Phytoremediation- Humification Strategies for RDX in Surface Soil

Transcription

1 Phytoremediation- Humification Strategies for RDX in Surface Soil Mike Reynolds 1, Dave Ringelberg 1 Lee Newman 2, Steve Larson 3 Army EQ Research Program SERDP 1 Engineer Research and Development Center (ERDC), Cold Regions Research and Engineering Laboratory (CRREL) 1 Soil Microbiology Laboratory 2 University of South Carolina 3 ERDC - Environmental Laboratory Third International Phytotechnologies Conference April 20-22, 2005 Atlanta

2 RDX from low-order detonations Deposition onto surface soils Heterogeneous and widely dispersed Potential for range restrictions/closures Problem RDX NO 2 N O 2 N N N NO 2 Hexahydro-1,3,5-trinitro-1,3,5-triazine Relatively high solubility Weak soil binding Potential human health effects Seizures Possible carcinogen effects Remediation strategies? Cost effective, easily implemented, applicable to surface soils

3 RDX Degradation Background RDX Biodegradation Favored in saturated soils rather than surface soils Plant uptake of RDX is significant, but degradation in plants is limited RDX conjugated in plant tissue can be redeposited onto soils as plants die Surface soils are not constant with regard to temperature, soil water potential, and carbon Can we identify, predict, or enhance processes that reduce the potential for RDX movement? RDX NO 2 N O 2 N N N NO 2 Hexahydro-1,3,5-trinitro-1,3,5-triazine

4 Relationship to Other Phytoremediation Previous research rhizosphere enhanced remediation for petroleum Similarities Surface soil Limited site access Root Accessible Few alternatives Different mechanisms

5 Objective/Description Objective Sequester RDX-derived C in soil humic fractions Mineralization Uptake Plant as sink phytotransportation Plant 3 Senescence, Plant as RDX and C source 1 2 RDX T-RDX Soil Humic Humification Fractions Transformation Reduced and aerobic conditions Hypotheses Leaching Soil RDX concentrations can be decreased by microbially driven transformations and plant uptake Humification can serve as an RDX sink Bioavailable carbon drives the microbiology Mineralization-Immobilization Turnover (MIT) drives humification Plant-conjugated RDX gives a humification advantage There is characteristic microbiology associated with humification

6 Approach- Theory & Hypothesis 2 cycles Native carbon RDX carbon Native carbon >>>>> RDX carbon MIT drives soil processes *Plant *CO 2 MIT Mineralization- Immobilization Turnover biotic *RDX *T-RDX *Biomass *Humic Materials

7 Soil Water Biofilm A-OM Particle Unsaturated Surface Soil Field moist Air dry ψ = MPa ψ = ~- 100 MPa? Carbon Fate???? soil profile soil mineral colloid Amorphous OM coating Biofilm Soil-solution film Soil atmosphere

8 Approach RDX humification in surface soils Humification studies using both 14 C and nonlabeled RDX Add 14 C-RDX directly to soil Use 2 soils with different OM levels Defined soil moisture and temperature conditions Plant-associated RDX (underway) Grow plants and load with 14 C-RDX Add plant tissue with RDX-derived 14 C to soils Use same soil moisture and temperature RDX photo-degradation using variegated plants (underway)

9 Approach- Methods KOH to scrub CO 2 Soil H 2 SO 4 to adjust RH of airstream to maintain or alter soil Ψ SOIL, ~500g, with RDX uniformly mixed ahead of time Not a slurry Maintained at ~ 1/3 bar H 2 O KOH to trap CO 2 ~ 1500g RT ~1/3 bar *Plant CO 2 KOH trap BaCO 4 LSC MIT Mineralization- Immobilization Turnover biotic *RDX *T-RDX *Biomass *Humic Materials RDX ACN HPLC LSC Lipid BD & GCMS LSC T-RFLP OM MIBK LSC

10 4 reps 2 soils (hi and lo OM) Controls (no RDX) Dark Mini-core sampling

11 Results Partial Summary *Plant CO 2 biotic *RDX *T-RDX *Biomass *Humics RDX loss slow but consistent T-RDX transient *C in microbial biomass low and consistent RDX-specific microbial community changes?? Mass balance decreases with time?? Cumulative error?? Missing a pool??

12 Results RDX directly to Soil Fulvic Humic bound- Humic Fulvic Humic boundlipid bound- Humic boundlipid High Ft. OM Greely Soil Ft. Low Wainwright OM Soil (OM fractionation MIBK method)

13 Results RDX directly to Soil Soil biomass, normalized to soil dry weight showed: No sig. RDX effect on biomass More consistency in high OM soil (biomass responds to soil C rather than RDX-C) Yet respiration was greater in the high OM soil, and increased with time. Biomass and respiration sometimes viewed as equivalent but they diverge for both soils These data suggest: greater activity or throughput or MIT for the high OM soil, greater cellular storage for the low OM soil microbial biomass (pmol PLFA g -1 ) mg C as CO 2 g -1 soil Days: Days: control RDX High OM soil High OM soil Biomass via PLFA Days: 8 Days: Respiration Low OM soil control RDX Low OM soil

14 Results RDX to Soil 1.1 Fate of 14C derived from RDX? Is there a difference between soils? In high OM soil, a significantly greater amount of RDX derived C moves into the bound humic fraction -- humification And This appears related to MIT 14C location Bound Humic Humic Bound humic/fulvic ratio (µci 14 C g -1 ) Humic/Fulvic ratio (µci 14 C g -1 ) time (days) time (days)

15 Results Plant Tissue RDX to soil Fate of 14C derived from Plant RDX? Is there a difference between soils? Yes, but a different pattern than seen for RDX added directly to soil is emerging 14C location Bound Humic Humic Bound Humic/Fulvic ratio (µci 14 C g -1 ) Humic/Fulvic ratio (µci 14 C g -1 ) time (days) time (days)

16 1.1 Plant Tissue RDX to soil RDX to soil Plant Tissue RDX to soil C location Humic/Fulvic ratio (µci 14 C g -1 ) Bound humic/fulvic ratio (µci 14 C g -1 ) time (days) time (days) 14C location Bound Humic Humic Humic/Fulvic ratio (µci 14 C g -1 ) Bound Humic/Fulvic ratio (µci 14 C g -1 ) time (days) time (days)

17 Results 1.3 Using Humic/Fulvic Ratio Direct soil RDX vs Plant Tissue RDX High OM soil convergence Low OM soil - divergence 14C location Low OM soil High OM soil Humic/Fulvic Ratio ( μci 14 C g -1 ) Humic/Fulvic ratio (µci 14 C g -1 ) Leaf sampling period + Leaf +Leaf + Leaf sampling period

18 Evolving Soil Communities Sudden variability in 14C evolution

19 Results Odd 14 C Rep for Plant Tissue RDX to soil Phanerochaete?

20 Summary 5 3 *Plant CO 2 1 *RDX 2 4 *T-RDX *Biomass *Humics biotic * CO 2 1. Biotic transformation of RDX in surface soils is slow but does occur. 2. *C in biomass low but constant suggesting steady state role in flow of RDX into other pools. 3. *CO 2 low but constant. General CO 2 may be important as an indicator of MIT 4. RDX (soil) - Greater amount of *C associated with bound-humic fraction in the high OM, high respiration soil relative to the lower OM soil. RDX (plant) changes in *C in humic fractions for both soils, more so for low OM soil. 5. Photo-degradation in plant tissue, variegated plants (underway) Data suggest possible plant-based, agronomic site management practices that encourage binding of RDX residues to soil