Source: TEXAS A&M UNIVERSITY submitted to
INORGANIC CHEMICAL PROCESSES INFLUENCING SOIL AND WATER QUALITY
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
HATCH
Reporting Frequency
Annual
Accession No.
0198442
Grant No.
(N/A)
Cumulative Award Amt.
(N/A)
Proposal No.
(N/A)
Multistate No.
(N/A)
Project Start Date
Sep 26, 2003
Project End Date
Sep 25, 2009
Grant Year
(N/A)
Program Code
[(N/A)]- (N/A)
Recipient Organization
TEXAS A&M UNIVERSITY
750 AGRONOMY RD STE 2701
COLLEGE STATION,TX 77843-0001
Performing Department
SOIL & CROP SCIENCES
Non Technical Summary
Inorganic chemical processes influence soil quality, reactions of toxic metals in soil, and acquisition of nutrients and toxic elements by plants. The purpose of this project is to understand the role of inorganic chemical and mineralogical processes on the reactions of toxic metals in soil and the acquisition of nutrients and toxic metals by plants, for improved soil quality and environmental quality.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1020110200040%
1020110204010%
1020210200010%
1022499100010%
1040110200010%
1330110200010%
1330210200010%
Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 133 - Pollution Prevention and Mitigation; 104 - Protect Soil from Harmful Effects of Natural Elements;

Subject Of Investigation
0110 - Soil; 0210 - Water resources; 2499 - Plant research, general;

Field Of Science
2040 - Mineralogy; 2000 - Chemistry; 1000 - Biochemistry and biophysics;
Goals / Objectives
Soil, a critical natural resource, is the basis of our agriculture, the purifier (or source of pollution) of our water, the repository of our wastes, and a critical component of the overall global equation. Civilizations and risen and fallen with the health of the soil. Hence, soil quality is and will continue to be an important consideration in issues of local, national, and global sustainability. Deterioration of soil quality can occur either as a result of natural processes or anthropogenic activities. Considerable progress has been made towards an improved understanding of chemical factors influencing soil quality and contributing to soil deterioration, but much more has yet to be learned. An improved understanding of these processes for the optimized management of agricultural and environmental ecosystems is a national priority. The emphasis in this project is with inorganic (as opposed to organic) soil chemical processes that impact soil quality and soil deterioration, and implications of these processes to improved agricultural, environmental, and ecosystem management. Within this framework, there are three specific areas of emphasis: (i) toxic metals and metalloids in soils, (ii) acquisition beneficial nutrients and toxic elements by plants, and (iii) inorganic and mineralogical factors impacting soil quality Specific project activities are dictated by local, state, regional, and national priorities, and are designed to be highly interdisciplinary with allied disciplines in the chemical, life, environmental sciences. Toxic Metals in Soil. The toxic metals of primary concern are the USEPA priority pollutants Sb, As, Be, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, Tl, and Zn. Our current emphasis is with As, due to the proposed lowering of the drinking water standard from 50 to 10 ppb, severe arsenic contaminations in Texas, and the catastrophic arsenic contaminations in south and southeast Asia. Acquisition of Beneficial Nutrients and Toxic Elements by Plants. Plants sometimes exhibit specific physiological and biochemical adaptations to increase the mobilization and availability of the nutrient under nutrient-deficiency stress conditions. These reactions are especially notable in the cases or Fe and P. Plant adaptations to Fe deficiency include the exudation of iron chelating compounds (phytosiderophores) for monocots and the exudation of H+ and enhanced root plasma-membrane reductase activity for dicots. Plant adaptations to phosphate deficiency include organic acid exudation, enhanced root phosphatase activity, and changes in root architecture. There is considerable genetic variability with respect to these processes. Inorganic and Mineralogical Factors Impacting Soil Quality. Initial results have indicated that changes in soil management can result in relatively rapid changes in soil mineralogy, especially reductions in reactive Fe oxide and Ca carbonate contents. These changes can have significant influence on soil properties, e.g., carbon stabilization, soil structure and nutrient acquisition (especially of iron and phosphate), and might detrimentally impact soil quality.
Project Methods
Toxic Metals and Metalloids in Soils. Experiments are conducted to understand the factors influencing the solubility, adsorption, speciation, redox transformations, and biomobilization of toxic metal, as a prerequisite to optimized management/reclamation of contaminated soil and water. Our current emphasis is with arsenic (inorganic As(III) and As(V) and the methylarsenic compounds). Studies are conducted with both pure mineral phases and soils. Reactions of arsenic in soil are studied by wet chemical (adsorption isotherms, adsorption envelopes, competitive adsorption), spectroscopic (FT-IR, XANES, EXAFS), electrometric (voltametric, potentiometric), and kinetic methods. Arsenic is speciated and analyzed by chromatographic, HG-FAAS, and ICP-MS procedures. Plant growth and uptake studies are performed in both soil and hydroponic culture. Arsenic in plant tissue is monitored following plant digestion and non-destructively by x-ray microprobe and XANES spectroscopy using facilities of the National Synchrotron Light Source, Brookhaven, NY. We currently have a major project in collaboration with scientists at Cornell Univ., CIMMYT, and BAU and BRRI in Bangladesh involving the optimized management of arsenic contaminated sites for assurance of land sustainability and food security. Acquisition of Beneficial Nutrients and Toxic Elements by Plants. There have been significant advances in the understanding of plant nutrient-deficiency stress adaptations, but major gaps in knowledge still exist, and there has been little emphasis towards incorporation of these characteristics into plant selection and breeding programs. The reactions have significant environmental and ecological importance because of their impact on plant nutrition, fertilizer use efficiency, and environmental quality. Our emphasis is with inorganic chemical processes involved in nutrient acquisition by plants. This work is highly collaborative with plant physiologists, plant breeders, and molecular geneticists. Current involvement includes: (i) studies of the reactions of phytosiderophores with soil and soil components, (ii) studies role of plant released organic acids in the mobilization of P, and (iii) the combined role of phosphatase activity and organic-acid exudation on P mobilization and acquisition by plants. Efforts are being made to extend these basic studies to soil and plant management considerations. Mineralogical Factors Impacting Soil Quality. Studies are designed to address: (i) the impact of reactive Fe oxide and Ca carbonate contents on soil properties (carbon form and retention from decomposing organic matter; P form, bonding environment and bioavailability from inorganic P and decomposing organic matter sources), and (ii) the influence of soil management on short- and long-term soil mineralogical composition. Incubation studies are conducted in the laboratory. Carbon retention is assessed by evaluation of CO2 loss. Phosphate form and bioavailability is assessed by NMR, selective digestion and selective extraction procedures. Soil from long term management plots is accessed for changes in C content and Fe oxide mineralogy.

