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ChemicalOceanographyMetal Geochemistry
Dr. David K. RyanDepartment of ChemistryUniversity of Massachusetts Lowell&Intercampus Marine Sciences Graduate Program
http://faculty.uml.edu/David_Ryan/84.653
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Metal Geochemistry
Read Emerson & Hedges Chapter 12Read paper Donat & Bruland (1995)Read paper by Nieboer & Richardson (1980)
(Papers are posted on website for today’s class)
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Concerned with Metal Ions (Geochemistry)
Typically cations (Cu2+, Cd2+)Some anions (CrO4
2-, MoO42-, AsO4
3-)General properties of interest Reactivity
Redox – oxidation/reduction reactions Complexation or Sorption Speciation – forms
Cycling – ultimate fate Transport – mobility Toxicity/Bioavailability/Bioaccumulation
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Biogeochemical Processes
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Classification Schemesfor Metals
Concentration – Major, Minor, TraceBiological Reactivity – Biolimiting, Biointermediate, Biounlimited, NoncyclingChemical Reactivity – d0, d10, Intermediate or Class A, Class B, IntermediateOverall Reactivity – Nutrient Type, Particle Reactive, OtherEnvironmental Origin – Crustal, Pollutant (anthropogenic)
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Concentration levels
Major ions – discussed previouslymetals & non metals (Ca2+, Mg2+, Na+ , K+)Minor ions – some mention (Ba2+, Sr2+, etc.)Trace ions (Trace Metals) – all the restMillero Major: 0.05 to 750 mM Minor: 0.05 to 50 μM Trace: 0.05 to 50 nM
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Depth Profiles for Mo & WConservative behavior (Millero 2006)
Major Components, Rb+, Cs+, etc.
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Depth Profiles for Cd & PNutrient behavior (Millero 2006)
Nitrate, Silicate, Zinc, Barium, etc.
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Depth Profiles for AlMid-depth minimum (Millero 2006)
Copper, Tin, etc.
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Depth Profiles for PbSurface enriched (Millero 2006)
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Depth Profile for MnSurface enriched(Millero 2006)
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Depth Profile for FeRedox (Millero 2006)
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Depth Profile for MnAnomolous (Millero 2006)
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Classification Schemesfor Metals
Concentration – Major, Minor, TraceBiological Reactivity – Biolimiting, Biointermediate, Biounlimited, NoncyclingChemical Reactivity – d0, d10, Intermediate or Class A, Class B, BorderlineOverall Reactivity – Nutrient Type, Particle Reactive, OtherEnvironmental Origin – Crustal, Pollutant (anthropogenic)
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Nieboer & Richardson 1980
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Importance of Humic MaterialsGlobal Carbon ReservoirTake Part in Interfacial PhenomenaUndergo Coagulation and AggregationInvolved in Photochemical ReactionsContain RadicalsKnown Reducing AgentsMethylate MetalsForm Chlorinated Species, THMs DBPsDetoxify MetalsLimit Bioavailability of MetalsAlter SolubilityInfluence TransportBind Metals & Organic PollutantsTerminal Electron Acceptor for Bacteria
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Metal Complexationby Humic Materials
Leenheer et al. (1998)Morel (1983)
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Importance of Humic MaterialsGlobal Carbon ReservoirTake Part in Interfacial PhenomenaUndergo Coagulation and AggregationInvolved in Photochemical ReactionsContain RadicalsKnown Reducing AgentsMethylate MetalsForm Chlorinated Species, THMs DBPsDetoxify MetalsLimit Bioavailability of MetalsAlter SolubilityInfluence TransportBind Metals & Organic PollutantsTerminal Electron Acceptor for Bacteria
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Humic material will aggregate & may“salt out” with cations
Leenheer, J.A. et al. (1998) Environ. Sci. Technol. 32, 2410
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Dissolved Metal Species
Mx+(aq)
InorganicMetal
Complexes
MetalOrganic
Complexes
Oxidizedor Reduced
Forms
OrganometallicSpecies
Metals Sorbed toParticles/Colloids
All Dissolved Organic Compounds
Organic
Dissolved
Natural
Carbon
Matter
HumicMaterials
Substances
Humic AcidFulvic Acid
OCDOCNOC
OMNOMDOM
HM
HS
HAFA
Chromophoric or Colored DOM
CDOM
Humic Subset
23NOMy- = natural organic matter of varying negative charge y-
NOMy-
NOMy-
NOMy-
M-NOM(x-y)-
Mx+
Mx+
Mx+
Mx+ = metal ion, toxic or non, of charge x+ (e.g., Cu2+, Al3+, etc.)
Metal Organic Complexes
Mx+
M-NOM(y-x)- = metal complex of natural organic matter
