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Revista de la ciencia del suelo y nutrición vegetal

versión On-line ISSN 0718-2791

R.C. Suelo Nutr. Veg. v.8 n.especial Temuco  2008 


J. Soil Sci. Plant Nutr. v8 no especial 2008 (121-131)



Session 3. Soil-Root-Microbe Interaction & Their Effects on Biophysical Transformation, Fate, and Toxicity of Metal and Metalloids

Fourier Transform Analysis of Time Series Applied to In situ Measurement of the Composition of Soil Solutions in Irrigated Riziculture


G. Bourrié1*. P. Moreau1, P. Henry2, M. Mayor1 and F. Trolard1

'INRA UR1119, Géochimie des sols et des eaux, Aix-en-Provence, France. 2College de France, Université Paul Cézanne, CNRS Cerege, Aix-en-Provence, France. *E-mail:

Keywords: Fourier transforms; soil solutions; irrigated riziculture

Interactions between soil, root and microorganisms directly influence the chemical composition of soil solution. Such changes can easily be studied in irrigated crops by in situ measurements. A hourly frequency was chosen to monitor temperature, pH, redox potential and conductivity in irrigated riziculture. Those parameters were continuously monitored during several months, from April to September. Complete chemical analyses were made by sampling weekly soil solution, filtering and analyzing for major elements by ion chromatography and ICP-AES. Samples were collected with a syringe preventing contact of the sample with air. Ammonium, nitrate, Mn, Fe (II), sulfate and sulfide were measured directly in the field. In Camargue (Rhone Delta), soils are silty to clayey, very young and neutral to alkaline due to present calcite sedimentation. The results show temperature variations from 10 to 32°C (Fig. 1), very large pH variations (Fig. 2), with sudden drops from 8 to 3 and Eh variations from +600 to -300 mV (Fig. 3).



Fourier transforms (F.T.) (Fig. 4) show a common period of 24 h (i) with phase opposition for t and pH during all the period of cultivation; (ii) with phase opposition too for t and Eh, after definitive ponding. As Leaf area increases, the shade damps temperature daily variation. Nutrient absorption by roots cause pH lowering, due to proton pump, which explains excursions from the steady value about 8, in equilibrium with calcite and atmospheric C02 to low values. After definitive ponding, consumption of 02 by microflora leads to a decrease of Eh with daily variations due to the nycthemeral variations of the activity of microflora. F.T. are thus an appropriate tool to analyze the complex interplay of environmental parameters and biogeochemical cycles in the field.


Extractability of Nickel, Zinc and Lead as Affected by Time from a Contaminated Soil Treated with Farm Manure

M.A. Aziz, A. Ghafoor, H.R. Ahmad* and Zia-ur-Rehman

Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad-38040, Pakistan. * E-mail:

Keywords: nickel; zinc; lead; farm manure.

Application of farm manure not only affects the fertility properties of soils but also alter the physical and chemical attributes of the soil including the bioavailability of heavy metals. Organic matter may increase or decrease the availability of heavy metals depending upon the nature of decomposition products. A laboratory scale experiment was conducted to evaluate the effect of farm manure application on the availability of Ni, Zn and Pb. Farm manure application initially decreased the availability of Ni and Zn but increased as the organic matter decomposition proceeded. However, Pb availability decreased throughout the period of study. It is concluded that it is very difficult to predict the effect of farm yard manure on Ni, Zn and Pb availability or extractability; as it is affected by the nature of metals, metal contamination level, composition of soil and organic amendment itself.



Fate of Metals Associated with Particulate Organic Matter in Soils: Unravelling Abiotic versus Biotic Processes

I. Lamy*. J. Sebastia, J. Labanowski and F. van Oort

INRA, UR251, Physico-chemistry and ecotoxicology of contaminated soils, RD 10, F-78026 Versailles cedex, France. * E-mail:

Keywords: Metals; paniculate organic matter; abiotic and biotic processes.

