Effect of Oxygenation on Speciation, Behavior, and Fate of Chromium in Estuarine Sediments www.epa.gov/.../newsletter/images/allied1988.jpg www.epa.gov/.../images/allied_tents.jpg Amar R. Wadhawan and Edward J. Bouwer Department of Geography and Environmental Engineering Johns Hopkins University Sustainability: Reducing Toxic Pollutants Environmental Management for Enclosed Coastal Seas (EMECS9), 8/29/11
Contaminated Sediments in the Baltimore Harbor The problem of contaminated marine sediments has emerged as an environmental issue of national importance NRC report -1989 Status of chemical contaminant effects on living resources in the Chesapeake Bay s tidal rivers Chromium Processing Plant Chromium ore processing from 1845 1985 Chromium Ore Processing Residue (COPR) used as fill material throughout the harbor and its surrounding area Cr VI leaching from COPR material into the harbor
Cr Species and Their Behavior Cr III Oxidation Reduction Cr VI Less soluble Inert (hydr)oxides Nutritional supplement Less toxic Soluble Readily bioavailable Carcinogen
Talk Overview Project Motivation Toxicity in the Baltimore Harbor Sediments Cr speciation and biogeochemistry in anoxic estuarine sediments Experimental Approach Batch reaction experiments and HPLC-ICP-MS technique Influence of Sediment Oxygenation Loss in sediment reductive capacity and oxidation of Cr III Cr III Oxidizing Potential of Sediments Correlating rates of Cr III characteristics Lag time behavior oxidation with measurements of bulk sediment Cr VI Reoccurrence in Sediments Effect of sediment loading and Cr III aging Summary
Toxicity in the Baltimore Harbor IH CC dmt 33 BC Site AVS (umoles/g dry wt) CrT (mg/kg dry wt) FeT (g/kg dry wt) MnT (mg/kg dry wt) AVS/SEM 48 DMT 0.3 25 65-1270 10-30 110-800 0.01 0.2 BSM 68 70-80 350-360 44 375 530 0.1-0.7 BSM 54 10-50 80-130 83 440-520 0.1-0.6 BSM 45 110-250 140-280 75-80 410-700 0.2-0.4 BSM 33 175-580 525-820 73 140-490 0.4-0.7 BC 307 600 87.0 611 0.47 IH 147 294 40.8 483 NM BSM 38 132 239 42.9 559 0.93 McGee et al 1999. Environ. Toxicol. & Chem., 18, (10), 2151-2160.
Research Objective O 2 Aerobic water column Cr VI Mn II Redox-active zone AVS Anaerobic sediment NOM Reduced Fe Reduced sulfur Microbes Cr VI Cr III NOM Precipitated Cr III NOM Mn III,IV (hydr)oxides Mn II MnHS + MnS Adapted from Masscheleyn et al 1992. Environ. Sci. & Technol., 26, 1217-1226. Determine biogeochemical changes in the sediments that will favor Cr III oxidation to Cr VI
Experimental Design Aeration instantaneous on Cr III aq spike Aeration once all spiked Cr VI aq reduced to Cr III Cr III aq or Cr VI aq spike 5 ml sample 5 mm Phosphate extraction ph 7 Filtration Filtration Cr T Data Acquisition System Batch Reactors Cr d HPLC ICP-MS Magnetic Stir Plate 1-10 g/l N 2 -sparged sediment sediment suspension 10 mm NaCl + 10 mm (DEPP ph 4, MES ph 5 & 6, MOPS ph 7, EPPS ph 8, CHES ph 9, CAPS, ph 10 & 11)
Analytical Evidence Cr(III) t1 Cr(VI) t5, t6 t2 t3 t4 t5 t6 t4 t3 t2 t1 Direct chromatographic evidence of Cr III oxidation
[AVS] (mm/g) dry wt) [dissloved Fe] ( mg/l) [dissloved Mn] ( mg/l) Influence of Sediment Oxygenation 20 g/l Inner Harbor (IH) sediment suspension aerated under continuous stirring Samples collected and analyzed for AVS over several hours An aliquot of each sample collected was filtered, acidified, and analyzed for dissolved Fe and Mn by ICP-MS 180 160 140 120 100 80 60 250 200 150 100 80 70 60 50 40 30 40 20 0 0 300 600 900 1200 1500 1800 Time (mins) 50 0 0 300 600 900 1200 1500 1800 Time (mins) 20 10 0 0 300 600 900 1200 1500 1800 Time (mins) k AVS = 0.0085 min -1 Half life = ~82 mins
Influence of Sediment Oxygenation (continued) 100 µm Cr III aqspike 5 g/l dmt-207 suspension 10 mm NaCl + 10 mm MOPS, ph 7 No Cr III oxidation under anaerobic conditions and in sediment / Cr III controls
