Suppression of arsenic leaching from excavated soil and the contribution of soluble and insoluble components in steel slag on arsenic immobilization.

A huge amount of soil is excavated by tunnel and road construction projects in urban, coastal, and mountainous regions. These projects enable the effective use of underground spaces, and generally, the excavated soil is expected to be reused after treatment, which is required due to the potential release of geogenic arsenic from the soil. The present study investigated the level of water-soluble arsenic and arsenic phases in excavated soil in order to identify how arsenic is immobilized by soluble calcium and insoluble components in steel slag. The soluble calcium was found to suppress the level of water-soluble arsenic as well as arsenic in fraction 1 (nonspecifically bound) identified by sequential extraction from the soil but increased the level of fraction 2: specifically bound arsenic. The insoluble component did not suppress the level of water-soluble arsenic, but decreased and increased the arsenic levels in fractions 2 and 3 (amorphous iron/aluminum oxide bound), respectively. A column percolation test demonstrated that the arsenic that was inhibited from leaching by the addition of steel slag was the fractions 1 and 2 arsenic. The amounts of arsenic released in the serial batch leaching test were comparable with levels leached regardless of the addition of steel slag. These results indicate that both soluble calcium and insoluble components of steel slag have different roles in suppressing arsenic leaching from excavated soil. Based on these results, it is suggested that steel slag could be utilized to suppress arsenic release, thus enabling the reuse of excavated soil.

Impact of arsenic releaching from excavated rock after once-arsenic leaching on potential arsenic leaching.

Massive quantities of naturally arsenic-containing rocks are excavated from urbanized and mountainous areas for construction. Treatments such as chemical immobilization are applied to such excavated rocks for reuse. To design such treatments, determining the potentially leachable arsenic amounts in excavated rocks is imperative. This study aims to understand whether the arsenic releached amount from the excavated rock after once-arsenic leaching should be included in the potentially leachable arsenic amount or estimated using the sequential extraction procedure (SEP). Arsenic was releached at exceeding 0.01 mg L-1, even from the excavated rock that leached arsenic to less than 0.01 mg L-1, and this amount corresponded to approximately 12% of that of arsenic leached from the arsenic non-leached rock. The arsenic (re)leached amount corresponded to 84-116% (102 ± 7%) of that of arsenic in the readily soluble fraction using SEP, regardless of whether the arsenic was leached or not. These results indicate that the source of arsenic (re)leached from the excavated rock is arsenic extracted as the readily soluble fraction through SEP, regardless of whether the rock was arsenic-leached or not. This study's findings suggest that the arsenic releached amount from the excavated rock should be considered in the potentially leachable arsenic amount. In addition, the potentially leachable arsenic amount can be relatively and readily estimated by performing SEP.

Root response and phosphorus uptake with enhancement in available phosphorus level in soil in the presence of water-soluble organic matter deriving from organic material.

Understanding the available phosphorus (P) levels in the presence of water-soluble organic matter (WSOM) deriving from organic materials can be important for the improvement of the P use efficiency. This study aimed to: (i) determine which types of WSOM (deriving from the organic material) can suppress P immobilization, and (ii) understand whether plants can uptake P that the immobilization is suppressed by the presence of WSOM, as well as how the plant roots response depending on the available P levels. The P sorption test revealed that the presence of WSOM deriving from cattle manure compost (CM), sewage sludge compost (SSC), and hydrothermal decomposed liquid fertilizer (HDLF) can suppress the P sorption by 44, 44, and 24%, respectively, as compared to single P. In the incubation test, the percentage of the available P to that added as P fertilizer was found to be >21% higher in the presence of a CM- or a SSC-derived WSOM than those of single P, but the effect of the HDLF-derived WSOM was not. In the cultivation test, P uptake was found to be improved in the CM-, the SSC-, and the HDLF-deriving WSOM by 17, 13, and 11%, respectively, as compared to single P. Moreover, the root weight was found to decrease along with an increase in the amount of P uptaken by the plant. These findings provide the first experimental evidence that the presence of the WSOM deriving from CM, SSC, and HDLF simultaneously enhance the available P level in the soil and P uptake by the plant at the lab-scale test. In addition, the higher the available P levels in the presence of WSOM, the lower the root developments. The presence of WSOM, particularly of one of high maturity, can suppress the P sorption by 24-44%; as a result, >20% of the P added remains as the available P depending on the type of organic material used.

