CEE 680 Lecture #51 4/29/2020 Print version Updated: 29 April - - PDF document

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CEE 680 Lecture #51 4/29/2020 Print version Updated: 29 April - - PDF document

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CEE 680 Lecture #51 4/29/2020 Print version Updated: 29 April 2020 Lecture #51 Redox Chemistry: Lead II (Stumm & Morgan, Chapt.8 ) Benjamin; Chapter 9 David Reckhow CEE 680 #51 1 Pb T =10 4 C T =10 2 From: Aquatic

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CEE 680 Lecture #51 4/29/2020 1

Lecture #51 Redox Chemistry: Lead II

(Stumm & Morgan, Chapt.8 )

Benjamin; Chapter 9

David Reckhow CEE 680 #51 1

Updated: 29 April 2020

Print version

 PbT=10‐4  CT=10‐2

David Reckhow CEE 680 #51 2

From: Aquatic Chemistry Concepts, by Pankow, 1991

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CEE 680 Lecture #51 4/29/2020 2

 PbT=10‐6  CT=10‐2

David Reckhow CEE 680 #51 3

From: Aquatic Chemistry Concepts, by Pankow, 1991

 PbT=10‐4  CT=10‐3

David Reckhow CEE 680 #51 4

From: Aquatic Chemistry Concepts, by Pankow, 1991

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CEE 680 Lecture #51 4/29/2020 3

 PbT=10‐6  CT=10‐3

David Reckhow CEE 680 #51 5

From: Aquatic Chemistry Concepts, by Pankow, 1991

David Reckhow CEE 680 #51 6

Schock et al., 2007

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CEE 680 Lecture #51 4/29/2020 4

David Reckhow CEE 680 #51 7

Chlorine to chloramines

Schock et al., 2007

 Rajasekharan et al.,

2007

 ES&T 41:4252

 15 ppb PbT  CO3T = 1.5 mM

David Reckhow CEE 680 #51 8

Effect of chloramines: experimental data

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CEE 680 Lecture #51 4/29/2020 5

Pb(II) solubility

 3 mg/L DIC

David Reckhow CEE 680 #50 9

From: Internal Corrosion and Depositional Control, by Schock & Lytle, Chapt. 20 in Water Quality and Treatment (6th ed), 2011

Pb(II) solubility

 30 mg/L DIC

David Reckhow CEE 680 #50 10

From: Internal Corrosion and Depositional Control, by Schock & Lytle, Chapt. 20 in Water Quality and Treatment (6th ed), 2011

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CEE 680 Lecture #51 4/29/2020 6

Pb(II) solubility; hydropyromorphite

David Reckhow CEE 680 #50 11

From: Internal Corrosion of Water Distribution System, (2nd ed) by Snoeyink, Wagner et al., 1996

Pb(II) solubility; lead orthophosphate

David Reckhow CEE 680 #50 12

From: Internal Corrosion of Water Distribution System, (2nd ed) by Snoeyink, Wagner et al., 1996

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CEE 680 Lecture #51 4/29/2020 7

Pb Solubility

 Experimental data

David Reckhow CEE 680 #50 13

From: Internal Corrosion and Depositional Control, by Schock

  • Chapt. 17 in Water Quality and

Treatment (5th ed), 1999

 Equilibria used in EPA’s Leadsol program

 Schock, Wagner and Oliphant, 1996

David Reckhow CEE 680 #51 14

Equilibria Log K Pb+2 + H2O = PbOH+ + H+ ‐7.22 Pb+2 + 2H2O = Pb(OH)2

0 + 2H+

‐16.91 Pb+2 + 3H2O = Pb(OH)3

‐ + 3H+

‐28.08 Pb+2 + H+ + PO4

‐3 = PbHPO4

+15.41 Pb5(PO4)3OH (s) = 5Pb+2+3PO4

‐3+H2O

‐62.83

From: Internal Corrosion of Water Distribution System, (2nd ed) by Snoeyink, Wagner et al., 1996

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CEE 680 Lecture #51 4/29/2020 8

Pb(II): pH vs DIC

David Reckhow CEE 680 #50 15

From: Internal Corrosion of Water Distribution System, (2nd ed) by Snoeyink, Wagner et al., 1996

 0.5 mg‐P/L

Pb(II): pH vs PO4T ;low CO3T

David Reckhow CEE 680 #50 16

From: Internal Corrosion of Water Distribution System, (2nd ed) by Snoeyink, Wagner et al., 1996

 6 mg/L DIC

AL = 15 μg/L = 10-1.8 mg/L

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CEE 680 Lecture #51 4/29/2020 9

