[PPT] - Discipline: Microbial Diversity and Bioremediation Important PowerPoint Presentation

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Discipline: Microbial Diversity and Bioremediation

Important Concepts of Chemical for Bioremediation Process

Professor Luciana Maria Saran Technology Department School of Agricultural and Veterinarian Sciences São Paulo State University Jaboticabal, SP, Brazil lmsaran@fcav.unesp.br

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1. Oxidation States
It is the number of eletrons (e-) that an atom loses,

gains or appears to use when joining with another atom in compounds.

It determines the ability of an atom to oxidize or to

reduce other atoms or species.

OXIDATION: results in an increase in the oxidation

state.

REDUCTION: results in a decrease in the oxidation

state.

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1. Oxidation States
Almost all of the transition metals have multiple

potential oxidation states. WHY?

Transition Metals (d-block)

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1. Oxidation States
It is relatively easy to lose electron(s) for transition

metals compared to the alkali metals (Li, Na, K) and alkaline earth metals (Ca, Mg, Ba). WHY?

Alkali metals: 1e- in their valence s-orbital. Their
xidation state is almost always +1 (from losing it).
Alkaline earth metals: 2e- in their valences-orbital,

resulting with an oxidation state of +2 (from losing both).

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SLIDE 5

Transition metals: have 5 d-orbitals and d-orbital has a

variety of oxidation states.

These d-orbitals have unpaired valence electrons.
These unpaired valence electrons are unstable and

eager to bond with other chemical species.

Highest Oxidation State for a Transition Metal =

Number of Unpaiered d-electrons + Two s-electrons

1. Oxidation States

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1. Oxidation States
Example: iron (26Fe)

Electronic Configuration: 1s2 2s22p6 3s23p63d6 4s2 Electronic Argon (Ar) Configuration  [Ar] Therefore: 26Fe: [Ar] 4s 3d

Possible oxidation states for iron: +2, +3, +4, +5 and

+6.

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1. Oxidation States

Somes rules:

Free elements (elements are not combined with other

elements) have an oxidation state of zero. Example: the oxidation state of Fe (iron) is 0.

For monoatomic ions, the oxidation is equal to the

charge of the ion. Example: the ion Fe3+ (ferric ion) has oxidation state of +3.

The oxidation state of a neutral compound is zero.

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1. Oxidation States
What is the oxidation state of Fe in FeCl2?

a) Chlorine (Cl) is in the halogen group of the periodic table, than it has a charge of -1 or simply Cl-. b) Since there are 2 Cl atoms the negtive charge is -2. c) There is no overall charge for FeCl2 and therefore the oxidation state of Fe is +2.

Its name is: ferrous chloride or iron(II) chloride.

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1. Oxidation States
What is the oxidation state of manganese (Mn) in

MnO4

?

a) MnO4

is a poliatomic ion.

b) This especies has an overall charge of -1. It is not neutral. c) Generally oxygen (O) has an oxidation state of -2 and there are four O atoms and these atoms contribute with a total charge of -8. d) Since the overall charge of the ion is -1, the Mn atom must have an oxidation state of +7.

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1. Oxidation States

Oxidation states of a metal affect:

the solubility of its compounds;
its mobility;
its reactivity;
its cellular permeability;
its toxicity.

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“Heavy metals” are naturally occurring elements that

have a high atomic weight and a density at least 5 times greater than water”.

“Heavy metals” include metalloids, such as arsenic

(As), that are able to toxicity at low level of exposure.

They are also considered as trace elements because
f their presence in trace concentrations (ppb range

less than 10 ppm) in various environmental matrices.

Source: Tchounwou P.B. et al. 2012. Heavy Metal Toxicity and the Environment. In: Luch A. (eds) Molecular, Clinical and Environmental Toxicology. Experientia Supplementum, v. 101. Springer, Basel. DOI https://doi.org/10.1007/978-3-7643-8340-4_6.

