Dilute Acid Extraction Research Articles

A proposed method for determining potentially environmentally available trace metals in paddy soil

ABSTRACT The validity of the Asami-Kumada method (sodium hydrosulfite + EDTA extraction, AK method) for determining the potentially environmentally available trace metals (Cr, Mn, Co, Ni, Cu, Zn, Cd, Pb) in paddy field soil was evaluated. This was accomplished by comparing it with the results of the dilute HNO3 extraction method (ISO method), nitrate acid – perchloric acid degradation method, and dilute hydrochloric acid extraction method on 250 paddy field soil samples. The coefficient of determination for the AK method in metals, excluding Cr, ranged from 0.92 (Ni of non-Andisols) to 0.99 (Mn, Cu, Zn and Cd of non-Andisols) compared to the ISO method. The slope of the linear regression of the AK method’s measured values against those of the ISO method for metals, excluding Cr, ranged from 0.99 (Cd of non-Andisols) to 1.52 (Cu of Andisols). However, the measurements of Fe using the AK method were significantly higher than those obtained using the ISO method. The slope was measured to be 3.6 (for non-Andisols) or 5.7 (for Andisols). The increase in trace metal measurements using the AK method was probably due to the dissolution of Fe oxides and hydroxides, which release trace metals after reduction by sodium hydrosulfite. Thus, although the measured values using the AK method of trace metals, excluding Cr, tended to be slightly higher than those obtained using the ISO method as Fe oxides and hydroxides dissolved, the measured values of those metals by both methods were closely correlated. The AK method is a viable alternative to the ISO method for measuring the potentially environmentally available trace metal contents, excluding Cr, in paddy field soils. Additionally, the AK method conveniently measures free Fe oxides simultaneously.

Rapid and High-Yield Recovery of Sodium Alginate from Undaria pinnatifida via Microwave-Assisted Extraction

Alginate, a promising biopolymer in the food, biomedical, pharmaceutical, and electronic materials industries, is characterized by its biodegradability, biocompatibility, low toxicity, and gel-forming properties. It is most abundantly found in brown algae. However, conventional dilute acid and alkali extraction methods face limitations in commercialization due to their long processing time, low throughput, and high solvent requirements. In this study, a microwave-assisted extraction (MAE) process for sodium alginate was designed to improve extraction efficiency. The solid/liquid ratio, extraction temperature, and extraction solvent concentration were major variables affecting sodium alginate extraction from Undaria pinnatifida (sea mustard). They were then statistically optimized using response surface methodology. Under optimal conditions (13.27 g/L, 91.86 °C, 2.51% (w/v), and 15 min), the yield was 38.41%, which was 93.43% of the theoretical content of sodium alginate in Undaria pinnatifida. Our work has confirmed the productivity and industrial feasibility of the efficient extraction of sodium alginate from marine biomass, and we hope that it will serve as an encouraging case for the application of biopolymers as one of the desirable options for alternative petrochemicals to construct a sustainable society.

Identification of Monomethylmonothioarsonic Acid as the Major Thioarsenical Generated During Extraction Processes for Arsenic Species Analysis.

Acid extraction is commonly used to analyze arsenic species in rice. During the extraction process, spiked monomethylarsonic acid (MMA) is often transformed into different compounds. A similar phenomenon is observed in the arsenic speciation analysis of seafood. To identify these compounds, we analyzed a previously prepared extract using liquid chromatography-time-of-flight/mass spectrometry in differential analysis and liquid chromatography-inductively coupled plasma-MS. The compound was identified as monomethylmonothioarsonic acid (MMMTA), a thioarsenical, which is estimated to be more cytotoxic than MMA. As MMMTA was readily produced by bubbling hydrogen sulfide through MMA, this suggests that MMA reacts with sulfur in rice during the extraction process. Our data also suggested that dimethylarsinic acid could be transformed into another compound, although the generation rate was low. For reliable arsenic speciation analyses, the transformation of arsenic compounds during extraction must be avoided. This study demonstrates that arsenic compounds can be transformed by dilute acid extraction.

