““OK, so what’s the speed of OK, so what’s the speed of dark?”dark?”

““When everything is coming your When everything is coming your way, you're obviously in the wrong way, you're obviously in the wrong lane”lane”

““Who laughs last, Who laughs last, thinks slowest”thinks slowest”

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

A)A) NOM: Power of ecosystems - redox chainNOM: Power of ecosystems - redox chainB)B) Oxido-Reduction: Environmental speciation Oxido-Reduction: Environmental speciation

and remediationand remediationC)C) Metals in the environment: some case studiesMetals in the environment: some case studies

U6220: Environmental Chem. & Tox.Thursday, June 30 2005

Central Park LakeCentral Park LakeQuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture. Massive fluxes of soot:Massive fluxes of soot:

30 fold higher than other urban lakes 30 fold higher than other urban lakes

Manhattan (Central Park)

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- Ecosystem conditions controls speciationEcosystem conditions controls speciation- Speciation controls mobility and toxicitySpeciation controls mobility and toxicity

Speciation: The role of EcosystemsSpeciation: The role of Ecosystems

Metals

Fate of contaminants: SpeciationFate of contaminants: Speciation

Metals do not “change” per se speciate

Single variable diagram: pH

What is the most abundant species of iron in natural What is the most abundant species of iron in natural waters?waters?

Geochemical controls of As cycling:Geochemical controls of As cycling:– Fe/Mn oxyhydroxidesFe/Mn oxyhydroxides

Single Variable Diagrams: Single Variable Diagrams: pHpH

What is the most abundant What is the most abundant species of arsenic in natural species of arsenic in natural waters?waters?

How does pH influence How does pH influence As distribution?As distribution?

Oxidation-Reduction (Redox):Oxidation-Reduction (Redox):

Chemical ReactionsChemical Reactions

The redox state of an element can be of considerable The redox state of an element can be of considerable interest, because it often determines the chemical interest, because it often determines the chemical and biological behavior, including toxicity, of that and biological behavior, including toxicity, of that element as well as its mobility in the environmentelement as well as its mobility in the environment

CrOCrO442-2- Cr Cr3+3+

(mobile and very toxic) (less solube and toxic)(mobile and very toxic) (less solube and toxic)CrOCrO44

2-2- + 3e- + 8H + 3e- + 8H++ Cr Cr3+ 3+ + 4H+ 4H22O O

Two Variable Diagrams: pE-pHTwo Variable Diagrams: pE-pHAs a general rule, most reactions that involve electrons also As a general rule, most reactions that involve electrons also involve protons. Oxidation usually releases protons or acidity involve protons. Oxidation usually releases protons or acidity (basic cause for acid mine drainage). Conversely, reduction (basic cause for acid mine drainage). Conversely, reduction usually consumes protons, and the pH rises:usually consumes protons, and the pH rises:

FeFe2+2+ + 3H + 3H22O O Fe(OH) Fe(OH)33 + 3H + 3H++ + e + e--

The reaction affects the pH The reaction affects the pH of the medium (solution) of the medium (solution) and vice versa and vice versa the pH of the pH of the environment affects the the environment affects the redox potential established redox potential established by Feby Fe3+3+ (and other species). (and other species).

Natural Organic Matter:Natural Organic Matter:Power of ecosystemsPower of ecosystems

Photosynthesis:Photosynthesis:

6H6H22O + 6COO + 6CO22 + + E (hE (h) ) C C66HH1212OO66 + 3O + 3O22

Respiration:Respiration:

CC66HH1212OO66 + 3O + 3O2 2 6H 6H22O + 6COO + 6CO22 + + EE

NOM: Power of EcosystemsNOM: Power of Ecosystems

-Oxidation-Reduction:Oxidation-Reduction:CHCH22O + 1/4HO + 1/4H22O O 1/4CO 1/4CO22 + e + e-- + H + H++

1/4O1/4O22 + e + e-- + H + H++ 1/2H 1/2H22O O

CHCH22O + 1/4OO + 1/4O22 1/4CO 1/4CO22 + 1/4H + 1/4H22OO

Gº = -29.9 kcal/molGº = -29.9 kcal/molHowever:However:

GGttGº + RT lnQGº + RT lnQAndAnd

Q = (PCOQ = (PCO22))1/41/4/((PO/((PO22))1/41/4[CH[CH22O])O])

