1. 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 radionuclides

2. Radionuclides Radiotoxicity – from emitted particles – DNA damage Chemotoxicity – 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 (depleted uranium) 4 oxidation states (+4, +6 most common) U(VI) water-soluble, U(IV) in-soluble Metals and radionuclides

3. Bioremediation Bioremediation strategies for metals and radionuclides are extremely varied and include both above ground and in situ treatments and many of the treatments already perfected for organic biodegradation. –Above ground strategies include bioreactors, biosorption, prepared beds, biopiles, bioleaching, phytoremediation, etc. –In situ strategies include bioimmobilization, biomobilization, soil washing, infiltration galleries, bioventing, etc.

4. Bioimmobilization U(VI), Cr(VI) – soluble, toxic and mobile U(IV), Cr(III) – insoluble, less toxic, immobile e-e- Electrons from organic C (lactate, acetate, ethanol) or H 2 Metal reducing bacterium Direct reductive precipitation – using microbes to precipitate heavy metals by changing their valency Useful in above-ground and in situ treatments Oxidation Reduction

5. Bioimmobilization Fe(III), SO 4- Fe(II), H 2 S e-e- Electrons from organic C (lactate, acetate, ethanol) or H 2 Metal reducing bacterium Indirect reductive precipitation - microbial reduction of other TEAs (Fe 3+ or SO 4 -) results in abiotic reduction and precipitation of heavy metals Useful in above-ground and in situ treatments U(VI), Cr(VI) soluble mobile toxic U(IV), Cr(III) insoluble, immobile less toxic Ox Red OxRed

6. Time Distance from Source Dominant Terminal Electron Accepting Process +10 0 0 -10 Electron Acceptors pE Aerobic Respiration Aerobic Respiration O2O2 O2O2 Organics O2O2 O2O2 SO 4 - Sulfate Reduction Sulfate Reduction SO 4 - H2SH2SH2SH2S H2SH2SH2SH2S Methanogenesis CO 2 CH 4 H2H2 H2H2 Denitrification NO 3 - Iron (III) Reduction Iron (III) Reduction Fe (III) Fe (II) Chemical Species Equivalents Critical Biogeochemistry PCE/TCE Mn (IV) Cr (VI) U (VI)