The effects of redox conditions on arsenic re-release from excavated marine sedimentary rock with naturally suppressed arsenic release.

Massive quantities of marine sedimentary rock are excavated from urban coastal areas. The excavated rock often releases arsenic with concurrent oxidation of framboidal pyrite, but the arsenic release is naturally suppressed with subsequent atmospheric exposure. The present study evaluated the re-release of arsenic from excavated rock in which arsenic release has been naturally suppressed by the atmospheric exposure in the presence of sulfate ions under various redox conditions using the biological reduction method. The atmospheric exposure and subsequent batch leaching test revealed that the amount of arsenic release that was naturally suppressed corresponded to 1.2% of the total arsenic content. The sequential extraction analysis also showed that the arsenic in the exposed rock was altered to insoluble phases. We observed a re-release of 6.0-18.2% of the total arsenic content under reductive conditions (< + 70 mV of Eh), exceeding the amount of arsenic that was naturally suppressed, even in the presence of sulfate ions. The correlation in the amount of arsenic and iron re-released demonstrates that arsenic re-release under reductive conditions is mainly regulated by the iron dissolution up to 10 mg kg-1 even in the presence of sulfate ion. Further reduction and dissolution of iron did not cause further increase in the arsenic re-release. Therefore, excavated marine sedimentary rock should be reused under redox conditions in which iron is not reduced. Otherwise, treatments such as chemical immobilization should be performed.

Characteristics of the immobilization process of arsenic depending on the size fraction released from excavated rock/sediment after the addition of immobilization materials.

Chemical immobilization is an effective technique to suppress the release of arsenic from naturally arsenic-containing excavated rock/sediment. For designing the chemical immobilization technique, it is important to understand that the immobilization of arsenic depends on the sizes of ionic arsenic and arsenic retained on the colloids and suspended particles that are released from the excavated rock/sediment. Tests on the size fractionation of the arsenic released and the subsequent immobilization were conducted. The total amount of the size fraction of arsenic released from six excavated rock/sediment ranged from 0.16 to 0.75 mg kg-1. The distributions of size fraction of arsenic released were categorized into three types: the dominant fraction was suspended particle fraction (SP-F) and ionic fraction (I-F), and a compatible amount of SP-F and I-F was included. Steel slag, calcium oxide, and ferrihydrite, which can effectively and stably immobilize ionic arsenic with different mechanisms, decreased the total amounts of the size fraction of arsenic released at 28%-84%, 59%-83%, and 57%-84%, respectively. Ferrihydrite and calcium oxide greatly reduced the I-F and the small and large colloid fractions. The steel slag was effective in reducing the SP-F at >86 %. In most arsenic fractions, the immobilized arsenic was not re-released at <7 %. This study provides the first experimental evidence of the variation in the released arsenic size depending on the excavated rock/sediment. In addition, the size fraction of the arsenic that could be immobilized depended on the immobilizing material. Thus, it is suggested that the combined application of immobilization materials would present a useful approach for immobilizing various released arsenic phases and preventing immobilized arsenic from re-release.

Loss of H3K27 trimethylation is frequent in IDH1-R132H but not in non-canonical IDH1/2 mutated and 1p/19q codeleted oligodendroglioma: a Japanese cohort study.