Particulate organic matter (POM) is operationally defined as 50-2000 um-sized organic particles in soils. The quantity and quality of this labile organic constituent were shown to be strongly influenced by soil management, but the use of POM as an index for soil quality is still a matter of discussion. Recently, POM was identified as a metal-enriched organic fraction in both metal-contaminated and uncontaminated soils. The mechanisms for such metal-enrichment remain poorly understood, as there is little information on the chemical properties of POM and the fate of metal-associated POM during biodegradation. Abiotic as well as biotic processes may be involved. In this work we report both lab and in situ investigations of various polluted or unpolluted soils, aiming to assess the intrinsic - abiotic-reactivity of soil POM fractions and to follow the status of metals in POM during biodegradation. In the lab various POM size fractions were extracted by means of physical fractionation. EDTA was used to extract metals from the isolated organic fractions and metal concentrations were determined by AAS. Chemical reactivity of each POM fractions was quantified by potentiometric titrations. In situ, we collected undisturbed samples for sub-microscopic studies. The nature, morphology and microfabrics of soil constituents were studied on thin sections and elemental mapping was performed by u-Xray fluorescence on decaying POM. In spite of their relatively low abundance in soil (< 5% of total bulk soil weight), the POM fractions often contain a significant proportion of the total metal stock of the soils, i.e. around 10-20% for Zn and Pb, and up to 20-30% for Cu and Cd. The results show that total metal concentrations increase with decreasing POM size, while metal extractability decreases. Each POM-size fraction provides a buffer capacity due to the presence of reactive sites but affinity for copper was found comparable between the coarse and fine POM fractions. Finer POM fractions were found however to exhibit the highest contents in reactive sites per g of organic carbon. This suggests that with decreasing POM size, mainly due to decomposition, new reactive surface sites are generated. The micromorphological study reveals the occurrence of black opaque parts in decaying large POM fragments, which coincide with hot spots of heavy metals. Combined with microscopic observations, the analytical results suggest that metals are immobilized as organo-metallic complexes on very small POM-derived organic fragments. Such a process would explain the increasing organic C and metal contents frequently observed in the < 20 um fractions of metal contaminated soils, and suggest that small POM-derived organic particles may favour long-term metal sequestration in soils. These findings show that POM is undoubtedly an interacting medium and suggest a role of fine POM fractions as a metal sink in soils and of coarser POM fractions as a metal source.


M. BalabaneandF. vanOort. (2002). SoilBiol. Biochem. 34: 1513-1516. J. Ducaroir and I. Lamy. (1995). Analyst 20: 741-745.

J. Labanowski, J. Sebastia, E. Foy, T. Jongmans, I. Lamy and F. van Oort. (2007). Environ. Pollut. 149: 59-69. J. Sebastia, F. van Oort and I. Lamy, I. (2008). Europ. J. Soil Sc. 59: 304-314.



Influence of Soil Organic Status on the Dynamics and Impact of Copper on Microbial Communities in a Vineyard Soil

J. Martins1*. D. Lejon2, J. Lévéque2, A. Navel1, L. Spadini3, N. Pascault2, D. Landry2, M. Milloux2, V. Nowak2, R. Chaussod2 and L. Ranjard2

'CNRS; Université Grenoble I, UMR5564 LTHE, 1025 Rue de la piscine, BP53, 38041 Grenoble Cedex 9, France. 2INRA- Université Bourgogne, UMR MSE, CMSE, 17 rue Sully, BP-86510, F-21065 Dijon, France. 3CNRS; Université Grenoble I. UMR5559 LGIT, Grenoble, France. * E-mail:

Keywords: Copper; microbial communities; vineyard soils

The effect of soil organic status (SOS) on copper impact was investigated by means of a microcosm study carried out on a vineyard soil that had been amended with varying types of organic matter during a previous long-term field experiment. Soil microcosms were assessed in the solid matrix by a sequential extraction procedure and in the soil solution by measuring total and free exchangeable copper concentrations. Copper bioavailability was also measured with a whole-cell biosensor. Modifications of microbial communities were assessed by means of biomass-C measurements and characterization of genetic structure using ARISA (Automated-Ribosomal-Intergenic-Spacer-Analysis). The results showed that copper distribution, speciation and bioavailability are strongly different between organically amended and non-amended soils. Surprisingly, in solution, bioavailable copper correlated with total-copper but not with free-copper. Similarly the observed differential copper impact on micro-organisms suggested that organic matter controlled copper toxicity. Bacterial-ARISA modifications also correlated with the estimated metal bioavailability and corresponded to the enrichment of the Actinobacteria. Contrarily, biomass-C and Fungal-ARISA measurements did not relate trivially to copper speciation and bioavailability suggesting that the specific composition of the indigenous-soil communities controls its sensitivity to this metal.

