Speciation of metals (trace and heavy) in marine environments · Speciation of metals (trace and heavy) in marine environments By Dr Parthasarathi Chakraborty Scientist CSIR-National

Speciation of metals (trace and heavy) in marine environments

By

Dr Parthasarathi Chakraborty

Scientist

CSIR-National Institute of Oceanography

Goa, India

National Geoscience Award 2013

What is metal speciation??? Importance of metal speciation

Identification of metal species (complexes) is known as metal speciation.

Total metal concentration in an environment does not represent its bioavailability

Concentrations of bioavailable metal is ONLY responsible for biological activity (as nutrient or toxicant) of metal

transport and biogeochemical cycling processes of metals is determined by speciation


Focus of my research interests?

Metal (trace and heavy) speciation in marine environments (water and sediments)

Metal-ligand (natural) interactions in coastal/ estuarine/ hydrothermally altered marine systems

Understand the relation between metal speciation, bioavailability and uptake by biotic ligand in marine environments.

Geochemistry of toxic metals (Hg, Pb, Cd) in marine sediments


Sources of trace and toxic metals marine systemsSources of metals

Sink of metals

Benthic fluxBenthic flux

Geogenic and anthropogenic sources of metals


1. Water soluble metal complexes (Fr. 1)2. Exchangeable + carbonate/bicarbonate

forms of metals (Fr.2) (Thermodynamically less stable)

3. Metal associates with Fe/Mn- oxyhydroxidephase in sediment (Fr.3) (Thermodynamically more stable than Fr.1 and Fr 2)

4. Metal associates with organic carbon phase (Fr. 4)

5. Metal present within the structure of the sediment (represent source rocks) (Fr. 5)

Different forms of metal in sediments

Study area


Geochemical fractionation of Cu in coastal sediments around India

Cu T Fr 1

Fr 4Fr 3

Fr. 2

Fr. 5


Low LowLow

Low

LowLow

HighHighHigh

HighHighHigh

Geochemical fractionation of Ni in coastal sediments around India


Low LowLow

Low

LowLow

HighHighHigh

HighHighHigh

Geochemical fractionation of Pb in coastal sediments around India


LowLowLow

LowLowLow

HighHighHigh

HighHighHigh

Metals ERLmg/kg

ERMmg/kg

NE coast CE coast SE coast SW coast

CW coast

NW coast

Ni 20.9 51.6 higher

that ERM

higher

that ERM

good good higher

that

ERM

Slightly

higher

that ERL

Cu 34 270 Slightly

higher

that ERL

good Slightly

higher

that ERL

good higher

that ERL

good

Pb 46.7 218 good good good good good good

Quality of coastal sediments around India


ERL: Effect Range LowERM: Effect Range Median

Sediment Quality Guidelines from National Oceanic and Atmospheric Administration

Outcomes and implicationsOutcomes implication

Fe-Mn oxy hydroxides phase was themajor binding phase for metals. Thisphase controls metals speciation inthe surface coastal sediments aroundIndia

Organic carbon was the second majorbinding phase of metals in the coastalsediments.

Labile complexes of metals increasedwith the increasing total metalsloading in the coastal sediments.

The concentrations of metals inresidual phase were found to carrysource rock signature along the coast

Increasing oxygen minimum zone in shelf areas may brings up trace/toxic metals (associated with Fe/Mnoxyhydroxy phase of sediments) to the overlying water column.

Better understanding the impact of trace/toxic metals on primary productivity is not known

Impact of seasonal upwelling on metal bioavailability in the coastal Arabian Sea


with inorganic ligands (OH-, CO32-, HCO3

-,..)

with dissolved NOM2 (measured as DOC3: humic and fulvic acids)

each of these processes may reduce metal bioavailability/toxicity

Dissolved Metal Complexes

Forms of metals in the overlying water column

– Free-ion forms tend to bind to biological ligands,

these species mainly causes metal toxicity

Dissolved Free Metal

– adsorbed to suspended solids (POC1 or mineral surfaces)

each of these processes may reduce metal bioavailability/toxicity

Metals in Particulate Matter

1POC: Particulate Organic Carbon2NOM: Natural Organic Matter3DOC: Dissolved Organic Carbon



Dissolved organic carbon (DOC) is a broad classification for organic molecules of varied origin and composition within aquatic systems.

Chemically hetergeneous1.Polyfunctionality2.Polyelectrolytic properties 3.Conformational properties

Physical heterogeneity of HS is due to their polydispersity

CdCu Pb

Electroanalytical technique for metal speciation in water column


ElementsChemical speciation

parameters

Mole Ratio of M(II) / DOC

0.01 0.001 0.0005

Cu(II)

Log K* (L mol-1) 6.38 0.14 6.93 0.12 7.41 0..08

DML(m2s-1) (4.10 0.14) 10-10 (4.50 0.10) 10-11 (7.50 0.12) 10-12

Zn(II)

Log K*(L mol-1) 5.56 0.14 5.58 0.06 6.01 0.12

DML(m2s-1) (5.01 0.08) 10-10 (4.07 0.14)10-10 (1.60 0.10)10-10

Cd(II)

Log K* (L mol-1) 5.26 0.14 5.41 0.04 5.47 0.08

DML (m2s-1) (6.86 0.10) 10-10 (5.77 0.15) 10-10 (5.14 0.14) 10-10

Pb(II)Log K* (L mol-1) 6.07 0.70 6.47 0.18 6.52 0.25

DML(m2s-1) (5.74 0.10)10-10 (3.86 0.14)10-10 (2.62 0.10)10-10

Determination of speciation parameters in water column


Outcomes Implications

Increasing M loading in water column may decrease the stability of M-DOC complexes

Diffusion of M-DOC complexes increases with increasing M loading

M-DOC interaction depends on M chemistry

Decreasing stability of M-DOC complexes may increase bioavailability of the M

may increase M-mobility in the water column

Control M-bioavailability in water column


Overall outcomes Fe-Mn oxy hydroxides phase was the major binding

phase for metals. This phase controls metals speciation in the surface coastal sediments around India

Increasing oxygen minimum zone in shelf areas may brings up trace/toxic metals (associated with Fe/Mnoxyhydroxy phase of sediments) to the overlying water column

Increasing M flux from sediment to water column may decrease the stability of M-DOC complexes and may increase bioavailability of the M



Acknowledgments

CSIR-NIO

Ministry of MinesGovt. Of India

I APPRECIATE YOUR ATTENTIONTHANK YOU

Documents

Speciation of metals (trace and heavy) in marine environments · Speciation of metals (trace and heavy) in marine environments By Dr Parthasarathi Chakraborty Scientist CSIR-National