Progress 01/01/09 to 12/31/09

Outputs
OUTPUTS: Objective 1 - Evaluation of chemical and mineralogical characteristics of problem soils for improved agricultural sustainability, environmental quality and health: (1) continued evaluation of constraints to environmental quality and ecological and agricultural sustainability of serpentine soils in Zimbabwe and the U.S. (central Texas); (2) evaluation of mineralogy, chemistry and weathering of mixed mineralogy mine tailings (containing both pyrite and calcium carbonate); rates and mechanisms of continued oxidation of pyrite and approaches to minimizing the potential production of acid mine drainage. Objective 2 - Managing plant nutrients for improved agricultural sustainability and environmental quality: (1) initiated a project in sub-Saharan Africa (McKnight Foundation) to address improved sustainability (with emphasis on improved P acquisition and utilization) of marginal soils through a combined soils/plant genetic/cropping systems approach; (2) initiated a project to address the localization and mode of Zn bonding and solubility of Zn in flooded rice culture; the emphasis is on localization and retention of Zn by Fe oxides vs. Fe sulfides and implications to improved Zn nutrition in rice. Objective 3 - Management of rice to minimize potential detrimental impacts of arsenic: (1) completed a study that has demonstrated the significant impacts of water management on rice tolerance to arsenic and rice-grain arsenic concentration and speciation; (2) completed a study to address the movement or arsenic within the soil profile and the general mobility and localization of irrigation applied arsenic; (3) completed a preliminary study to address the impact of water management (continuous flooding vs. intermittent flooding) on bulk soil and rhizosphere microbial community structure; experiments are currently in progress to evaluate microbial community structure in the rice root plaque; (4) initiated a major new effort to address arsenic speciation at the rice root surface, with emphasis on methyl arsenic species, especially methyl arsenic (III) species. Objective 4 - Long term crop management for improved soil carbon sequestration and agricultural sustainability: (1) continued evaluation of the influence of long term cropping system alternatives on reactive Fe oxide mineralogy and properties in soil. PARTICIPANTS: Partner Organizations: USDA/ARS (Stuttgart, AR), Colegio de Postgraduados en Ciencias Agricolas (Montecillo, Edo. de Mexico), Cornell University, University of Illinois, Bangladesh Agricultural University; Collaborators: Courage Bangira (Texas A&M University), Dr. Rogelio Carrillo (Colegio de Postgraduados en Ciencias Agricolas, Montecillo, Mexico), Dr. Youjun Deng (Texas A&M University), Dr. J. M. Duxbury (Cornell University), Dr. Terry Gentry (Texas A&M University), Dr. Carmen Gonzalez (Colegio de Postgraduados en Ciencias Agricolas, Montecillo, Mexico); Dr. C.T. Hallmark (Texas A&M University), Dr. Frank Hons (Texas A&M University), Dr. Amir Ibrahim (Texas A&M University), Dr. Md. Jahiruddin (Bangladesh Agricultural University), Dr. Sabiou Mahamane (INRAN, Niamey, Niger), Roberta McClure (Texas A&M University), Dr. Craig Meisner (CIMMYT-Bangladesh), Dr. Anna McClung (USDA/ARS); ), Dr. J.C. Miller (Texas A&M University), Dr. Dr. G.M. Panaullah (CIMMYT-Bangladesh), Dr. W.A. Payne (Texas A&M University), Dr. Jacqui Peterson (Texas A&M University), Dr. Tushara Pillai (Texas A&M University), Dr. Kirk Scheckel (US-EPA), Dr. B.B. Singh (Texas A&M University), Anil Somenahally (Texas A&M University), Dr. J.W. Stucki (Univ. of Illinois), Wengui Yan (USDA/ARS), Dr. D.A. Zuberer (Texas A&M University) TARGET AUDIENCES: Training and Professional Development: Graduate education; Target audiences: scientific community (soil scientists, agronomists, environmental scientists environmental engineers, plant breeders); rice industry; mining industry; international partners (Bangladesh, Mexico, Niger, Zimbabwe); policy experts (agricultural policy, environmental policy). PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Objective 1 - Evaluation of chemical and mineralogical characteristics of problem soils for improved agricultural sustainability, environmental quality and health: (1) the serpentine soils of Zimbabwe exhibit both nutritional constraints (very low K and P status, high P fixing capacity, and high Mg/Ca ratios) and toxic constraints (high Ni and chromate concentrations); the extremely low K status would be especially detrimental to agricultural development without appropriate remedial strategies; major constraints vary with location and position along the Great Dyke); (2) evaluation of mineralogy, chemistry and weathering of mixed mineralogy mine tailings; though the pH values of pyrite-rich calcareous mine tailings are approximately 7-8, there is evidence for substantial continued oxidation of pyrite and the subsequent release of metals; these reactions have long term implications to environmental quality and strategies for site management. Objective 3 - Management of rice to minimize the potential detrimental impacts of arsenic: (1) the two predominant factors that impact As toxicity to rice and concentration and speciation of As in the rice grain are rice genetics and water management; crop management systems with reduced water use can be used to greatly reduce grain-arsenic concentration; arsenic hazard to rice could be virtually eliminated by means of varietal selection and appropriate water management strategies; even trace quantities of methyl arsenic in the soil can result in reduced rice yields and increased grain-arsenic concentration; (2) in a comprehensive study of two diverse arsenic-impacted soils it was determined that irrigation water arsenic is largely retained within the top 10 cm of soil and within the active rooting zone where it would have the greatest potential impact on plant metabolic processes; there was very little arsenic movement to sub-surface horizons; (3) water management (continuously flooded vs. intermittently flooded) strongly impacted microbial community structure.

