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Biological Transformation of Selenium in Soil-Plant Systems

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Biological Transformation of Selenium in Soil-Plant Systems. Z-Q Lin1 and Gary Ba uelos2 ... testing the potential use of high-selenium canola forage as feed. ... – PowerPoint PPT presentation

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Title: Biological Transformation of Selenium in Soil-Plant Systems


1
Biological Transformation of Selenium in
Soil-Plant Systems
  • Z-Q Lin1 and Gary Bañuelos2
  • 1Environ. Sci. Program Dept. of Biol. Sci.
  • Southern Illinois Univ., Edwardsville
  • 2USDA-ARS, Water Management Research Lab

2
Selenium
  • A narrow margin between nutritionally required
    and toxic concentrations
  • Essential for humans animals
  • Not essential for plants

3
Chemical Forms of Se
  • Se(VI), selenat
  • Se(IV), selenite
  • Se(0), elemental Se
  • Se(-II), selenide
  • e.g., Selenomethionine (SeMet) Dimethylselenide
    (DMSe)

4
Toxicity of Se
  • Toxicities of different chemical forms
  • Toxic to fish SeMet gt selenite gt selenate
  • Elemental Se is not toxic because it is not water
    soluble.
  • DMSe, a volatile Se compound, is less toxic to
    rats, compared with inorganic Se.

5
Toxicity of Different Forms of Se to Fish
T0
Se(-II) Se(IV) Se(VI) CK
T24 hrs
6
What are the major chemical forms of Se
accumulated in soil-plant systems?
7
Chemical Speciation of Se by X-ray absorption
spectroscopy (XAS)
  • XAS is one of the most advanced techniques that
    currently available for chemical speciation of Se
    and other environmentally important trace
    elements.
  • Element specific
  • Direct determination non-destructive
  • Various complex environmental substrates

8
Chemical Speciation in Environmental Samples by
XAS
9
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10
Factors Affecting Se Transformation in Soil-Plant
Systems
  • Sulfate
  • Chemical similarity between selenate sulfate
  • Redox potential
  • Anaerobic microbial reduction of selenate
  • pH
  • Enhanced Se methylation in alkaline soils
  • Organic matter
  • Adsorption of selenite
  • Soil moisture
  • Se bioavailability
  • Plants associated microbial communities in soil
  • Root exudates

11
Selenium pollution sources predominant chemical
forms
  • Industry
  • Oil refinery wastewater with selenite
  • Agriculture
  • Drainage water with 90 of selenate

12
  • The San Joaquin Valley
  • One of the most productive agriculture areas
  • Subsurface tile-drainage contains Se other
    salts.

Soils contain high levels of Se
West
East
13
Drainage Water Reuse System- Zero Discharge of
Drainage Water into Environment
Solar Evaporator
52 ha
Halophytes Field
7.6 ha
Cotton
Alfalfa
192 ha
Salt-tolerant Trees and Grasses
Lin et al., 2002, Water Research
14
  • The Halophyte Study Field

Cordgrass (Spartina sp.)
Pickleweed (Salicornia bigelovii)
15
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16
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17
Distribution of Salicornia bigelovii Torr. in the
U.S. (Data from USDA)
18
Why Does Salicornia Volatilize More Se Than Other
Species ?
  • Unique physiological processes in Salicornia?
  • Volatilization by microbes associated with
    Salicornia?
  • Interaction of Salicornia and microbes in soil?

19
Major Steps of Se Volatilization Pathway in Plant
Dimethyl selenide
Methyl-SeMet
Se-Methionine
Se-Cysteine
Selenate
Selenite
APSe
20
DMSe
Hypothesis
Salicornia
Selenite
SeMet
Selenate
SeMet
DMSe
Selenate
SeMet
Soil Microbes
Selenate in Soil
21
Question 1
  • Does Salicornia have an enhanced capacity of
    reducing selenate into organoselenium (SeMet)
    compounds?

22
  • Salicornia was supplied with selenate or
    selenite.
  • Experiments were conducted under sterile vs
    non-sterile conditions.
  • Se speciation in Salicornia shoots roots was
    determined by XAS.