2. “Heavy Metals” and

Oxidation States

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2.1 “Heavy Metals”: Meaning

According to the IUPAC (International Union of Pure and Applied Chemistry):

The term “heavy metals” is both meaningless and

misleading. Why???

Source: Duffus, J.H. Pure Appl. Chem. 2002, 74(5), 798-807.

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2. “Heavy Metals” and

Oxidation States

2.1 Mercury (Hg)

This

“heavy metal” naturally

corrs

in the environment in metallic form (Hg0) and it is a liquid metal at a typical ambient temperatures and pressures.

In addition to its elemental state, Hg exists in two
xidation states Hg(I) or Hg2

2+ and Hg(II) or Hg2+.

Hg0 (elemental state); Hg2

2+ (mercurous ion); Hg2+

(mercuric ion) .

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2.1 Mercury (Hg)

It is not essential for plant or animal life.
Mercury and its compounds are toxic to humans,

aquatic

rganisms,

terrestrial

rganisms

and microorganisms.

The toxicity varies among the different types of

mercury.

Generally, organic forms are much more toxic than

the inorganic form.

2. “Heavy Metals” and

Oxidation States

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2.1 Mercury (Hg)

Ionic mercury, under reducing conditions in the

environment, changes to the uncharged elemental mercury (Hg0) wich is volatile and may be transported

ver long distances by ar.
Hg0 has na average residence time in the atmosphere
f about one year.
Elevated levels of mercury can be found in remote

areas far from the sources.

2. “Heavy Metals” and

Oxidation States

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2.1 Mercury (Hg)

Oxidised mercury (Hg2+) may be deposited relatively

quickly by wet and dry deposition processes leading to a residence time of hours to months.

It may be chemically or biologically transformed to
rganic forms: methylmercury and dimethylmercury.
Methylmercury represents the most important toxic

impact of mercury to humans.

2. “Heavy Metals” and

Oxidation States

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2.1 Mercury (Hg)

methylmercury (bioaccumulative) dimethylmercury (volatile)

2. “Heavy Metals” and

Oxidation States

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2.1 Mercury (Hg)

It is toxic to microorganisms.
Inorganic mercury: has been reported to have toxic

effects at concentrations of the metal in the culture medium of 5 µg L-1 (or 5 ppb).

Organomercury compounds: have toxic effects at

concentrations at least 10 times lower than 5 ppb.

2. “Heavy Metals” and

Oxidation States

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2. “Heavy Metals” and

Oxidation States

2.2 Chromium (Cr)

Chromium has several oxidation states.
The trivalent, Cr(III) and hexavalent, Cr(VI) states are

the most stable.

Cr(III): in small amounts is an essential component of

a balanced human and animal diet.

Cr(VI): is a potent, extremely toxic carcinogen and

may cause death to animals and humans.

Source: Zayed , A.M.; Terry, N. Plant and Soil. 2003, 249, 139-156.

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2. “Heavy Metals” and

Oxidation States

2.2 Chromium (Cr)

Chemical Species Oxidation State Remarks Elemental Cr Cr(0) Does not occur naturally. Divalent Cr Cr(II)

Unstable. Oxidized to Cr(III).

Trivalent Cr Cr(III) Forms stable compounds. Tetravalent Cr Cr(IV) Does not occur naturally. Pentavalent Cr Cr(V) Does not occur naturally. Hexavalent Cr Cr(VI) 2nd most stable state of Cr.

Source: Zayed , A.M.; Terry, N. Plant and Soil. 2003, 249, 139-156.

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2. “Heavy Metals” and

Oxidation States

2.2 Chromium (Cr)

Cr(III) and Cr(VI) are drastically different in charge,

physicochemical properties as well as chemical and biochemical reactivity.

Cr(III) forms strong complexes with various ligands. It

has an affinity for O-, N- and S-containing ligands and forms many organic complexes.

The solubility of Cr(III) is limited by the formation of

highly insoluble oxides, hydroxides and phosphates.

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2. Heavy Metals and

Oxidation States

2.2 Chromium (Cr)

In the presence of excessive oxygen, Cr(III) oxidizes

into Cr(VI).

