Pb in DC
Michael J Clarke
Department of Chemistry
Boston College
Chestnut Hill, MA 02467
clarke@bc.edu
© M.J.Clarke, Boston College
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Pb in DC
© M.J.Clarke, Boston College
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Tap water in thousands of District houses has recently tested
above the federal limit for lead contamination, a new
phenomenon that has baffled the D.C. Water and Sewer
Authority and forced the agency to begin replacing service
pipes.
Two-thirds of the 6,118 residences that WASA tested last
summer, or 4,075 homes, had water that exceeded the lead
limit of 15 parts per billion set by the Environmental Protection
Agency in 1991. This is the first time the city's water has shown
significant lead contamination since the late 1980s, officials
said.
Four-year-old
Michael Joseph
often visits at the
Georgetown home
of his grandfather
Charles Eason,
whose tap water
registered 36 times
the EPA limit in the
random testing. "It's
shocking," Eason
said of the test
results.
© M.J.Clarke, Boston College
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Council Furious With Water Agency
Delayed Report of High Lead Levels Prompts Calls for Review
By David Nakamura and Neely Tucker
Washington Post, Sunday, February 1, 2004; Page C01
Council Chairman Linda W. Cropp called for hearings on the lead issue
Several D.C. Council members said yesterday that they were outraged that
District leaders were not informed about lead contamination in thousands of
city homes and called for an immediate review of the D.C. Water and Sewer
Authority's performance.
The city officials said they were not aware that tap water in 4,075 homes
had tested above the federal limit for lead until they read about the tests in
yesterday's Washington Post. WASA, which first learned of lead
contamination problems in 2002, should have been more diligent in
informing the public and answering questions, they said.
© M.J.Clarke, Boston College
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© M.J.Clarke, Boston College
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Pb Service Lines
© M.J.Clarke, Boston College
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D.C. Water Worries Sellers, Buyers
Real Estate Industry Unsure What to Do About Lead Reports
By Sandra Fleishman, Washington Post
Saturday, February 14, 2004; Page F01
On Wednesday, at a news conference with the mayor and D.C. Council, WASA
promised to send letters to owners of all 23,000 properties that the agency believes
have lead service lines. If those homeowners have concerns about the water, they
can call WASA for information about testing.
© M.J.Clarke, Boston College
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Chlorine vs Chloramine
Safe water is the biggest
improvement in public health
ever (more than antibiotics).
Chlorine is an effective,
persistent, and relatively safe
bacterial disinfectant that has
been used for about a century
in municipal water supplies.
One disadvantage is that
chlorine interacts with organics
to produce halogenated
hydrocarbons, such as CHCl3,
etc, which are carcinogenic.
© M.J.Clarke, Boston College
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Experts Seek Answers On Tainted D.C. Water
Panel to Study Abrupt Rise of Lead Levels in City
By David Nakamura and D'Vera Cohn
Washington Post, Sunday, February 8, 2004; Page C01
A team of chemists, water-quality experts and engineers will gather in
Washington this week in an attempt to answer a baffling question on a tight
deadline: Why did lead levels in the tap water at thousands of city homes spike
above federal safety limits?
Scientists plan to conduct tests to determine whether new chemicals used to
treat water for bacteria at the city's two treatment plants have a highly corrosive
effect on service lines, allowing lead to dissolve from the pipes. They are
especially interested in studying a compound called chloramine, a combination
of chlorine and ammonia that the city's water treatment plants began using four
years ago. Chlorine produces cancer-causing byproducts, so chloramine
has become an increasingly popular alternative at water treatment plants
across the country.
The District is among about three dozen water systems nationwide whose lead
tests have exceeded the federal safety standard since 2000, according to data
supplied by the EPA. Most were in small communities.