Universal probe with oriented antibody to improve the immunochromatographic assay of lead ions inProcambarus clarkii

AbstractObjectivesBased on the information from the random inspection of foods by the China Food and Drug Administration in 2022, the contamination levels of lead ions are high in many edible products. Traditional methods of detecting lead ions cannot meet the requirements of on-site analysis of food due to the need for large equipment. The immunochromatographic assay (ICA) is an effective, rapid, on-site analytical technique for determining lead ions in foods. However, the performance of ICA based on the traditional probe (AuNP-mAb) is limited by ignoring the influence of the antibody orientation.Materials and MethodsIn this study, we developed an efficient technology for constructing a universal probe (AuNP-PrA-mAb) based on the oriented immobilization of antibody. The performance of ICA was largely improved due to specific binding of the Fc region of the antibody with recombinant protein A (PrA) on the surface of a gold nanoparticle (AuNP). The ICA based on a universal probe was applied for the qualitative and quantitative detection of lead ions in Procambarus clarkii within 30 min. Meanwhile, a simple and fast pretreatment method based on dilute acid extraction was developed for pretreating the P. clarkii containing lead ions.ResultsThe visual limit of detection and the scanning limit of quantization of the developed ICA strip for lead ions were 0.5 ng/mL and 0.28 ng/mL, respectively. The sensitivity of ICA based on universal probe was 10-fold higher than that of the ICA using traditional probe. Furthermore, the detection results had no obvious difference between the ICA and ICP-MS with t-test statistical method.ConclusionsThe developed ICA based on a universal probe presented broad application prospects in detecting contaminants in foods.

Improving the Measurement of Iron(III) Bioavailability in Freshwater Samples: Methods and Performance.

The toxicity of iron(III) in fresh waters has been detected at concentrations above the iron solubility limit, indicating a contribution of colloidal and particulate forms of iron(III) to the toxicity response. Current water quality guideline values for iron in fresh water are based on analytical determinations of filterable or total iron. Filtration, however, can underestimate bioavailable iron by retaining some of the colloidal fraction, and total determinations overestimate bioavailable iron measurements by recovering fractions of low bioavailability from suspended solids (e.g., iron oxides and oxyhydroxides) naturally abundant in many surface waters. Consequently, there is a need for an analytical method that permits the determination of a bioavailable iron fraction, while avoiding false-negative and false-positive results. Ideally, a measurement technique is required that can be readily applied by commercial laboratories and field sampling personnel, and integrated into established regulatory schemes. The present study investigated the performance of pH 2 and pH 4 extractions to estimate a bioavailable iron(III) fraction in synthetic water samples containing iron phases of different reactivities. The effects of aging on fresh precipitates were also studied. The total recoverable, 0.45-µm filtered, and pH 4 extractable fractions did not discriminate iron phases and age groups satisfactorily. Contrastingly, the pH 2 extraction showed specificity toward iron phases and aging (0.5-2-h interval). Extraction times above 4 h and up to 16 h equally recovered >90% of the spiked iron regardless of its age. Furthermore, <1% of the well-mineralized iron was targeted. The present study shows that a pH 2 dilute-acid extraction is a suitable candidate method to operationally define iron fractions of higher bioavailability avoiding false-negative and false-positive results. Environ Toxicol Chem 2023;42:303-316. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Production and Characterisation of Pectin from Cocoa Bean Shells

Cocoa bean shells constitute the major waste generated from the industrial processing of cocoa beans. The shells contain about 9% of pectin and extracting it would be of economic and ecological importance. However, limited knowledge on the characteristics of the pectin from cocoa bean shells and the extraction conditions, which would yield pectin of good quality and sufficient quantity, restrict the possible use of the shells as a source of commercial pectin. The objective of this study was to extract and characterise pectin from cocoa bean shells, with focus on finding the optimum extraction conditions. The conventional hot dilute acid extraction method was used. 12 M hydrochloric acid was used to acidify water to pH 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0. Extractions were carried out at temperatures of 60, 70, and 80 °C, for different times of 0.5, 1, and 2 h. The effects of each of the conditions on yield and other properties of pectin were evaluated. Depending on the conditions under which cocoa bean shells were treated, both high methoxyl and low methoxyl pectins were extracted. At the optimum conditions of pH 3.5, extraction time of 2 h and 80 °C extraction temperature, high methoxyl pectin was obtained. The yield was 4.7%, the degree of esterification was 68.9% and the anhydrouronic acid content was 71.2%. While the methoxyl content was 8.6%, the equivalent mass was found to be 805.8 g/eq. Moisture and ash contents were 6.7 and 10.3%, respectively, and the pH of the pectin hydrocolloid was 3.7. Fourier Transform Infrared (FT-IR) spectra confirmed the presence of functional groups found in the pectin structure. The intrinsic viscosity varied between 0.075–0.088 m3/kg and the molecular mass ranged from 23,470 - 42,384 g/mol. The results revealed that the shells are a viable source for commercial pectin, while necessary investigations focusing on the gelling, thickening, emulsifying, texturing, and stabilising potentials of the pectin from cocoa bean shells would inform of the areas of application

