(Total and)methyl Mercury Export from Denitrifying Bioreactors in Tile-Drained Fields of Central Illinois

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1 (Total and)methyl Mercury Export from Denitrifying Bioreactors in Tile-Drained Fields of Central Illinois Robert J.M. udson, NRES Richard A.C. Cooke, ABE University of Illinois at Urbana-Champaign

2 Acknowledgements Illinois Sustainable Technology Center Funding for the project Patience with our pace Brian Vermillion (foremerly NRES) Meg analysis Richard Cooke group Access to field sites and assistance with sampling Expertise

3 A Tale of Two Elements A Tale of Two Elements Both have complex biogeochemical cycles involving chemical species in multiple phases and oxidation states: Nitrogen N 2 (g), NO 3- (aq), N 4+ (aq), Soil Organic N, etc. Mercury g(g), g 2+ (aq), C 3 g + (aq), gs(s), etc.

4 A Tale of Two Elements Pollutant Sources and Impacts Nitrogen Non-point source pollutant derived from fertilizer overuse Nitrate exported from agricultural fields impacts: Gulf of Mexico ecosystem (hypoxia) Water quality for communities that obtain drinking water from rivers in agricultural areas Mercury Non-point source pollutant generated via coal combustion and waste incineration Methylmercury strongly bioaccumulates in food webs: Fish consumption is main source of human exposure to g. Leading cause of freshwater fish consumption advisories in the U.S. Significant percentage of U.S. women of childbearing age have blood g higher than the USEPA Threshold Level.

5 A Tale of Two Elements Anaerobic Processing Key processes that determine the environmental impacts of each element occur in anaerobic environments: Denitrification (alleviates impacts) NO 3- (aq) NO 2- (aq) N 2 (g) Mercury methylation (greatly increases impacts) g 2+ (aq) C 3 g + (aq)

6 A Tale of Two Elements Anaerobic Transformations in Aquatic Ecosystems g II O 2 Plants g II Nitrate in surface waters inhibits g methylation since denitrifiers can out compete Fe- and Sulfate-reducing bacteria for energy (reduced carbon compounds).

7 Methylation Theoretical Considerations Bioavailability of g II in Natural Ecosystems RS + g(o) RS-g (unavailble) 2 S + RS-g g(s) 2 Sulfate-reducing bacteria control this reaction by producing 2S. SRB also have the right enzymes to methylate. Fe reducers do as well, but may depend on SRB to make g II bioavailable.

8 Clear Pond, Kickapoo State Park Profile (August 2010) Meg Analysis at UIUC by W.Y. Chen

9 Landscape-Scale Effects of Natural Anaerobic Ecosystems on Mercury Cycling Brigham et al. (2009)

10 Constructed Anaerobic Ecosystems

11 Denitrifying Bioreactors Denitrifying Bioreactors: Constructed Anaerobic Ecosystems Pioneered by Richard Cooke, ABE-UIUC. Designed to reduce nitrate export from tile-drained fields. Economical Small footprint Wood chips are inexpensive Minimal cost of water control structures (<$10k) Little time required to operate/maintain Field tests show their high efficiency at NO 3 - removal.

12 Monticello Bioreactor Site Denitrifying Bioreactors

13 Denitrifying Bioreactors

14 Denitrifying Bioreactors Diversion Structure Second Generation Bioreactors Capacity Control Structure Woodchips

15 Andrus et al. (2010) Denitrifying Bioreactors

16 10 Wide 5 Soil backfill Up to soil surface Denitrifying Bioreactors Top View version ucture 5 section of non-perforated tile Length dependent on treatment area Capacity control structure Side View Trench bottom 1 below tile invert

17 Load Reduction, LR (%) Denitrifying Bioreactors 100 BIOREACTOR EFFICACY CURVE LR = LD R² = Loading density, LD (Acres per 100 sq. feet of the bioreactor)

18 Abrus et al. Denitrifying Bioreactors Biogeochemistry

19 Bioreactor Methylmercury Study Objective 1. Determine whether denitrifying bioreactors produce methylmercury due to anoxic environments formed within bioreactor. 2. Determine total g export flux. 3. Compare to natural levels in environment.

20 Bioreactor Methylmercury Study Design Synoptic sampling design Collect samples after storm events and other periods when tiles are flowing Inlet and outlet sampled simultaneously Sampled periodically from summer 2008-June 2009 Sampled again in summer Preserved by filtration/acidification or freezing. Analyze Dissolved Methylmercury (Meg) Dissolved organic carbon Sulfate, nitrate, chloride Only a limited number of samples have been analyzed to date.

21 Sampling Bioreactors Inlet Samples Outlet Samples Figure 1. Schematic diagram of a sub-surface bioreactor (R. Cooke).

22 UIUC Method for g Speciation Analysis Shade and udson (2005) Environmental Science and Technology Shade, udson, et al. patent (circa 2007) Vermillion and udson (2007). Analytical and Bioanalytical Chemistry. Preparation method for water samples.