© M.J.Clarke, Boston College
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Pb Increase Correlates with
Chloramines
pH Raised with CaO
NH3 added
to give Chloramines
Grumbles & Welsh, WASA, House Testimony 3/5/04
© M.J.Clarke, Boston College
90% of the homes
tested were under
this level
10
Chloramine
Chlorine is still added and converts to
hypochlorous acid and hypochlorite
Cl2 + H2O  H+ + Cl- + HOCl
Ammonia is then added to form chloramines
NH3(aq) + HOCl  NH2Cl + H2O
Chloramines are more persistent oxidants than Cl2
and lead to less CHCl3 through CHBr3
© M.J.Clarke, Boston College
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© M.J.Clarke, Boston College
Marc Edwards, Civil Engineering, Virginia Tech
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Experimental data proving the adverse consequences of chloramines on lead leaching
from certain types of brass. “Before” is simulated WASA water with free chlorine. “After” is
the same water with chloramine.
© M.J.Clarke, Boston College
Marc Edwards, Civil Engineering, Virginia Tech
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© M.J.Clarke, Boston College
Marc Edwards, Civil Engineering, Virginia Tech
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© M.J.Clarke, Boston College
Marc Edwards, Civil Engineering, Virginia Tech
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O2 + Cu in Contact with Pb
Sets up a Galvanic Cell
4H+ + O2 + 2Pb  2Pb2+ + 2H2O E = 0.99V
© M.J.Clarke, Boston College
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A Cu Pipe Preceding a Pb Pipe (or Pb
solder) will Cause it to Dissolve
Cu2+ + 2 e- = Cu
0.3419
Pb2+ + 2 e- = Pb
-0.1262
Fe2+ + 2 e- = Fe
O2 + 4 H+ + 4e- = 2H2O
-0.447
0.86
Pb + Cu2+  Cu + Pb2+ E = 0.47 V
© M.J.Clarke, Boston College
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© M.J.Clarke, Boston College
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District To Widen Testing For Lead
Problem May Go Beyond 23,000 Suspect Homes
By Craig Timberg and Carol D. Leonnig
Washington Post, Thursday, March 11, 2004; Page A01
Federal and D.C. officials announced yesterday they would
broaden testing of the city's water supply as Mayor Anthony
A. Williams and others warned that lead contamination
reaches beyond the homes known to have service lines
made of the toxic metal.
Corrosive water can leach lead from many sources,
including brass fixtures and lead solder used to connect
pipes, EPA officials said.
© M.J.Clarke, Boston College
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Preferred Methods Pb Analysis
• Graphite-furnace atomic absorption (GFAA)
• Anodic stripping voltammetry (ASV)
© M.J.Clarke, Boston College
D.S. Bannon, J.I. Chisholm, Clinical
Chemistry. 2001;47:1703-1704.)
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An Immeasurable Threat in D.C.
High Lead Levels Hurt Developing Children,
But Scientists Say Danger Is Hard to Gauge
By Avram Goldstein, Washington Post, Friday, February 20, 2004; Page B01
News that lead in drinking water may exceed federal safety
guidelines in thousands of District homes has raised anxieties
among many parents of small children. But finding out whether
this exposure to lead will have lasting consequences -- on
intelligence, attention span and behavior -- generally takes years.
Lead tricks brain cells into absorbing lead when they seek
calcium, the most abundant mineral in the human body and one
that is necessary to enable thoughts to form. Calcium is critical to
cardiac health, the development of bones and teeth and other
functions.
© M.J.Clarke, Boston College
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Increase in Miscarriages Coincided with High
Levels of Lead in D.C. Water
Carol D. Leonnig, Wahington Post, Dec. 9, 2013
Late-term miscarriages and
spontaneous abortions occurred at
an unusually high rate among
Washington women from 2000
through 2003 — during the same
time frame that lead levels were
dangerously high in the city’s
drinking water.
Overall results are consistent with
prior research linking increased lead
exposure to higher incidence of
miscarriages and fetal death, even at
blood lead elevations (≈5 μg/dL)
once considered relatively low.
Marc Edwards, Environmental Science and Technology, 2014, 48, 739-46.
© M.J.Clarke, Boston College
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Other Uses of Lead
• Paints, glazes, and other protective coatings.
• Lead storage batteries, ceramics, plastics.
• (CH3CH2)4Pb, antiknock fuel additive, reduced
to 0.1 g/gal in 1984.
– 4-5 million metric tons used in US.