Publications

  • Kramer, T.A., R.H. Loeppert and H. Wee. 2008. Assessment of arsenic treatment residuals: Analysis and stabilization techniques. AWWA, Denver, CO. 104 pp.
  • James, W.D., T. Raghvan, T.J. Gentry, G. Shan and R. H. Loeppert. 2008. Arsenic speciation: HPLC followed by ICP-MS or INAA. J. Radioanal. Nucl. Chem. 278:267-270.
  • Panaullah, G.M., T. Alam, B.K. Hossain, R.H. Loeppert, J.G. Lauren, C.A. Meisner, Z.U. Ahmed and J.M. Duxbury. 2008. Arsenic toxicity to rice (Oryza sativa L.) in Bangladesh. Plant Soil 317:31-39.
  • Hossain, M.B., M. Jahiruddin, R.H. Loeppert, G.M. Panaullah, M.R. Islam and J. M. Duxbury. 2009. The effects of iron plaque and phosphorus on yield and arsenic accumulation in rice. Plant Soil 317:167-176.
  • Khan, M.A., M.R. Islam, G.M. Panaullah, J.M. Duxbury, M. Jahiruddin and R.H. Loeppert (2009) Fate of irrigation water arsenic in rice soils of Bangladesh. Plant Soil 322:263-277.
  • Pillai, T.R., W.G. Yan, H.A. Agrama, W.D. James, A.M. Ibrahim, T.J. Gentry, A.M. McClung and R.H. Loeppert. 2009. Total Grain-Arsenic and Arsenic-Species Concentrations in Rice as Impacted by Genotype and Water Management. (2009 Annual Meeting (November 1-5, 2009))
  • Somenahally, A., R.H. Loeppert, W.G. Yan and T.J. Gentry. 2009. Microbial Community Response to Two Water Management Systems for Wetland Rice Production in High Arsenic Soils. (2009 Annual Meeting (November 1-5, 2009))
  • Bangira, C. and R.H. Loeppert. 2009. Reactions with Poorly Crystalline Fe Oxides: Implications On Solubility and Bioavailability Under Flooded-Rice Production. (2009 Annual Meeting (November 1-5, 2009))
  • Loeppert, R.H. 2009. The Important Roles of Natural Fe-Oxide Nano-Phases in Nutrient Dynamics and Nutrient Acquisition by Plants. (2009 Annual Meeting (November 1-5, 2009))