Primary structure, physicochemical properties, and digestive properties of four sequentially extracted polysaccharides from Tremella fuciformis

Polysaccharides from Tremella spp. are known to have various functions and applications. To fully understand the polysaccharide compositions of fruiting body of T. fuciformis, cold water extract (CWE), hot water extract (HWE), dilute alkaline extract (ALE), and dilute acid extract (ACE) were sequentially prepared and characterized. Their physicochemical properties, chemical composition, micromorphology, and functional properties were determined. Firstly, the four extracts showed significant difference in chemical compositions. Secondly, in the structural aspect, liquid chromatographic elution curves of the extracts had only one main peak except that CWE had two peaks. Fucose, galactose (or glucose), xylose, and mannose were detected in CWE and HWE. Differently, ALE had fucose, glucose, and xylose, and ACE had only galactose and glucose, which agreed with the information obtained from Fourier transform infrared spectra. Thirdly, in the physicochemical and nutritional aspects, the thermal stability of the four extracts decreased in the order of: ACE>HWE≈ALE>CWE. HWE and ALE had similar dynamic viscoelasticity, exhibiting viscous characteristics at low frequencies and elastic characteristics at higher vibration frequencies. The four extracts were digestive-resistant after in vitro mimic experiments. This study could provide some theoretical data support for the scientific research and its application in food, medicine, and cosmetics of tremella polysaccharides.

Performance of PES Membrane Contactor on the Separation of Dilute Acetic Acid from Aqueous Forms

The azeotropic characteristics of acetic acid between water make its separation from its aqueous phase essential. Many methods are studied for separating such a mixture. Solvent extraction using membrane contactors can increase the contact surface area. The dilute aqueous acetic acid extraction with the solvents petroleum ether and diisopropyl ether in a Poly Ether Sulfone (PES) hollow fiber membrane contactor was studied. The solvents and membrane extraction abilities are evaluated by exchanging the fluids on the shell and tube sides based on the distribution coefficients and total mass transfer coefficient at various flow rates. The findings show that when the solvent flow is increased, whether on the shell side or the tube side, the concentration of acetic acid increases in its solvent phase. As the shell side Reynolds number increased, it was noticed that the distribution coefficient value also increased. Both solvents' extraction ability was minimal, but diisopropyl ether gave better results when compared with the petroleum ether in terms of distribution coefficient. Three film resistance parameters in the series model have determined the overall mass transfer coefficient. The Reynolds number values showed that the mass transfer occurs in a laminar zone. Changes in the petroleum ether's Reynolds number on the tube side resulted in a maximum mass transfer coefficient of 11.41x10-6 m/s. Data on such hydrodynamics studies on membrane solvent extraction can help recover value-added material studies.

Environmental Fate of Trace Elements in Depositional Sediments after Flashflood Events: The Case of Mandra Town in Greece

Flash floods are one of the harshest natural hazards, having a wide range of substantial impacts for human and environmental health in the short-term and long-term. On 15 November 2017, a high-intensity storm caused a catastrophic flash flood event in the town of Mandra, a western, outer suburb of the Athens Metropolitan Area in Greece. In this study, we determine the aqua regia extractable concentrations of trace elements in residual sediments and associated soils after the flash flood and evaluate the fractionation of contaminants in geochemical compartments. Geochemical data are coupled with physicochemical parameter measurements and mineralogy to identify possible factors explaining the variability of trace element concentrations, while a dilute acid extraction is used to monitor changes of the reactive fraction of the trace elements over the term of 1 year following the flood event. Aqua regia concentrations in flood-deposited sediments reached values of 1 mg/kg (Cd), 24 mg/kg (Co), 183 mg/kg (Cr), 599mg/kg (Cu), 1080 mg/kg (Mn), 195 mg/kg (Ni), 122 mg/kg (Pb) and 945 mg/kg (Zn). Multivariate statistical techniques classified the elements according to their natural or anthropogenic origin. Trace elements of geogenic origin (As, Co, Cr, Mn, Ni) dominate in flood deposited material. The cluster of anthropogenic elements (Cd, Cu, Pb, Zn,) shows significant correlation with total organic carbon and magnetic susceptibility, while a significant seasonal variation has been observed for total organic carbon, Cd and Mn contents in the deposited sediments. Results allow a better understanding of the distribution of elements in the surface cover during and after catastrophic events in urban areas and provide useful information on the long-term exposure of the residents.