– Use stopped because of poisoning of car antipollution
catalyst.
– Additionally present in fossil fuels
© M.J.Clarke, Boston College
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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 signalling.
Ion
Ionic
Radius (Å)
Ca2+
1.14
Pb2+
1.19
© M.J.Clarke, Boston College
Ca
Pb
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Important Biological Properties
• Lead bioaccumulates in bones, teeth, nails, and
hair.
• Transferrable across the placental and bloodbrain barriers.
• Multiple ingestion routes – by eating, drinking
and breathing.
• Treatable with chelation therapy
© M.J.Clarke, Boston College
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Chronic Exposure
• Long term, low dose
– Reproductive and early development
• Various studies suggest fetal toxicity (birth outcome,
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.
© M.J.Clarke, Boston College
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© M.J.Clarke, Boston College
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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+.
© M.J.Clarke, Boston College
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Pb and IQ
Environmental Health Perspectives
Volume 113, Number 5, May 2005
© M.J.Clarke, Boston College
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Epidemiology
Study
Included data from many
earlier studies, which was
corrected for numerous
variables, i.e., parents’
I.Q., parents occupation,
age, parents’ age, etc.
© M.J.Clarke, Boston College
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Effects on Reading
© M.J.Clarke, Boston College
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Pb & Violent Crime
© M.J.Clarke, Boston College
PLoS Med. 2008, DOI: 10.1371/journal.pmed.0050101
Lauren K. Wolf, C&EN, 2/3/14, 92/5, 27-29
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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.
© M.J.Clarke, Boston College
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Pb2+ Binds in Place of Ca2+ and Zn2+
Lead binding to structural zinc-binding domains can be quantitatively determined
by monitoring lead–thiolate charge-transfer bands in the ultraviolet.
Competition experiments with zinc, the relative affinities of Pb and Zn were
determined for a series of consensus zinc finger peptides with different metalbinding residues.
Pb(II) binds 100x more tightly than Xn(II) to Cys4 sites in Zn-fingers and that
Pb(II) can displace Zn(II) from these sites on a physiologically relevant timescale.
© M.J.Clarke, Boston College
H.A. Godwin, Current Opinion in Chemical Biology 2001, 5:223–227
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Pb2+ Binds in Place of Ca2+ and Zn2+
Lead targets proteins that naturally bind calcium and zinc.
Including 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.
© M.J.Clarke, Boston College
H.A. Godwin, Current Opinion in Chemical Biology 2001, 5:223–227
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Pb(II) displaces Zn(II) from sulfur-rich structural
binding pockets in the proteins, causing them to
fold improperly
• Possibly because lead preferentially binds to only three
sulfurs in a trigonal pyramidal configuration, even when
additional sulfurs are available
© M.J.Clarke, Boston College
Godwin & Magyr, J. Am. Chem. Soc. 2005, 127, 9495
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2+
Pb Inhibits
NMDA Receptor
• As childhood blood-lead levels increase, gray matter
decreases in the ventrolateral prefrontal cortex and the
anterior cingulate cortex, areas known for impulse
control, emotional regulation, and decision making.
• Lead might affect learning and intellect by inhibiting the
N-methyl-d-aspartate receptor (NMDAR) on the surface
of nerve cells that is activated by glutamate and glycine.
• NMDAR inhibition reduces Ca2+ uptake by nerve cells.
Ca2+ activates enzymes such as calmodulin kinase,
which participates in strengthening nerve cell
connections that form memories.
PLoS Med. 2008, DOI: 10.1371/journal.pmed.0050112
Brain Res. Rev. 2005, DOI: 10.1016/j.brainresrev.2005.02.004
© M.J.Clarke, Boston College
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ALAD- Porphobilinogen Synthase
is inhibited by Pb2+
• The Zn enzyme, δ-aminolevulinic acid dehydratase
(ALAD, also called porphobilinogen synthase),
catalyzes the second reaction in the heme
biosynthetic pathway.
• Inhibition of this enzyme by the substitution of Zn2+
by Pb2+ explains (at least in part) the anemia often
seen in adults and children with high BLLs.