When you solve for Q:When you solve for Q:GGtt-29.8 kcal/mol-29.8 kcal/mol

NOM: Power of EcosystemsNOM: Power of Ecosystems

-Oxidation-Reduction:Oxidation-Reduction: Anoxic biodegradation (lack of Anoxic biodegradation (lack of molecular Omolecular O22))1) 1) Nitrate reductionNitrate reduction

1/4 CH1/4 CH22O + 1/5NOO + 1/5NO33-- 1/10 N 1/10 N22 + 1/4 CO + 1/4 CO22 + 7/20 H + 7/20 H22O O

Gº = -30.3 kcal/molGº = -30.3 kcal/molHowever:However:

GGtt-27.5 kcal/mol-27.5 kcal/mol

2) 2) Iron hydroxide reductionIron hydroxide reduction1/2 CH1/2 CH22O + Fe(OH)O + Fe(OH)3 3 + 2H+ 2H++ Fe Fe2+2+ + 1/2 CO + 1/2 CO22 + 11/4 H + 11/4 H22O O

Gº = -24 kcal/molGº = -24 kcal/molHowever:However:

GGtt-12 kcal/mol-12 kcal/mol

NOM: Power of EcosystemsNOM: Power of Ecosystems-Oxidation-Reduction:Oxidation-Reduction: Anoxic biodegradation (lack of Anoxic biodegradation (lack of molecular Omolecular O22))3) 3) Manganese oxide reductionManganese oxide reduction

1/2 CH1/2 CH22O + MnOO + MnO2 2 + 2H+ 2H++ Mn Mn2+2+ + 1/2 CO + 1/2 CO22 + 11/4 H + 11/4 H22O O GGtt-24.3 kcal/mol-24.3 kcal/mol

4) 4) Sulfate reductionSulfate reduction1/2 CH1/2 CH22O + 1/8 SOO + 1/8 SO44

2-2- + 1/8 H+ 1/8 H++ 1/8 HS 1/8 HS-- + 1/4 CO + 1/4 CO22 + 1/4 + 1/4

HH22O O GGtt-7.4 kcal/mol-7.4 kcal/mol

5) 5) Methanogenesis (Methanogenesis (fermentationfermentation))1/4 CH1/4 CH22O O 1/8 CO 1/8 CO22 + 1/8 CH + 1/8 CH44

GGtt-5.5 kcal/mol-5.5 kcal/mol

- The ecological redox scale:- The ecological redox scale:

NOM: Power of EcosystemsNOM: Power of Ecosystems

Change in oxidant Change in oxidant concentrations with concentrations with respect to time in a respect to time in a flooded soilflooded soil

-The ecological redox scale: The ecological redox scale: Change in oxidant Change in oxidant concentrations with respect to distance in groundwaterconcentrations with respect to distance in groundwater

1/2 CH1/2 CH22O + Fe(OH)O + Fe(OH)3 3 + + 2H2H++ Fe Fe2+2+ + 1/4 CO + 1/4 CO22 + 11/4 H + 11/4 H22OO

1/4 CH1/4 CH22O + 1/2 MnOO + 1/2 MnO2 2 + + HH++ 1/2 Mn 1/2 Mn2+2+ + 1/4 CO + 1/4 CO22 + 3/4 H + 3/4 H22OO

1/2 CH1/2 CH22O + 1/8 SOO + 1/8 SO442-2-

+ + 1/8 H1/8 H++ 1/8 HS 1/8 HS-- + 1/4 CO + 1/4 CO22 + 1/4 H + 1/4 H22OO

NOM: Power of EcosystemsNOM: Power of Ecosystems

Two Variable Diagrams: pE-pHTwo Variable Diagrams: pE-pH- Let’s consider the reaction:Let’s consider the reaction:

FeFe2+2+ + 3H + 3H22O O Fe(OH) Fe(OH)33 + 3H + 3H++ + e + e--

As desorption and dissolution due to changes As desorption and dissolution due to changes in reducing conditionsin reducing conditions

Two Variable Diagrams: pE-pHTwo Variable Diagrams: pE-pHWhat is the most abundant species of arsenic in natural What is the most abundant species of arsenic in natural

waters? waters?