Bioethanol Production from Selected Species of Astera Plants by Simultaneous Saccharification and Fermentation using Dilute Acid and Alkaline Extraction Pretreatment Methods

Bioethanol Production from Selected Species of Astera Plants by Simultaneous Saccharification and Fermentation using Dilute Acid and Alkaline Extraction Pretreatment Methods

Assessing metal contaminants in Antarctic soils using diffusive gradients in thin-films

Metal contaminants in Antarctic soils are typically found around research stations which are concentrated in ice-free coastal areas. The risk of these contaminants to the Antarctic environment is not well understood, given Antarctica’s unique organisms and climate. This study assessed the use of diffusive gradients in thin-films (DGT), a passive sampler that measures fluxes of labile metals from soils to porewaters, in Antarctic soils. DGT-labile measurements were compared to three chemical extractants of increasing strength including high-purity water, dilute acid (1 M HCl), and concentrated acids (3:1 v/v HNO3:HCl), to understand differences in contaminant geochemistry that may affect environmental risk. One site had high lead concentrations measured with dilute (114 ± 4 mg kg−1) and concentrated (150 ± 10 mg kg−1) acids, while DGT-labile concentrations were below the method detection limit (0.5 μg L−1), indicating that the lead species has low solubility or lability. Another site had low concentrations of zinc measured by dilute (36.2 ± 0.5 mg kg−1) or concentrated (76 ± 6 mg kg−1) acid extracts, but had high DGT-labile concentrations (350 ± 80 μg L−1). This reflects an active source of zinc supplied from soil to pore water over time. Copper was found to be acid extractable, water-soluble, and DGT-labile, with DGT-labile concentrations of up to 12 μg L−1. Despite the soil and metal-specific geochemical differences, any of the extracts could be used with statistical clustering techniques to identify differences in sites with elevated metal concentrations. This study shows that the DGT-method can identify contaminated sites comparably to chemical extracts but provides environmentally relevant measurements of metal contaminant lability in Antarctic soils.

Biorefining of lignocellulosic feedstock and waste materials using ionic liquid

The ionic liquid trihexyltetradecylphosphonium hydrogen sulphate (THTDP HSO4) was used to extract cellulose from various lignocellulosic sources:- wheat straw, perennial ryegrass, willow, anaerobic digestate (AD) and spent mushroom compost (SMC). This was compared with a traditional dilute sulphuric acid extraction to evaluate the potential for this ionic liquid to be of use in the biorefining industry. The use of ultrasonication to facilitate the reaction was also tested. Results showed that this ionic liquid, which combines the features of a hydrophobic solvent with an acidic catalyst was effective in hydrolysing lignocelluloses. Compared to the use of dilute sulphuric acid, the ionic liquid produced purer, more thermally stable cellulosic fibres. It was also shown to be as effective as the dilute sulphuric acid in pretreating lignocelluloses for enzymatic hydrolysis. Finally, ultrasonication was shown to be compatible with the ionic liquid and suggests an energy efficient method for pretreatment of lignocellulose.

Soils in lakes: the impact of inundation and storage on surface water quality.

