Lead as a Teratogen

 

This child has lost his teeth due to exposure to lead.

http://www.canada.com/topics/news/story.html?id=d3cfc3c1-2f72-4538-bdb8-5a7a184ccc6c

 

 

Lead is a heavy metal that can act as a teratogen, or a substance capable of damaging the development of a fetus.

 

 

Lead in the Environment

 

Individuals may be exposed to lead via either ingestion or inhalation (Pathways, 2004).  Lead can be found in:

 

• lead-based paints and dust from such products (though production was banned in the United States in 1978, there are still plenty of surfaces painted with them).
• certain imports, such as pottery, folk medications, toys, crayons, and window blinds.
• car repair shops, specifically in radiator repair and automotive batteries.
• stained glass and pottery production, especially by non-professionals.
• many mines and foundries. 
• bullets.
• fishing weights.
• contaminated ground and water (Sources, 2004). 

 

Many cases of exposure are due to home renovations, due to dealing with lead paint;  in one study conducted in New York, 24% of exposed pregnant women's houses had recently been renovated (Bellinger, 2005).  Expectant mothers with previous exposure are also in danger of having lead act as a teratogen, as the substance is stored within bones, and the changes in bone metabolism during pregnancy can carry lead to the fetus (Bellinger).  Pregnant women who smoke or drink alcohol, live in developing countries, or have low calcium levels are also at increased risk (Bellinger).

 

 

Effects on Male Fertility

 

The research on the effects of lead exposure on male fertility is at present ambiguous, with some studies finding fewer non-complicated pregnancies with exposed fathers, others finding a correlation between exposure and difficulties in conceiving, and still others with no significant results to speak of (Bellinger).  In studies of the amount of time it takes exposed men to conceive, differing results have ranged from less time to more time, as well as indicating no appreciable difference (Bellinger).  Less uncertain research has found that men with blood lead levels above a certain point (40 μg/dl), or with slightly lower levels (25 μg/dl) over a period of years, are at a definite risk for producing complications during pregnancies (Bellinger).  Sperm concentrations, numbers, and motility may all be diminished around this level of exposure (Lead Toxicity).  At lower levels of exposure, the results are less clear.

 

 

Effects for Pregnant Women

 

While male exposure levels must be quite high to create serious fertility and gestation problems, pregnant women with levels as low as 5-9 μg/dl may have twice the usual risk of spontaneous abortion (Bellinger).  At levels of less than 10 μg/dl, women are also at increased risk for pregnancy hypertension, with a greater risk if exposure has been over a prolonged period of time (Bellinger).

 

 

How Lead Interacts with the Brain

 

Most of the health problems associated with lead exposure are related to the fact that the metal is able to both inhibit and mimic the action of calcium in the body.  Scientists believe that lead enters cells through calcium channels, since lead uptake is increased by the same drugs that increase calcium uptake.  In addition, high levels of one chemical decrease the transport of the other, which means that they are “competitive inhibitors to each other” (Schuld).  Lead also seems to change the way in which the calcium channels act; normal calcium uptake through the channels is decreased after ten minutes, while lead uptake through the same channels continues at a high rate for over 45 minutes.  This explains why lead is able to reach such high concentrations in some cells (Schuld).

 

Calcium is important to normal brain functioning, as calcium ions can cause neurotransmitters to be released, which aids in the conduction of nerve impulses.  When lead is present in the body, even in small amounts, it increases the quantity of neurotransmitters released into the synaptic cleft; the effect has been seen to occur in both the central and peripheral nervous systems.  It is able to do so by activating Calmodulin protein kinase II, which is believed to play a part in preparing synaptic vesicles for fusion with the neuron’s membrane, thereby allowing neurotransmitters to be deposited into the synaptic cleft (Schuld).

 

With regard to the way in which lead inhibits the action of calcium, the presence of lead in the body has also been known to prevent neurotransmitter release in neurons.  This combination of excess firing of neurons and blocking of neuronal activity can lead to problems developmental problems in children.  Under normal conditions, pruning occurs in the brain, as a means of getting rid of those connections that have not been found to be useful and maintaining those connections that are important.  The brain decides which neuronal pathways are important based on the amount of firing that occurs in childhood.  Therefore, when lead causes some neurons to fire in excess and prevents other neurons from firing, the improper connections are maintained, which leads to poor brain organization.  It is possible that this interaction is the cause of the learning and behavioral problems that exist in children that are exposed to lead (Schuld).