• This enzyme (of all Zn enzymes) is inhibited
because it has a unique zinc-binding site with three
cysteine residues.
• When coordinated to –S-Cys, Pb2+ exhibits intense
lead–thiolate UV charge-transfer bands.
© M.J.Clarke, Boston College
H.A. Godwin, Current Opinion in Chemical Biology 2001, 5:223–227
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Pb Effects on Zn-Fingers
• Pb2+ alters the structure of the zinc proteins to
which it binds because of the differences in
coordination preferences (6–8 for Pb2+ versus 4
for Zn2+ and geometries (irregular for Pb2+
versus Td for Zn2+).
• These results suggest that lead binding to
structural zinc-binding domains should disrupt
the DNA-binding activity of proteins and
transcription factors results in pervasive
neurological problems in both children and
adults.
© M.J.Clarke, Boston College
H.A. Godwin, Current Opinion in Chemical Biology 2001, 5:223–227
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Pb2+ Effects on Neurons
•
•
•
•
•
Lead interferes with the ability of calcium to trigger exocytosis of
neurotransmitters in neuronal cells, suggesting that lead might generally
target proteins involved in calcium-mediated signal transduction.
Picomolar concentrations of lead can activate calcium-dependent PKC,
which is involved in the regulation of cell growth, learning and memory.
Pb2+ appears to bind to the C2 domain of PKC, which contains a
multinuclear binding site on an exposed loop that normally binds
phospholipids in a Ca-dependent fashion. Pb2+ promotes phospholipid
binding more than Ca2+.
There are C2 domains in synaptotagmin, which acts as a calcium sensor in
neurotransmission. Nanomolar Pb2+ promotes binding of synaptotagmin to
phospholipids, but interferes with its ability to bind to its protein partner,
syntaxin, which may explain why Pb2+ interferes with calcium-triggered
neurotransmitter release.
EF-hand calcium proteins, such as calmodulin, can be activated by Pb2+,
but only at μM concentrations.
© M.J.Clarke, Boston College
H.A. Godwin, Current Opinion in Chemical Biology 2001, 5:223–227
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Unusual Geometry-Steric Lone Pair
Inert-Pair Effect
Relativistic effects
cause the 6s electrons
to be held tighter and
not enter into covalent
bonding
Because the center of charge for the metal ion is different from that
of the 6s2 lone pair, metal–ligand bonds in the direction of the
lone pair are longer than those facing away from the lone pair.
© M.J.Clarke, Boston College
L. Shimoni-Livny, J.P. Glusker, C.W. Bock, Inorg.
Chem., 37 (8), 1853 -1867, 1998
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Stereochemistry of Pb(II)
Compounds
• Hemidirected for low
coordination numbers
(2-5)
• Holodirected for high
coordination numbers
(9-10)
• Either for intermediate
coordination numbers
(6-8)
© M.J.Clarke, Boston College
L. Shimoni-Livny, J.P. Glusker, C.W. Bock, Inorg.
Chem., 37 (8), 1853 -1867, 1998
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Steric Lone Pair in Pb2+
•
Converting a hemidirected complex into a holodirected complex requires
approximately 8-12 kcal/mol for the simple formally uncharged ligands NH3,
PH3, OH2, and SH2. Interactions between ligands can increase or decrease
this energy cost significantly.
•
The lone pair of electrons on the Pb(II) in the hemidirected complexes is
primarily 6s, polarized by a surprisingly small p contribution that is
responsible for the void in the distribution of ligands.
•
The lone pair orbitals in the holodirected complexes are entirely s in
character.
•
For hemidirected Pb(II) complexes, charge is transferred from the ligands to
the lead. As the electronegativity of the liganding group decreases, more
charge is transferred to the 6p orbitals on the lead. This added charge does
not increase the p character of the lone pair orbitals, but increases the p
character of the PbII-X bonding orbitals, resulting in a decrease in the
exterior X-PbII-X angles.
•
The two shorter PbII-X bonds in the hemidirected four-coordinate complexes
have greater covalent character than do the two longer PbII-X bonds.
