effect of KDP on Pb by increasing the amount of colloidal Pb in soil solution, especially in acid silty clay loam paddy soil. Such colloid-facilitated transport might promote the uptake of Pb in rice and pose a potential threat to human health.

Investigating the use of microdialysis and SEC-UV-ICP-MS to assess iodine interactions in soil solution

Element cycling in the terrestrial environment is heavily reliant upon processes that occur in soil solution. Here we present the first application of microdialysis to sample iodine from soil solution. In comparison to conventional soil solution extraction methods such as Rhizon™ samplers, centrifugation, and high-pressure squeezing, microdialysis can passively sample dissolved compounds from soil solution without altering the in-situ speciation of trace elements at realistic soil moisture conditions. In order to assess the suitability of microdialysis for sampling iodine, the permeability factors and effect of perfusion flowrate on I− and IO3− recovery was examined in stirred solutions. Furthermore, microdialysis was used to sample native soluble iodine at a range of water contents and iodine-enriched soils to investigate iodine soil dynamics. Total iodine concentrations were measured using ICP-MS. Inorganic species and the molecular weight distribution of organically bound iodine were determined by anion exchange and size exclusion chromatography (SEC) coupled to an ICP-MS, respectively. The most effective recovery rates in stirred solution were observed with the slowest perfusion flowrate yielding 66.2 ± 7.1 and 70.5 ± 7.1% for I− and IO3−, respectively. Microdialysis was proven to be capable of sampling dissolved iodine from the soil solution, which accounted for <2.5% of the total soil iodine and speciation followed the sequence: organic-I > I− > IO3−. The use of SEC coupled to (i) UV and (ii) ICP-MS analysis provided detail regarding the molecular weight distribution of dissolved org-I compounds. Dissolved org-I was detected with approximate molecular weights between 0.1 and 4.5 kDa. The results in this study show that microdialysis is a suitable technique for sampling dissolved iodine species from soils maintained at realistic moisture contents. In addition, inorganic iodine added to soils was predominately bound with relatively low molecular weight (<4.5 kDa) soluble organic matter.

Bioavailability/speciation of arsenic in atmospheric PM2.5 and their seasonal variation: A case study in Baoding city, China

Arsenic (As) can be easily enriched in atmospheric particulate matters (PMs), especially in fine particulate matters (PM2.5). In this study, thirty two PM2.5 samples were collected in four seasons in Baoding, China, where the haze pollution was very serious in recent years. The total contents, species and bioavailability of arsenic in PM2.5 samples were investigated. Species of arsenic in the PM2.5 samples were discriminated as five fractions using a sequential extraction method: non-specifically sorbed fraction (F1), specifically-sorbed fraction (F2), amorphous and poorly-crystalline hydrous oxides of Fe and Al fraction (F3), well-crystallized hydrous oxides of Fe and Al fraction (F4) and residual fraction (F5). Bioavailabilities of arsenic in the PM2.5 samples were evaluated by in vitro tests using both solubility bioavailability research consortium (SBRC) and Gamble's solution extraction methods. The total volume concentrations of As in PM2.5 were significantly higher in winter than the other seasons. However, the highest mass concentration of As was found in spring. Scanning electron microscopy (SEM) characterization indicated that the physical morphology of the particles varied in different seasons. Significant differences of fraction distribution and BFs were found between different seasons. Arsenic in PM2.5 samples mainly presented in F1 with high bioavailability factor (BF), especially for the samples in summer. In vitro tests indicated that arsenic in PM2.5 could be dissolved more easily in gastric phase rather than intestinal and lung phases. There was a significant correlation between species and in vitro tests. Interestingly, a synergy effect was found between F2 and F3. Health risk assessment indicated that arsenic in PM2.5via inhalation exposure for both children and adults could cause adverse effects. Principal component analysis suggested that the arsenic in PM2.5 was from the similar sources between summer and autumn, winter and spring, respectively.