Oligodendrogliomas are defined by mutation in isocitrate dehydrogenase (NADP(+)) (IDH)1/2 genes and chromosome 1p/19q codeletion. World Health Organisation diagnosis endorses testing for 1p/19q codeletion to distinguish IDH mutant (Mut) oligodendrogliomas from astrocytomas because these gliomas require different treatments and they have different outcomes. Several methods have been used to identify 1p/19q status; however, these techniques are not routinely available and require substantial infrastructure investment. Two recent studies reported reduced immunostaining for trimethylation at lysine 27 on histone H3 (H3K27me3) in IDH Mut 1p/19q codeleted oligodendroglioma. However, the specificity of H3K27me3 immunostaining in this setting is controversial. Therefore, we developed an easy-to-implement immunohistochemical surrogate for IDH Mut glioma subclassification and evaluated a validated adult glioma cohort. We screened 145 adult glioma cases, consisting of 45 IDH Mut and 1p/19q codeleted oligodendrogliomas, 30 IDH Mut astrocytomas, 16 IDH wild-type (Wt) astrocytomas, and 54 IDH Wt glioblastomas (GBMs). We compared immunostaining with DNA sequencing and fluorescent in situ hybridization analysis and assessed differences in H3K27me3 staining between oligodendroglial and astrocytic lineages and between IDH1-R132H and non-canonical (non-R132H) IDH1/2 Mut oligodendroglioma. A loss of H3K27me3 was observed in 36/40 (90%) of IDH1-R132H Mut oligodendroglioma. In contrast, loss of H3K27me3 was never seen in IDH1-R132L or IDH2-mutated 1p/19q codeleted oligodendrogliomas. IDH Mut astrocytoma, IDH Wt astrocytoma and GBM showed preserved nuclear staining in 87%, 94%, and 91% of cases, respectively. A high recursive partitioning model predicted probability score (0.9835) indicated that the loss of H3K27me3 is frequent to IDH1-R132H Mut oligodendroglioma. Our results demonstrate H3K27me3 immunohistochemical evaluation to be a cost-effective and reliable method for defining 1p/19q codeletion along with IDH1-R132H and ATRX immunostaining, even in the absence of 1p/19q testing.

Phosphorus recovery from soil through phosphorus extraction and retention on material: A comparison between batch extraction-retention and column percolation.

Phosphorus (P) recovery from wastewater and soil is important for preventing the depletion of P resources; however, a method for recovering P from soil has not yet been developed. We designed and tested systems to recover P from excavated and in situ soil. P extraction from soil using citric acid, EDTA, and water is combined with P retention by calcium (Ca)- and magnesium (Mg)-containing material in both the batch extraction-retention and column percolation approach. In the batch extraction-retention test, Ca hydroxide retained more P than the other materials at 0.38-0.76 mg g-1, and the P was retained as Ca phosphate-like minerals. The amount of P retained by materials using chelating solutions was higher than with water, regardless of the material. The amount of P in the Ca-containing materials after the column percolation test was higher than in the Mg-containing materials, with the exception of Ca carbonate. In the column percolation test, the percentage of P recovery from the available P in the soil was 4.9% and 3.5% using Ca hydroxide and Ca oxide with water, respectively, and the application of chelating solutions did not improve P recovery. In the batch extraction-retention test, the percentage of P recovery using Ca hydroxide and Ca oxide with water was the same as that obtained by the column percolation test; however, the use of chelating solutions could improve the P retention to more than 11% and 7%, respectively. These results demonstrate that more than 10% and 5% of the available P in the soil could be recovered using Ca hydroxide in the batch extraction-retention test with citric acid and EDTA solutions and the column percolation test with water, respectively. The P-retained material may be used as a source for the production of chemical fertilizer.

Enhancing pyromorphite formation in lead-contaminated soils by improving soil physical parameters using hydroxyapatite treatment.

During chemical immobilization in soil, enhancement of insoluble phases is required to prevent toxic metal from leaching into the surrounding environment. Understanding the effects of physicochemical parameters of soil on the reaction between lead and hydroxyapatite is important to enhance the formation of the insoluble pyromorphite-lead phase. However, the combined effect of soil physical parameters on pyromorphite formation and compressive strength has not been reported. This study aimed to investigate the relationship between soil texture and pyromorphite formation, as well as unconfined compressive strength in lead-contaminated soils treated with hydroxyapatite under different compaction states and moisture conditions. Our findings showed that in compacted soil, >20% of lead was formed as pyromorphite compared with 10% of lead in uncompacted soil. In particular, low porosity and a high saturation ratio of soil under the unsaturated moisture condition were favorable for pyromorphite formation. Under the saturated moisture condition, the addition of hydroxyapatite enhanced pyromorphite formation compared with that under the unsaturated moisture condition. In addition, the leaching of soluble lead into the surrounding environment could be suppressed to <0.05% of lead in soil. The addition of hydroxyapatite also increased compressive strength of the compacted soil with increased curing period despite the soil texture. Our results suggest that treatments such as compacting and seepage control with hydroxyapatite may simultaneously increase pyromorphite formation and compressive strength. Furthermore, when performing soil recycling with hydroxyapatite at sites in the groundwater zone, the soluble lead in the soil is prevented from leaching to the surrounding environment. Hydroxyapatite could be used to enable the reuse of lead-contaminated soil for lead immobilization and to increase compressive strength.

