Derivation and validation of soil total and extractable cadmium criteria for safe vegetable production

Determining the appropriate soil cadmium(Cd)criteria for vegetable production is important for ensuring that the Cd concentrations of the vegetables meet food safety standards.The soil extractable Cd criteria for vegetable production are also essential for both food safety and environmental management,especially in areas with a high natural background level.In the present study,soil total and extractable Cd criteria were derived using the approach of species sensitivity distribution integrated with soil aging and bioavailability as affected by soil properties.A dataset of 90 vegetable species planted in different soils was compiled by screening the published in literature in five bibliographic databases using designated search strings.The empirical soil-plant transfer model was applied to normalize the bioaccumulation data.After normalization,the intra-species variability was reduced by 18.3 to 84.4%.The soil Cd concentration that would protect 95%(HC_(5))of the species was estimated by species sensitivity distribution curves that were fitted by the Burr III function.The soil Cd criteria derived from the added approach for risk assessment were proposed as continuous criteria based on a combination of organic carbon and pH in the soil.Criteria for total Cd and EDTA-extractable Cd in the soil ranged from 0.23 to 0.61 mg kg^(-1)and from 0.09 to 0.25 mg kg^(-1),respectively.Field experimental data were used to validate the applicability and validity of these criteria.Most of the predicted HC5 values in the field experimental sites were below the 1:1 line.These results provide a scientific basis for soil Cd criteria for vegetable production that will ensure food safety.

Heavy Metal Remediation in AgoèNyivéLandfill Soils: Enhancing Stability through Organic Amendments

The burial of waste in developing countries, which is often carried out without respect for environmental standards, constitutes a risk of contamination of soils and even groundwater given the toxic elements they contain. The objective of this work is to carry out a study of the retention of heavy metals through the contribution of cattle manure to soil samples from the final Agoè Nyivé landfill in Lomé, Togo. Soil samples from the final landfill were taken from the surface and depth at several locations to form a composite sample. The amendment of the composite sample was carried out with bovine manure on the mock-up in the Laboratory for six months. The determination of the total contents of heavy metals by the atomic absorption spectrophotometer (SAA) on the composite sample showed high contents exceeding the thresholds recommended by the AFNOR NF U 44-041 standard. Sequential extraction on these composite samples showed that the mobile portions of lead, cadmium, copper and zinc are respectively estimated at 78.06%, 50%, 28.89% and 91.59%. The bovine manure used to amend the landfill samples presents physicochemical parameters that can contribute to rendering heavy metals immobile in the soil matrix under natural conditions. The addition of manure initially made it possible to increase the values of pH, electrical conductivity, cation exchange capacity and organic matter, which promote the retention of heavy metals. Secondly, the addition of manure made it possible to reduce the mobile portion of the heavy metals studied;from 78.06% to 14.39% for lead, from 50% to 11.52% for cadmium, from 28.89% to almost 0% for copper and from 91.15% to 80.58% for zinc. The use of cattle manure as an amendment on the composite sample was decisive in reducing the mobility of heavy metals in the polluted soils of the final landfill.

Studies on Oxidation States of Cobalt Extracted from Soils with EDTA·HO Ac·NH_4OAc

A method determining di-and tri-valeht cobalt extracted from soils with EDTA·2HOAc·NH4OAc solution (pH 4.65) was developed based on the difference of the stability constants of Co(II)EDTA and Co(III)EDTA. Analytical results indicated that soil cobalt existed in both two oxidation states, i. e. , di-and tri-valent cobalt. Extractable di-valent cobalt in 60 soil samples collected from various soils in China ranged from 0.02 ppm to 3.54 ppm, with the mean of 0.62 ppm, and extractable tri-valent cobalt from 0.04 ppm to 27.65 ppm, with the mean of 2.93 ppm.

