May 26, 2001

The Health Hazards of Lead

By Maureen Alvarez, CIH, CSP

What's Different about Lead and Lead Poisoning?

Lead is one of the few natural substances that has no known use in the human body.  At even very low levels, lead has been shown to cause health problems.  The difficulty with lead is that once it is mined from the earth, there is no known way to destroy or make it harmless.  This makes it extremely important that we reduce our use of lead and dispose of it properly.

The good news about lead poisoning is that unlike many other diseases, it is a totally preventable disease.

How Does Lead get into the Body?

Most of the lead used today is inorganic lead and it enters the body through breathing (inhalation) and swallowing (ingestion), which are called "routes of exposure".  Lead dust or particles cannot go through the skin if the skin is unbroken.  The type of lead used in gasoline is organic lead and it can get through the skin. 

For small children, ingestion is the main route of exposure.  For bridge workers and those working with leaded paint the main route of exposure is inhalation.  However, lead dust can be ingested if it is on your hands and you smoke a cigarette or eat before washing your hands. 

What Happens to Lead in the Body?

Once lead gets into the body it is not used in any way to benefit the body.  It is absorbed and distributed throughout the body.  The amount the body absorbs depends on the route of exposure.  In general, an adult will absorb 10-15% of the lead in the digestive system, while children and pregnant women can absorb up to 50%.  People will absorb more lead if they are fasting or if their diet is lacking in iron or calcium.

When lead is inhaled, about 30%-50% of the particles will reach the lungs, depending on the size of the particle.  Large particles land in the upper respiratory tract where they get trapped by the mucous lining and are moved out by the cilia.  Unfortunately, the mucous is often swallowed, allowing these large particles to then go into the digestive system.

Smaller particles can reach deeper in the lungs and from there be absorbed into the bloodstream. This means that when there is burning or welding on lead-painted surfaces, the lead fumes can be especially dangerous.  The small particles created as a fume will reach the blood if they are inhaled.  Once lead is in the blood, some of it moves into soft tissues (organs such as the brain and kidneys).

The total amount of lead that is stored in the body is called the "body burden".  In adults, bones and teeth contain about 95% of the body burden.  Lead that is stored in the bones can leave them and enter the blood and then the soft tissue.  This can damage the organs or the blood's ability to make red blood cells.  This trend may increase during pregnancy, breast-feeding and osteoporosis.  It can also happen when lead is removed from the blood through medical treatment called chelation. 

How Long Does Lead Stay in the Body?

Lead stays in the body for different periods of time, depending on where it is.  Half of the lead in the blood will be excreted in 25 days (this is called the "half-life").  In soft tissues, it takes 40 days for half of the lead to be excreted.  In bones and teeth it takes much longer, up to 10 years or longer.

Since lead is stored in the body, a person can get poisoned from exposure to just small amounts of lead over a long period of time (chronic exposure).  You do not need to get exposed to just large doses of lead to be poisoned (acute exposure).  It can take months or years for the body to get rid of lead.  A person will continue to be exposed to lead internally even after the actual exposure to lead stops.

How is Lead Measured in the Body?

Blood tests to measure the amount of lead circulating in the body were developed over 60 years ago. The results are measured in micrograms of lead per deciliter of blood (the symbols used are ug/dl or mcg/dl).  Because there is so much lead contamination of the environment, people who live in cities usually have blood lead levels as high as 15 ug/dl.

The blood lead test is important for you.  It gives an immediate estimate of the level of your recent exposure to lead.  This test will tell you how much lead is in your bloodstream, but not what is stored in your soft tissues or bones.  The test will not tell you your body burden of lead or the damage, if any, that has occurred.

Another test is called the ZPP Test or zinc protoporphyrin.  This test is different from the blood test in that it reflects your lead exposure over a 2-3 month period.  The EP (erythrocyte protoporphyrin) test is a similar test.

OSHA

The OSHA permissible exposure limit (PEL) for lead, set by the standard is 50 micrograms of lead per cubic meter of air (50 ug/m3), averaged over an 8-hour workday.  The interim final standard establishes an action level of 30 micrograms of lead per cubic meter of air (30 ug/m3), averaged over an 8-hour workday.  The action level triggers several requirements of the standard such as exposure monitoring, medical surveillance, and training.

The health protection goals of the standard state that prevention of adverse health effects for most workers from exposure to lead throughout a working lifetime requires that a worker's blood lead level (BLL, also expressed as PbB) be maintained at or below forty micrograms per deciliter of whole blood (40 ug/dl).  The blood lead levels of workers (both male and female workers) who intend to have children should be maintained below 30 ug/dl to minimize adverse reproductive health effects to the parents and to the developing fetus.  The measurement of your blood lead level (BLL) is the most useful indicator of the amount of lead being absorbed by your body.

Does Lead Cause Reproductive Problems in Both Women and Men?

Yes.  In men, lead can damage sperm and affect the sperm's ability to move.  It can affect the number of sperm that is produced in the testes.  These effects on sperm can harm a man's ability to father children and have been linked to miscarriages and birth defects in their partners.  These health effects can occur at 40-50 ug/dl.  Some studies have also indicated that lead can affect a man's sex drive and ability to have an erection.

In women, exposure to high levels of lead may cause miscarriages, premature births, stillbirths and decreased fertility.  More recently, some studies found that pregnant women with levels of lead in the umbilical cord blood of 10-15 ug/dl had children who suffer from learning and behavioral problems later in life.  This is because lead in the pregnant mother's blood passes into the blood of the fetus and may affect brain development.

OSHA's policies have not generally addressed the reproductive health of workers.  In the OSHA lead standards for general industry and for construction, workers must be informed of the reproductive hazards of lead, and a doctor is allowed to medically remove a worker who is pregnant or who is planning to conceive a child.

What Jobs Have a Lead Hazard?

There are many jobs that expose workers to lead. Some examples are:  deleaders, firing range employees, printers, radiator repair workers, shipbuilders, workers in lead smelters, ironworkers, lead miners, plumbers, steel welders or cutters, pipefitters, industrial and construction painters. 

Has the Lead in Paint Been Replaced by Safer Alternatives?

By the early years of this century, the paint manufactures had found other pigment substitutes for lead in paint.  In the 1930’s, white lead began to be replaced by titanium dioxide and zinc oxide.  While in 1955 the paint industry had set a voluntary standard for itself of 1% lead in interior paints, this was not always followed.  As late as 1971, more that 10% of the paints tested in New York City had between 2% -11% lead content.  In 1973, the federal government finally limited the amount of lead in interior pant to .5% and, in 1978, this limit was lowered to .06%.

The story for industrial paint is different.  Lead is still allowed in paint for bridge construction and machinery.  It is used for its ability to expand and contract with the metal surface of a structure without cracking.  It is also able to resist corrosion.  Unfortunately, this paint is a significant source of lead exposure.  Even if its use were banned today, there would still be exposure to workers and surrounding communities for years to come due to the number of metal structures, such as bridges, that are coated with it.

Good Hygiene

Remember to practice good hygiene when working around lead.  Always wash your hands prior to eating, drinking or smoking to help prevent the ingestion of lead.  Proper ventilation and respiratory protection can prevent inhalation exposures to lead.  Lead poisoning is preventable if everyone follows safe work practices.

Copyright © 2001 by WorkCare™ All Rights Reserved

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