Suppression of arsenic release from alkaline excavated rock by calcium dissolved from steel slag.

Massive quantities of alkaline rocks are excavated from urban coastal and mountain areas to make underground spaces available for infrastructure projects; however, such excavated rock often releases arsenic. In the present study, arsenic release from the excavated rocks with steel slag was investigated using dialysis and batch leaching tests to understand where arsenic is immobilized and which components in the steel slag suppress arsenic release from the excavated rock. Dialysis test indicated that the addition of steel slag at 10 wt% could suppress arsenic release at a level greater than 66%. The total arsenic content in the steel slag did not increase as compared with that before the test. Sequential extraction analysis indicated that the arsenic released during the dialysis test is mainly derived from arsenic fraction 1 (nonspecifically bound) due to the higher amount of this arsenic fraction in the excavated rock with the steel slag. Moreover, the steel slag extract could suppress arsenic release from the excavated rock and remove the arsenic from aqueous solution. The pH dependence test further indicated that the arsenic immobilized by the steel slag extract was stable under alkaline pH conditions. The levels of arsenic release decreased with increasing calcium release from the steel slag regardless of the type of excavated rock with an alkaline pH and were particularly seen at calcium released > 500 mg kg-1. These results indicate that the arsenic immobilization could be occurred not on the surface of steel slag, but on the excavated rock, and the calcium dissolved from the steel slag regulates the behavior of arsenic release from the surface of excavated rock. The findings of the present study suggest that the steel slag could be utilized to enable the reuse of excavated sedimentary and metamorphic rock of alkaline pH for the control of arsenic release.

Feature of lead complexed with dissolved organic matter on lead immobilization by hydroxyapatite in aqueous solutions and soils.

Lead (Pb) complexed with dissolved organic matter (DOM-Pb) is a dominant Pb species in soils, but it is not clear that DOM-Pb is stably immobilized by hydroxyapatite. This study investigates how DOM-Pb is immobilized by hydroxyapatite in both aqueous solutions and soils. A sorption test showed that 69.5% of DOM-Pb is removed in an aqueous solution, but less DOM-Pb is retained by hydroxyapatite compared with Pb ions. On the basis of the ratio of Pb and dissolved organic carbon before and after the sorption test, 7% of Pb was retained as DOM-Pb by hydroxyapatite, but 93% of Pb was dissociated from DOM-Pb, and was sorbed as Pb ions. The concentrations of water-soluble Pb re-released were higher in the DOM-Pb solution than those in the Pb ion solution in sandy loam soil with hydroxyapatite. A column-leaching test that flowed the DOM-Pb solution showed that Pb concentrations in leached water from sandy loam soil gradually increased after the middle stage of the test despite the presence of hydroxyapatite. The amount of water-soluble Pb re-released from soils with and without the hydroxyapatite that flowed the DOM-Pb solution was the same as or greater than that without the hydroxyapatite that flowed the Pb ion solution. This study concludes that in soils with low Pb sorption ability, some of the Pb retained as DOM-Pb is water soluble and possibly re-released despite the presence of hydroxyapatite, although most Pb in DOM-Pb is stably sorbed as Pb ions.

Estimation of potential arsenic leaching from its phases in excavated sedimentary and metamorphic rocks.

It is important that hazardous excavated sedimentary and metamorphic rocks are treated appropriately and reused without posing an environmental risk. Up-flow column leaching tests were conducted to examine whether arsenic leaching behavior varied among five hazardous excavated sedimentary and metamorphic rocks (two mudstones, clay sediment of marine origin, slate, and black schist) and to determine whether the potential amount of arsenic leaching could be estimated based on the arsenic-bearing mineral phases in the rock. Changes in arsenic concentration with pore volume (PV) showed the same pattern across all rock types, except for one that contained an extremely low amount of water-soluble arsenic, exhibiting an initial increase to reach a peak, followed by a decrease. The arsenic amounts leached before and after the PV at which the arsenic concentration peaked, corresponded to 88% ± 20% of the amount of arsenic fraction 1 obtained by sequential extraction and 76% ± 10% of the amount of arsenic fraction 2, respectively, while the potential amount of arsenic leaching corresponded to 65-89% of the summed total of arsenic fractions 1 + 2. These findings indicate that arsenic exhibits the same leaching behavior among different types of hazardous excavated sedimentary and metamorphic rocks except where extremely low amounts of water-soluble arsenic are present and that the potential amount of arsenic leaching can be approximated by calculating the summed total of arsenic fractions 1 + 2, which allows us to estimate the minimum amount of material required for treatments such as immobilization conducted to prevent arsenic leaching.