Changes in Soil Hot-Water Extractable C,N and P Fractions During Vegetative Restoration in Zhifanggou Watershed on the Loess Plateau

The study was conducted in Zhifanggou Watershed,Shaanxi Province,China,to evaluate the effect of different vegetation types on hot-water extractable C,N and P fractions,with the aim to determine whether hot-water extractable fractions could be used as indicators of soil quality change in Loess Plateau.The six vegetation types established in 1975 were（i） Robinia pseudoacacia L.,（ii） Caragana korshinkii Kom.,（iii） Pinus tabulaeformis Carr.,（iv） P.tabulaeformis-Amorpha fruticosa L.,（v） R.pseudoacacia-A.fruticosa,and（vi） grassland.A cropped hillslope plot and a Platycladus orientalis L.native forest plot were used as references.The results indicated that the conversion of native forest to cropland resulted in a significant decline in the hot-water extractable C,N and P fractions.Hot-water extractable C,N,and P increased when cultivated land was revegetated,but after 30 years the amount of hot-water extractable C,N,and P in revegetated fields was still much lower compared to native forest.Hot-water extractable fractions increased more under mixed-forest than under pure-forest stands.Furthermore,there was a significant correlation between the hot-water extractable fractions and soil chemical and microbiological properties.The results showed that hot-water extractable fractions could be used as indicators of soil quality change on the Loess Plateau.

Effect of Temperature, pH and Salt on Fluorescent Quality of Water Extractable Organic Matter in Black Soil

Water erosion is the major reason for the loss of soil organic carbon in the Northeast China, which leads to the soil quality deterioration and adjacent water pollution. In this study, the effect of extraction temperature, pH value, and salt on the water extractable organic matter （WEOM） was determined by means of the UV absorbance, fluorescence excitation-emission matrix, and derived fluorescence indexes. In general, the carbon content and aromaticity of WEOM increased with the increasing of extraction temperature, with the exception that there was no significant difference in the amount at 0 and 20℃. More fluorophores, especially microbially-derived organic matter were extracted at high temperature. The pH values of extractant, including 5, 7, and 10, showed no effect on the carbon amount of WEOM, whereas the aromaticity and microbially-derived component gradually increased with the increasing of pH values. The fluorescence intensity of humic acid-like fluorophore was stronger in neutral and alkali condition than that in acidic condition. The addition of 10 mmol L-1 CaCl2 significantly decreased the carbon amount of recovered WEOM. Moreover, it significantly decreased the aromaticity of WEOM and the quantity of fulvic acid-like and humic acid-like fluorophores, whereas increased the percentage of tyrosine-like and tryptophan-like fluorophores in the total fluorophores and the amount of microbially-derived organic matter. Generally, 10 mmol L-1 KCl showed the same influence trend, but with low influence degree.

Biodegradation of dissolved organic carbon in soil extracts and leachates from a temperate forest stand and its relationship to ultraviolet absorbance

The amount and biodegradability of dissolved organic carbon (DOC) in forest floors can contribute to carbon sequestration in soils and the release of CO 2-C from soil to the atmosphere.There is only limited knowledge about the biodegradation of DOC in soil extracts and leachates due to the limitations inherent in degradation experiments.Differences in the biodegradation of DOC were studied in forest soil extracts using cold and hot water and 4 mmol/L CaCl 2 solution and in soil leachates sampled under different conditions over a wide range of DOC concentrations.From these results,we developed a simple and rapid method for determining the biodegradable organic C in forest floors.The hot water extracts and CaCl 2 extracts after CH 3 Cl fumigation contained higher concentrations of biodegradable organic C than the cold water extracts and CaCl 2 extracts before fumigation,with rapid DOC degradation occurring 24-48 h after incubation with an inoculum,followed by slow DOC degradation till 120-168 h into the incubation.During a 7-d incubation with an inoculum,the variation in DOC degradation in the different soil extracts was consistent with the change in special UV absorbance at 254 nm.Relatively higher levels of biodegradable organic C were detected in soil leachates from the forest canopy than in forest gaps between April and October 2008 (P <0.05).Relatively lower concentrations of DOC and biodegradable organic C were observed in soil leachates from N-fertilized plots during the growing season compared with the control,with the exception of the plot treated with KNO 3 at a rate of 45 kg N ha 1 a 1.Around 77.4% to 96.3% of the variability in the biodegradable organic C concentrations in the forest floors could be accounted for by the initial DOC concentration and UV absorbance at 254 nm.Compared with the conventional inoculum incubation method,the method of analyzing UV absorbance at 254 nm is less time consuming and requires a much smaller sample volume.The results suggest that the regression models obtained using the initial DOC concentration and UV absorbance can provide a rapid,simple and reliable method for determining the biodegradable organic C content,especially in field studies involving relatively large numbers of samples.