Progress 09/26/03 to 09/25/09

Outputs
OUTPUTS: Primary outputs included the conduct and analysis of experiments in five principal areas: (1) evaluation of constraints to environmental quality and the ecological and agricultural sustainability of serpentine soils of the U.S. and southern Africa as a basis for improved environmental and agricultural management; (2) evaluation of the major factors impacting environmental hazard, effective management and re-vegetation of mixed metal sulfide mine wastes; (3) evaluation of soil factors and plant physiologic and genetic factors impacting phosphate acquisition and utilization by cowpea, as a basis for improved yields on marginal soils in Africa and the U.S.; (4) evaluation of the mode of zinc bonding and its bioavailability to rice in flooded soils, as a basis for improved zinc fertilizer management in problem soils; and (5) evaluation of the rice genetic and water management factors impacting grain-arsenic concentration and arsenic toxicity to rice, as a basis for minimizing arsenic hazard in rice production. Three PhD students completed degrees during 2010. Where possible, recent findings were incorporated into graduate instruction materials. PARTICIPANTS: Individuals --- Courage Bangira (Graduate Student), Tushara Pillai (Graduate Student), Anil Somenahally (Graduate Student) ; Collaborators --- Rogelio Carrillo (Colegio de Postgraduados, Mexico), Youjun Deng (Texas A&M University), John Duxbury (Cornell University), Scott Fendorf (Stanford University), Terry Gentry (Texas A&M University), Carmen Gonzalez (Colegio de Postgraduados, Mexico), F.M. Hons (Texas A&M University), Amir Ibrihim (Texas A&M University), Dennis James (Texas A&M University), Md. Jahiruddin (Bangladesh Agricultural University), Asad Khan (Bangladesh Agricultural University), Sabiou Mahamane (INRAN, Niger), Yoko Masue Slowey (Stanford University), Anna McClung (USDA-ARS), J.M. Panaullah (Cornell University), Jacquelin Peterson (Texas A&M University), B.B. Singh (Texas A&M University), Joe Stucki (Univ. of Illinois), Wengui Yan (USDA-ARS) ; Training and Professional Development --- graduate instruction TARGET AUDIENCES: Target audiences --- environmental scientists, agronomists, soil Scientists, rice producers, mining industry, students ; Efforts --- classroom instruction, laboratory instruction PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
(1) Continuing studies have further verified the substantial roles of rice genetics and water management in controlling both the toxicity of arsenic to rice and arsenic concentration in the rice grain. Arsenic hazard to rice can be virtually eliminated by means of genetic selection and water management strategies that leave the rice rhizosphere more highly oxidized during periods of the growth cycle, e.g., by intermittent flooding as opposed to continuous flooding. (2) The methyl arsenic species are both readily adsorbed and toxic to rice plants. Methyl arsenic herbicides (even in trace quantities) can be highly toxic to rice an are not compatible with rice production. (3) The heterogeneity of the rice rhizosphere, e.g., as expressed in localized variability in redox potential and in localized mineralogy, has become increasingly apparent. This heterogeneity can also result in complex and variable microbial community structures and processes. (4) Advances have made in the understanding of processes that control the solubility and mobility of both iron and arsenic in reduced soils. (5) The properties of serpentine soils of the great Dyke of Zimbabwe and their associated constraints to environmental quality and agricultural sustainability are highly impacted by both their parent mineralogy and their weathering history. Our recent studies have important implications to similar serpentine soils in the U.S. and worldwide. (6) Continuing studies have verified the considerable genetic variability of cowpea in the acquisition of phosphate from rock phosphate and iron-oxide bound phosphate. Studies continue on the physiologic and genetic bases of this variability. These studies have important implications to improved productivity in phosphate limited regions of sub-Saharan Africa and to improved phosphate fertilizer utilization in intensive agricultural systems.

Publications

  • Khan, M.A., M.R. Islam, G.M. Panaullah, J.M. Duxbury, M. Jahiruddin amd R.H. Loeppert. 2010. Accumulation of arenic in soil and rice under wetland conditions in Bangladesh. Plant Soil 333:263-274.
  • Masue-Slowey, Y.M., R.H. Loeppert and S. Fendorf. 2011. Alteration of ferrihydrite reductive dissolution and transformation by adsorbed As and structural Al: Implications for As retention. Geochim. Cosmochim. Acta 75:870-886.
  • Gonzalez-Chavez, M.C., J.A. Aikenhead-Peterson, T.J. Gentry, D. Zuberer, F. Hons and R.H. Loeppert. 2010. Impact of long-term tillage and crop rotations on labile and recalcitrant C and N pools and soil microbial commuities. Soil and Tillage Research 106:285-293 (doi:10.1016/j.still.2009.11.008).
  • Pillai, T.R., W.G. Yan, H.A. Agrama, W.D. James, A.M.H. Ibrahim, A.M. McClung, T.J. Gentry and R.H. Loeppert. 2010. Total grain-arsenic and arsenic-species concentrations in diverse rice cultivars under flooded conditions. Crop Sci. 50:2065-2075 (doi: 10:2135/cropsci2009.10.0568).