Cr(VI) is the principal species in surface waters and

aerobic soils.

Cr(VI) forms stable anions: Cr2O7

2- (dichromate) and

CrO4

2- (chromate).

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SLIDE 23

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2. “Heavy Metals” and

Oxidation States

2.2 Chromium (Cr)

K2CrO4 K2Cr2O7 CrCl3.6H2O CrO4

2-(aq)  Cr(VI)

Cr2O7

2-(aq)  Cr(VI)

[Cr(H2O)6]3+(aq)  Cr(III)

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2. Heavy Metals and

Oxidation States

2.2 Chromium (Cr)

Cr(VI) is in general more toxic to organisms in the

environment that the Cr(III).

Almost all the Cr(VI) in the environment is a result of

human activities.

Cr(VI) is relatively stable in air and pure water.
Cr(VI) is reduced to the Cr(III) when it comes into

contact with organic matter in biota, soil and water.

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2. “Heavy Metals” and

Oxidation States

2.2 Chromium (Cr)

Cr(VI): is a strong oxidizing agent. It is not readily

adsorbed to surfaces.

The high oxidizing potential, high solubility and ease
f permeation of biological menbranes make Cr(VI)

more toxic than Cr(III).

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3. “Heavy Metals”

Speciation

Speciation refers to the various physical and

chemical forms in wich an element may exist in the system.

It

can have an affect

n

bioavailability and accumulation of these species.

“Heavy metal” toxicity is dependant upon chemical

speciation.

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Source: Ansari, T.M.; Marr, I.L.; Tariq, N. J. Applied Sci. 2004, 4(1), 1-20.

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3. “Heavy Metals”

Speciation

Metal Principal species Cd CdCl2, CdCl3

, CdCl+, Cd2+

Cr CrO4

2-, NaCrO4

Cu

Cu2+, CuCO3, CuOH+ Fe Fe(OH)3 Hg HgCl4

2-, HgCl3

, HgCl2

Mn Mn2+, MnCl+ Ni Ni2+, NiCO3, NiCl+ Pb PbCO3, Pb(CO3)2

2-, PbCl+

Zn ZnOH+, Zn2+, ZnCO3

Speciation of some heavy metals in seawater.

Source: Ansari, T.M.; Marr, I.L.; Tariq, N. J. Applied Sci. 2004, 4(1), 1-20.

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3. “Heavy Metals”

Speciation

Calculated inorganic chromium (III) speciation as a

function of pH in natural aquatic systems.

pH Species Distribution (%)

Source: Ansari, T.M.; Marr, I.L.; Tariq, N. J. Applied Sci. 2004, 4(1), 1-20.

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amphoteric hydroxide

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3.“Heavy Metals” Speciation

It depends on the environmental pH and the other

chemical species present.

Hydroxides of heavy metals are insoluble but some of

them are amphoteric.

Hydroxide Reaction as Base Reaction as Acid

Al(OH)3 Al(OH)3(s) + 3H3O+(aq)  Al3+(aq) + 6H2O(l) Al(OH)3(s) + OH-(aq)  [Al(OH)4]-(aq) Zn(OH)2 Zn(OH)2(s) + 2H3O+(aq)  Zn2+(aq) + 4H2O(l) Zn(OH)2(s) + 2OH-(aq)  [Zn(OH)4]2-(aq) Sn(OH)4 Sn(OH)4(s) + 4H3O+(aq)  Sn4+(aq) + 8H2O(l) Sn(OH)4(s) + 2OH-(aq)  [Sn(OH)6]2-(aq) Cr(OH)3 Cr(OH)3(s) + 3H3O+(aq)  Cr3+(aq) + 6H2O(l) Cr(OH)3(s) + OH-(aq)  [Cr(OH)4]-(aq)

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4. Solubility of Heavy Metal

Compounds

Solubility of heavy metal compounds in aquatic

environment is an interesting query with regards to dissolved metal levels in water.

