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Metals Greater solubility usually = greater toxicity Chromium (Cr) – Six oxidation states, +1, +2, +3, +4, +5, +6 • +3, +6 most common • used to prevent corrosion (stainless steel) • Cr(VI) is toxic (skin, lungs, kidneys) and carcinogenic • Hexavalent Cr(VI) is most toxic and most soluble • Induces free-radical formation • oxidative stress – DNA/membrane damage Erin Brockovich PG&E used it as rust inhibitor • Migration into water supply Metals and Metals and radionuclides radionuclides

Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments

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Page 1: Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments

MetalsGreater solubility usually = greater toxicity

Chromium (Cr) – Six oxidation states, +1, +2, +3, +4, +5, +6• +3, +6 most common• used to prevent corrosion (stainless steel)• Cr(VI) is toxic (skin, lungs, kidneys) and carcinogenic• Hexavalent Cr(VI) is most toxic and most soluble• Induces free-radical formation

• oxidative stress – DNA/membrane damage

Erin Brockovich

• PG&E used it as rust inhibitor• Migration into water supply

Metals and Metals and radionuclidesradionuclides

Page 2: Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments

RadionuclidesRadiotoxicity – from emitted particles – DNA damageChemotoxicity – oxidative stress – DNA/membrane damage

Uranium – heaviest natural element - 17 isotopes

• Natural form % = U-238 (99.27), U-235 (0.72), U-234 (0.006)• U-238 (t1/2 = 4.5 billion years), U-235 (t1/2 = 7 million years)• Emit alpha, beta and gamma

• Used in nuclear fuel – U-235 (readily fissionable)• Used in nuclear and conventional weapons

• Uranium enrichment (increase percentage of U-235)• U-238 used as a precursor of Pu-239• U-238 used to strengthen ammunition (depleteduranium)

• 4 oxidation states (+4, +6 most common)• U(VI) water-soluble, U(IV) in-soluble

Metals and Metals and radionuclidesradionuclides

Page 3: Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments

Bioremediation

Bioremediation strategies for metals andradionuclides are extremely varied andinclude both above ground and in situtreatments and many of the treatmentsalready perfected for organicbiodegradation.

– Above ground strategies include bioreactors,biosorption, prepared beds, biopiles,bioleaching, phytoremediation, etc.

– In situ strategies include bioimmobilization,biomobilization, soil washing, infiltrationgalleries, bioventing, etc.

Page 4: Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments

Bioimmobilization

U(VI), Cr(VI) – soluble, toxic and mobile

U(IV), Cr(III) – insoluble, less toxic, immobile

e-

Electrons from organic C (lactate, acetate, ethanol) or H2

Metal reducing bacterium

Direct reductive precipitation – usingmicrobes to precipitate heavy metals bychanging their valency

Useful in above-ground and in situ treatments

Oxidation

Reduction

Page 5: Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments

Bioimmobilization

Fe(III), SO4-

Fe(II), H2S

e-

Electrons from organic C (lactate, acetate, ethanol) or H2

Metal reducing bacterium

Indirect reductive precipitation -microbial reduction of other TEAs (Fe3+

or SO4-) results in abiotic reduction andprecipitation of heavy metals

Useful in above-ground and in situ treatments

U(VI), Cr(VI)solublemobiletoxic

U(IV), Cr(III)insoluble,immobile less toxic

Ox

Red Ox Red

Page 6: Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments

TimeTime

Distance from SourceDistance from Source

Dominant Terminal Electron Accepting ProcessDominant Terminal Electron Accepting Process

+10+10

00

-10-10

Electron AcceptorsElectron AcceptorsElectron Acceptors

pE

pE

AerobicRespiration

AerobicRespiration

O2O2

OrganicsOrganics

O2O2

SO4-SOSO44--

SulfateReduction

SulfateReduction

SO4-SO4-

H2SHH22SS

MethanogenesisMethanogenesis

CO2CO2

CH4CH4

H2H2

DenitrificationDenitrification

NO3-NO3-

NO3-NONO33--

Iron (III)ReductionIron (III)

Reduction

Fe (III)Fe (III)

Fe (II)Fe (II)

Chemical SpeciesChemical Species

Eq

uiv

alen

tsE

qu

ival

ents

Critical BiogeochemistryCritical BiogeochemistryCritical Biogeochemistry

PCE/TCE

Mn (IV)

Cr (VI)U (VI)