Progress 01/01/08 to 12/31/08

Outputs
OUTPUTS: Objective 1 - Evaluation of chemical and mineralogical characteristics of problem soils for improved agricultural sustainability, environmental quality and health: (1) completed an initial evaluation of the mineralogy and toxic metal concentration and speciation of several important serpentine soils of Zimbabwe and the U.S. as a part of an evaluation of potential hazards to agriculture, environment and human health. Objective 2 - Managing phosphate for improved agricultural sustainability and environmental quality: (1) completed an experimental evaluation of more than 270 entries of the U.S core cowpea collection for adaptation to low P soils, genetic variability in P-utilization efficiency, and responsiveness to applied rock phosphate; evaluated selected cowpea varieties for their genetic variability in organic-cid exudation as a P-deficiency stress adaptation; (2) developed protocols for rapid analysis of phytate in grain; completed an initial experimental evaluation of genetic variability of phytate concentration in wheat grain; (3) completed an experimental study of the relative influence of oxidizing/reducing conditions on K+ retention by soils dominated by Fe-rich layer silicates. Objective 3 - Management of rice to minimize potential detrimental impacts of arsenic: (1) completed an evaluation of genetic variability in rice-grain arsenic concentration and speciation of selected U.S. and international rice varieties; completed an initial experimental evaluation of the impact of water management on rice-grain arsenic concentration and speciation; (2) completed an experimental study in Bangladesh under field conditions on the impact of soil arsenic on rice grain yield and grain-As concentration; (3) completed an experimental study in Bangladesh of the downward movement of arsenic under flooded rice culture under both natural field conditions and in undisturbed soil columns; (4) completed an experimental study in Bangladesh on the influences of dissolved iron, phosphate and arsenic on plaque composition on the rice-root surface and arsenic concentration in rice. Objective 4 - Long term crop management for improved soil carbon sequestration and agricultural sustainability: (1) completed an experimental study of the influence of long term cropping system alternatives on reactive Fe oxide occurrence and properties in soil. PARTICIPANTS: Partner Organizations: USDA/ARS, Stuttgart, AR; Cornell University; Bangladesh Agricultural University; CIMMYT Collaborators: Dr. Youjun Deng (Texas A&M University); Dr. J. M. Duxbury (Cornell University); Dr. Terry Gentry (Texas A&M University); Dr. C.T. Hallmark (Texas A&M University); Dr. Frank Hons (Texas A&M University); Dr. Amir Ibrahim (Texas A&M University); Dr. Md. Jahiruddin (Bangladesh Agricultural University); Dr. Craig Meisner (CIMMYT-Bangladesh); Dr. Anna McClung (SDA/ARS); ); Dr. J.C. Miller (Texas A&M University); Dr. Dr. G.M. Panaullah (CIMMYT-Bangladesh); Dr. W.A. Payne (Texas A&M University); Dr. Jacqui Peterson (Texas A&M University); Dr. D.W. Reed (Texas A&M University); Dr. J.W. Stucki (Univ. of Illinois); Wengui Yan (USDA/ARS); Dr. D.A. Zuberer (Texas A&M University); Training and Professional Development: Graduate education; distance education to Bangladesh TARGET AUDIENCES: Target audiences: scientific community; rice researchers; rice industry; soil scientists/agronomists; African scientists; Bangladesh scientists and agricultural policy experts PROJECT MODIFICATIONS: We are taking a much more interdisciplinary approach to involve soil and crop scientists; microbiologists; food scientists; nutritionists.

Impacts
Objective 2 - Managing phosphate for improved agricultural sustainability and environmental quality: (1) identified genetic variability of cowpea in P-utilization efficiency and responsiveness to applied rock phosphate. Objective 3 - Management of rice to minimize potential detrimental impacts of arsenic: (1) identified considerable genetic variability in rice-grain arsenic concentration and speciation among U.S. and international rice varieties; (2) documented the impact of soil arsenic on yield reduction of flooded rice in Bangladesh; (3) documented that the downward leaching of arsenic in the soil profile accounted for less than 10% of the total arsenic applied in irrigation water; the largest proportion of retained arsenic was retained in the plow layer of the flooded rice paddy; (4) documented that the Fe oxide plaque at the rice root surface had a mitigating effect on total arsenic uptake under flooded rice culture.