Impact of Maize Roots and Rhizospheric Microorganisms on the Mobility, Redistribution and Availability of Metals Associated to Ferralsol Oxyhydroxides

J. Berthelin* and I. Paskiewicz

LIMOS UMR 7137 CNRS-Nancy Université, Faculté des Sciences, BP 239, F-54506 Vandoeuvre-les Nancy, France. * E-mail:

Keywords: Metals; rhizospheric microorganisms; Ferralsol

In different type of soils, ferric oxy-hydroxides and oxides contain large amounts of trace metals (Mn, Co, Ni, Cr...) which can become available to soil solution and living organisms, depending on the environmental parameters. In New-Caledonia ferralsols, large metal contents and relatively high metal availability were observed in colluvio-alluvial and plain soils. Toxicity was noted in cultivated plants suggesting possible transfer to the food chain. Processes of iron bacterial reduction was proposed to occur in association with the biodegradation of soil organic matter. To progress in knowledge on the processes and parameters involved, in particular with the rhizosphere phenomenons, experiments were performed using soil columns or mixture of ferrasol samples and sand as support of plant culture in controlled conditions. Soil columns were either planted or not in maize in well defined water regime and subjected to different treatments: plant cultivated alone in sterile condition (without microorganism), or in non sterile soil with the whole non symbiotic microbial community and/or addition of autochtonous communities of iron reducing bacteria. Analysis concerned plant growth and metal uptake, soil solutions for pH, Eh, organic matter, metals, nitrates, ... solid phases and in particular microbial communities, sequential extraction of metals, mineral analysis. The results showed that the maize rhizosphere alone (comparatively to non cultivated soils) increased the weathering of Mn and Fe oxyhydroxides. The amounts of well crystallized oxy-hydroxides (e.g. Fed) decreased with a redistribution of Fe and Mn to the ill (non well) crystallized forms (e.g. Fe0), soluble acids, exchangeable, water soluble compartments. The presence and activity of the whole non symbiotic microbial community and much more of the autochtonous iron reducing bacterial community increased such redistribution processes of the different forms of Fe and Mn. All the metals became more available. The microbial communities increased the transfer factor of metals from soil to plant (maize), the redistribution indexes and the indexes of availability of Fe, Mn, Cr, Ni, Co determined by calculation from different analytical results. The behavior of Fe, Cr, Ni are similar and those of Mn and Co are much related. Some parameters such as the dynamic and activity of bacterial communities, the availability of organic compounds originating from soil or roots and the speciation of metals have to be better defined to proposed a more accurate model of rhizosphere functioning.


Cadmium Uptake and Distribution in Radish Plants Affected by Rhizosphere Salinization and Metal Contamination

G. Ondrasek1*, D. Romic1, Z. Rengel2, M. Romic1 and M. Zovko1

1University of Zagreb, Faculty of Agriculture, Svetosimunska 25, 10000 Zagreb, Croatia. 2Soil Science & Plant Nutrition, Faculty of Natural & Agricultural Sciences, University of Western Australia, Crawley WA 6009, Australia. * E-mail:

Keywords: Salinity; total organic carbon; cadmium organo-complexation.