Transfer functions for solid‐solution partitioning of cadmium, copper, nickel, lead and zinc in soils: derivation of relationships for free metal ion activities and validation with independent data

Models to predict the solid‐solution partitioning of trace metals are important tools in risk assessment, providing information on the biological availability of metals and their leaching. Empirically based models, or transfer functions, published to date differ with respect to the mathematical model used, the optimization method, the methods used to determine metal concentrations in the solid and solution phases and the soil properties accounted for. Here we review these methodological aspects before deriving our own transfer functions that relate free metal ion activities to reactive metal contents in the solid phase. One single function was able to predict free‐metal ion activities estimated by a variety of soil solution extraction methods. Evaluation of the mathematical formulation showed that transfer functions derived to optimize the Freundlich adsorption constant (Kf), in contrast to functions derived to optimize either the solid or solution concentration, were most suitable for predicting concentrations in solution from solid phase concentrations and vice versa. The model was shown to be generally applicable on the basis of a large number of independent data, for which predicted free metal activities were within one order of magnitude of the observations. The model only over‐estimated free‐metal ion activities at alkaline pH (&gt;7). The use of the reactive metal content measured by 0.43 m HNO3 rather than the total metal content resulted in a close correlation with measured data, particularly for nickel and zinc.

In Situ Probes for Measurement of Electrical Conductivity of Soilless Substrates: Effects of Temperature and Substrate Moisture Content

Growing medium electrical conductivity (EC) is used in laboratory analysis and greenhouse production as a measure of the nutrient content of the growing medium. Fast, accurate ways to measure growing medium EC will make it easier to determine EC and maintain it within a suitable range for a particular crop. Several probes have been developed that can be inserted directly into the growing medium of container-grown crops for measurement of EC. We tested the sensitivity of four in situ EC probes (Field Scout, HI 76305, WET sensor, and SigmaProbe) at a range of temperatures, substrate volumetric water contents (VWC), and fertilizer concentrations. The HI 76305 probe was highly sensitive to temperature, while the WET sensor was temperature-sensitive at high ECs above its normal operating range. The probes responded differently to increasing VWC. The SigmaProbe and WET sensor measure the EC of the pore water specifically and show a decrease in EC with increasing water content, as the fertilizer ions in the pore water become more diluted as VWC increases. EC readings of the HI 76305 and Field Scout probes, which measure the EC of the bulk substrate (growing medium, water, and air combined) increased with increasing water content as the added water helps conduct the current of these meters. At a VWC above 35%, there was little effect of VWC on EC readings of all probes. The EC measured with the various in situ probes differed slightly among the probes but was highly and positively correlated with all three of the standard solution extraction methods [pour-through, 1:2 dilution, and saturated media extract (SME)] over the range of fertilizer concentrations at a given temperature and VWC. These results make it possible to convert substrate EC guidelines that have been established for any of the three standard methods for use with the in situ probes, though our results indicate the substrate VWC must be above 35% for the interpretation to be valid. The in situ probes are a viable alternative for measurements of substrate EC and eliminate the step of substrate solution extraction, thus simplifying data collection.

In Situ Probes for Direct Measurement of Substrate Soluble Salts: Effects of Substrate Moisture Content and Fertilizer Concentration

Several probes have been been recently developed that can be inserted directly into the growing medium of container-grown crops to get electrical conductivity (EC) or pH measurements. However, for many floriculture and greenhouse crops, EC interpretation ranges are based on substrate solution extraction methods such as the 1:2 v/v dilution, saturated media extract (SME), and more recently, the pour-through. We tested the sensitivity and accuracy of four in situ EC probes at a range of substrate moisture content and fertilizer concentrations. We also compared results from in situ probes with currently used methods of EC measurement. Concerning the effects of substrate volumetric water content (VWC) on the in situ probes, our results indicate little differences exist among probes when VWC exceeds 0.50, though drier substrates yielded differences depending on the measurement method. The SigmaProbe and W.E.T Probe measure the EC of the pore water specifically and show a decrease in EC with increasing water content, as the fertilizer ions in the pore water becomes more diluted as VWC increases. Results with the Hanna and FieldScout probes increased with increasing water content as the added water helps conduct the current of these meters. The EC measured with the various in situ probes differed slightly among the probes, but was highly and positively correlated with all three of the solution extraction methods over the range of fertilizer concentrations. It would be possible to convert substrate EC guidelines that have been established for any of the laboratory methods for use with the in situ probes, though our results indicate the substrate VMC must be above 0.35 for the interpretation to be valid.

