Post on 15-Mar-2020
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
National Geoscience Award 2013
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
National Geoscience Award 2013
Sources of trace and toxic metals marine systemsSources of metals
Sink of metals
Benthic fluxBenthic flux
Geogenic and anthropogenic sources of metals
National Geoscience Award 2013
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
National Geoscience Award 2013
Geochemical fractionation of Cu in coastal sediments around India
Cu T Fr 1
Fr 4Fr 3
Fr. 2
Fr. 5
National Geoscience Award 2013
Low LowLow
Low
LowLow
HighHighHigh
HighHighHigh
Geochemical fractionation of Ni in coastal sediments around India
National Geoscience Award 2013
Low LowLow
Low
LowLow
HighHighHigh
HighHighHigh
Geochemical fractionation of Pb in coastal sediments around India
National Geoscience Award 2013
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
National Geoscience Award 2013
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
National Geoscience Award 2013
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
National Geoscience Award 2013
National Geoscience Award 2015
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
National Geoscience Award 2013
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
National Geoscience Award 2013
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
National Geoscience Award 2013
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
National Geoscience Award 2013