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Investigation of selenium and arsenic in soil

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Investigation of selenium and arsenic in soil Powered By Docstoc
					Investigation of selenium and arsenic in soil
 samples from a long-term field experiment


             Béla Kovács, Éva Széles,
           József Prokisch, Zoltán Győri



 University of Debrecen, Centre of Agricultural Sciences
  Department of Food Science and Quality Assurance
     4032 Debrecen Böszörményi str. 138. Hungary
            Budapest   Debrecen


       Nagyhörcsök




Pecs
We have to study the following goals in
     this research programme


 The behaviour of arsenic and selenium in
   soil:
  total concentration,
  available concentration,
  leaching,
  transformation.
                      Worldwide variation in Se status
                             (Combs, 2001)
           350
                                                    Venezuela
           300
                               Croatia
           250
                     Hungary                              USA
 plasma Se 200                  Finland   China (urban)
    ng/ml 150
China (Keshan dis. areas)
          100
            50
             0
                                    country
  normal level
The applied elements and doses in the long-term field
  experiment (Nagyhörcsök Experimental Station)
                      Rate (kg/ha)
    Elements        in spring of 1991          Chemicals used
     applied
               1        2        3       4
       Al      0       90      270      810   AlCl3

       As      30     90      270       810   As2O3/NaAsO2
       Ba      0       90      270      810   BaCl2
       Cd      30      90      270      810   CdSO4
       Cr      0       90      270      810   K2CrO4
       Cu      0       90      270      810   CuSO4
       Hg      30      90      270      810   HgCl2
       Mo      0       90      270      810   (NH4)6Mo7O24
       Ni      0       90      270      810   NiSO4
       Pb      0       90      270      810   Pb(NO3)2

       Se      30     90      270       810   Na2SeO3
       Sr      0       90      270      810   SrSO4
       Zn      0       90      270      810   ZnSO4
              Total element contents of soil samples depending
                         on doses (sampling: 1994)

                            250
Concentration of elements




                                      As
                            200
                                      Se
                            150
        (mg/kg)




                            100

                             50

                              0
                                  0    150   300      450      600   750
                                             Dose in 1991 (kg/ha)
                                      Lakanen-Erviö soluble element contents of soil
                                      samples depending on doses (sampling: 1994)
Concentration of elements (mg/kg)



                                    100
                                     90
                                     80         As
                                     70
                                     60         Se
                                     50
                                     40
                                     30
                                     20
                                     10
                                      0
                                          0   150     300       450           600   750
                                                       Dose in 1991 (kg/ha)
Rate of Lakanen-Erviö soluble and total element contents
 of soil samples depending on doses (sampling: 1994)

                                     60
 Concentration of elements (mg/kg)




                                     50

                                     40

                                     30
                                                                           As
                                     20
                                                                           Se
                                     10

                                     0
                                          0   150   300      450       600      750
                                                    Dose in 1991 (kg/ha)
              Concentration of arsenic depending on duration of
                 field experiment and doses in soil samples
                           100
                            90                                            30
Concentration of arsenic




                            80                                            90
                            70                                            270
                            60                                            810
       (mg/kg)




                            50
                            40
                            30
                            20
                            10
                             0
                                 1991   1992        1994          1997   2000
                                               Year of sampling
             Plot treated with arsenic (4. level)
            Nagyhörcsök Experimental Station




barley (2000)
                            Concentration of selenium depending on duration of
                                field experiment and doses in soil samples
                                    140
Concentration of selenium (mg/kg)




                                    120                                            30
                                                                                   90
                                    100
                                                                                   270
                                     80                                            810

                                     60

                                     40

                                     20

                                      0
                                          1991   1992        1994          1997   2000
                                                        Year of sampling
barley (?!) (2000)



      Plots treated with selenium (4. and 3. levels)
           Nagyhörcsök Experimental Station
                                   Selenium content of treated (the highest level)
                                   and control plots in different soil layers (2000)

                              20
concentration of Se (mg/kg)




                              18
                                                                                             treated plot
                              16
                              14                                                             control plot
                              12
                              10
                               8
                               6
                               4
                               2
                               0
                                   0-30



                                          30-60



                                                  60-90



                                                          100-130



                                                                    130-160



                                                                              160-190



                                                                                        200-230



                                                                                                  230-260



                                                                                                            260-290
                                                              soil layer (cm)
Analysis of selenium standards by IC-ICP-MS instrument
  100 ppb Se-Meth+100 ppb selenite+100 ppb selenate
          Detection limits: 0.01 – 0.05 – 0.1 ppb

                             60000
                                         Se-methionine
                                            COOH
                             50000          CHNH2
                                            CH2
       ICP-MS signal [cps]




                             40000          CH2
                                            Se CH3

                             30000
                                             selenite
                                                  (Se(IV), SeO32-)
                             20000                                               selenate
                                                                                 (Se(VI), SeO42-)
                             10000


                                 0
                                     0        5          10          15     20         25           30
                                                               time [min]
     Comparison of contents of selenium forms in 1991
(I: 1. repetition, 1, 2, 3, 4 doses: 30, 90, 270 and 810 kg/ha)

                          40000

                                          selenite
    ICP-MS signal (cps)




                          30000
                                                             selenate
                                                                             1991 I/1
                                                                             1991 I/2
                          20000
                                                                             1991 I/3
                                          organic selenium
                                             forms                           1991 I/4