Evolução da salinidade em um Argissolo sob cultivo de melão irrigado por gotejamento

Com objetivo de estudar a evolução da salinidade em Argissolo sob cultivo de melão irrigado por gotejamento com diferentes níveis de salinidade e práticas diferenciadas de manejo de irrigação, desenvolveu-se um experimento na Fazenda São João, Município de Mossoró, RN. Os tratamentos estudados se compunham da combinação de três fatores: salinidade da água de irrigação com 3 níveis (S1 - 1,2; S2 - 2,5 e S3 - 4,5 dS m-1), duas cultivares de melão (C1 - Honey Dew cultivar Orange flesh e C2 - Cantaloupe híbrido Trusty) e duas freqüências de irrigação (F1 - intervalos de um dia até os 30 dias após a semeadura (DAS) e duas vezes por dia a partir dos 30 DAS e F2 - intervalos de dois dias até os 30 DAS e uma vez por dia, a partir dos 30 DAS). O delineamento estatístico adotado foi o de blocos casualizados completos com 4 repetições e os fatores estudados foram arranjados no esquema fatorial de 3 x 2 x 2. Avaliou-se a evolução da salinidade do solo usando-se o método padrão, com uso de extratores. Os resultados mostraram que a salinidade do solo evoluiu com o tempo, estando os maiores níveis próximos de superfície do solo; a salinidade do solo atingiu o máximo na fase intermediária, tendendo a reduzir no final do ciclo do meloeiro; a evolução da salinidade do solo foi proporcional à concentração de sais na água de irrigação, independente da freqüência de irrigação. A salinidade medida com o extrator e corrigida pela umidade atual do solo foi equivalente à salinidade determinada pelo método padrão.

Column Leaching Using Dry Soil to Estimate Solid-Solution Partitioning Observed in Zero-Tension Lysimeters. 1. Method Development

In order to understand the reactions taking place between the soil solid phase and the soil solution, we require knowledge of the chemistry of the soil solution as it occurs in the field. This knowledge allows us to conduct experiments with environmentally relevant concentrations of macro and microelements in solution. Zero-tension lysimeters directly sample the mobile fraction of soil solutions. Unfortunately, they are expensive to sample and require long equilibration periods. Other solution extraction methods do not provide solutions similar in concentration to lysimeters, either because they sample a different fraction of the soil solution or due to the impacts of the sampling process. The processes that produce lysimeter solutions cannot be emulated; however, to estimate lysimeter solution chemistry, we developed a standard protocol to produce solutions that resemble lysimeter solutions from podzolic soils using air-dried samples. We washed air-dried soil columns sequentially with de-ionized water until the electrical conductivity (EC) of the leachates stabilized and then leached the columns using an environmentally relevant concentration of a weak salt solution. We hypothesize that the stabilization point of the EC of the soil solution is indicative of the point at which soluble salts and organic material precipitated during sampling and storage are removed from the soil surface. Solutions produced by leaching, once the EC of wash solutions had stabilized, were comparable to lysimeter solutions from the area where samples were collected with respect to the concentrations of divalent cations, pH, EC and DOC.

Development of the Press Extraction Method for Plug Substrate Analysis: Quantitative Relationships Between Solution Extraction Techniques

Substrate electrical conductivity (EC), pH, and nutrient content should be monitored frequently during seedling plug production. Current testing methods are either complicated, unsuited to plug production, or interpretation standards do not exist. This study compares the press extraction (PE) method developed at North Carolina State Univ. with the saturated media extract (SME) method and the 1 substrate: 2 water suspension method (1:2). These solution extraction methods were applied to plug trays containing peat-based germination mix treated with four levels of fertilizer. Two sample sizes of 20 or 60 plug cells were used to determine if the smaller, less destructive sample size would produce satisfactory results. Resulting pH values varied within 0.3 units among methods, but variability in EC and nutrient content was greater. The PE method resulted in the highest values for EC, NH4+-N, NO3--N, K, Ca, and Mg while sample size had little effect on analyses. The three extraction methods were then compared on peat- and coir-based substrates. Within substrates, pH, EC, and nutrients tested were similar for the PE and the SME. The coir extract had a higher pH and much higher levels of K and Na than did the peat extract but was lower in N, P, Ca, and Mg. Overall, fairly strong correlations among testing methods were found, especially between the SME and PE.

Applications of capillary electrophoresis in corrosion science and engineering

Four applications of capillary electrophoresis of inorganic ions to the study of corrosion processes are presented. Analyses were conducted of solutions formed on high surface area carbon papers during exposure to corrosive gases, solutions extracted from corroding regions under organic coatings on an aluminum alloy, leachate from chromate conversion coatings on an aluminum alloy, and solutions reconstituted from corrosion products removed from aging aircraft. The flexibility, sensitivity, and robustness of the CE techniques were critical in the analyses required, as was the development of solution extraction methods that were able to retain the important characteristics of the solutions of interest. Analyses for a range of inorganic anions as well as metal cations, including Al 3+, Mg 2+ and Cu 2+, are presented.