1)1) HH33AsOAsO44 H H22AsOAsO44-- + H + H++

2)2) HH22AsOAsO44-- + 3H + 3H++ + 2e + 2e--

HH33AsOAsO33 + H + H22OO

Speciation is important Speciation is important because it often determines:because it often determines:- Mobility (solubility)Mobility (solubility)- ToxicityToxicityi.e. arsenite (III) is about 60 i.e. arsenite (III) is about 60 times more toxic than times more toxic than arsenate (IV)arsenate (IV)

Redox Potential - Acid Mine DrainageRedox Potential - Acid Mine DrainageSulfate reduction:Sulfate reduction:

SOSO442-2-

+ 10H+ 10H++ + 8e + 8e-- HS HS-- + 4H + 4H22OO

CHCH22O + HO + H22O O CO CO22 + 4H + 4H++ + 4e + 4e--

SOSO442-2-

+ 2CH+ 2CH22O + 2HO + 2H++ H H22S + 2HS + 2H22O + 2COO + 2CO22

With the presence of FeWith the presence of Fe2+2+

FeFe2+2+ + H + H22S S FeS + 2H FeS + 2H++ And FeS + S And FeS + S FeS FeS22

FeSFeS22 + H + H22O + 7/2OO + 7/2O22 Fe Fe2+2+ + 2SO + 2SO442-2- + +

2H2H++

AndAnd

FeSFeS22 + 14Fe + 14Fe3+3+ + 8H + 8H22O O 15Fe 15Fe2+2+ + + 8H8H22SOSO44

LaterLater

4Fe4Fe2+2+ + O + O22 + 10H + 10H22O O 4Fe(OH) 4Fe(OH)33 + 8H + 8H++

Redox potential and Speciation of Redox potential and Speciation of Environmental ContaminantsEnvironmental Contaminants

Chromium (tanning processes). Small scale tanneries Chromium (tanning processes). Small scale tanneries produce approx 0.4 kg of Cr(III) waste per 100 kg of treated produce approx 0.4 kg of Cr(III) waste per 100 kg of treated hide.hide.

2Cr2Cr3+3+ 2Cr 2Cr6+6+ + 6e + 6e--

oxidation of Cr(III) to Cr(VI)oxidation of Cr(III) to Cr(VI)2Cr2Cr3+3+ + 7 H + 7 H22O O Cr Cr22OO77

2-2- + 14H + 14H++ + 6e + 6e--

3/2 O3/2 O22 + 6H + 6H++ + 6e + 6e-- 3 H 3 H22OO2Cr2Cr3+3+ + 4 H + 4 H22O + 3/2 OO + 3/2 O22 Cr Cr22OO77

2-2- + 8H + 8H++

However, in anaerobic systems:However, in anaerobic systems:CrOCrO44

2+2+ + 3Fe + 3Fe2+2+ + 8 H + 8 H22O O Cr(OH) Cr(OH)33 + 3Fe(OH) + 3Fe(OH)33 + 4H + 4H++

Redox Potential - Acid Mine WatersRedox Potential - Acid Mine Waters

OO22 solubility and ventilation solubility and ventilationOO22 solubility is dependent on water temperature: solubility is dependent on water temperature:Usually oscillates between 6-14 mg/L in aerated natural waters. OUsually oscillates between 6-14 mg/L in aerated natural waters. O22 diffusion in surface waters is a slow process aided by turbulent diffusion in surface waters is a slow process aided by turbulent mixing of water (and cold temperatures)mixing of water (and cold temperatures)

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How much OHow much O22 do do aquatic organisms aquatic organisms need?need?• 8-15 mg/L: Excellent8-15 mg/L: Excellent• 6-8 mg/L: OK6-8 mg/L: OK• 4-6 mg/L: Stressed4-6 mg/L: Stressed• 2-4 mg/L: Critical2-4 mg/L: Critical• <2 mg/L: Hypoxia<2 mg/L: Hypoxia

Density change and turnover (ventilation)Density change and turnover (ventilation)

Fresh water maximum density at ~4Fresh water maximum density at ~4C C Seasonal inversion and Seasonal inversion and stratificationstratification

Seasonal mixing and Dissolved OSeasonal mixing and Dissolved O22Strong seasonal dependence on ventilation and nutrient-oxygen mixingStrong seasonal dependence on ventilation and nutrient-oxygen mixing

- The ecological redox scale: - The ecological redox scale: Change in oxidant Change in oxidant concentrations with respect to distance in groundwater concentrations with respect to distance in groundwater flowflow

Saturated zonesSaturated zones

Arsenic in Texas Drinking WaterArsenic in Texas Drinking Water

What is the environmental legacy of What is the environmental legacy of U mining in South Texas…...U mining in South Texas…...

Finalized EPA Drinking Standard for ArsenicFinalized EPA Drinking Standard for Arsenic The The Safe Drinking Water ActSafe Drinking Water Act, as amended in , as amended in

1996, requires EPA to revise the existing 1996, requires EPA to revise the existing drinking water standard for arsenic. drinking water standard for arsenic.

