+
Lead in
Drinking
Water
STARTING IN EARLY 2015, Flint, Michigan entered
the news spotlight for having high levels of lead, a
toxic substance, in the drinking water provided by
the city. Flint pediatrician, Dr. Mona Hanna-Attisha,
found that the proportion of infants and children with
elevated levels of lead in their blood nearly doubled
after the city switched to a new water source.
Why is lead toxic?
Lead is toxic because it is very similar
to another metal —calcium— that
is essential for many important cell
functions. You may have been told
to drink or eat calcium-rich foods
for strong bones and teeth, which is
certainly important, but calcium does
much, much more.
BLOOD
Infants and young children face well-known
dangers when exposed to lead. Even at low
levels, lead exposure in early development
affects brain development and leads to
problems with learning and behavior.
These brain efffects appear to be
permanent.
MUSCLE
NEURONS
The Centers for Disease Control lists the two biggests sources of
environmental lead contamination as lead-based paint in homes built
before the 1970’s and lead in soil from use of gasoline with a lead additive to
boost performance. (Leaded gas was outlawed in the U.S. after 1996.)
The Flint situation has drawn media attention to drinking water as a source
of environmental lead. The USA Today news network reviewed EPA data and
reported that since 2012, nearly 2,000 water systems across the U.S. have had
elevated lead levels in tap water samples.
How much lead is harmful?
As scientists have learned more about the effects of lead on the developing
brains of children, ideas about how much lead is harmful have changed.
In May 2012, the U.S. Centers for Disease Control and Prevention (CDC)
announced that 5 micrograms per deciliter (µg/dL) is now the level of lead
at which notification of parents and follow-up actions,
60 including eliminating sources of lead in the child’s
environment, are recommended. This new level is half
the previous level of 10 µg/dL. The graph above shows
how the level of lead considered harmful
to children has changed
30
since 1960.
25
10
1960 – 1970
1970 – 1985
1985 – 1991
1991 – 2012
5
BONE
Once lead enters your body through
ingestion (eating or drinking) or
inhalation (breathing), cells absorb
lead in the same way that they
absorb calcium. Once in cells, lead
interferes with normal cell functions
that depend on calcium.
The many jobs of calcium
•
Calcium is involved in the
coagulation of blood.
•
Calcium is essential for muscle
contraction.
•
Calcium helps maintain normal
blood pressure.
•
The flow of calcium ions between
nerve cells is essential for brain
development and function.
•
Calcium is the main component
of bones and teeth.
2012 – present
Blood lead levels considered harmful to children
Blood lead level (µg/dl)
1
How does lead get into water?
Have you ever gone fishing? You might have tied a small piece of lead
metal called a sinker to the fishing line to help it sink into the water. A lead
sinker would be pretty useless if it dissolved in water! The same goes for
plumbing pipes made of copper, iron, or lead metal. These pipes couldn’t
carry water if the metal dissolved in water!
You’ve probably
seen what happens
when iron metal
loses electrons
to oxygen. This
chemical reaction
forms that orange
flaky stuff that we
don’t want to see on
our cars. Yes, rust!
Rust is a compound
made of iron ions
joined to oxygen
ions.
So…if these metals don’t dissolve in water, how does lead get into drinking water? The
answer depends on the difference between copper, iron, or lead atoms and copper, iron, or
lead ions. Atoms of copper, iron, or lead rarely go into water, but ions of these metals do.
An atom becomes an ion through a chemical reaction. In the reaction, negative particles
(electrons) are lost by one atom or ion and gained by another atom or ion. For example,
metal atoms of copper, iron, or lead can lose electrons to O2 (oxygen), Cl2 (chlorine), or H+
(hydrogen ion).
The pictures below show how lead atoms from a pipe can become ions and get into the
water. A substance is called “corrosive” when it breaks down metal through a chemical
reaction. In the example below, vinegar is the corrosive material. In the case of Flint,
Michigan, chlorine was a corrosive material in the water that caused lead ions to form and
enter the water.
The “BEFORE” picture shows a lead metal pipe
containing neutral atoms (Pb) with water (H-O-H) and
vinegar (HOAC) molecules flowing through it. Some of the
vinegar is separated into ions (H+ and OAC–).
The “AFTER” picture shows that an atom of lead has lost
two electrons, is now an ion (Pb2+), and has left the metal
pipe and entered the water. The hydrogen ions gained
the two electrons from the lead and joined together to
form hydrogen gas (H-H).
BEFORE
AFTER
H
+
H
Pb Pb
+
H
Pb Pb
O
solid
lead
pipe
–
H
O
H
H
HOAC
OAC
–
Pb Pb
Pb Pb
Pb Pb
Pb Pb
solid
lead
pipe
solid
lead
pipe
H
O
H
H
Pb Pb
Pb Pb
H O
H—H
OAC
–
HOAC
H
H
O
H
H
H
water flowing
through lead
pipe
water flowing
through lead
pipe
HOAC = vinegar
(Vinegar is slightly corrosive.)
Some HOAC is present as H+ + OAC –
H—H
2
Pb Pb
solid
lead
pipe
H
O
Lead in Drinking Water
–
2+
Pb
Pb
Pb Pb
OAC
O
OAC
H
O H
Pb Pb
HOAC
HOAC
represents hydrogen gas
about to float away
calcium atom (Ca)
Why can lead mimic calcium?
calcium ion (Ca2+)
2+
Lead can mimic calcium in cells because lead and calcium are
both metals that readily form an ion with a charge of 2+.