Pb(II): pH vs PO4T ;high CO3T

David Reckhow CEE 680 #50 17

From: Internal Corrosion

  • f Water Distribution

System, (2nd ed) by Snoeyink, Wagner et al., 1996

 24 mg/L DIC

AL = 15 μg/L = 10-1.8 mg/L

Pb(II); pH/PO4 contour plot

David Reckhow CEE 680 #50 18

From: Internal Corrosion of Water Distribution System, (2nd ed) by Snoeyink, Wagner et al., 1996

AL = 15 μg/L = 10-1.8 mg/L

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CEE 680 Lecture #51 4/29/2020 10

Pb mitigation in Boston

David Reckhow CEE 680 #51 19

From: Internal Corrosion and Depositional Control, by Schock

  • Chapt. 17 in Water Quality and Treatment (5th ed), 1999

 Karalekas

study

Pb Mitigation

 Impacts on other

corrosion byproducts

David Reckhow CEE 680 #51 20

From: Karalekas et al., 1983 [J.AWWA 75:2:92]

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CEE 680 Lecture #51 4/29/2020 11

Iron Scale

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Background: Other Sources

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From: The Extraordinary Chemistry of Ordinary Things, C.H. Snyder

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CEE 680 Lecture #51 4/29/2020 12

Why is Pb2+ Toxic

Diagonal Relationships in the Periodic Table

 There is a chemical resemblance between an element and the element one

down and to the right

 Diagonal relationships result from similarity in charge density (ratio of

charge to ion size)

 Because of the lanthanide contraction Ca2+ and Pb2+ have similar sizes.  So Pb2+ can interfere with Ca2+ metabolism, particularly in neuronal

signaling.

CEE 680 #50 Ca Pb

Ion

Ionic Radius (Å)

Ca2+ 1.14 Pb2+ 1.19

Important Biological Properties

 Lead bioaccumulates in bones, teeth, nails, and

hair.

 Pb doesn’t degrade.  Transferrable across the placental and blood‐brain

barriers.

 Multiple ingestion routes – by eating, drinking and

breathing.

 Treatable with chelation therapy

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David Reckhow 24

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CEE 680 Lecture #51 4/29/2020 13

Chronic Exposure

 Long term, low dose

 Reproductive and early development

 Various studies suggest fetal toxicity (birth

  • utcome, growth, mental development) starts at a

relatively low blood concentration, 8‐20 µg/dL in the mother.  Cognitive and other neurobehavioral effects

 CDC and the EPA have proposed a 10 µg/dL blood

concentration limit.

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Neurodevelopmental Toxicity Mechanisms

 Lead alters the effectiveness of the intracellular

adhesion molecule in the brain, thereby affecting brain structural development.

 Lead strongly interferes with the Ca2+ messenger

system.

 Ca2+ is used throughout the body as an intracellular

messenger that converts electrical impulses to hormonal signals.

 Pb2+ either replaces or inhibits removal of Ca2+.

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David Reckhow 26

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CEE 680 Lecture #51 4/29/2020 14

Acute Pb Toxicity

Blood concentration > 50 ‐ 100 µg/dL

 Anemia, reduced red blood cell levels.

Central nervous system

 Encephalopathy: characterized by excess water in the

brain.

 Mechanism: blood/brain barrier properties altered as

Pb2+ substitutes for Ca2+.

Renal (kidney) system

 Disturbs amino acid and glucose cycling.

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Pb2+ Binds in Place of Ca2+ and Zn2+

Lead targets proteins that naturally bind calcium and zinc. Examples of proteins that are targeted by lead include synaptotagmin, which acts as a calcium sensor in neurotransmission, and ALAD, the second enzyme in the heme biosynthetic pathway. Despite its size, lead (1.19 Å, blue sphere and circles) can substitute for calcium (0.99 Å, green spheres) in synaptotagmin and zinc (0.74 Å, red spheres) in ALAD.

H.A. Godwin, Current Opinion in Chemical Biology 2001, 5:223–227

David Reckhow CEE 680 #50 28

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CEE 680 Lecture #51 4/29/2020 15

Pb Chelation Therapy

 Succimer (meso‐2, 3‐dimercaptosuccinic acid, DMSA) is

the drug of choice for Pb chelation therapy and is also recommended for asymptomatic children with blood lead levels 40 – 70 mg/dL.

 Next are CaNa2EDTA  D‐penicillamine

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CEE 680 #51

David Reckhow 30

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CEE 680 Lecture #51 4/29/2020 16

To next lecture

David Reckhow CEE 680 #51 31