Research progress on the soil vapor extraction

Soil vapor extraction (SVE), the most common, efficient and economical means of remediation, is an in-situ remediation technique for removing volatile pollutants from unsaturated soil. The paper brie fly introduced the technological rationale and characteristics, summarized the theories and application research for SVE at home and abroad, and made the expectations and suggestions for the research on SVE. The international scholars have systematically researched the influence factors, remediation mechanism and numerical simulation of SVE. At present, SVE has been mostly integrated with other techniques to form enhanced SVE techniques, such as thermally enhanced SVE and AS-SVE (Air sparging- SVE), to be used for the field remediation widely. Compared with foreign countries, researches of Chinese scholars mainly focus on the laboratory research, especially on the influence factors, but rarely study the SVE model and the mass transfer mechanism of pollutant in SVE process. The SVE pilot studies are rare in China, and the field application has not been reported. In view of this situation, Chinese scholars in the future research can focus on the following aspects: (1) strengthening the research and systematized summary of SVE technical parameters and related knowledge;(2) strengthening the research on the mechanism and model of gas-phase mass transfer of pollutants in soil during SVE process;(3) strengthening the research on the enhanced SVE techniques and its application to actual site remediation.

Kinetic Mass Transfer Between Non-aqueous Phase Liquid and Gas During Soil Vapor Extraction

The mass transfer between non-aqueous phase liquid(NAPL) phase and soil gas phase in soil vapor extraction(SVE) process has been investigated by one-dimensional venting experiments. During quasi-steady volatilization of three single-component NAPLs in a sandy soil, constant initial lumped mass transfer coefficient (λgN,0) canbe obtained if the relative saturation (ξ) between NAPL phase and gas phase is higher than a critical value (ξc), andthe lumped mass transfer coefficient decreases with ξ when ξ＜ξc. It is also shown that the lumped mass transfercoefficient can be increased by blending porous micro-particles into the sandy soil because of the increasing of theinterfacial area.

An Experimental Method to Quantify Extractable Amino Acids in Soils from Southeast China

The extraction and comparison of soil amino acids using different extractants （deionized water, K2SO4, Na2SO4, NaC1, KCI） were reported. Results showed that 0.5 tool L-1 K2SOa with a 5 times extraction was a better method to assess the concentration of extractable amino acids in soils. The total amino acids extracted from soil planted for tea were similar to the total inorganic nitrogen. While they extracted from vegetable soil and paddy soil were much lower than the total inorganic nitrogen.

Use of Sequential, Single and Kinetic Extractive Schemes to Assess Cadmium (Cd) and Lead (Pb) Availability in Vietnamese Urban Soils

Modified BCR sequential extraction, single equilibrium-based EDTA extraction and kinetic fractionation were used for estimating the Pb and Cd availability in a series of soil samples from 3 sites located in urban areas of Hanoi (Vietnam). These schemes were compared to identify a simple, rapid and cheap protocol for routine estimation of Pb and Cd remobilizable fraction and the related potential risk. The comparison of these three approaches revealed their convergence in terms of mobility patterns observed for Pb and Cd. Cd was characterized by higher extractibality and mobility whatever the approach. Pb was distinguished of Cd by its high association to Feoxides, lower extractability, lower rate of desorption and then lower mobility. For this environmental scenario, EDTA single scheme at equilibrium could be suggested as the best suited and a simple protocol for determination of the labile pool of Cd and Pb. The pseudo-total concentrations of Pb and Cd are actually below the Vietnamese standard level, contrary to the results obtained by other authors for agricultural soils at other urban sites of Hanoi.