Arsenic release from marine sedimentary rock after excavation from urbanized coastal areas: Oxidation of framboidal pyrite and subsequent natural suppression of arsenic release.

Massive quantities of marine sedimentary rock are excavated from urban coastal areas for making underground spaces available for infrastructure projects globally. The excavated rock often contains low levels of framboidal pyrite, which can release arsenic (As) to levels that exceed environmental standards. In the present study, changes in As release and its phases were investigated during oxidation of framboidal pyrite in marine sedimentary rock following exposure to the atmosphere. Batch leaching tests showed that As release increases with atmospheric exposures over 14 days, and then decreases. In unexposed rock, 79% of As released was As(III), but the proportion of As(V) increased with atmospheric exposure times. The ratio of readily soluble As fractions (fraction 1 + 2) following sequential extraction also increased during the first 14 days of atmospheric exposures, and then decreased. In comparisons of As phases before and after leaching tests of atmosphere-exposed rocks, ratios of readily soluble As fractions decreased over 90-day atmospheric exposures. Amounts of amorphous iron also increased with the duration of atmospheric exposures. However, X-ray diffraction and scanning electron microscope analyses showed that framboidal pyrite morphology was maintained after 90 days of atmospheric exposure. Herein, we identify factors that control As release and its phases from marine sedimentary rock after excavation. The results will inform future studies that will indicate when and how to evaluate the risks of As release from marine sedimentary rocks containing framboidal pyrite.

Post-depositional changes in elemental leaching from recovered soils separated from disaster waste and tsunami deposits generated by the Great East Japan Earthquake and tsunami.

The Great East Japan Earthquake and subsequent tsunami in 2011 generated massive amounts of disaster waste and tsunami deposits, one-third of which comprised soil and sediment, which are expected to be re-used; however, there has been no previous experience or knowledge of recovered soil. In this study, up-flow column leaching tests were conducted to investigate the elemental leaching behavior in this soil and sediment following its separation and treatment (hereafter termed "recovered soil") to assess whether it can be safely re-used without posing any environmental risk. The pH of the leaching water was slightly alkaline throughout the test period, regardless of the source of the recovered soil. Concentrations of calcium and sulfate ions in the leaching water varied in a similar way to the electrical conductivity (EC), with a stable state being observed initially followed by a rapid decrease until typical concentrations were reached, whereas sodium and chloride ions derived from seawater made a relatively small contribution to the EC. In terms of toxic elements, zinc and copper concentrations decreased as the volume of leaching water increased, whereas lead, fluoride, and arsenic concentrations increased as the concentration of calcium and sulfate ions decreased, indicating that the dissolution of large quantities of compounds such as calcium sulfate controlled the toxic element behavior in the recovered soils. Consequently, there is a need for continuous and careful monitoring of areas where recovered soil is re-used or treatment of the recovered soil prior to its re-use.

Formation of a lead-insoluble phase, pyromorphite, by hydroxyapatite during lead migration through the water-unsaturated soils of different lead mobilities.

This study combined the original unsaturated-column-percolation test with X-ray diffraction (XRD) analysis to understand how lead is transformed into lead-insoluble phase and immobilized by hydroxyapatite during lead migration in the water-unsaturated soil of different lead mobilities. The amounts of lead migrated from the soils without hydroxyapatite ranged from 4 to 46%, depending on the lead mobilities of soils. On the other hand, those of soils with hydroxyapatite were greatly suppressed by > 95% as compared with those without hydroxyapatite. The XRD analysis showed that the amounts of lead transformed into pyromorphite were compatible with those of lead migrated from the soil irrespective of the different lead mobilities. To the best of our knowledge, this study provides the first experimental evidence that lead migration can induce lead to transform into pyromorphite in the water-unsaturated soil. In addition, this study quantitatively demonstrates that the amount of lead migrated is almost equal to that of lead formed into pyromorphite. Thus, it was found that even if soluble lead remains after the application of immobilization material, it would be immobilized by the material during the lead migration as long as adequate material is applied to the soil.