The influence of a factorial combination of four salinity levels (0, 20, 40 and 60 mM NaCl) in nutrient solution, and three cadmium (Cd) levels (0.3, 2.5 and 5 mg kg-1) in peat growing media on mineral accumulation, vegetative growth and edible hypocotyl yield of radish plants (Raphanus sativus L. var. sativus) was studied in a greenhouse. After 34 days of exposure to NaCl treatment, salt-stressed plants had a reduced number of fully developed leaves (up to 30%) and total fruit yield (up to 35%) in addition to the progressively increased Na and Cl accumulation as well as significantly lower K concentration in leaf and hypocotyl tissues. Salinity significantly increased the uptake and accumulation of Cd in leaves (up to 20%). In contrast, raising salinity levels did not affect the Cd translocation and deposition into the edible hypocotyls (Cd contents being 4- to 6-fold lower than in leaves), which may indicate that the phloem mobility of Cd in radish plants is relatively poor and unaffected by NaCl exposure. Contamination of growing media by Cd had no effect on any measured parameter, except that accumulation of Cd in radish tissues was increased by one order of magnitude compared with non-contaminated control. Salinity resulted in decreased total organic carbon (TOC) content in rhizosphere solution (up to 21%). Chemical speciation modeling using Visual MINTEQ indicated the predominant role of organic reactive surfaces in Cd chemisorption and complexation processes within the whole range of tested salinity/contamination conditions, emphasizing the importance of organic matter content in restricting Cd phytoavailability and accumulation in edible parts of radish plants.


Soil Organic Matter Affects Copper Toxicity to Earthworms in the Avoidance Test

A. Neaman1*. G. Ávila1, H. Gaete2 and S. Sauvé3.

'Facultad de Agronomía, Pontificia Universidad Católica de Valparaíso, Quillota, Chile. 2Departamento de Biología y Ciencias Ambientales, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile. 3Département de Chimie, Université de Montreal, Montreal, Quebec, Canada. *E-mail:

Keywords: Soil organic matter; copper toxicity; earthworms.

The earthworm avoidance test has been proposed as a potential tool for quality assessment of contaminated soils. In this test, the earthworms (Eisenia fétida) are presented with a choice between the tested contaminated soil and a control soil placed into the same container. Eleven agricultural topsoils (0-20 cm) were sampled at varying distances from copper mining industries in the Aconcagua River basin, central Chile. Total copper concentrations in the tested soils were in the range of 230-850 mg kg-1. A control soil (95 mg kg-1 of total soil copper) was sampled in an area where no mining or other anthropogenic metals sources could be found nearby. All tested soils exhibited near neutral pH, in the range of 6.8-7.8. The earthworms' avoidance was poorly correlated with concentrations of soluble and free (Cu2+) copper in the water extracts. The avoidance was best explained in terms of total soil copper and soil organic matter (SOM) concentrations. A tested soil containing less than 20% of the earthworms was considered to be toxic. Tested soils with total copper concentrations above 500 mg kg-1 were toxic for the earthworms, regardless SOM concentrations. However, SOM determined the earthworms' avoidance in the soils with total copper concentrations below 500 mg kg-1. The latter soils with SOM concentrations below 4.5% were toxic for the earthworms. In contrast, soils with total copper concentrations below 500 mg kg-1 and SOM concentrations above 4.5% were not toxic. The kinetic of metal mobilization from the solid phase to the soil solution is known to decrease with the increase of SOM concentrations. The present data suggest that earthworms avoidance depends not only on the copper pool in the soil solution but also on the kinetic of copper mobilization that, in turn, is affected by the SOM concentrations.

Acknowledgments: This study is funded by the FONDECYT projects 1050403, 7070011, and 1085005.


Forms of Rare Earth Element Sorbed by Quartz and Goethite in the Presence of Microorganisms

L. Perelomov1* and S. Yoshida2

'Tula State University, Lenin Avenue, 92, Tula, 300600, Russia. 2National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba-shi, Chiba, 263-8555, Japan. *E-mail:

Keywords: Quartz; goethite; microorganisms.