Profile distribution and seasonal dynamics of water-extractable carbohydrate in soils under mixed broad-leaved Korean pine forest on Changbai Mountain

Carbohydrate represents an important part of the soil labile organic carbon pool. Water soluble carbohydrate drives the C cycle in forest soil by affecting microbial activity and hot water extractable car- bohydrate is thought related to soil carbon sequestration due to the asso- ciation with soil aggregation. In a temperate forest region of northeast China, Changbai Mountain, we investigated the abundance, spatial dis- tribution, and seasonal dynamics of cool and hot-water extractable car- bohydrate in soils under mixed broad-leaved Korean pine forest. The concentrations of cool-water extractable carbohydrate （CWECH） in three soil layers （0-5, 5-10, 10-20 cm） ranged from 4.1 to 193.3 g.kg-1 dry soil, decreasing rapidly with soil depth. On an annual average, the CWECH concentrations in soils at depths of 5-10 and 10-20 cm were 54.2% and 24.0%, respectively, of that in the 0-5 cm soil layer. CWECH showed distinct seasonal dynamics with the highest concentrations in early spring, lowest in summer, and increasing concentrations in autumn. Hot-water extractable carbohydrate （HWECH） concentrations in three soil layers ranged from 121.4 to 2026.2 g.kgq dry soil, which were about one order of magnitude higher than CWECH. The abundance of HWECH was even more profile-dependent than CWECH, and decreased more rapidly with soil depth. On an annual average, the HWECH concentration in soils 10-20 cm deep was about one order of magnitude lower than that in the top 0-5 cm soil. The seasonality of HWECH roughly tracked that of CWECH but with seasonal fluctuations of smaller amplitude. The car- bohydrate concentrations in cool/hot water extracts of soil were positively correlated with UV254 and UV2s0 of the same solution, which has implications for predicting the leaching loss of water soluble organic carbon.

Extraction of Lead, Cadmium and Nickel from Contaminated Soil Using Acetic Acid

The accumulation of heavy metals in soil is a serious environmental problem. It is well known that heavy metals have an affinity for different compartments of soil. The risk associated with the presence of metals in soil is the ability of their transfer in water or plants. In the present research, batch extraction experiments were conducted using acetic acid (AA) as an extractant solution at various concentrations and contact times to determine the best conditions of soil washing process to achieve high heavy metal removal efficiencies. AA was investigated for its applicability for the removal of lead, cadmium and nickel from soil. Batch soil washing experiments were performed on 1.0 g portions of the spiked soil using different concentrations (0.001, 0.005, 0.01, 0.05, and 0.1 mol/L) of AA (CH3COOH) with solid: liquid ratio of 1:10. The results showed that AA extracted greater Pb than Cd and Ni. The extraction was carried out with shaking times from 15 to 180 min. The removal percentage of Pb varies from 42.2%-100% and Cd from 5.2%-31.1% with increasing concentration of AA, while the removal efficiency of Ni was not exceeded about 1%. Comparing with Pb and Cd, the removal efficiency of Ni was very low;this means that the solubility of Ni in AA was very low. It was found that 0.1 mol/L AA for soil washing was effective in removing absorbed Pb from contaminated soil (100% efficiency) at time 15 min. While the efficiency reaching 100% with washing solution of 0.05 and 0.01 mol/L at times 120 and 180 min, respectively. The efficiencies of Cd and Ni extraction were improved when 1 mol/L of AA solution was used (41.3% to 70.6% for Cd and 16.3% to 23.3% for Ni).

A Comparison of Different Preservation Methods for Nitrogen Isotopes of Soil Extractable NO3^-

Nitrogen(N) isotope ratio(δ^(15)N) of soil extractable NO_3^- plays a pivotal role in the study of N biogeochemical circulation in ecosystems. However, the NO_3^-concentration and its isotope composition of soil samples are unstable, making sample storage critical for preserving the N isotope composition of extracted soil NO_3^-. Nevertheless, studies on the appropriate selection of storage methods after soil sampling are scarce. In this study, we compared two commonly used methods for storing soil samples and investigated the stability of N isotopes of soil NO_3^-. The results demonstrated that no significant changes in the NO_3^-concentration and δ^(15)N value occurred in the samples stored at-18?C. However, the soil NO_3^-concentration markedly increased, and NO_3^-δ^(15)N value significantly changed after air-drying storage. Meanwhile, we also found that NO_3^-and its δ^(15)N were well preserved in the filtered soil extracts after 1 month. In contrast, the NO_3^-concentration gradually decreased and the^(15)N in NO_3^-was gradually enriched in the bactericidal agent-containing soil mixture solution during the storage period. Overall, our results indicated that N isotopes of NO_3^-could be effectively preserved in frozen-stored soil samples or filtered soil extracts. For field investigations conducted in remote areas and continued for a long-time period(and lacking a refrigerant supply), soil extraction/filtration using a CaSO_4-saturated solution may be a superior preparation and storage method for analyzing N isotopes of soil NO_3^-.