Immobilization of Lead Migrating from Contaminated Soil in Rhizosphere Soil of Barley (Hordeum vulgare L.) and Hairy Vetch (Vicia villosa) Using Hydroxyapatite.

This study conducted plant growth tests using a rhizobox system to quantitatively determine the distance of immobilization lead migrating from contaminated soil into uncontaminated rhizosphere soil, and to assess the lead phases accumulated in rhizosphere soil by sequential extraction. Without the hydroxyapatite, exchangeable lead fractions increased as the rhizosphere soil got closer to the contaminated soil. Exchangeable lead fractions were higher even in the rhizosphere soil that shares a boundary with the root surface than in the soil before being planted. Thus, plant growth of hairy vetch was lower in the soil without the hydroxyapatite than in the soil with the hydroxyapatite. The presence of hydroxyapatite may immobilize the majority of lead migrating from contaminated soil into the rhizosphere soil within 1 mm from the contaminated soil. The dominant lead fraction in the rhizosphere soil with the hydroxyapatite was residual. Thus, plant growth was not suppressed and the lead concentration of the plant shoot remained at the background level. These results indicate that the presence of hydroxyapatite in the rhizosphere soil at 5% wt may immobilize most of the lead migrating into the rhizosphere soil within 1 mm from the contaminated soil, resulting in the prevention of lead migration toward the root surface.

Reproducibility of up-flow column percolation tests for contaminated soils.

Up-flow column percolation tests are used at laboratory scale to assess the leaching behavior of hazardous substance from contaminated soils in a specific condition as a function of time. Monitoring the quality of these test results inter or within laboratory is crucial, especially if used for Environment-related legal policy or for routine testing purposes. We tested three different sandy loam type soils (Soils I, II and III) to determine the reproducibility (variability inter laboratory) of test results and to evaluate the difference in the test results within laboratory. Up-flow column percolation tests were performed following the procedure described in the ISO/TS 21268-3. This procedure consists of percolating solution (calcium chloride 1 mM) from bottom to top at a flow rate of 12 mL/h through softly compacted soil contained in a column of 5 cm diameter and 30 ± 5 cm height. Eluate samples were collected at liquid-to-solid ratio of 0.1, 0.2, 0.5, 1, 2, 5 and 10 L/kg and analyzed for quantification of the target elements (Cu, As, Se, Cl, Ca, F, Mg, DOC and B in this research). For Soil I, 17 institutions in Japan joined this validation test. The up-flow column experiments were conducted in duplicate, after 48 h of equilibration time and at a flow rate of 12 mL/h. Column percolation test results from Soils II and III were used to evaluate the difference in test results from the experiments conducted in duplicate in a single laboratory, after 16 h of equilibration time and at a flow rate of 36 mL/h. Overall results showed good reproducibility (expressed in terms of the coefficient of variation, CV, calculated by dividing the standard deviation by the mean), as the CV was lower than 30% in more than 90% of the test results associated with Soil I. Moreover, low variability (expressed in terms of difference between the two test results divided by the mean) was observed in the test results related to Soils II and III, with a variability lower than 30% in more than 88% of the cases for Soil II and in more than 96% of the cases for Soil III. We also discussed the possible factors that affect the reproducibility and variability in the test results from the up-flow column percolation tests. The low variability inter and within laboratory obtained in this research indicates that the ISO/TS 21268-3 can be successfully upgraded to a fully validated ISO standard.

Removal of lead by apatite and its stability in the presence of organic acids.

In this study, lead sorption and desorption tests were conducted with apatite and organic acids (i.e. citric, malic, and formic acids) to understand lead removal by apatite in the presence of an organic acid and lead dissolution from the lead- and organic-acid-sorbed apatite by such organic acid exposure. The lead sorption test showed that the amount of lead removed by apatite in the presence of organic acid varied depending on the type of acid used. The molar amounts of calcium dissolved from apatite in the presence and absence of organic acid were exactly the same as those of lead removed even under different pH conditions as well as different organic acid concentrations, indicating that the varying amount of lead removal in the presence of different organic acids resulted from the magnitude of the dissolution of apatite and the precipitation of lead phosphate minerals. The percentages of lead dissolved from the organic-acid-sorbed and non-organic-acid-sorbed apatite by all the organic acid extractions were equal and higher than those by water extraction. In particular, the highest extractions were observed in the non-organic-acid-sorbed apatite by citric and malic acids. These results suggest that to immobilize lead by the use of apatite in the presence of organic acids, much more apatite must be added than in the absence of organic acid, and that measures must be taken to ensure that the immobilized lead is not dissolved.