Cr III Oxidizing Potential of Sediments 10 g/l suspension *2.75 g/l 100 µm Cr III aq spike 10 mm NaCl + 10 mm MOPS ph 7 ~ 0.1 1% oxidation at ph 7 in most samples ~ 25% oxidation at ph 7 in dmt-109 sample 5 g/l suspension 100 µm Cr III aq spike 10 mm NaCl + 10 mm EPPS ph 8 ~ 0.5 3% oxidation at ph 8 in most samples ~ 70% oxidation at ph 8 in dmt-109 sample
Predicting Cr III Oxidation Sites showing Cr III oxidation potential
Correlation with Sediment Parameters
Cr VI Reoccurrence upon Sediment Aeration Cr VI reduced to Cr III ( Cr(OH) 3 (s), Cr x Fe 1-x (OH) 3 (s) ) anaerobically within 4 hrs for all sites except DMT-207 and DMT-109, which took ~ 5 days Sediment aerated after all Cr VI reduced to Cr III 1 15% Cr III oxidation 5 g/l sediment suspension, 10 µm Cr VI aqspike 10 mm NaCl + 10 mm EPPS, ph 8
Cr VI Reoccurrence: Effect of Sediment Loading N 2 -sparged 68-909 suspension 20 µm Cr VI aq spike Aeration - 55 hours after Cr VI aq spike for 1.6 g/l and 25 hours for the rest 10 mm NaCl + 10 mm EPPS, ph 8 N 2 -sparged 68-909 suspension 4 µm Cr VI aq spike / 1 g sediment Aeration 25 hours after Cr VI aq spike 10 mm NaCl + 10 mm EPPS, ph 8
Cr VI Reoccurrence: Cr III Aging Effects 5 g/l dmt-909 suspension 10 µm Cr VI aqspike 10 mm NaCl + 10 mm EPPS, ph 8
Summary O 2 Aerobic water column Cr VI Mn II Redox-active zone AVS Anaerobic sediment NOM Reduced Fe Reduced sulfur Microbes Cr VI Cr III NOM Precipitated Cr III NOM Mn III,IV (hydr)oxides Mn II MnHS + MnS
Acknowledgements Prof. Edward Bouwer Prof. Alan Stone Bouwer research group Funding Sources supported by Honeywell International Inc. National Science Foundation
Questions!
Correlation with Sediment Parameters
Effect of Sediment Loading: Cr III Oxidation Sediment suspension 100 µm Cr III aq spike 10 mm NaCl + 10 mm EPPS, ph 8
Effect of ph: Cr III Oxidation Cr 3+ CrOH 2+ Cr(OH) 2 + Cr(OH) 4 - Cr(OH) 3 0 Calculation performed using HYDRAQL Equilibrium data from Ball W.B. and D. K. Nordstorm 1998. J. Chem. Eng. Data, 43, 895-918 5 g/l dmt-207 suspension 100 µm Cr III aqspike 10 mm NaCl + 10 mm ph buffer No Cr VI formation at ph 3, 5 and 6
Effect of ph: Cr III Oxidation (continued) 5 g/l 68-909 sediment suspension 100 µm Cr III aqspike 10 mm NaCl + 10 mm ph buffer
Effect of ph: Cr III Oxidation and Cr VI Reoccurrence Cr VI Reoccurrence 5 g/l 68-909 suspension 37.5 µm Cr VI aqspike Aeration 1 day post Cr VI aqspike 10 mm NaCl + 10 mm ph buffer Cr III Oxidation 5 g/l 68-909 sediment suspension 100 µm Cr III aqspike 10 mm NaCl + 10 mm ph buffer
Effect of Mn II Addition: Cr III Oxidation 5 g/l sediment suspension 100 µm Cr III aq spike 10 mm NaCl + 10 mm EPPS, ph 8
Effect of Mn II Addition: Cr VI Reoccurence 5 g/l N 2 -sparged sediment suspension 10 µm Cr VI aq spike, Aeration 4.5 hrs post Cr VI aq spike 10 mm NaCl + 10 mm EPPS, ph 8
Effect of Dissolved Mn: Cr III Oxidation 5 g/l sediment suspension 10 µm Cr VI aq spike Aeration 4.5 hrs post Cr VI aq spike 10 mm NaCl + 10 mm EPPS, ph 8
Mn III,IV (hydr)oxide formation: Abiotic vs Microbial Mn oxidation 5 g/l dmt-207 sediment suspension 100 µm Cr III aqspike 10 mm NaCl + 10 mm MOPS, ph 7
Cr III Oxidation: Influence of Sediment Oxygenation Oxygenation of bulk sediments followed by Cr VI extraction (EPA method 3060A) and HPLC-ICP-MS analysis
Mn conc (µmoles/g dry wt basis) Mn conc (µmoles/g dry wt basis) Mn Characterization in Sediments Total reducible Mn determined by extracting the sediments with 1.5 M NH 2 OH.HCl and 0.1 M HNO 3 Easily reducible Mn determined by extracting the sediments with 0.02 M hydroquinone and 1 M CaCl 2 16 14 12 10 8 6 4 Total reducible Mn Easily reducible Mn Dissolved Mn Methods adapted from: Bartlett, R., and B. James. 1979. J. Environ Health Persp. 92, 17-24. Negra et al. 2005. Soil Sci. Soc. Am. J., 69, 87-95. SEM Mn determined by extracting the sediments with 1 N HCl during AVS analysis under N 2 sparging 2 0 10 9 8 7 6 5 4 3 2 1 0 DMT 68 54 45 33 69 bear creek Sampling stations total reducible Mn easily reducible Mn SEM Mn Colgate Creek DMT BSM 45 BSM 54 Sampling stations inner harbor