Automatic extraction and structuration of soil–environment relationship information from soil survey reports

In addition to soil samples, conventional soil maps, and experienced soil surveyors, text about soils(e.g., soil survey reports) is an important potential data source for extracting soil–environment relationships. Considering that the words describing soil–environment relationships are often mixed with unrelated words, the first step is to extract the needed words and organize them in a structured way. This paper applies natural language processing(NLP) techniques to automatically extract and structure information from soil survey reports regarding soil–environment relationships. The method includes two steps:(1) construction of a knowledge frame and(2) information extraction using either a rule-based method or a statistic-based method for different types of information. For uniformly written text information, the rule-based approach was used to extract information. These types of variables include slope, elevation, accumulated temperature, annual mean temperature, annual precipitation, and frost-free period. For information contained in text written in diverse styles, the statistic-based method was adopted. These types of variables include landform and parent material. The soil species of China soil survey reports were selected as the experimental dataset. Precision(P), recall(R), and F1-measure(F1) were used to evaluate the performances of the method. For the rule-based method, the P values were 1, the R values were above 92%, and the F1 values were above 96% for all the involved variables. For the method based on the conditional random fields(CRFs), the P, R and F1 values for the parent material were, respectively, 84.15, 83.13, and 83.64%; the values for landform were 88.33, 76.81, and 82.17%, respectively. To explore the impact of text types on the performance of the CRFs-based method, CRFs models were trained and validated separately by the descriptive texts of soil types and typical profiles. For parent material, the maximum F1 value for the descriptive text of soil types was 90.7%, while the maximum F1 value for the descriptive text of soil profiles was only 75%. For landform, the maximum F1 value for the descriptive text of soil types was 85.33%, which was similar to that of the descriptive text of soil profiles(i.e., 85.71%). These results suggest that NLP techniques are effective for the extraction and structuration of soil–environment relationship information from a text data source.

Influence of the Storage Duration at Different Temperatures on the Concentrations of Extractable Inorganic Soil Nutrients

The influence of the short storage periods at different temperatures on the concentrations of extractable soil cations (Ca2+, Mg2+, Na+ and K+) and anions (Cl-, SO4- and PO4- ) has been investigated in nine soil samples from Nile river terraces at River Nile State, North of Sudan (17.82289 to 17.82389N and 33.99974 to 34.02127E). Each soil extract is divided into three treatments: i) control (immediately analyzed);ii) storage for 10 days and;iii) storage for 30 days. Each treatment is replicated three times: i) storage at 10°C;ii) storage at ambient laboratory temperature (25°C) and;iii) storage at 45°C in incubator. Statistical analysis of results reveals that significant difference are found at level (P - and PO4- (0.043, 0.002, 0.001, 0.021, 0.004 and 0.001) respectively at 25°C and 45°C and storage periods of 10 and 30 days. In contrast, significant difference is also found at level (P - concentrations are significantly decreased when the storage period exceeds 10 days and temperature more than 25°C. Depending upon our study results;we conclude that, all extractable inorganic nutrients are clearly affected by storage periods at various temperatures, exception of Na+. Most cations and anions are increased significantly with increased of storage period and temperatures. We therefore highly recommend that the extractable inorganic soil nutrients should be rapidly analyzed in order to obtain accurate results;otherwise, the time between extraction and analysis should be carefully recorded which may help considerably interpreting data from various studies.