                          10000



                              0
                                  0   5      10      15      20         25
                                             Time (min)
                                      Fate of selenite in soil (1:10 water extract)
                            Heavy metal load field experiment: Dr. Imre Kádár, Nagyhörcsök
                                                                                                selenite
                        1000000
                                      selenite                                      25000                                                   25000         oxidation
                        900000

                        800000                  1993                                20000                  1993                             20000                  2003
                        700000
  ICP-MS signal [CPS]




                                                              ICP-MS signal [CPS]




                                                                                                                      ICP-MS signal [CPS]
                        600000                                                      15000                                                   15000

                        500000

                        400000                                                      10000            selenate                               10000

                        300000

                        200000                                                      5000                                                    5000

                        100000            selenate
                             0                                                         0                                                       0
                                  0          10         20                                  0         10         20                                 0         10         20
                                       duration [min]                                           duration [min]                                          duration [min]
                                                             organic selenium
Conclusion: selenite will be oxidised in soil to selenate
            selenate more available for plants (it is analogous to sulphate)
            risk of leaching
                      Comparison of contents of selenium forms in
                              2000 from different layers


                      120000                selenate

                      100000
                                             selenite
ICP-MS signal (cps)




                                               0-30 cm
                       80000
                                               30-60 cm
                                               60-90 cm
                       60000
                                               100-130 cm
                                               130-160 cm
                       40000
                                               160-190 cm
                                               200-230 cm
                       20000                   230-260 cm
                                        organic selenium forms
                           0
                               0    5              10            15   20

                                            duration (min)
     Acknowledgements

• Dr. Imre Kádár (RISSAC)
• Hungarian Scientific Research
  Fund (OTKA T38450)
• István Széchenyi Scholarship
     Thank you for your attention!

                        Se

         Se     As

As
                   Separation of selenium ions by High Performance Liquid
                    Chromatography – Inductively Coupled Plasma Mass
                      Spectrometer hyphenated system (HPLC-ICP/MS)

Eluent: Phtalic-
acid-Tris buffer




                                 Inductively Coupled Plasma
                                 Mass Spectrometer (ICP-MS)


                      High Performance Liquid Chromatography
                      (HPLC) column: IC-AN1 anion exchanger
                  Other information
 Different levels of the selected metal salts (13) were added
  to plots once at starting year (1991) and were mixed into the
  ploughed layer (0-20 cm)
 The treatments were arranged in a split-plot design with
  replications (2)
 These experimental plots are cultivated with commonly
  used agrotechnics, chemical fertilizers are added yearly to
  ensure sufficient macronutrient (NPK) supply
 Composite soil samples consisting of 20 subsamples are
  collected yearly from the ploughed layer of each plot
 To check the vertical movement of these pollutants,
  samples are also taken from the subsoil of plots with the
  highest level of added metal salts in some years (1993,
  1996, 2000)
 Type of soil in the experiment : calcareous loamy
  chernozem
Plot treated with cadmium (4. level)
Nagyhörcsök Experimental Station
  Plot treated with lead (4. level)
Nagyhörcsök Experimental Station
Plots treated with molybdenum (1. and 4. levels)
       Nagyhörcsök Experimental Station
            Nagyhörcsök Experimental Station
                 plant and soil samples

- The experiment includes:
   4 levels in duplicate, i.e. 8 plots, each with a size of 21 m2.
- Experimental plants:
   maize (1991), carrot (1992), potato (1993), peas (1994), red beet (1995),
   spinach (1996), wheat (1997), sunflower (1998), sorrel (1999), barley (2000),
   rape (2001), poppy (2002), wheat (2003), alfalfa (2004), alfalfa (2005)

- Soil sampling and analyses on soil samples:
  1991: 0-20 cm soil layer of the plots,
  1993: "mobile" fraction in the 0-20, 20-40, 40-60 cm soil layers from plots with
         the highest level of added metal salts,
  1996: "mobile" and "total" fractions in the 0-30, 30-60, 60-90 cm soil layers
         from plots with the highest level of added metal salts.
  2000: As: 0-20, 20-40, 40-60, 60-90 cm soil layers from plots with the highest
              level of added metal salts,
         Se: 0-30, 30-60, 60-90, 100-130, 130-160, 160-190, 200-230, 230-260,
              260-290 cm from plots with the highest level of added metal salts.
          Results considering plant analyses
1.Owing to the highest level of arsenic treatment, the quantity of crop of each
applied plant decreased in each year. However arsenic content was not
increased in different parts of plants, it was about 1-2 mg/kg concentration
range. Arsenic is not mobile in the soil-plant system. From the applied plants,
peas and spinach were the most sensitive affected by arsenic. Presumably the
applied arsenite (As(III)) is transformed to arsenate (As(V)) which is the more
toxic species.
 2. The destroying effect of Se does not decrease with years, and what is more
the effect of Se increases. Presumably the applied Na-selenite form is
transformed to the more toxic Ca-selenate, it is oxidized among those soil
conditions. We have to determine the concentration of different selenium
species (selenite and selenate) in soil samples during our research. Similarly to
Mo, Se is extremely mobile, the plant parts contain many hundreds mg/kg of
selenium accompanied toxic symptoms. High applied concentration of selenium
destroys even weed-plants recently also.

    The arsenic and selenium caused decrease of yield of different plants owing
to the fitotoxic effect between 1991-1997:
   - maize seed: As and Se          - red beet root: Se
   - carrot root: As and Se         - spinach leaf: As and Se
   - potato tuber: As and Se        - wheat seed: As and Se
   - peas seed: As and Se

				
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