© M.J.Clarke, Boston College
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Pb Chelation Therapy
• Succimer (meso-2, 3-dimercaptosuccinic acid,
DMSA) is the drug of choice for Pb2+
chelation therapy and is also
recommended for asymptomatic children
with blood lead levels 40 – 70 mg/dL.
• Next are CaNa2EDTA
• D-penicillamine
© M.J.Clarke, Boston College
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Clinical Metal Ion Chelating Agents
Could a chelating
agent take advantage
of the stereochemical
lone-pair effect to be
particularly effective at
eliminating Pb2+ ?
© M.J.Clarke, Boston College
Environmental Health Perspectives Supplements Volume 110,
Number S5 October 2002
45
Lewisite
British Anti-Lewisite (BAL)
Lewisite is named after the US chemist and soldier Winford Lee Lewis (1878-1943). In
1918 he found the thesis of Julius Arthur Nieuwland at Maloney Hall, a chemical
laboratory at The Catholic University of America, Washington DC in which Nieuwland
detailed the synthesis by the combination of arsenic trichloride with acetylene in an
hydrochloric acid solution of mercuric chloride.
After receiving the first Ph.D. in chemistry from CUA in 1904, Nieuwland returned to
Notre Dame as professor of botany (until 1918), then professor of organic chemistry (until
1936). In 1920, Nieuwland successfully polymerized acetylene into divinylacetylene.
Elmer Bolton, the Director of Research at DuPont, used this basic research during the
development of neoprene.
When he was 22, Knute Rockne had saved enough money to continue his education and
headed to South Bend, Indiana. He was the laboratory assistant to noted polymer chemist
Julius Arthur Nieuwland at Notre Dame, but rejected further work in chemistry after
receiving an offer to coach football.
© M.J.Clarke, Boston College
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Lead Nephropathy
• Lead induces acute nephrosis of the proximal
tubule and affects blood pressure to the kidney.
• Low molecular weight proteins bind Pb2+, leading
to resorption by endocytosis.
• Cellular and mitochondrial swelling, enlarged
nucleus (karyomegaly), mitosis and intranuclear
inclusion bodies are seen.
• Decreased tubular resorption of glucose,
phosphate and amino acids +/- proteinuria
• Chronic exposure causes tubulo-interstitial
disease.
© M.J.Clarke, Boston College
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Lead Levels in Water Misrepresented Across U.S.
Utilities Manipulate or Withhold Test Results to Ward Off Regulators
Cities across the country are manipulating the
results of tests used to detect lead in water, violating
federal law and putting millions of Americans at
risk of drinking more of the contaminant than their
suppliers are reporting.
Nimi Sandhu of Seattle
worries that lead in the
water may have
endangered her children.
Photo Credit: Patrick Hagerty For The Washington Post
Some cities, including Philadelphia and Boston,
have thrown out tests that show high readings
© M.J.Clarke, Boston College
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Chloramine and Elevated Pb Levels in Drinking Water
Jay A. Switzer, University of Missouri-Rolla
SGER CHE-0437346
Although NH2Cl may produce less
chlorinated hydrocarbons than OClwhen used as a disinfectant in
drinking water, it may lead to
increased Pb levels. A 0.5 µm thick
Pb film nearly completely dissolves
in a NH2Cl solution, but it is
passivated in a OCl- solution by the
formation of insoluble PbO2
(Environmental Scuence &
Technology, 2006).
OCl-
NH2Cl
© M.J.Clarke, Boston College
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Lime Juice? Or CaO?
New Water Treatment Proposed for Maui
Timothy Hurley, Honolulu Advertiser, Thursday, May 20, 2004
WAILUKU, Maui — The Maui Department of Water Supply wants to try yet
another chemical additive in the Upcountry water supply in an attempt to
relieve residents of skin rashes, itching and other health problems.
The complaints started after June 2001, when the Department of Water
Supply began adding zinc orthophosphate, a compound designed to
control high levels of lead caused by leaching of pipes in older homes.