Publications

  • Mahamane, S., W.A. Payne, R.H. Loeppert, J.C. Miller and D.W. Reed. 2008. Evaluation of cowpea genotypes for adaptation to low soil P conditions and rock phosphate application. Hortscience 43:618-619.
  • Hossain, M.B., M. Jahiruddin, G.M. Panaullah, R.H. Loeppert, M.R. Islam and J.M. Duxbury. 2008. Spatial variability of arsenic concentration in soils and plants, and its relationship with iron, manganese and phosphorus. Environ. Pollut. 156:739-744.


Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: A major emphasis for 2007 has been a continuing evaluation of mineralogical, soil, plant and microbial factors that impact arsenic speciation, adsorption, mobility and bioavailability in soils. Several small studies to better understand the reactions of arsenic with specific soil minerals and mineral assemblages (including calcite; mixed valency and mixed metal-oxide phases; layer silicates; weathered mica aggregates) have been completed. This information is useful development of strategies for treatment and management of arsenic contaminated soil and water. We are in the middle of a large interdisciplinary project, also involving plant scientists, to assess the impact of soil management and plant genetics on arsenic concentration in rice grain, for improved "food for health". Rice varieties grown under defined water-management regimes have been phenotyped with respect to the characteristics of accumulation and speciation of arsenic in rice grain. These analyses are the bases of mapping populations that have been established to better understand the genetic control of arsenic characteristics (concentration and speciation) in rice. The goal is to minimize arsenic in rice grain for public assurance of rice as a food for health, through a combination of sound management and varietal selection. A second major interdisciplinary effort (also in cooperation with plant scientists) involves studies to elucidate the complex plant genetic and soil factors that impact phosphate acquisition by plants under low to moderate soil-fertility conditions. The goal is to utilize these characteristics for improved agricultural sustainability, nutrient-use efficiency and environmental quality. PARTICIPANTS: Dr. Wen Gui Yan, co-investigtor, USDA-ARS, Stuttgart, AR Dr. Terry Gentry, co-investigator, Texas A&M University Dr. Bill Payne, co-investigator, Texas A&M University Dr. Rogelio Carrillo, Visiting Scholar, Colegio de Postgraduados, Texcoco, Mexico Dr. Carmen Gonzalez, Visiting Scholar, Colegio de Postgraduados, Texcoco, Mexico Tushara Raghvan, Graduate Student (PhD) Anil Somenahalli, Graduate Student (PhD) Courage Bangira, Graduate Student (PhD) Sabiou Mahamane, Graduate Student (PhD) Robert Jones, Graduate Student (MS) TARGET AUDIENCES: Rice industry Rice breeders/geneticists/agronomists Cowpea breeders/geneticists/agronomists Water treatment professionals Ground water geologists Environmental scientists

Impacts
Reactions of arsenic with several soil minerals have been further clarified, especially reactions involving calcite, mixed valency oxides and layer-silicate minerals. The important role of counter ion in arsenic adsorption and release by oxide minerals has been demonstrated in results from our laboratory. Failure by engineers and systems modelers to adequately consider counter ion has resulted in reduced efficiency (and failure, in some cases) to adequately remove arsenic from water and to model arsenic solubility and movement in aquifers. Our results have prompted discussion among water-treatment professionals and geologic engineers regarding approaches to effective water utilization and treatment. Our phenotyping of rice varieties for arsenic concentration and speciation is currently being utilized by rice breeders in the establishment of mapping populations to more effectively understand and utilize rice genetics to minimize arsenic concentration and obtain favorable arsenic speciation in rice grain. Likewise, our initial studies of arsenic dynamics in rice paddies, have resulted in the establishment of management trials aimed at minimizing arsenic in rice grain. In collaboration with plant breeders and physiologists, we have demonstrated genetic variability of cowpea varieties in the acquisition of bound P from rock phosphate and Fe oxide. These results have important implications to the development sustainable production systems on marginal soils such as those of sub-Saharan Africa. Our phenotyping approaches to determine genetic variability in phosphate acquisition among cowpea varieties has generated interest among several plant breeders in the establishment of mapping populations to evaluate the genetic bases of variable phosphate acquisition.

Publications

  • Masue, Y., R. H. Loeppert and T. A. Kramer. 2007. Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum:iron hydroxides. Environ. Sci. Technol. 41:837-842
  • Bhattacharya, P., A. B. Mukherjee, J. Bundschuh, R. Zevenhoven and R. H. Loeppert (eds.). 2007. Arsenic in Soil and Groundwater Environment. Elsevier, Amsterdam. 653 p.