Simultaneous lead and antimony immobilization in shooting range soil by a combined application of hydroxyapatite and ferrihydrite.

This study investigated whether a combined application of hydroxyapatite and ferrihydrite could immobilize lead and antimony in shooting range soil in which the level of lead contamination is markedly higher than that of antimony. In addition, we evaluated the stability of lead and antimony immobilized by the combined application with varying soil pH. The levels of water-soluble lead and antimony for the combined application were lower than those of single applications of hydroxyapatite or ferrihydrite, indicating that the combined application could suppress the levels of water-soluble lead and antimony by 99.9% and 95.5%, respectively, as compared with the levels in shooting range soil without immobilization material. The amounts of residual lead and amorphous Fe/Al oxide-bound antimony fractions in sequential extraction increased with a decrease in the exchangeable and carbonate lead fractions as well as in non-specifically bound and specifically bound antimony fractions. The alteration of lead and antimony phases to chemically more stable ones as a result of the combined application would result in the suppression of their mobility. The stability of immobilized lead and antimony in the combined application was equal to that of lead with a single application of hydroxyapatite and that of antimony with a single application of ferrihydrite within neutral to alkaline pH conditions, respectively. Therefore, this study suggests that the combined application of hydroxyapatite and ferrihydrite can simultaneously immobilize lead and antimony in shooting range soil with neutral to alkaline pH.

Stability of Lead Immobilized by Apatite in Lead-Containing Rhizosphere Soil of Buckwheat (Fagopyrum esculentum) and Hairy Vetch (Vicia villosa).

This study conducted plant growth experiments using a rhizobox system to understand the growth of buckwheat and hairy vetch as well as the stability of lead immobilized by hydroxyapatite (HAP) in the lead-containing rhizosphere soil. The shoot dry weight of buckwheat did not significantly differ between the lead-containing rhizosphere soil with and without HAP, whereas that of hairy vetch with rhizosphere soil without HAP was reduced. Lead was not accumulated from the rhizosphere soil to the shoots of either plant when HAP was added. The percentage of each lead fraction in sequential extraction was approximately the same through the 3 mm of rhizosphere soils from the root surface and non-planted soil, with and without the addition of HAP. For hairy vetch, the amount of water-soluble lead in the HAP-added rhizosphere soil within 3 mm thickness from the root surface did not increase. However, for buckwheat, the amount of water-soluble lead in the HAP-added rhizosphere soil 1 mm from the root surface increased to the same level as that in the non-planted soil without HAP. Our results suggest that when applying phytostabilization combined with apatite to lead-contaminated soil, the plant that cannot re-mobilize lead should be selected.

Impact of phosphorus and water-soluble organic carbon in cattle and swine manure composts on lead immobilization in soil.

In the present study, we aimed to understand how amelioration of animal manure compost (AMC) with high phosphorus and low water-soluble organic carbon (WSOC) contents can simultaneously immobilize lead and reduce lead mobility and bioavailability in soil irrespective of the animal source. The amount of water-soluble lead in the soil amended with swine compost (SC) was not suppressed as compared with that in the soil without compost, whereas it was suppressed in the case of the soil amended with cattle compost (CC). The lead phases in the soil amended with SC became less soluble; however, those in the soil amended with CC were equivalent to those in the soil without compost. The ameliorated cattle and SCs with high phosphorus and low WSOC contents simultaneously induced a significant reduction in the concentration of water-soluble lead and ensured the formation of higher concentrations of insoluble lead phases. The microbial enzyme activities in the soil amended with the ameliorated compost were lower than those in the soil amended with the SC. This study suggests that ameliorated AMC can alter lead phases to insoluble forms and suppress the level of water-soluble lead, simultaneously. Therefore, such ameliorated AMC with high phosphorus and low WSOC contents would be suitable as a lead immobilization material.