Ca
A 2+ charge means that the calcium ion is missing two of the
electrons found in the calcium atom. The charge of an ion
is an important factor in its interactions with other ions and
compounds.
Ca
lead atom (Pb)
Ca
2+
Ca
lead ion (Pb2+)
2+2+
The 2+ charge allows calcium ion to form a connection or
“bridge” between two other ions or compounds. In bones and
teeth, this calcium bridging forms a very hard mineral called
hydroxyapatite. This bridging capability also allows calcium ion
to be involved in transferring nerve signals, helping muscles
move, and maintain blood pressure and coagulation.
Pb
Pb
Pb
Pb
Because they have the same 2+ charge, lead ions enter the body
in the same way as calcium ions. Lead ions can substitute for
calcium ions in bones, nerves, and muscles, but once in place,
they don’t work exactly the same way. For example, lead ions do
not correctly transfer nerve signals the way calcium ions do.
In its elemental form, calcium is a metal found in group 2A on the periodic table.
Calcium metal reacts with water to form calcium 2+ ion and hydrogen gas. In our
bodies, which contain a lot of water, calcium couldn’t exist as a metal, and is present
in the form of calcium 2+ ions. Ions dissolve in water because water is polar.
Can we test for metals in liquids?
We’ve just discussed the ability of 2+ calcium ions to form connections or bridges between compounds. Other 2+
metal ions can form these connections. Another name for this process is crosslinking.
We can use a material called sodium alginate to test whether 2+ metal ions are in a liquid. Sodium alginate is made
up of long strands of a natural polymer from seaweed with sodium ions attached. When dissolved in water, these
strands flow freely around each other. If we add sodium alginate to water containing calcium 2+ ions, the calcium
ions replace the sodium ions and form crosslinks between the polymer strands. The sodium alginate is now calcium
alginate, and instead of flowing freely, calcium alginate is a thick, gooey gel. Other 2+ metal ions also crosslink with
alginate. Adding sodium alginate to liquids containing 2+ ions of copper, iron, or lead results in the the alginate
forming a gel. So, the formation of gel is a positive test for the presence of these metal ions. If we add the
sodium alginate slowly in drops, rather than stirring it in, the crosslinking process produces small gel balls.
calcium alginate is a gel
add calcium
chloride solution
sodium alginate dissolved in water
Na+
Na
+
Na+
Na
+
Ca2+
Na+
Na+
Na
+
Na+
Na+
Ca2+
Ca2+
Ca2+
Na+
Na+
Ca2+
Na+
Na+
Ca2+
Ca2+
Na+
Alginate’s gelling
property makes it a
good food thickener,
helping products such as
pudding, ice cream, and
sauces become thicker
and feel more creamy in
customers’ mouths.
Ca2+
3
Lead in Drinking Water
Bone — An accidental lead bank
Because of its ability to mimic calcium, some of the lead that enters the body
ends up being stored in the bones along with calcium. Medical researchers
studying the accumulation of lead in bones sometimes use radiographs (pictures
made with X-rays) to view bone lead content.
One of the functions of bone is to provide a storehouse of calcium ions. The
hardness of bone might lead you to think it never changes. But bone actually
breaks down and rebuilds throughout life in a process called remodeling. During
remodeling, calcium ions are constantly leaving dying bone cells, circulating in
the blood, and then becoming part of new bone cells.
This x-ray shows the knee of
a three-year-old girl with a
blood lead level of 10.6 µg/dL.
The lighter areas show lead
accumulation.
If bones also contain lead, the lead ions can leave the bones and circulate in the
blood just like calcium. When the lead circulates, it can cause problems with cell
functions that involve calcium. Because of this “lead bank,” lead can continue to
affect the body years past the original exposure.
Fighting the effects of lead exposure
Avoiding exposure to lead, especially for young children, is always the goal,
but in environments with more risk of lead exposure, food choices can
actually help fight the effects!
Dr. Mona Hanna-Attisha, the Flint, Michigan pediatrician who reported on
elevated blood lead levels in local children, has recommended that local
families focus on diets rich in calcium, iron, and vitamin C. Here’s why eating
these foods helps:
The Hurley Medical Center in Flint, MI
has created a “Nutrition and Lead”
recipe guide. One of the recipes, called
Cheesy Hamburger Skillet, includes
bell peppers, tomatoes, cheese, and
beef. One serving provides a child 1–3
years old with these percentages of the
recommeded daily amounts:
•
•
•
21% calcium
24% iron
386% vitamin C
Absorb less lead: Before something we ingest gets into our
bloodstream and cells, it must be absorbed by the digestive system. Scientific
research shows that increased intake of calcium and iron decreases the
absorption of lead by the digestive system. So, even if you are exposed to
lead and possibly ingesting it, getting enough calcium and iron means less
lead will be absorbed. The vitamin C keeps iron in the +2 ion form where it is
better absorbed by the body.
Bethany Thayer, director for the Center for Health Promotion and Disease
Prevention at Henry Ford Health System, supports the role of diet, but adds
that just having food in your stomach will decrease the absorption of the lead.
She recommends that children at risk of lead exposure eat more frequent but
smaller meals throughout the day.
Release less lead: The process of bone remodeling releases calcium
into the blood. If the bones contain lead, lead is released at the same time.
Getting enough calcium in the diet reduces the amount of calcium your
body needs to get from bones. If less bone remodeling is needed to provide
calcium, less lead is released. Nutrition is especially important in periods of
stress or during pregnancy, when more calcium is released from bone.
Lead in Drinking Water
4
Developed by
Good nutrition to battle
environmental toxicants.
through funding from
Grant number R25 OD011090