Lead and Lead Poisoning
What is lead?
Lead is a metallic element with the chemical symbol Pb. Pb is an abbreviation for
plumbum, the Latin word for lead. Lead was widely used since ancient times
for piping, and the English word "plumber" is derived from "plumbum". However,
lead was first refined as a byproduct of silver production around 4000 BC.
Lead has had many other uses until recent times, including cooking utensils,
glazes applied to pottery, solder for both plumbing and electrical wiring,
combustion enhancement in gasoline, and pigments used in house paint, artist's
colours including crayons, and even in cosmetics. Except for solders, and for
shielding to protect people from radioactive materials or from X-rays), lead
is usually not used in industrial or consumer products in the United States or
other Western countries. It's not supposed to be, at any rate: lead is still
found in consumer goods in developing countries, and has been found far too
often lately in goods produced in other countries for sale in the United States.
Lead was used as a gasoline additive for many years, and it can now be found
in heaviliy-traveled roads and the soil and buildings next to them, as well as
the sites of old gas stations or currently-open gas stations that were around
in the 1920s to 1970s. Lead water pipes in a home may release lead into tap
water, but lead solder used to join copper pipes may actually release more
lead into water than a lead pipe.
Many other elements, including metals such as zinc and copper but also other
elements including selenium and vanadium, are needed by the human body in
trace (very small) amounts even though they may be poisonous in large amounts.
Lead is different: there is no biological use for lead, and no way for
the environment to get rid of lead contamination by itself. Lead is poisonous
to vegetation as well as to animals and people: there are areas where lead was
mined and smelted in the Middle Ages which are still so badly contaminated
that grass and other plants cannot grow well (one example is
in North Wales).
Since lead has no biologic function in the body, any amount is considered
abnormal. The "toxic lead level" is set by the
United States Centers for Disease Control and Prevention and has been
lowered over the last 30-40 years, from 60 µg/dL (micrograms/100 milliliters)
in 1970 to 10 µg/dL since 1991.
How does lead affect people?
The problem with lead, as with other heavy metals, is that it interferes with
many different chemical reactions in the body. Lead may enter the body by
eating or inhaling contaminated material, and is better absorbed by children
and by pregnant women than by the average adult. People who are fasting, and
those who are low on body stores of iron or calcium, may absorb ingested
(eaten) lead better than others. Adults retain only 1% of the lead they
take in, but young children (under 2 years old) may keep up to 2/3'ds of
their lead intake in their bodies. Some of the lead taken into a person's
body may be deposited in bone, and stay for decades (half of the lead in
bones now will still be there in 25 years, as opposed to 28-40 days in
blood and soft tissues). The lead in bone is inert except when the body is
stressed (chronic diseases, fractures, pregnancy, and breastfeeding) when it
may be released into the blood.
Although many children with toxic blood lead levels have no symptoms when
their levels are tested at well-child checkups, lead can affect many different
systems in the body.
Many of these effects are subtle and may not be full-blown until some time
after lead is absorbed by the body. Most of the effects of lead on the body
are irreversible. Therefore, we routinely test every child's lead level
at of before ages 1 year, 2 years, and 3 years even if they have no known
lead exposure -- and, of course, we do extra or early testing on any child
who may have been exposed, even if the potential exposure is living
on a busy road. Other risk factors that concern us include:
- Neurologic (brain and nervous system)
- High lead levels (over 100 µg/dL) can cause
encephalopathy(abnormalities of the brain): in particular,
(inflammation of the brain matter). Symptoms may include persistent
vomiting, seizures, and/or changes in level of consciousness ranging
from listlessness to coma.
Lower levels (20 µg/dL) may cause nerve impulses (signals from
sensory organs to the brain and from the brain to muscles) to travel
more slowly than normal. Levels as low as 10 µg/dL affect children's
brain development -- both behavioural and cognitive (ability to
learn, think, and reason). Exposure of a baby to lead during its
preganancy will affect development as well. Lead exposure may also lead
to hearing loss, which may make learning and behaviour problems worse.
- Hematologic (blood cells and the tissues where blood cells are made)
- Children with lead levels above 40 µg/dL often do not manufacture
hemoglobin (the red pigment in red blood cells that carries oxygen
from the lungs to the rest of the body), which results in anemia
due to low hemoglobin levels. At higher levels (above 70 µg/dL)
lead may cause hemolysis (breakdown of red blood cells).
- Lead levels of or over 60 µg/dL may result in abdominal pain, vomiting,
- Renal (kidneys)
- Chronic exposure to lead may reduce the kidneys' ability to adjust blood
levels of glucose, amino acids, and minerals such as phosphorus. It may
also make a child more prone to hypertension in later life.