The large-scale storage and inundation of contaminated soils and sediments in deep waterlogged former sand pits or in lakes have become a fairly common practice in recent years. Decreasing water depth potentially promotes aquatic biodiversity, but it also poses a risk to water quality as was shown in a previous study on the impact on groundwater. To provide in the urgent need for practical and robust risk indicators for the storage of terrestrial soils in surface waters, the redistribution of metals and nutrients was studied in long-term mesocosm experiments. For a range of surface water turbidity (suspended matter concentrations ranging from 0 to 3000mg/L), both chemical partitioning and toxicity of pollutants were tested for five distinctly different soils. Increasing turbidity in surface water showed only marginal response on concentrations of heavy metals, phosphorus (P) and nitrogen (N). Toxicity testing with bioluminescent bacteria, and biotic ligand modelling (BLM), indicated no or only minor risk of metals in the aerobic surface water during aerobic mixing under turbid conditions. Subsequent sedimentation of the suspended matter revealed the chemical speciation and transport of heavy metals and nutrients over the aerobic and anaerobic interface. Although negative fluxes occur for Cd and Cu, most soils show release of pollutants from sediment to surface waters. Large differences in fluxes occur for PO4, SO4, B, Cr, Fe, Li, Mn and Mo between soils. For an indicator of aerobic chemical availability, dilute nitric acid extraction (0.43M HNO3; Aqua nitrosa) performed better than the conventional Aqua regia destruction. Both the equilibrium concentrations in surface waters, and fluxes from sediment, were adequately (r2 = 0.81) estimated by a 1mM CaCl2 soil extraction procedure. This study has shown that the combination of 0.43M HNO3 and 1mM CaCl2 extraction procedures can be used to adequately estimate emissions from sediment to surface waters, and assess potential water quality changes, when former sand pits are being filled with soil materials.

Pectic polysaccharides extracted from pot marigold (Calendula officinalis) industrial waste

Residues from the essential oil and the natural pigment industry are cheap, abundant and insufficiently investigated wastes with a great valorization potential. Such underexplored biomass is derived from the pot marigold (Calendula officinalis) used industrially for lutein extraction and obtaining of essential oil. The aim of the present work was to investigate the potential of two pot marigold wastes as a source of polysaccharides: the first obtained after 1,1,1,2-tetrafluoroethane (freon R134a) extraction of marigold (F-waste), and second obtained after hydrodistillation (HD-waste). The potential of wastes as a source of polysaccharides was estimated by dilute hydrochloric acid extraction whereupon the F and HD yielded 9.81 ± 0.58% and 3.12 ± 0.24% of polysaccharides, respectively. The chemical composition, physicochemical properties and infrared spectroscopy data suggested that they were acidic pectic type polysaccharides with galacturonic acid content 632.86 ± 2.30 μg mg−1 and 617.99 ± 3.15 μg mg−1 polysaccharide, degree of methoxylation 63.7 ± 1.5% and 48.9 ± 2.5%, and degree of acetylation 3.5 ± 0.1% and 3.3 ± 0.1% for F and HD polysaccharides, respectively. The rheological properties of acid-extractable polysaccharides were investigated and it was found that F-polysaccharide yielded strong gel. The polysaccharides were investigated by differential thermal analysis and the analyses revealed that they start decomposing significantly after 230–240 °C. Consecutive fractional extraction with four extractants was performed for the first time, and information about the polysaccharide content and the different polysaccharide fractions present in the wastes was obtained. The overall polysaccharide yield of 14.35 ± 1.01% and 20.01 ± 0.56% from HD and F marigold waste respectively, suggested that marigold waste could be an alternative source of pectic polysaccharides.

Nutrient release capability in Nordic and Baltic forest soils determined by dilute nitric acid extraction – Relationships with indicators for soil quality, pH and sustainable forest management