[i] (mm) Total Dissolved [i] (mm) Influence of ph on Mn Speciation and Solubility in a Sulfidic Environment 1 1 0.9 0.8 HS- HS- Mn2+ 0.9 0.8 Mn2+ 0.7 H2S 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 3 5 7 9 11 ph Mn(OH)4 Mn2(OH) 3 MnHS MnOH s2 MnS(grn) MnS(pnk) 0.6 0.5 0.4 0.3 0.2 0.1 Calculations performed using Visual MINTEQ 0 3 5 7 9 11 ph
Conclusions Cr VI formation occurs under aerobic conditions but not under anaerobic conditions. The Cr VI formation correlates negatively with the AVS concentration in the sediments and positively with porewater-mn / AVS ratio. The rate of Cr III oxidation increases with increase in sediment loading for dmt-207 site which is low in AVS but decrease with increase in sediment loading for 68-909 site which is high in AVS. This suggests that Cr VI formation is a function of the sediment oxidizing capacity but its persistence is a function of the sediment reducing capacity. Once all Cr VI is reduced to Cr III under anaerobic conditions, we observe Cr VI reoccurrence upon sediment oxygenation. This Cr VI reoccurrence is a function of the aging time. No Cr VI formation is observed below ph 7. The rate of Cr VI formation increases with increase in ph above ph 7. This Cr VI formation is coupled with loss of dissolved Mn above ph 7. Cr VI formation increases with increase in Mn II addition. This coupled with the observations of initial lag time, the loss of dissolved Mn upon aeration at ph 7, and no effect of microbial activity suggest that Cr III oxidation in Baltimore Harbor sediments is controlled by heterogeneous autocatalytic oxidation of dissolved Mn by O 2 that results in the formation of Mn III,IV (hydr)oxides responsible for oxidizing Cr III in sediments.
Conclusion Oxygenation of anoxic estuarine sediment facilitates Cr III oxidation and Cr VI persistence in these sediments at ph 7. Cr III oxidizing potential of sediments, the lag time, and the variation in Cr VI formation rates among different sediment sites appear to correlate negatively with [AVS] and positively with [PW-Mn]/[AVS]. Loss of dissolved Mn from solution due to autocatalytic oxidation by O 2 at ph 7 should result in the formation of reactive Mn III,IV (hydr)oxides responsible for oxidizing Cr III in sediments upon oxygenation. However, Cr VI persistence in sediments depends on [AVS]. Cr VI reoccurrence is observed upon oxygenation of anoxic Cr VI spiked sediments at ph 7. The rate of Cr VI reoccurrence decreases with increase in Cr III aging and increase with increase in ph at ph 7.
Summary: Cr III Oxidation in Sediments Spatial and temporal variation Lag time and rates of CrVI formation among different sites correlate negatively with [AVS] and positively with [PW-Mn]/[AVS] Effect of [Cr III ] 0 Rates of CrIII increase with increase in [Cr III ] 0 upto 150 µm. At higher concentration surface Cr(OH) 3, Cr x Fe 1-x (OH) 3 precipitates seem to inhibit the reaction Effect of sediment loading Rates increase with increase in sediment loading for low AVS sites but decrease with increase in sediment loading for high AVS sites. CrIII oxidation appears to be a function of dissolved [Mn] whereas CrVI persistence appears to be a function of [AVS] Effect of ph CrVI formation observed at ph 7 and above and it correlates with loss of dissolved Mn suggesting that autocatalytic Mn oxidation is potentially responsible for CrIII oxidation in sediments Effect of MnII addition Increase in [Mn II ] spike increases the reaction rate Cr VI reoccurrence is observed upon oxygenation of anoxic Cr VI spiked sediments at ph 7. The rate of Cr VI decreases with increase in CrIII aging and increase with increase in ph at ph 7.