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

2. Selenium A narrow margin between nutritionally required and toxic concentrations –Essential for humans & animals –Not essential for plants Se

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

4. Toxicities of different chemical forms –Toxic to fish: SeMet > selenite > 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. Toxicity of Se

5. Toxicity of Different Forms of Se to Fish Se(-II) Se(IV) Se(VI) CK T=0 T=24 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

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. Industry –Oil refinery wastewater with selenite Agriculture –Drainage water with ~90% of selenate Selenium pollution sources & predominant chemical forms

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 WestEast

13. Drainage Water Reuse System - Zero Discharge of Drainage Water into Environment Solar Evaporator Halophytes Field Salt-tolerant Trees and Grasses 192 ha 52 ha 7.6 ha Alfalfa Cotton Lin et al., 2002, Water Research

14. The Halophyte Study Field Cordgrass (Spartina sp.) Pickleweed (Salicornia bigelovii)

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 Selenate APSe Se-Cysteine Se-Methionine Dimethyl selenide Selenite Methyl-SeMet

20. Selenate in Soil SeMet Selenate SeleniteSeMet Soil Microbes Salicornia DMSe Hypothesis: DMSe

21. Question 1: Does Salicornia have an enhanced capacity of reducing selenate into organoselenium (SeMet) compounds?

22. Lee & Lin et al. 2001. Planta 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.

23. Findings: –Compared with other species, Salicornia has an enhanced capacity to reduce selenate into organic forms. Salicornia reduced >65% 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. Salicornia bigelovii Torr. Plants Treated With: Selenate, Selenite, or Selenomethionine

26. Se Volatilization Measurements

27. Finding: The soil-Salicornia system volatilized organic SeMet ~20 times faster than inorganic selenate (or ~15 times with selenite).

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 Salicornia root Saltgrass 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 Salicornia With saltgrass

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. Lin et al., 2000, JEQ Transport of Volatile Se in the Atmosphere

38. Phytoremediation Approaches: Phyto- stabilization Phyto- degradation Rhizodegradation Phytoextraction Phytovolatilization

39. Salicornia: A 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

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)