Responding to public pressure last year, the water department switched to
phosphoric acid, but the complaints persisted. Squires joined other
speakers in calling for an immediate halt to use of phosphoric acid, which also
is used in the manufacture of fertilizers, pharmaceuticals and detergents, and
as a flavoring agent in soda pop, beer, jams and jellies, and cheeses.
Department spokesperson Jacky Takakura said yesterday that officials will
seek state permission to use food-grade lime as an alternative to the
phosphoric acid added to the water to reduce high levels of lead.
© M.J.Clarke, Boston College
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Montgomery Tests Delay School
Lead Remediation
In Pr. George's, Replacement of Drinking Fountains Underway
By Amit R. Paley, Washington Post, Sunday, August 29, 2004; Page C01
The school system then began retesting those
256 sources to determine the source of
contamination. Initial test results indicate the
cause in almost all cases is the fixtures, which
prior to 1986 were soldered with lead. Schools
across the country are finding that fixtures are
the primary source of lead, said Stephen
Gerwin, operation support manager at WSSC.
© M.J.Clarke, Boston College
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© M.J.Clarke, Boston College
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WASA Affirms 10-Minute Pipe
Flush
High Lead Levels Cut By 95%, Agency Says
By Craig Timberg and David Nakamura
Tuesday, March 9, 2004; Page B01
Recent tests at D.C. homes with high levels of
lead contamination in the water showed that
running the taps for 10 minutes eliminated 95
percent of the lead, rendering the water safe to
drink in most cases, water authority officials said.
WASA retested 96 homes with lead
concentrations above 300 parts per billion, 20
times the Environmental Protection Agency's
"action level."
© M.J.Clarke, Boston College
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Mail 23,000 Water Filters,
Williams Tells WASA
By Craig Timberg and Petula Dvorak
Wednesday, March 17, 2004; Page A01
Mayor Anthony A. Williams instructed D.C. Water and
Sewer Authority officials yesterday to begin mailing free
water filters to each of the 23,000 homes in Washington
known to have lead service lines.
"Every one of the 23,000 homes will get a filter shipped to
their door," Williams (D) announced to a group of about
three dozen residents meeting last night at Shiloh Baptist
Church in Northwest Washington to discuss the city's lead
problem.
© M.J.Clarke, Boston College
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A Solution?
In Lead Crisis, Aqueduct Adjusts Chemical Cocktail
By Marc Fisher
Washington Post, Tuesday, March 23, 2004; Page B01
Treating water is the kind of job that chemists love. There is no perfect mix,
and each city uses a different approach. Bottom line: "Water is corrosive by
definition," Jacobus says. "The purer the water, the faster it will rust metal."
The trick is to find the optimal balance of chemicals to produce safe water that
is also tasty and pleasant to the nose.
If the Potomac delivers more muck than usual, the aqueduct adjusts the levels
of alum, lime or other chemicals in the recipe for Washington water.
But there is no such thing as a perfect solution: Treating water introduces
chemicals, which have their own downside. The corrosion inhibitor to be
added this summer is made from phosphates, which were removed from
cleansers some years back because of environmental concerns.
© M.J.Clarke, Boston College
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Solubility of Lead Phosphate
Compound Log(Ksp)
PbCl2
-4.77
Pb3(PO4)2
-42
Pb3(HPO4)3
-9.6
PbCO3
-6.77
Pb(OH)2
-7.11
© M.J.Clarke, Boston College
See Schock, JAWWA, 75(2), 1987), and
http://personal.stevens.edu/~dvaccari/lead.xls56
Bacteria Put D.C. Water in Breach
Levels Violate Health Standard
By D'Vera Cohn, Washington Post, Friday, September 24, 2004; Page B01
Bacteria levels in D.C. tap water exceeded federal health standards this
month for the first time since 1996, city and Environmental Protection Agency
officials announced yesterday, but they said most people are not at risk.
The sudden rise in bacteria, detected in routine testing this month, probably
stemmed from use of a new water treatment chemical intended to reduce
lead levels in the water at thousands of city homes, officials said during a news
conference. They said the chemical, orthophosphate, may have shaken off a
layer of rust and bacteria inside city water pipes.
Phosphate is a fertilizer and nutrient needed for cell growth.