EPA reduced the maximum level of arsenic EPA reduced the maximum level of arsenic allowed in drinking water that reduces the allowed in drinking water that reduces the maximum level allowed from 50 parts per billion maximum level allowed from 50 parts per billion (ppb) to 10 ppb.(ppb) to 10 ppb.

This was challenged by the Bush AdministrationThis was challenged by the Bush Administration

New standard will be applied to all community New standard will be applied to all community water systems (serving 254 million people) water systems (serving 254 million people)

12% of these systems will likely have to take 12% of these systems will likely have to take corrective actioncorrective action

Estimated National Cost:Estimated National Cost:

3 ppb = 645 M$, 5 ppb = 379 M$3 ppb = 645 M$, 5 ppb = 379 M$

10 ppb = 166 M$, 20 ppb = 65 M$10 ppb = 166 M$, 20 ppb = 65 M$

Fallonites, Don Cooper, 82, and wife Norma, 81, raise a toast to Nevada's arsenic-rich homebrew on the outskirts of town. Concentrations in drinking water are approximaately 100 ppb.

Outside magazine, February 2001

Data map: 31,350 ground-water arsenic samples collected in 1973-2001Data map: 31,350 ground-water arsenic samples collected in 1973-2001Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater: Geotimes v.46 no.11, p.34-36.Ryker, S.J., Nov. 2001, Mapping arsenic in groundwater: Geotimes v.46 no.11, p.34-36.

ArsenicArsenicin Texas Groundwaterin Texas Groundwater

TWDB and NURE Data Sets

TWDB and NURE Data Sets

MolybdenumMolybdenumin Texas Groundwaterin Texas Groundwater

Geogenic Source of MetalsGeogenic Source of Metals

Catahoula formation, an oxidized Catahoula formation, an oxidized volcanic ash is a source of U, As, volcanic ash is a source of U, As, Mo and other trace metalsMo and other trace metals

Metal cycling and groundwater redox: A case of “chromatographic separation”

Metal cycling and groundwater redox: A case of “chromatographic separation”

Adapted from Devoto (1978)

U MoSe As

OxidizedRegionally Reduced

South Texas Uranium Roll FrontSouth Texas Uranium Roll Front

Uranium cycling - A proxy for nuclear Uranium cycling - A proxy for nuclear waste?waste?

Fe(III) are generally the most important potential sorbents for Fe(III) are generally the most important potential sorbents for U (with organic matter). If reduction doesn’t follow adsorption, U (with organic matter). If reduction doesn’t follow adsorption, uranyl can be desorbed by an increase in alkalinity or increase uranyl can be desorbed by an increase in alkalinity or increase in pH (low sorption capacity for carbonate complexes!)in pH (low sorption capacity for carbonate complexes!)

Texas’ Uranium HistoryTexas’ Uranium History

““Oxidized” uranium ores were Oxidized” uranium ores were open-pit mined from sandstone-open-pit mined from sandstone-hosted roll-front deposits (1960 - hosted roll-front deposits (1960 - 1983)1983)

Open pit mining feasible because Open pit mining feasible because of shallow depth to ore (<300 feet) of shallow depth to ore (<300 feet) and the poorly cemented nature of and the poorly cemented nature of overburden overburden

Voluminous spoils stockpiled near Voluminous spoils stockpiled near pits. Two processing mills in pits. Two processing mills in western Karnes Co. generated large western Karnes Co. generated large tailings pilestailings piles

U Mining in the Nueces and U Mining in the Nueces and San Antonio River BasinSan Antonio River Basin

NuecesRiver

San AntonioRiver

Reduced sediments near the uranium ore were enriched in As, Mo, Se and radionuclides.Termed “protore” (proto ore), this material was placed on the top of spoil piles where it was most readily eroded.

Surface Exposure of ProtoreSurface Exposure of Protore

Oxidized overburden (upper strata) were placed at the bottom of spoilDeeper strata enriched in trace elements was placed on top of spoil.

Stratigraphic InversionStratigraphic Inversion

Eroded Spoil at the Haase Moy Wiatrek MineEroded Spoil at the Haase Moy Wiatrek Mine

Gonzales County

South Texas Ecological Impacts of MetalsSouth Texas Ecological Impacts of Metals

Molybdenosis in Black Angus Molybdenosis in Black Angus Cattle, South TexasCattle, South Texas

Arsenic exposure to wildlife at ground water Arsenic exposure to wildlife at ground water seeps in the Nueces River watershedseeps in the Nueces River watershed