Reflux extraction and analysis of polyethylene wax in soil

An efficient reflux extraction of polyethylene wax(PEW) in soil is presented, followed by molecular structure characterization methods to explore its degradation mechanism. To more realistically simulate the actual degradation of PE film powders in soil, low density PE(M=5 000) powders, being used as simulated PEW residue sample, were uniformly mixed with soil and then recovered by reflux extraction with decahydronaphthalen(decalin) at 90 ?C for 60 min. The average recovery of PEW from fortified soils was 96.5% with the developed reflux extraction procedure. The recovered PEW residue samples were characterized by infrared spectroscopy(IR), element analysis(EA), X-ray fluorescence(XFR), and high-temperature gel permeation chromatography(GPC). The results from spectra analysis show that there were no significant changes in molecular structures and molecular mass distribution of PEW samples after the reflux extraction, which demonstrate the reliability of this method. These results also indicate that the reflux extraction procedure and analytical methods of characterization could serve as a novel measurement technique to evaluate the degradation of low-density PE powders in soil over time.

DNA extraction method selection for agricultural soil using TOPSIS multiple criteria decision-making model

There is an increased interest in the extraction of nucleic acids from various environmental samples since culture-independent molecular techniques contribute to deepen and broaden the understanding of a greater portion of uncultivable microorganisms. Due to difficulties to select the optimum DNA extraction method in view of downstream molecular analyses, this article presents a straightforward mathematical framework for comparing some of the most commonly used methods. Four commercial DNA extraction kits and two physical-chemical methods (bead-beating and freeze-thaw) were compared for the extraction of DNA under several quantitative DNA analysis criteria: yield of extraction, purity of extracted DNA (A260/280 and A260/230 ratios), degradation degree of DNA, easiness of PCR amplification, duration of extraction, and cost per extraction. From a practical point of view, it is unlikely that a single DNA extraction strategy can be optimum for all selected criteria. Hence, a systematic Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was employed to compare the methods. The PowerSoil? DNA Isolation Kit was systematically defined as the best performing method for extracting DNA from soil samples. More specifically, for soil:manure and soil:manure:biochar mixtures, the PowerSoil?DNA Isolation Kit method performed best, while for neat soil samples its alternative version gained the first rank.

Efficiency Evaluation of Extraction Methods for Analysis of OCPs and PCBs in Soils of Varying TOC

Organochlorine pesticides and polychlorinated biphenyls are toxic, carcinogenic, and have a high potential for bioaccumulation. Due to their stability, they are still considered an environmental problem even though the use of most of them has been phased out several decades ago. Soil is a matrix which can retain these contaminants to a great extent. This ability is often associated with the total organic carbon content (TOC). In order to judge the pollution status of soil and to make monitoring data more easily comparable a simple, yet robust extraction method is needed. Agitation solid-liquid-extraction is well suited for this purpose. However, the influence of TOC on the analyte recovery has to be known. For the presented study, 12 organochlorine pesticides and 7 polychlorinated biphenyls were spiked into four model soils with organic carbon contents between 1.6% - 13.3%. The matrices were extracted using solid-liquid extraction between 45 minutes and 16 hours. For comparison, all soils were also extracted using pressurised liquid extraction and Soxhlet extraction. After clean-up the extracts were measured using a gas chromatography-mass spectrometry (GC-MS) system. Statistical analysis of the results implied that the TOC content of the soils did not have significant influence on the extraction efficiency. A longer solid-liquid extraction time did not necessarily increase analyte recovery: Extraction for one hour resulted in 88% recovery while 16 hour extraction led to 89%. Thus, the efficiency of all the methods was comparable for all model soils. Additional investigations regarding GC liner performance highlighted the need for isotopically labelled standards during the analysis of thermolabile pesticides.

土壤中Sb(Ⅲ)和Sb(Ⅴ)的有效提取与测定

锑的各种形态中三价锑和五价锑的毒性较高,在城市土壤锑组成中占比也较高。研究了萃取方式、萃取剂、萃取条件、色谱分离流动相条件等因素对土壤中价态锑提取和分析的影响,建立了完整的土壤价态锑萃取-分析方法。研究推荐以柠檬酸溶液为萃取剂,70℃恒温振荡萃取的方式提取价态锑,萃取液以乙二胺四乙酸二钾+邻苯二甲酸为流动相,经色谱分离后利用电感耦合等离子体质谱仪对不同价态的Sb进行分析。所建立的方法检出限低,准确性精密度好,可用于实际土壤样品中价态锑的有效提取与测定。