Investigation of environmental and biological effects of rare earth elements (REE) or lanthanides has recently attracted much attention because as a result of the development of modern separation and purification techniques, lanthanides have been widely applied in many fields of industry, pharmacy, and agriculture. A great many types of human activity cause REE emissions to soil, air and water. Much of the current research has focused either on the adverse influence of lanthanides on the biota or on the physicochemical interactions between metals and soil minerals, and little investigation has been directed toward the triple interaction between rare earth elements, minerals, and the biota. In our research the effect of Rhodopseudomonas pallustris bacterium on the sorption of sixteen isotopes of lanthanides by quartz and goethite at different pH values was studied. The sea quartz sand with particle size 420-840 um was used. Goethite (a-FeOOH) was precipitated on the sand using a modification of the procedure of Kinniburgh et al. (1975). The cell suspension of microorganisms (4.8xl08cellml-1) was added to quartz sand or goethite with mixed solution of lanthanides (C=15 ppb) and incubated at 22°C for 7 days. The pH values of experimental solutions were 4, 7 and 9. After incubation period the chemical states (exchangeable or non-exchangeable) of the lanthanides, sorbed by minerals, were determined. Exchangeable state of the elements was extracted by adding 10 ml of 0.5 M NH4NO3. Non-exchangeable lanthanides were recovered by 40 ml of 0.3 M NH2OH-HCl in 1 M HN03 after decanting the NH4NO3 solution according to Stahl and James (1991). Our study shows that pH of sorption solution and affinity of elements to surface seems to be most important parameters in the interactions between metal ions and surfaces of biological and mineral sorbents. At acidic and neutral conditions these interactions was affected by electrostatic forces; at alkaline conditions the mechanism of lanthanides precipitation was dominant. Microorganisms sufficiently affected on lanthanides sorption by quartz at acidic and neutral conditions, but largest one was at pH 7. They increased sorption of all elements by goethite at pH 4. There was negligible effect of bacteria on the sorption of lanthanides at pH 7 and pH 9 by goethite that demonstrates greater affinity of the elements to goethite surface. Microorganisms increased concentration of lanthanides in the non-exchangeable states on the surfaces of quartz at pH 7 and 9, and on the surface of goethite at pH 7 in comparison to the minerals alone. It may be attributed to formation of low-soluble complexes of lanthanides with organic substances, produced by bacterium.

Acknowledgments: The authors would like to acknowledge the Russian Foundation for Basic Research and Japan-Russia Youth Exchange Center (Obuchi fellowship) for financial support


D.G. Kinniburgh, J.K Syers andM.L. Jackson. (1975). Soil Science Society of America Proceedings 39: 464 -470. R.S. Stahl and B.R. James. (1991). Soil Science Society of America Journal 55: 1287-1290.


Identification of Mercury Chemical Forms in Polluted Soils by Chemical Assays and Combined Synchrotron X-Ray Techniques

R. Terzano, A. Santero, M. Spagnuolo and P. Ruggiero*

Department of Agro-forestal and Environmental Biology and Chemistry, University of Bari, Bari, Italy.

* E-mail:

Determining mercury (Hg) chemical forms in polluted soils is an indispensable step towards a correct risk assessment and the development of effective remediation strategies. In this research, soil samples were collected inside and outside an industrial polluted area of National environmental interest located in "Val Basento" (Basilicata, Italy) where a chlor-alkali plant was active during the 1960-80's. Hg concentration in these soil samples ranged from 12 up to 240 mg g"1. Mercury speciation in these samples was studied by a combination of sequential extraction procedures, thermal desorption analyses, and different bulk- and micro-analytical techniques exploiting high intensity synchrotron generated X-rays. Bulk XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) spectra were collected for direct Hg-speciation in soil samples sieved at 2 mm as well as in the clay fraction (< 2um), where the highest amount of Hg was concentrated. The interpretation of the complex mixture of Hg-chemical forms in the soil samples was made simpler by performing, beside bulk XAS investigations, microanalyses on soil thin sections by combined u-XRF/u-XRD (micro X-ray Fluorescence/micro X-ray Diffraction) and u-XANES, with a resolution of 20 um. The information coming from the micro-scale was then used to understand the bulk data. u-XRF maps were collected to localize microscopic Hg-containing particles in areas of several hundreds of um2. Simultaneous to u-XRF spectra, microdiffraction patterns were collected in each point of the map, to identify possible crystalline Hg-mineral forms or mineral associations. Once points of interest were localized, u-XANES spectra were collected and compared with the spectra of known Hg-standard compounds. In one of the samples, Hg-containing particles with a size above 50 um were clearly identified as HgS in the form of cinnabar by combined u-XRF/u-XRD. For microscopic Hg-containing particles with no detectable diffraction, u-XANES spectra were collected. In general, two main characteristic XANES spectra (SI and S2) could be collected from Hg-rich spots at the microscopic level. Interestingly, all the bulk XANES spectra from all soil samples could be fitted by a linear combination of the microscopic SI and S2 spectra. However, the SI and S2 spectra could be only partly interpreted by simply combining the XANES spectra of Hg-standards such as: cinnabar (HgS), Hg (0), calomel (Hg2Cl2), and corderoite (Hg3S2Cl2). The presence of these forms is also in agreement with the chemical behaviour of the soil samples as assessed by sequential extractions and thermal desorption analyses. Also, more complex chemical forms beside those hypothesized seem to be present as it can be inferred by the interpretation of the bulk EXAFS spectra. In conclusion, notwithstanding the diffuse Hg-pollution in the investigated area, it seems that Hg is speciated in scarcely soluble and hardly mobilisable forms. Keywords: Mercury; polluted soils; X-ray.