Progress 01/01/06 to 12/31/06

Outputs
Much of our current research focuses on arsenic in soil and water. Arsenic is toxic to plants and animals and in some cases can endanger agricultural sustainability. This report summarizes our efforts in on-going studies that are aimed at understanding and minimizing arsenic hazard in soil, water and agricultural systems. Our current research with arsenic is focused in four primary areas, as summarized below. (1) Studies of the reactions of arsenic with soil minerals as a basis for more fully understanding the processes that impact arsenic adsorption and solubility. Our current emphases are with calcite and its solid phase reaction products upon exposure to arsenic; mixed valence oxides (e.g., green rust) which can exist in wetland situations; and Al-substituted ferric-hydroxide minerals. (2) Methylation and demethylation of arsenic in wetland systems and evaluation of the potential for arsenic volatilization. These reactions are essential components in understanding arsenic mobility and mass balance in soils. (3) Environmental and genetic factors impacting tolerance of wetland rice to arsenic and uptake and transport of arsenic to the grain. Paddy rice is especially susceptible to arsenic because of the greater solubility of arsenic in soil under reduced conditions. Currently there is increasing concern with the potential impact of arsenic on agricultural sustainability in several critical locations, e.g., in Bangladesh. Our studies have provided evidence of decreasing rice yields in Bangladesh as a result of increasing arsenic levels in the soil from irrigation with arsenic-contaminated water. In the U.S and worldwide there is increasing concern with arsenic in rice grain. Our current work has demonstrated considerable genetic variability in both uptake and speciation of arsenic in rice. Arsenic speciation in the grain is a critical consideration since the methyl forms of arsenic are much less toxic than inorganic arsenic. The goal of minimizing arsenic hazard will be achieved through a combination of (i) management to reduce arsenic inputs and bioavailability of arsenic and (ii) the selection of rice varieties for reduced uptake and favorable arsenic speciation. (4) Studies of the factors that impact the release of arsenic during the land disposal of water-treatment residuals. We are collaborating with water scientists to investigate the stabilization of arsenic in both the water treatment process and during land disposal. Our studies of both arsenic methylation/demethylation and arsenic in rice are highly interdisciplinary and involve active collaborations with microbiologists, plant geneticists and physiologists, and field agronomists. We also continue to collaborate with scientists at CIMMYT, BARI, BRRI, BAU and SRDI in Bangladesh on field studies to better understand arsenic behavior in soils and plants.

Impacts
Arsenic is toxic to both plants and animals. Major arsenic contaminations exist worldwide and can occur as a result of both anthropogenic activities and natural geologic processes. These contaminations can in some cases impact water quality, food quality and security, human health, and agricultual sustainability. The catastrophic arsenic contamination of the groundwater in south Asia, has placed approximately 30,000,000 people at risk in Bangladesh alone. Concern with arsenic in water and the food chain (especially in rice) has brought worldwide attention to arsenic. The rice industry in the U.S. is facing new challenges, because of concern with arsenic. This project is addressing the chemical and biological factors that control arsenic dynamics in soil and water and absorption by plants as a basis for improved management to minimize arsenic hazard.

Publications

  • No publications reported this period


Progress 01/01/05 to 12/31/05

Outputs
Studies are in progress to evaluate the mineralogical controls on trace-metal retention and release under alternating redox conditions as might occur in seasonally wet soils. This report focuses on studies to evaluate the mineralogical controls, specifically of Fe oxides, on adsorption/desorption of methyl arsenic compounds. In virtually all Earth surface environments, methylated forms of arsenic can be found. Because of the widespread distribution and potential toxicity of methyl-arsenic compounds, their adsorption by soil minerals is of considerable interest. In the studies reported here, the adsorption and desorption behavior of methylarsonic acid, MMAs(V); methylarsonous acid, MMAs(III); dimethylarsinic acid, DMAs(V); dimethylarsinous acid, DMAs(III); arsenate, iAs(V); and arsenite, iAs(III) on iron oxide minerals (goethite and 2-line ferrihydrite) were studied by means of adsorption isotherms, adsorption envelopes, and desorption envelopes (using sulfate and phosphate as desorbing ligands). MMAs(III) and DMAs(III) were not appreciably retained by goethite or ferrihydrite within the pH range of 3 to 11, while iAs(III) was strongly adsorbed to both iron oxides. MMAs(V) and iAs(V) exhibited high adsorption affinities on both goethite and ferrihydrite from pH 3 to 10, while DMAs(V) was adsorbed only at pH values below 8 by ferrihydrite and below 7 by goethite. Each of the arsenic compounds was desorbed more efficiently by phosphate than sulfate. MMAs(V), iAs(V), and DMAs(V) each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in both decreased adsorbed arsenic at low arsenic concentrations in solution and increased ease of arsenic release from the iron oxide surface. The results of this study indicated a weaker bond between MMAs(V) and iron-oxide surfaces than between iAs(V) and iron oxides (especially at high pH values). This difference in apparent bonding strength might be influenced by the electron donating characteristics of the methyl group of MMAs(V). As arsenic methylation increases from the inorganic forms of arsenic to the mono- and di-methyl arsenic forms, the general trend is for adsorption potential to decrease. These results indicate that in soil systems with conditions favorable for arsenic methylation, the arsenic could become more mobile. The greater mobility of methyl arsenic might also influence the greater plant uptake of DMAs(V) compared to iAs(III) and iAs(V) under some conditions. Greater mobility of arsenic could also be important in soils that have had methylated arsenic applied as pesticides or herbicides. The reduced adsorption affinity of methyl arsenic species could impact the movement of arsenic to groundwater. In soils under reduced conditions, the combined effects of iron reduction, increased iron oxide solubility, and the lower adsorption affinities of methyl arsenic species would together significantly increase the potential for arsenic mobility.