A clear understanding of the chemistry involved in

dissolution phenomenon of metal compounds helps to reach some interesting and sound conclusions especially the bioavailability, bioacumulation and toxicity of heavy metals in the aquatic environment.

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Source: Ansari, T.M.; Marr, I.L.; Tariq, N. J. Applied Sci. 2004, 4(1), 1-20.

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4. Solubility of Heavy Metal

Compounds

Bioavailability:

“It refers to the portion of the total quantity or concentration of a chemical in the environment or a portion of it that is potentially available for a biological action such as uptake by an aquatic

rganism”.

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4. Solubility of Ionic

Compounds in Water

4.1 Solubility Product Constant, Ksp

Ksp is the equilibrium constant for a solid substance

dissolving in na aqueous solution.

It represents the level at wich a compound dissolves

in a solution.

The higher the value of the Ksp more soluble is the

compound.

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4. Solubility of Ionic

Compounds in Water

Compound Ksp (25 oC) Cr(OH)3 6.7x10-31 Ni(OH)2 1.6x10-16 Cu(OH)2 1.6x10-19 Cd(OH)2 2.8x10-14 Pb(OH)2 4x10-15 Pb3(PO4)2 8.0x10-43 PbSO4 1.3x10-8 PbCl2 1.6x10-5

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Soluble Compounds Exceptions

Almost all the salts of Na+, K+ and NH4

+

Salts of nitrate (NO3
), chlorate (ClO3
), perchlorate

(ClO4

) and acetate (CH3COO-)
Almost all the salts of Cl-, Br- and I-
Halides of Ag+,

Hg2

2+ and Pb2+

Compounds that contain F-
Fluorides
f

Mg2+, Ca2+, Sr2+, Ba2+ and Pb2+

Sulfate salts, SO4

2-

Sulfates
f

Mg2+, Ca2+, Sr2+, Ba2+ and Pb2+

4.2 Rules for Predicting the Solubility of Ionic Compounds in Water

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4.2 Rules for Predicting the Solubility of Ionic Compounds in Water

Insoluble Compounds Exceptions

Almost all the salts of carbonate

(CO3

2-), phosphate (PO4 3-), oxalate

(C2O4

2-) and chromate (CrO4 2-)

Ammonium (NH4

+)

salts and salts alkali metal cations

Most of the metal sulphides (S2-)

Ammonium (NH4

+)

salts and salts alkali metal cations

Most of the metal hydroxides (OH-)

and oxides (O2-) Ammonium (NH4

+)

salts and salts alkali metal cations

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4.3 Predicting if There Will Be Precipitate Formation

There will be precipitation of cadmium hydroxide in

aqueous medium if we have 100 mg L-1 Cd2+ and pH = 9.0? Ksp Cd(OH)2 = 2.8x10-14 (a 25 oC) Ca(OH)2(s) Ca2+(aq) + 2OH-(aq)

There will be precipitation if: [Ca2+][OH-]2 > Ksp

[ ]  mol L-1

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4.3 Predicting if There Will Be Precipitate Formation

Then:

[Cd2+] = (0.1 g L-1)/(112.41 g mol-1) [Cd2+] = 8.9x10-4 mol L-1 [OH-] = ? pH + pOH = 14 (a 25 oC) 9.0 + pOH = 14  pOH = 5.0  [OH-] = 1.0x10-5 mol L-1

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4.3 Predicting if There Will Be Precipitate Formation

[Ca2+][OH-]2 = (8.9x10-4)(1.0x10-5)2 [Ca2+][OH-]2 = 8.9x10-14 > Ksp

Therefore, there will be precipitation of the Cd(OH)2.
Attention!

In growing liquid medium for microorganisms which contain inorganic sources of PO4

3-, Cl- and SO4 2- it may have the precipitation of

heavy metals salts. Cd3(PO4)2(s), PbSO4(s) and PbCl2(s), for example.