Spectrophotometric Method for the Determination of Trace Amounts of Gold using Prochlorperazine Bismethanesulphonate

A. Thimme Gowda* and H. Sanke Gowda

Department of Chemistry, A. V.K. College for Women, Hassan - 573201, Karnataka, India. *E-mail:

Keywords: Spectrophotometry; prochlorperazine bismethanesulphonate; gold.

Prochlorperazine bismethanesulphonate is proposed as a selective and sensitive reagent for the spectrophotometric determination of gold. The reagent forms a red species with gold (III) instantaneously in 4-7 M orthophosphoric acid medium. An 8-fold molar excess of the reagent is necessary for the full development of the color intensity. The red species exhibits an absorption maximum at 529 nm with a molar absorptivity of 4.14 x 104 L modern1. Beer's law is obeyed over the range 0.1-6.4 ppm of gold with an optimum concentration range of 0.3-5.8 ppm. The effects of acidity, time, and temperature, order of addition of reactants, reagent concentration and interferences from various ions are reported. The method has been used for the determination of gold in gold minerals and alloys containing silver, palladium, platinum, copper and zinc.


Solid Speciation of Uranium at the Kurdai Uranium Ore Deposit Site (Kazakhstan)

B. Uralbekov1'2*, M. Burkitbayev1, P. Stegnar2 and B. Salbu3

'Al-Farabi Kazakh National University, Almaty, Kazakhstan. 2International postgraduate school of Institute.Josef Stefan, Ljubljana, Slovenia. 3 Norwegian University of Life Sciences, Aas, Norway. * E-mail:

Keywords: Solid speciation; uranium; X-ray

The Central Asian Republics were major producers of uranium for the nuclear weapon programme in the former Soviet Union. Extensive mining and milling activities resulted in large amounts of uranium tailing materials and waste rock deposits, which may have a potential radiological impact on the environment. To assess the long term impact on the environment, the knowledge of radionuclide partitioning is a significant factor in order to predict and explain soil-to-plant transfer factors. In the present work, new data are presented on concentrations of 226Ra, 210Po, 210Pb, and natural uranium isotopes in soil samples from Kurdai uranium ore deposit site collected during field expeditions to Kurdai site, Kazakhstan in July, 2006. The mining activities in the Kurdai site generated approximately 6,280,000 cubic meters of radioactive waste in the form of rock spoil heaps. In addition, the association of uranium isotopes with different geochemical phases is investigated using a sequential extraction technique according to the standard procedures of Tessier et al. (1979). The uranium isotope disequilibrium was utilized as a key tool to identify sources of uranium in each geochemical phases. Soil samples were dried at 80°C, ground, homogenised and sieved through a 1 mm wire mesh. Cation exchange capacity, exchangeable calcium content, pH and organic matter were determined for the characterization of the soils. X-Ray diffraction analyses was performed to assess the selectivity of extraction for different geochemical phases and to determine mineralogical composition. The radionuclides were determined using different techniques: instrumental gamma-spectrometry, alpha-beta counting and alpha-spectrometry analysis following radiochemical separation (Fe hydroxide co-precipitation, dissolution by concentrated HN03, separation of U by solvent extraction using tri-n-butylphosphate, and electroplating). The results show that 226Ra, 210Po, 210Pb, 238U concentrations in soils within the Kurdai site were in the range 410-2913 Bq kg-1, 208-2181 Bq kg-1, 304-2229 Bq kg-1, 300-654 Bq kg-1, respectively. According to gamma-spectrometry for majority of soil samples, the determined uranium-series radionuclides were near radioactive equilibrium, which indicate that it has not been processed (such as chemical leaching) and subjected to significant radionuclide removal. Sequential extraction analysis results revealed that uranium isotope was predominantly associated with geochemical phase sensitive reducible and strongly bound (60-70%) extractants. The radionuclides ratio ( U/ U>1) indicated that uranium originate as result of sorption from water by mentioned geochemical phases.