 

 

Another way in which lead is thought to affect the body is by interacting with another protein kinase, known as protein kinase C, which regulates long-term potentiation.   Again, lead mimics the effects of calcium and binds with the protein kinase; however, lead is able to affect protein kinase C in smaller concentrations and the enzyme is activated for a longer duration when bound with lead.  Long-term potentiation is believed to be an integral part of memory storage, which may provide another explanation for why children who have suffered from lead exposure tend to have learning and behavioral deficits (Schuld).

 

 

A final way in which lead can affect the body is by affecting the central nervous system via the blood-brain barrier.  The blood-brain barrier normally manages what passes into the brain from the blood, using a series of interlocked cells.  When individuals are exposed to large amounts of lead, the blood-brain barrier is disrupted, leading to increased permeability.  Large molecules, water, and ions begin to freely enter the brain, which may lead to brain edema, or a buildup of excessive fluids in the brain, as well as increased intracranial pressure.  Researchers believe that the disruption may be related to the interlocking cells losing their ability to differentiate between brain tissue and outside tissue (Schuld).

 

 

The Effects of Lead on a Baby

 

The presence of lead exposure during pregnancy, which is generally judged by the presence of lead in cord blood, is linked with many adverse effects on fetuses and babies. Here these effects are split into three categories.

 

Effects Before or at Birth

 

The increased presence of lead has been linked with three major issues,

            Spontaneous abortion

            Stillbirths

            Premature birth

Now spontaneous abortion and stillbirths are very bad scenarios but premature birth can contribute to physical and mental problems.

 

 

Physical Effects

 

The increased presence of lead can be a contributing factor in many physical issues,

            Lower general birth size

            Low birth weight

            Smaller head size at birth

            Some malformations

            Hindered brain development

The three effects in concerned with size and weight at birth are connected to premature births but it is probably less the case that lead causes premature birth and these independently than the case that these effects interact with one another.

As far as malformations and hindered brain development lead has been seen to increase the risk but the correlation between cause and effect is less than that of the correlation between lead and premature birth.

 

 

Mental Effects

 

The increased presence of lead also has mental effects that are largely the result of the other effects already noted. There is a link between premature births and problems with intelligence and behavior. Due to the risk for hindered brain development, intelligence can obviously suffer. It seems inherent that when you have such physical effects they must result in mental effects when they occur.

 

 

 

How to Prevent Lead Poisoning

 

Before 1978, lead was used in all sorts of commonly handled goods.  It can be found in paint, soil, drinking water, and food.  Lead is tasteless and odorless and could be found anywhere around your home (Lead Poisoning, 2000).  Lead Poisoning is relatively easy to avoid.  With a few careful measures you can almost ensure that you and your child will be safe. 

• Keep Your Home Clean...Soil can contain trace amounts of lead:

  • Make sure to wash floors, window frames/sills, floors, and other surfaces weekly with an all-purpose cleaner.
  • Be sure to also was your children's toys regularly (Lead Poisoning, 2000).

• When remodeling, there are a few precautionary measures to take:

  • Seal off the rooms that are being remodeled. You could put a heavy sheet of plastic over all of the doorways and windows of the work areas so any dust containing lead won’t spread (Preventing, 2000).

  • Don’t remove lead paint yourself.  When paint containing lead is rubbed or scraped it creates a dust that also contains lead and will therefore be easier to breathe in.

  • Ask your local or state health department if they will test your home for lead paint.  Some will test for free.  Home test kits cannot detect small amounts of lead under some conditions.  Hire a person with special training for correcting lead paint problems to remove lead paint from your home, someone who knows how to do this work safely and has the proper equipment to clean up thoroughly (Lead Poisoning, 2000).

• Don’t bring lead dust INTO the home:

  • If you work in an environment or participate in a hobby that is in an environment containing lead, then you should refrain from bringing home the clothes worn there.
  • Pregnant woman should refrain from participating in such work or hobbies to avoid injury to the fetus (Lead Poisoning).