- As blood lead levels go up, levels of vitamin D go down. Since vitamin D
is needed to regulate calcium and for bone development, high lead levels
may affect bone and tooth development and may also affect calcium-dependent
processes in other cells -- including muscle cells, where calcium is needed
for contraction of muscles.
- A decrease in height with even small increases in lead level has been seen
in girls, as well as delays in signs of puberty such as breast development
and the appearance of pubic hair. (The delay in breast and pubic hair
development has been seen largely in black and Mexican-American girls.
It's not clear why this is so.)
- any history of pica (eating things that aren't edible -- especially
including paint chips).
- living in an old house. White house paint made before 1955 sometimes was
as much as 50% lead. Lead in paints was reduced in the mid-1950s, but wasn't
completely eliminated until 1978, so most older homes have some lead
paint on the walls and houses built before 1950 probably have a lot of lead
paint on their walls.
- any exposure to lead of parents or others in the home (they may be bringing
lead dust home on their skin or clothes).
- any family member with lead poisoning.
- food packaged in lead-soldered cans.
How do we treat lead poisoning?
The best treatment of lead poisoning is not to be poisoned in the first place.
This means that any source of lead must be removed, or at least made safe.
If we find that a child's lead level is 10 µg/dL or higher, we (and the
local health department) take several steps. First, we repeat the level to make
sure it was not an error. Screening lead levels are usually done with finger
sticks: this works pretty well, but a child with lead dust on his fingers may
have an erroneously high level, so blood for the repeat level is drawn from a
vein. If the repeat is still high we start doing other tests including
- a blood count to look for anemia or other lead-related blood cell changes.
- iron levels to see if the child is iron-deficient (which may happen even
with lead poisoning).
- X-rays to look for lead-laden particles such as paint chips in the
stomach or intestines.
Lead poisoning is treated differently depending on the child's lead level.
Local health departments will usually inspect the home of any child with a
lead level above a certain limit. (The limit may vary from community to
community, but the CDC recommends
home inspection if any child in the home has a lead level of 15 µg/dL
- Mild lead intoxication is a level between 10 and 44 µg/dL.
- A child whose level is 10-14 µg/dL is usually retested one month
after the first sample, even if the first blood sample was drawn from a
vein, to make sure that we catch a lead level that is going up rapidly.
If the level is still 10-14 µg/dL we let the health department
know what's going on, and talk extensively with the child's parents
about preventing lead exposure and about improving nutrition. We also
repeat the lead level again within 3 months, and test all other children
living in the same house.
- If the level is 15-24 µg/dL we also repeat the level 1 month later,
provide education and notify the health department if the repeat level
is in the same range, and test all other children in the house. We repeat
the child's level within 2 months, instead of 3 months.
- If the level is 25-44 µg/dL we may or may not repeat. In addition
to education and testing other children in the house, we talk to the
health department, which usually inspects the house and arranges to have
any sources of lead removed or rendered inert. In addition, we will often
start medications known as chelating agents, such as DMSA
(meso-2,3-dimercaptosuccinic acid, also known as succimer) or
D-pencillamine, which bind lead chemically so that it can be safely
excreted by the kidneys. Since lead incorporated into bone is almost
impossible to remove or isolate, chelation will not necessarily remove all
of the child's lead burden. Chelation does remove lead from the
bloodstream and from soft tissues including the brain, but it will not
reverse developmental effects of lead. Unfortunately the chelating agents
themselves can be toxic, so we use them only when lead levels are above
- Moderate lead intoxication is a level between 45 and 70 µg/dL
in blood drawn from a vein, without any symptoms of acute lead poisoning.
- In addition to health department action at home and education, we routinely
use chelation therapy at these levels, starting as soon as we confirm the
level with a second test.
- Severe lead intoxication is a level of 70 µg/dL or higher
in blood drawn from a vein in a child without symptoms, or symptoms of
lead encephalopathy. This is a medical
emergency, and requires immediate chelation therapy using IV medicines
such as dimercaprol (2,3-dimercapto-1-propanol, also known as
"British Anti-Lewisite" or BAL, and originally used as an antidote
to World War I-era chemical warfare gases) and EDTA (calcium
disodium ethyldiaminetetraacetate). These medicines must be given in the
hospital, since they have many potential side effects, but we start the
treatment immediately when a high lead level is reported without waiting
for confirmation with a second test.
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Copyright © 2007, 2011
Vinay N. Reddy, M.D. All rights reserved.
Written 09/17/07; last revised 08/27/2011