© M.J.Clarke, Boston College
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High Lead Found in Boston Area Water
EPA-State Decision Influenced by D.C. Utility's Handling of Contamination
By Carol D. Leonnig, Washington Post, Wednesday, April 28, 2004; Page A02
Federal and state regulators ruled yesterday that the drinking water
delivered to 2.5 million customers in the Boston region has lead levels
above the acceptable national standard
MWRA … was seeking to invalidate tests from 18 households, most with
high lead levels. Approval of the rare request would have allowed the
utility to declare itself in compliance with federal law.
The MWRA had unsafe lead levels from 1997 to 2001, forcing Boston to
replace hundreds of lead service lines. But the utility was in compliance in
2002 and 2003. Last year, the utility declared that it had reduced its lead
levels to a safe level.
State environmental authorities considered allowing the MWRA to strike
18 samples out of 425 taken in the required annual measurement of the
region's water quality.
© M.J.Clarke, Boston College
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MWRA Pb Levels
Chloramine Added
In 1997
CaO Added
In 1996
© M.J.Clarke, Boston College
59
MWRA says water tastier because of
different treatment
Agency's director warns that rates could rise 9%
Stephanie Ebbert, Boston Globe, June 8, 2006
Good news is coming from the Massachusetts Water Resources Authority: The water
is not only safe to drink, it tastes better.
In July, the system's John J. Carroll Water Treatment Plant in Marlborough began
using ozone gas bubbles to kill germs, resulting in fewer potentially harmful
byproducts of chlorination and better taste.
``It tastes great and it's clean as a whistle," said Frederick A. Laskey , MWRA
executive director. On the financial front, however, MWRA rates are expected to
climb 5 percent to 9 percent this summer, Laskey said.
Although the system as a whole did not exceed standards for lead in drinking water,
Laskey said, lead was detected in water samples taken in March in six communities -Boston, Framingham, Malden, Milton, Quincy, and Winthrop.
© M.J.Clarke, Boston College
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Summary
• Relativistic effects affect stereochemistry
• Diagonal relationships with Zn2+ and Ca2+
• Binds to synaptotagmin, which acts as a Ca2+ sensor
in neurotransmission and interferes with its ability to
bind to its protein partner, syntaxin.
• Binds to Zn-finger transcription factors
• Binds to Zn-porphobilinogen synthase
• Interferes with neuronal development
© M.J.Clarke, Boston College
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Links
Washington Post provides access to all Pb articles since January 31, 2004
http://www.washingtonpost.com/wp-dyn/metro/specials/water/
House Committee on Government Reform Hearing on The Federal Role in
Ensuring Safe Drinking Water in the District of Columbia and Senate
Committee on the Environment
http://reform.house.gov/GovReform/Hearings/EventSingle.aspx?EventID=797
http://epw.senate.gov/hearing_statements.cfm?id=220280
Time Magazine:
http://www.time.com/time/magazine/article/0,9171,1101040405-605469,00.html
© M.J.Clarke, Boston College
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© M.J.Clarke, Boston College
63
ION
Coord.
#
Ionic
Radius
Z/I.R.
Pb2+
6
1.19
1.68
Pb2+
8
1.29
1.55
Pb2+
10
1.40
1.43
Ca2+
6
1.00
2.00
Ca2+
8
1.12
1.79
Ca2+
10
1.23
1.63
Zn2+
4
0.60
3.33
Zn2+
6
0.74
2.70
Zn2+
8
0.90
2.22
Mg2+
4
0.57
3.51
Mg2+
6
0.72
2.78
Mg2+
8
0.89
2.25
Cd2+
4
0.78
2.56
Cd2+
6
0.95
2.11
Cd2+
8
1.10
1.82
Cd2+
12
1.31
1.53
Charge to Radius
Ratio
Pb2+ affects processes in the
body that involve calcium. A
comparison of charge to radius
ratios (last column) points to
similarities between the Pb2+
and Ca2+.
© M.J.Clarke, Boston College
64
http://stage.cchem.berkeley.edu/knrgrp/public_html/radii.html