23 Thiol Resin -S- -S- -S- + p-modulated Thiol-Thione Switch N C S g N After Laws (1970) + p<2: Desorption Favored + p > 3: Adsorption Favored N N C Thiol Resin S -S- -S- -S- g + N N C S University of Illinois at Urbana-Champaign

24 Thiourea Complexes of g 2+ and C 3 g + N C S N g N C S N g N C S N + 2+ Meg + g 2+ University of Illinois at Urbana-Champaign

25 Mercury-thiourea complex ion chromatography Shade and udson, ES&T 2005 University of Illinois at Urbana-Champaign

26 Dissolved methylmercury: Thiourea-catalyzed solid phase extraction Vermillion and udson Analytical and Bioanalytical Chemistry (2007) Brian Vermillion University of Illinois at Urbana-Champaign

27 Measured Meg Value (ug/g-dw) Validation of Sediment and Biota Sample Preparations 10 1 Biota: Leaching of tissues in acidic TU (Shade, ES&T 2008) 0.1 Sediments: 2 SO 4 +KBr Digestion/Toluene Extraction (Vermillion, Shade, and udson, in prep) 0.01 Biota Sediments 1: Certified Meg Value (ug/g-dw)

28 Comparison of Methods for Analysis of Dissolved Meg Ultraclean sample collection Sample preservation Distillation Extraction from Sample Matrix Ethylation /Purge & Trap Preconcentration/ Loading Gas Chromatography Chromatographic Separation of g species AFS Sensitive detection TU-Catalyzed SPE Elute SPE /Online Trap Ion Chromatography AFS University of Illinois at Urbana-Champaign

29 [Meg] DEID (ng/l) Intercomparison with Distillation/Ethylation ICP-MS Trent University (intelmann) [Meg] TU (ng/l) Peterborough Calumet Lake 658 Sulfidic Sulfidic Sulfidic R=100% R=50% R=20%

30 es Number of Samples FMeg DE (ng/l) FMeg DE (ng/l) Intercomparison with USGS Wisconsin District Mercury Lab (Krabbenhoft) Median = 0.20 ng/l y = 0.71x R² = y = 0.62x R² = N.D FMeg TU (ng/l) FMeg DE (ng/l) FMeg TU (ng/l) Median Median = 0.61 = 0.21 ng/l 25 Median = 0.28 ng/l

31 Bioreactor Study Results

32 Dissolved Meg in Bioreactor Inlets

33 Dissolved Meg in Bioreactor Outlets

34 Farm Progress City Bioreactor

35 Nitrate Removal

36

37 Typical g Levels Groundwater Total g is very low (<0.5 ng/l) Meg is often non-detectable. Surface Waters Total g is usually 1-5 ng/l in unpolluted systems Meg is usually <0.5 ng/l in unpolluted systems

38 Possible Relationship between Methylmercury Production to Sulfate Consumption in Bioreactors

39 Dissolved Organic Carbon Dissolved organic carbon is known to be a carrier of mercury and methylmercury. DOC in inlets: Geometric mean of 1.6 mg-c/l DOC in outlets: Geometric mean of 16 mg-c/l Exhibits seasonality

40 Summary of Results to Date Levels in bioreactor discharge are much higher than in tile drain water entering bioreactors. Methylmercury is clearly produced in bioreactors. Some combination of increase in DOC and decrease in sulfate may be responsible. Levels in bioreactor discharge are much higher than typical surface water values ( ng/l).

41 What is source of g? Tile water: Groundwater is typically very low except when preferential flow occurs Could accumulate on wood chips during high flow (aerobic conditions) and be released under high flow conditions Wood chips: Trees accumulate g from air and soil water in the wood

42 Methylation Theoretical Considerations Bioavailability of g II in Natural Ecosystems RS + g(o) RS-g (unavailble) 2 S + RS-g g(s) 2 Sulfate-reducing bacteria control this reaction by producing 2S. SRB also have the right enzymes to methylate. Fe reducers do as well, but may depend on SRB to make g II bioavailable.

43 Questions What controls the extent of methylation? Amount of sulfate in tile drainage? Extent of anoxia? Flow rate? Can reactors be designed to minimize Meg formation?

44 10 Wide 5 Soil backfill Up to soil surface Denitrifying Bioreactors Top View version ucture 5 section of non-perforated tile Length dependent on treatment area Capacity control structure Side View Trench bottom 1 at below tile invert tile invert

45 Implications Meg is produced in some bioreactors. Effect on Meg fluxes in watersheds needs to be considered An apparent trade-off: Reducing nitrate levels to make water drinkable may make the waters downstream unfishable.

46 Implications (cont.) Reduction of Meg production likely can be attained by adjusting design: Eliminate ponding zones Use of low-g wood (hypothesis)