The long-term carrying capacity for biomass production is highly dependent on available soil resources. A soil test method for potential nutrient release capability was applied to 23 Nordic and Baltic forest soil profiles. The soils had coarse (10), medium (12) and fine (1) soil texture and most were podsolising. Extraction with dilute (0.1 M, 1:50 sample:solution ratio) nitric acid for 2 h was followed by 48 h and 168 h of extraction in soil samples from pedogenetic horizons. Dilute nitric acid solution was replaced after each step and release of mineral nutrient elements in solution was determined. C-horizon nutrient release (µmol g−1 fine earth, 0–218 h) was negatively correlated with mean annual temperature (MAT 0.5–8.5 °C) and for potassium (K) also mean annual precipitation (MAP 523–1440 mm y−1) suggesting a gradient in the mineralogy of the parent material that sediment transports during Pleistocene glaciations have not distorted. In B-horizons of sandy parent materials with felsic mineralogy cumulative nutrient release was positively correlated with pH and with Al and Fe release suggesting accumulation and stabilisation of nutrients in pedogenic products. E-horizons had less nutrient release capability than C-horizons, indicating a more weathered state of E-horizon parent material. Soil formation due to mineral dissolution and leaching of base cations and the gradient in parent material origin and weathering state both affected the observed pattern of nutrient release. On soils with very low mineral P resources (e.g. <250 kg P ha−1 to 50 cm) by repeated dilute acid extraction, harvest of nutrient rich biomass will not be sustainable. However, it can’t be concluded that sites with high P availability by 0.1 M HNO3 can support an intensive harvest without compensation of P (and Ca) by fertilisation. Due to buffering of removed base cations in B-horizons, nutrient export with biomass may not be traceable as pH decline at decadal time scale. Therefore, the direct measurement of nutrient stocks by the extraction procedure (or other similar assessment of nutrient reserves by strong acid) is suggested as indicative for the mineral weathering capability of forest soils to recover from P and base cation depletion by biomass harvest.

Evaluation of a single extraction test to estimate the human oral bioaccessibility of potentially toxic elements in soils: Towards more robust risk assessment

Intake of soil by children and adults is a major exposure pathway to contaminants including potentially toxic elements (PTEs). However, only the fraction of PTEs released in stomach and intestine are considered as bioaccessible and results from routine analyses of the total PTE content in soils, therefore, are not necessarily related to the degree of bioaccessibility. Experimental methods to determine bioaccessibility usually are time-consuming and relatively complicated in terms of analytical procedures which limits application in first tier assessments. In this study we evaluated the potential suitability of a recently developed single extract method (ISO-17586:2016) using dilute (0.43M) nitric acid (HNO3) to mimic the bioaccessible fraction of PTEs in soils. Results from 204 soils from Portugal, Brazil and the Netherlands including all major soil types and a wide range of PTEs' concentrations showed that the extraction efficiency using 0.43M HNO3 of Ba, Cd, Cu, Ni, Pb and Zn in soils is related to that of in vitro methods including the Simple Bioaccessibility Extraction Test (SBET) and Unified BARGE Method (UBM). Also, differences in the degree of bioaccessibility resulting from differences in parent material, geology and climate conditions did not affect the response of the 0.43M HNO3 extraction which is a prerequisite to be able to compare results from different soils. The use of 0.43M HNO3 as a first screening of bioaccessibility therefore offers a robust and representative way to be included in first tier standard soil tests to estimate the oral bioaccessibility. CapsuleThe single dilute (0.43M) nitric acid extraction can be used in first tier soil risk assessment to assess both geochemical reactivity and oral bioaccessibility of PTEs.

Proper management of lead-contaminated agricultural lands against the exceedance of lead in agricultural produce: Derivation of local soil criteria

The Measures for Management of Soil Environment in Agricultural Land (Trial, Nov. 01, 2017, China) recently came into effect and highlighted the proper management of contaminated croplands to lower risks of exceedances of contaminants, especially toxic trace metals in agricultural produce. We aimed to develop local soil criteria for lead (Pb) in Hezhang county of southwestern China by the inverse use of reliable models linking Pb contamination levels between soils and vegetables. Dilute nitric acid (0.43 M) extraction, a new ISO standard (ISO-17586:2016) for extracting the geochemically reactive Pb fraction (PbNA), and calcium chloride (0.01 M) extraction (ISO-14255: 1998) for estimating the plant-available Pb (PbCC) were performed in fifty historically polluted and newly Pb-spiked soils with differing soil types, properties (pH 4.1–8.0), and total soil Pb levels (PbT, 20–6153 mg kg−1). Greenhouse experiments for Brassica pekinensis L., and in-situ soil porewater measurement for Pb were conducted to investigate the mechanism of Pb uptake, and to establish reliable Pb soil-plant relationships. The results indicated that about 83% of the variation for Pb concentrations in vegetable (PbCL, 0.009–1.06 mg kg−1) was contributable to free Pb2+ activity in soil porewater, which was mainly influenced by pH and dissolved organic matter. PbCL was satisfactorily predicted using PbNA and key soil properties (adj. R2 0.852). Soil Pb criteria for PbT and PbNA are then derived based on food standard. The full implementation of criteria derived for PbNA (i.e., 27–127 mg kg−1, soil pH 5.5–8.0) can avoid the exceedance of Pb in 95% of cabbage samples in this study, 95% of cabbage cultivars by model extrapolation, and one widely cultivated root vegetable, radish, in the study region. We provide a successful case study that has effectively tackled the challenge for the complexity of the soil management in contaminated croplands.

