Masahiko Katoh

Nutrient Leaching from the Plow Layer by Water Percolation and Accumulation in the Subsoil in an Irrigated Paddy Field(Soil Physics)

Abstract To estimate the impact of water percolation on the nutrient status in paddy fields, the seasonal variations of the concentrations of cations, anions, inorganic carbon (IC), and of dissolved organic carbon (DOC) in percolating water that was collected from just below the plow layer (PW-13) and from drainage pipes at the 40 em depth (PW-40), as well as in irrigation water were measured in an irrigated paddy field. Total amounts of Ca, Mg, K, Fe, and Mn leached from PW-13 during the period of rice cultivation were estimated to range from about 390 to 770, 65 to 130, 33 to 66, 340 to 680, and 44 to 87 kg ha-1, respectively. Amounts of losses that were estimated from the differences between the input by irrigation water and the output by percolation water from the plow layer corresponded to 11 to 26, 22 to 47,5.9 to 12, and 13 to 26% of exchangeable Ca and Mg, amorphous Fe, and easily reducible Mn in the plow layer, respectively. The concentrations of Ca, Mg, K, Fe, and Mn in PW13 were higher than those in PW-40. The amounts of these nutrients that were retained in the subsoil between the 13 em and 40 em soil depth corresponded to 83, 86, 61, 99, and 89% of the amounts that percolated from the plow layer, respectively. Total amounts of IC and DOC that percolated from the plow layer ranged from 750 to 1,500 and 85 to 170 kg-C ha-1, which corresponded to 5.0 to 10.0% and 0.6 to 1.1% of the total carbon content in the plow layer, respectively. Eighty eight % of IC in the percolating water from the plow layer was also retained in the subsoil.

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.

Single-Step Extraction to Determine Soluble Lead Levels in Soil

This study investigated single-step extraction using EDTA to extract the amount of potentially soluble Pb in soil, which would be almost as much as that in the first four Pb fractions of Tessiers sequential extraction procedure (SEP), with or without the immobilization amendment hydroxyapatite under different extraction conditions such as concentration and extractant pH. The results clearly showed that 0.1M EDTA (pH 7.5) with a soil/extractant ratio of 1:100 can extract almost 90% of the first four Pb fractions of SEP, and EDTA-extracted Pb was positively correlated with the first four Pb fractions even in Pb-immobilized soil. In conclusion, single-step extraction using EDTA was found to be a useful method to evaluate potentially soluble Pb even in Pb-immobilized soils.

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

ABSTRACT 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.

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.

Suitable Chemical Properties of Animal Manure Compost to Facilitate Pb Immobilization in Soil

Chemical immobilization using animal manure compost is one of the most useful for low-cost, in-situ soil remediation techniques. The present study aimed to determine suitable chemical properties of animal manure compost to facilitate lead (Pb) immobilization in soil. The level of mobile Pb in soil amended with swine compost was higher than that amended with cattle compost during the early stage of incubation. However, the level of mobile Pb was almost the same in soil amended with both types of compost on day 184 of incubation. The ratio of the residual fraction after sequential extraction was enhanced in soil amended with both types of compost, particularly swine compost. X-ray diffractometer (XRD) results demonstrated the precipitation of Pb phosphate minerals, such as pyromorphite, in Pb-sorbed composts, particularly swine compost. Amendment using swine compost could reduce Pb solubility even when it had a high content of water-soluble organic matter because it significantly lowered Pb phase solubility. The amendment with swine compost improved plant growth and microbial activity. This study suggests that composts with high phosphorus (P) content are suitable for Pb immobilization amendment even if they have a high water-soluble organic matter content.

Role of Inorganic and Organic Fractions in Animal Manure Compost in Lead Immobilization and Microbial Activity in Soil

This study aimed to identify how the ratio of inorganic-to-organic components in animal manure compost (AMC) affected both lead immobilization and microbial activity in lead-contaminated soil. When AMC containing 50% or more inorganic fraction with high phosphorous content was applied to contaminated soil, the amounts of water-soluble lead in it were suppressed by over 88% from the values in the soil without compost. The residual fraction under sequential extraction increased with the inorganic fraction in the AMC; however, in those AMCs, the levels of microbial enzyme activity were the same or less than those in the control soil. The application of AMC containing 25% inorganic fraction could alter the lead phases to be more insoluble while improving microbial enzyme activities; however, no suppression of the level of water-soluble lead existed during the first 30 days. These results indicate that compost containing an inorganic component of 50% or more with high phosphorus content is suitable for immobilizing lead; however, in the case where low precipitation is expected for a month, AMC containing 25% inorganic component could be used to both immobilize lead and restore microbial activity.

Sites and processes of nutrient accumulation in the subsoil through water percolation from the plow layer in a submerged paddy soil microcosm

Abstract The leaching of nutrients from the plow layer by water percolation and their accumulation in the subsoil observed in a Japanese paddy field (Katoh et al. 2004: Soil Sci. Plant Nutr., 50, 721-729) were determined semi-quantitatively in a soil column experiment. Ca2+, Mg2+, K+, Mn2+, Fe2+, and phosphate in percolating water from the plow layer soil column were retained in the subsoil columns that were connected to the plow layer soil column. Fe2+, K+, and phosphate accumulated in the uppermost part of the subsoil. Accumulation of Fe2+ in the uppermost part of the subsoil was presmnably due to the cation exchange process with concomitant desorption of Ca2+. In contrast, Ca2+ and Mg2+ in percolating water from the plow layer soil colmnn accumulated once in the subsoil, and translocated downwards slowly with successive water percolation. Considerable amounts of inorganic carbon (IC) and dissolved organic carbon (DOC) in percolating water from the plow layer soil column were also retained in the subsoil columns. IC did not accumulate a gaseous form.

MICROSCOPIC RANGE OF IMMOBILIZATION BETWEEN HEAVY METALS AND AMENDMENT IN SOIL THROUGH WATER MIGRATION

In order to identify the microscopic range of immobilization in soil, the pot test was conducted to evaluate the distance that lead (Pb) and antimony (Sb) transport through water migration and the transport phases during immobilization. The amount of amendment required to immobilize Pb and Sb was investigated on the basis of the microscopic range of immobilization. The results clearly showed that Pb and Sb were transported a maximum of 5 mm and 6 mm, respectively, through water migration which corresponded to precipitation for one month. Both metals were accumulated 1 mm from contaminated soil. The primary Pb transport phase was sorbed on Fe/Mn oxide, while that of Sb was water-soluble. The amount of amendment required for Pb and Sb immobilization was estimated to be 4.62% (w/w) from the microscopic range of immobilization (1 mm).