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Lead and Lead Poisoning

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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 Halkyn Mountain 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.

Neurologic (brain and nervous system)
High lead levels (over 100 µg/dL) can cause encephalopathy(abnormalities of the brain): in particular, encephalitis (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, and/or constipation.
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.)
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:

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

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 or higher.)

Mild lead intoxication is a level between 10 and 44 µg/dL.
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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PLEASE NOTE: As with all of this Web site, I try to give general answers to common questions my patients and their parents ask me in my (real) office. If you have specific questions about your child you must ask your child's regular doctor. No doctor can give completely accurate advice about a particular child without knowing and examining that child. I will be happy to try and answer general questions about children's health, but unless your child is a regular patient of mine I cannot give you specific advice.

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Copyright © 2007, 2011 Vinay N. Reddy, M.D. All rights reserved.
Written 09/17/07; last revised 08/27/2011 counter