Bioavailability of heavy metals in soil of the Tieguanyin tea garden, southeastern China

The bioavailability of 22 heavy metals was investigated at 19 sampling sites in Tieguanyin tea garden in Anxi County, Fujian Province, southeastern China. Heavy metal concentrations were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and evaluated by geo-accumulation index (I geo ). Dilute nitric acid extraction was used to evaluate biological activity. Cu, Pb, and Cd were highly bioavailable and most easily absorbed by tea trees. Heavy metal bioavailability in the surface soil was as the ratio of the effective state to the total amount. Cd had the highest I geo values, and the respective samples and sites were classified as moderately/strongly contaminated. Cd element is considered the main factor of heavy metal pollution in the tea garden in Anxi. The other heavy metals studied were present in lower concentrations; thus, the samples were classified as uncontaminated or slightly contaminated.

Estimating Inorganic Arsenic Exposure from U.S. Rice and Total Water Intakes.

Background:Among nonoccupationally exposed U.S. residents, drinking water and diet are considered primary exposure pathways for inorganic arsenic (iAs). In drinking water, iAs is the primary form of arsenic (As), while dietary As speciation techniques are used to differentiate iAs from less toxic arsenicals in food matrices.Objectives:Our goal was to estimate the distribution of iAs exposure rates from drinking water intakes and rice consumption in the U.S. population and ethnic- and age-based subpopulations.Methods:The distribution of iAs in drinking water was estimated by population, weighting the iAs concentrations for each drinking water utility in the Second Six-Year Review data set. To estimate the distribution of iAs concentrations in rice ingested by U.S. consumers, 54 grain-specific, production-weighted composites of rice obtained from U.S. mills were extracted and speciated using both a quantitative dilute nitric acid extraction and speciation (DNAS) and an in vitro gastrointestinal assay to provide an upper bound and bioaccessible estimates, respectively. Daily drinking water intake and rice consumption rate distributions were developed using data from the What We Eat in America (WWEIA) study.Results:Using these data sets, the Stochastic Human Exposure and Dose Simulation (SHEDS) model estimated mean iAs exposures from drinking water and rice were and , respectively, for the entire U.S. population. The Tribal, Asian, and Pacific population exhibited the highest mean daily exposure of iAs from cooked rice (); the mean exposure rate for children between ages 1 and 2 years in this population is body weight (BW)/day.Conclusions:An average consumer drinking 1.5 L of water daily that contains between 2 and is exposed to approximately the same amount of iAs as a mean Tribal, Asian, and Pacific consumer is exposed to from rice. https://doi.org/10.1289/EHP418

Evaluation of the Single Dilute (0.43 M) Nitric Acid Extraction to Determine Geochemically Reactive Elements in Soil.

Recently a dilute nitric acid extraction (0.43 M) was adopted by ISO (ISO-17586:2016) as standard for extraction of geochemically reactive elements in soil and soil like materials. Here we evaluate the performance of this extraction for a wide range of elements by mechanistic geochemical modeling. Model predictions indicate that the extraction recovers the reactive concentration quantitatively (>90%). However, at low ratios of element to reactive surfaces the extraction underestimates reactive Cu, Cr, As, and Mo, that is, elements with a particularly high affinity for organic matter or oxides. The 0.43 M HNO3 together with more dilute and concentrated acid extractions were evaluated by comparing model-predicted and measured dissolved concentrations in CaCl2 soil extracts, using the different extractions as alternative model-input. Mean errors of the predictions based on 0.43 M HNO3 are generally within a factor three, while Mo is underestimated and Co, Ni and Zn in soils with pH > 6 are overestimated, for which possible causes are discussed. Model predictions using 0.43 M HNO3 are superior to those using 0.1 M HNO3 or Aqua Regia that under- and overestimate the reactive element contents, respectively. Low concentrations of oxyanions in our data set and structural underestimation of their reactive concentrations warrant further investigation.