Impacts
Arsenic is toxic to both plants and animals. Major arsenic contaminations exist worldwide and can occur as a result of both anthropogenic activities and natural geologic processes. The catastrophic arsenic contamination of the groundwater in south Asia, that has placed approximately 30,000,000 people at risk in Bangladesh alone, and concern with arsenic in water and the food chain (especially in rice) has brought worldwide attention to arsenic. The methyl arsenic compounds can play an especially important role because of (i) their extensive use as agricultural herbicides and defoliants and (ii) the biological methylation of inorganic arsenic that can occur naturally in soil. The understanding of the adsorption/desorption behavior of methyl arsenic compounds is especially critical to understanding their potential mobility and bioavailability in soils and to effectively manage soils to minimize arsenic hazard.

Publications

  • Lafferty, B.J. and Loeppert, R.H. 2005. Methyl arsenic adsorption and desorption behavior on iron oxides. Environ. Sci. Technol. 39:2120-2127.


Progress 01/01/04 to 12/31/04

Outputs
Studies are in progress to evaluate the mineralogical controls on trace-metal retention and release under alternating redox conditions as might occur in seasonally wet soils. This report focuses on studies to evaluate the mineralogical composition and predominant mineralogical controls on soil arsenic (As) retention and release in the rice-paddy soils of Bangladesh. Soil samples for this study were collected from 0-15 cm depth from approximately 475 rice paddies in five thanas in diverse agroecological zones of Bangladesh that had known high concentrations of arsenic in the shallow groundwater that is utilized for irrigation. Soil mineralogy, As concentration and speciation, As retention and release characteristics, and predominant bonding sites for As retention in selected samples were investigated using wet chemical procedures in combination with XRD, FTIR, synchrotron x-ray microprobe, XANES, SEM, and TEM. Soil mineralogy, though relatively similar with respect to the principal mineralogy, was highly variable with respect to soil texture and mineral concentrations. The principal reactive minerals were di- and tri-octahedral micas, high-Fe vermiculites, smectites, Fe-chlorite, and the Fe oxides, goethite, lepidocrocite and ferrihydrite. Gibbsite was not identified in any of these rice-paddy soils. Relatively low concentrations of calcite were observed in soils from two of the thanas, but arsenic was not highly associated with this phase. The As contents of the 475 surface soils in this study varied from 0.7 to 66.0 ppm As. Ammonium-oxalate extractable As averaged approximately 70 % of the total As, indicating that As was highly associated with the poorly crystalline Fe-oxide component. An average of 23 % of total As was extracted to pH 4.0, 0.1 M Na phosphate, indicating that most of the As was strongly bound and was not readily exchanged by phosphate. In an assessment of 15 high As soils, with soil-As concentrations averaging 22.0 ppm As, As was associated with sand (29.9 ppm), silt (17.5 ppm), and clay (34.1 ppm) particle-size fractions. A synchrotron x-ray microprobe study indicated that As bonding to layer silicate (mica, chlorite, vermiculite) edge sites was negligible. In the sand fraction, As was largely associated with Fe oxide weathering rinds within schist and weathered mica aggregates. Fe sulfide phases (pyrite and mackinawite) were identified in only a few of the rice-paddy soils and thus would not be expected to contribute substantially to As bonding in these soils. Remnants of Fe oxide plaques, which were originally formed on the surfaces of rice roots, were observed. As concentrations on these plaques were uniformly high. The solubility of As increased substantially upon soil flooding and reduction, due to the dissolution of Fe oxide, especially the highly reactive poorly crystalline Fe oxides, such as ferrihydrite. All results indicate that As solubility in these soils is strongly impacted by Fe oxide dynamics.

Impacts
Arsenic is toxic to both plants and animals. Contaminations can occur as a result of either anthropogenic activities or natural geologic processes. Major natural arsenic contaminations exist worldwide, but especially in developing countries, because of the rapid rise in use of groundwater versus surface water for drinking and irrigation. A natural arsenic contamination of the Ganges-Brahmaputra-Meghna groundwater aquifer in south Asia currently places approximately 30,000,000 people at risk in Bangladesh and India. The current study is part of a larger project to understand arsenic dynamics in flooded rice culture, as a basis for development of management systems to minimize arsenic hazard.

Publications

  • No publications reported this period