• "Most well or city water does not naturally contain lead.  Water usually picks up lead inside your home from household plumbing that is made with lead materials"  (Lead Poisoning, 2000).  Get your water tested:

  • You should run your water for 15 to 30 seconds before drinking it, especially if you have not used your water for a few hours.
  • Water from public sources is regularly tested for lead. You can get information about your drinking water from your local board of health (Lead and Pregnancy, 2005).

• Be sure to eat right:

  • Be cautious of the foods that you eat, especially if they may contain large quantites of lead, such as fish.
  • There have been st udies that show that with a greater intake of vitamins such as Calcium, the absorption of lead is decreased. It is therefore even more important for pregnant women to take their prenatal vitamins (Lead and Pregnancy, 2005).
  • To get more information on a study conducted by Peter A. Meredith, that gave evidence (when tested in rats) that Calcium can impede lead absorption: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1165037 .

If by some chance, however, you feel that you or your children may have been contaminated by lead you should go to your doctor to receive a blood test. This test is the only way to truly find out the levels of lead in your blood.

 

• “Although most people will have some lead in their blood, levels greater than 10μg/dl indicate that there is some exposure at home or in the workplace that may need to be changed. While there is no clear safe level of lead in the body, the goal is to have the lowest level possible. Because lead is stored in bone, women who have worked or been exposed to lead in the past may have higher lead levels later in pregnancy. This happens because lead in the mother’s bones can be released into the blood during pregnancy. Women who had exposure to lead in the past should have levels checked before and during pregnancy” (Lead and Pregnancy, 2005).

There is treatment for lead poisoning.

 

• “If your child's blood lead level is above the acceptable range, your doctor will give you information on how you can lower your child's lead level. Your doctor will then test your child's blood lead level every few months until the level drops into the normal range. Fortunately, only a small number of babies and children have high enough levels of lead in their blood that they need treatment. If your child's blood lead level is very high, your doctor will treat your child with medicine to lower the amount of lead in the blood” (Preventing, 2000).

 

 

Common places to find lead in your home:

 

www.narconon.ca/treatment_children.htm

 

 

 

 

 

 

 

 

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References

 

 

Agency for Toxic Substances & Disease Registry. Lead Toxicity: What are the Physiologic Effects of Lead Exposure? Retrieved September 24, 2007, from http://www.atsdr.cdc.gov/csem/lead/pbphysiologic_effects2.html.

 

American Family Physician. (2000). Preventing and Treating Lead Poisoning in Children. Retrieved September 26, 2007, from http://www.aafp.org/afp/20000801/559ph.html.

 

^{Arizona Office of Environmental Health. (2004). Pathways of Lead Exposure. Retrieved September 27, 2007, from http://www.azdhs.gov/phs/oeh/invsurv/lead/bklet_leadpath.htm.}

 

Arizona Office of Environmental Health. (2004). Sources of Lead Exposure.  Retrieved September 27, 2007, from http://www.azdhs.gov/phs/oeh/invsurv/lead/bklet_leadsource.htm.

 

Babin, Angela M.S. (1994). Lead Hazards. Retrieved October 1, 2007, from http://www.chicagoartistsresource.org/?q=node/17166

 

Bellinger, D.C. (2005). Teratogen update: lead and pregnancy. Birth Defects Research, 73, 409-420.  Retrieved September 24, 2007, from PubMed.  

 

 

 

Environmental Protection Agency. (2000). Lead Poisoning and Your Children. Retrieved September 26, 2007, from http://www.epa.gov/lead/pubs/lpandyce.pdf.

 

Meredith, P. A., Moore, M. R., & Goldberg A. (1977). The effect of calcium on lead absorption in rats. Biochem J, 166, 531-537. Retrieved September 26, 2007 from http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=1165037&pageindex=1.

 

Organization of Teratology Information Services. (2005). Lead and Pregnancy. Retrieved September 26, 2007, from http://www.otispregnancy.org/pdf/lead.pdf.

 

Schuld, Mark J. Lead Toxicity: Its Effects on Fetal and Infant Development. Retrieved September 30, 2007, from http://www.indstate.edu/thcme/anderson/MJS.html.

 

 

 

 

 

 

 

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