Lee Lin et al. 2001. Planta
23
Findings
  • Compared with other species, Salicornia has an
    enhanced capacity to reduce selenate into organic
    forms.
  • Salicornia reduced gt65 of selenate or selenite
    into SeMet in tissues.
  • Chemical reduction of selenate without the
    presence of microbes.

24
Question 2
  • Will chemical forms of selenium (e.g., selenate,
    selenite, SeMet) affect rates of Se
    volatilization in the soil-Salicornia system?

25
Plants Treated With Selenate, Selenite, or
Selenomethionine
Salicornia bigelovii Torr.
26
Se Volatilization Measurements
27
FindingThe soil-Salicornia system volatilized
organic SeMet 20 times faster than inorganic
selenate (or 15 times with selenite).
28
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29
Se volatilization by soil bacterial strains
isolated from the Salicornia saltgrass fields
30
76 of the total Se accumulated in Salicornia
roots were SeMet-like organic compounds, while
saltgrass accumulated 48 of SeMet-like compounds
Saltgrass root
Salicornia root
31
Question 3
  • What is the role of soil microbes in Se
    volatilization?
  • Is there a special microbial community associated
    with Salicornia?
  • Are there any microbes that have an enhanced
    capacity to volatilize Se?

32
Soil Microbial Study
  • Soil samples were collected from the Salicornia
    and saltgrass fields.
  • Cultureable bacteria were studied only.
  • 5 identical bacterial strains were isolated and
    identified by 16 S rDNA technique.

33
Volatilization of Se by Bacteria Isolated From
the Salicornia and/or Saltgrass fields
34
Se volatilization by soil bacterial strains
isolated from the Salicornia saltgrass fields
With saltgrass
With Salicornia
35
Finding
  • Shewanella putrefaciens, a Salicornia-associated
    bacterial strain, volatilized more Se than any
    others.

36
Volatilization of Se into the Air
  • An environmentally-important pathway of Se
    removal
  • Volatile Se compound, DMSe, is less toxic
  • Se removed from polluted ecosystem
  • Less hazardous waste

37
Transport of Volatile Se in the Atmosphere
Lin et al., 2000, JEQ
38
Phytoremediation Approaches
39
SalicorniaA succulent, crunchy, and tasty
vegetable known as samphire, sea beans, or sea
asparagus.
40
Selenium accumulation in Canola Broccoli
  • Canola
  • In soil 2.5 ppm
  • Extractable soil Se 0.5 ppm
  • In irrigation water 0.25 ppm
  • In seed 1 ppm
  • Canola oil 1 ppm
  • Seed by-products 1 ppm
  • Dried leaves 2-5 ppm
  • Broccoli
  • In florets 4 ppm

41
  • Dr. Gary Bañuelos evaluates canola plants grown
    for cleaning selenium-rich soils. In studies on
    livestock, he is testing the potential use of
    high-selenium canola forage as feed.

42
Growing Canola in the San Joaquin Valley,
California
43
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44
Se-laden Drainage Sediment Phytoremediation
Studies
Bañuelos Lin, 2004, Ecotoxicology Environ.
Safety
45
Se Volatilization in Drainage Sediment
of measurements (n) varied from 3 to 11 in each
month.
46
Phytoremediation A Perspective of Ecosystem
Ecology
Salicornia is a staple food for the endangered
salt marsh harvest mouse.
47
ACKNOWLEDGEMENTS
  • Graduate Students, Ramya Nadella, Bikram
    Shrestha, Shawn Lipe, SIU Edwardsville
  • Irvin Arroyo, USDA-ARS, Water Management Research
    Lab
  • Drs. N. Terry, A. Tagmount, H. Mohamed, A. Lee,
    UC Berkeley
  • A. Illes, B. moose Peterson, H. Castle for the
    adapted illustration photos
  • California State Agricultural Research Initiative
    Grant (to Bañuelos)
  • The Joint Interagency (DOE/NSF/EPA/ONR)
    Phytoremediation Research Program
  • U.S. DOE, Grant No. DE-FG02-03ER63621 (to Lin)
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