Acknowledgements: This work is supported by the NATO Science for Peace programme (RESCA project, Contract SfP 981742) and the Joint Norway-Kazakhstan-Kyrgyzstan project.

References A. Tessier, P.G.C. Campbell and M. Bisson. (1979). Anal. Chem. 51 (7): 844-850.

Use of Soil Trace Element Model (STEM) to Assess Long-Term Fate of Cadmiun in Cropland Soils: Case Study of Intensive Corn (Zea mays L.) Production in Central Chile

M. Molina1*. F. Meza1, M. Escudey2, W. Chen3 and A.C. Chang3

'Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago, Chile. 2Departamento de Química de los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile. 3Department of Environmental Sciences, University of California, Riverside, CA 92521, USA. *E-mail:

Keywords: Cadmium; cropland soils; Zea mays.

Potentially toxic trace elements, such as cadmium (Cd), may be introduced into cropland soils by the application of fertilizers and other amendments. Frequent use of phosphorus (P) fertilizers is the most relevant Cd inputs in agricultural soils. Different concentrations of this heavy metal have been found in P fertilizers commonly used in Chilean agriculture. The long-term repeated application of these fertilizers may lead to an accumulation of Cd in soils, therefore increasing the risk of its transfer to the food chain. The Soil Trace Element Model (STEM) is a recently developed mass balance-based model to assess the fate and transport of trace elements in cropland soils. The objective of this work was to evaluate, through the STEM, the impact of long-term use of P fertilizers on the accumulation of Cd in the soil. The model was applied to a typical Chilean corn production system characterized by intensive use of inputs such as herbicides and fertilizers. Field and laboratory experiments were conducted to investigate the dynamics of Cd in a clay loam Mollisol which is representative of central Chile region. Data from soil and plant analysis were used to determine model parameters. Typical management practices such as irrigation and biomass returned to the soil after harvest were represented in our simulations. Climate information (precipitation and evapotranspiration) from the nearest meteorological station was used as well. Three possible scenarios were evaluated considering different Cd concentrations found in commercially used P fertilizers: 1) triple superphosphate (TSP) with the highest Cd concentration (regarded as an extreme case), 2) TSP with an average Cd concentration, and 3) monoammonium phosphate (MAP) with the lower Cd concentration. STEM simulation outcomes indicate that in scenario 1, after 46 years a total Cd concentration of 0.5 mg kg-1 may be reached, which indicate an anthropogenically contaminated soil. On a 100 years horizon, the total Cd concentration would be 0.72 mg kg-1, 2.4 times the actual content. In scenario 2, after 85 years a total Cd concentration of 0.5 mg kg-1 may be reached, and after 100 years the total Cd concentration would be 1.8 times the actual content. In the scenario 3, the Cd content of the soil would be slightly increased after 100 years, indicating a low impact of MAP fertilization. Considering P dose recommendations for high-yield corn production, we estimated that fertilizers with a Cd concentration ranging from 3.0 to 4.0 mg kg-1 would not increase the actual Cd content of the soil because of a balance between the inputs of Cd and the outputs by plant extraction and the downward movement of the element below the plow layer.

Acknowledgments: FONDECYT 1070116. Mauricio Molina would like to thank PUC-MECESUP (0210) Doctoral scholarship and PUC-VRAID international exchange scholarship.


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