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5. Bioremediation of Heavy

Metals by Microoganisms

Conventional procedures for heavy metal removal

and/or recovery from solutions:

1) Adsorption processes;

2) Chemical oxidation or reduction reactions; 3) Chemical precipitation; 4) Eletrochemical techniques; 5) Evaporative recovery; 6) Ion exchange; 7) Reverse osmosis; 8) Sludge filtration.

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5. Bioremediation of Heavy

Metals by Microoganisms

About Bioremetiation:

“This technique involves using living organisms to reduce and/ or recover heavy metal pollutants into less hazardous forms, using activities of algae, bacteria, fungi, or plants”.

Source: Ayangbenro, A.S.; Babalola, O.O. Int. J. Environ. Res. Publica Health. 2017, 14(94), 1-16.

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5. Bioremediation of Heavy

Metals by Microoganisms

Biosorption or passive uptake:

“The cellular structure of a microorganism can trap heavy metal ions and subsequently sorb them onto the binding sites of the metabolic cycle”.

This process is independent of the metabolic cycle.

Source: Ayangbenro, A.S.; Babalola, O.O. Int. J. Environ. Res. Publica Health. 2017, 14(94), 1-16.

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5. Bioremediation of Heavy

Metals by Microoganisms

Bioaccumulation or active uptake:

“Bioaccumulation is a process in wich the heavy metal ions pass across the cell membrane into the cytoplasm, through the cell metabolic cycle”.

This is a process of a living cell.

Source: Ayangbenro, A.S.; Babalola, O.O. Int. J. Environ. Res. Publica Health. 2017, 14(94), 1-16.

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5.1 Mechanisms of Heavy Metal Uptake by Microorganisms

Source: Ayangbenro, A.S.; Babalola, O.O. Int. J. Environ. Res. Publica Health. 2017, 14(94), 1-16.

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5.2 Groups Involved in Metal Adsorption

Some groups involved in metal adsorption:

# Amine; # Phosphoryl; # Carboxyl; # Sulfonate; # Ester; # Thyoether. # Hidroxyl; # Sulfhydryl or thyol;

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-

+ - + + +

Amide Group

SLIDE 46

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- +

Alcohol Group

SLIDE 47

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Amine Group

-

- - + + + + + + + + +

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Carboxyl and Ester Groups

-

-

- - + + + + + +

ester carboxyl

SLIDE 49

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Phosphoryl Group

SLIDE 50

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Sulfonate Group

SLIDE 51

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Sulfhydryl or Thyol Group

-

+ +

SLIDE 52

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Thioether Group

- + +

SLIDE 53

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Gram-Positive Bacteria

The active sites involved in metal binding processes

are: # Alanine; # Glutamic acid; # Meso-diaminopimelic acid; # Polymer of glycerol; # Teichoic acid.

SLIDE 54

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Gram-Positive Bacteria

The active site involved in metal binding processes

are:

alanine glutamic acid meso-diaminopimelic acid teichoic acid

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Gram-Negative Bacteria

The active site involved in metal binding processes

are: # Enzymes; # Glycoproteins; # Lipopolysaccharides; # Lipoproteins; # Phospholipids.

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Gram-Negative Bacteria

glycoproteins

SLIDE 57

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Gram-Negative Bacteria

lipopolysaccharide

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Gram-Negative Bacteria

phospholipids

SLIDE 59

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References

Ansari, T.M.; Marr, I.L.; Tariq, N. J. Applied Sci. 2004, 4(1), 1-20.
Ayangbenro, A.S.; Babalola, O.O. Int. J. Environ. Res. Publica
Health. 2017, 14(94), 1-16.
Duffus, J.H. Pure Appl. Chem. 2002, 74(5), 798-807;
Tchounwou P.B. et al. 2012. Heavy Metal Toxicity and the
Environment. In: Luch A. (eds) Molecular, Clinical and Environmental
Toxicology. Experientia Supplementum, v. 101. Springer, Basel. DOI

https://doi.org/10.1007/978-3-7643-8340-4_6.

Zayed , A.M.; Terry, N. Plant and Soil. 2003, 249, 139-156.