Metals and radionuclides - UC Berkeley College of Natural ... · radionuclides are extremely varied...

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

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

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.

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

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

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)