“Get the lead out!” is a common idiom referring to a heaviness of a body that cannot quite get moving. The heavy metal lead is the most common toxic mineral and the most abundant contaminant of our environment and our body. It is the worst and most widespread pollutant, though luckily not the most toxic; cadmium and mercury are worse. But when lead levels become too high, they can prove fatal, and this heavy metal will return our body to its origins in the earth.
Lead is found deep within the earth. Ancient civilizations had almost no exposure to it until four or five thousand years ago, when lead was found as a by-product of silver smelting. Since then, it has been used progressively throughout history. In the Roman Empire, lead was widely used in water pipes and drinking and storage vessels. Many scientists and historians now feel that lead led to the downfall of the Roman Empire, with the ruling classes suffering decreased mental capacities, decreased birthrate, and shortened life span.
In the twentieth century, lead has been widely used in paint, some containing a high percentage of lead. This has been a problem especially with children, who are more sensitive to lead than adults because of their better absorption and smaller bodies. Lead has a mildly sweet taste, and children often suck on or eat the paint chips off of houses or out of the dirt, leading to many cases of lead poisoning. In the 1920s, tetraethyl lead was added to gasoline as an antiknock, higher-octane additive. This has probably been the most widespread and pervasive source of environmental contamination from lead to date. Other common uses for lead are as seals for tin cans, in pewter, in ceramics and pottery glazes, in insecticides, and more.
In recent years, however, there has been an attempt to decrease this environmental contamination. Cars are now using unleaded gasoline. This does not, of course, eliminate the problems of carbon monoxide and burned hydrocarbons, but it will help to decrease lead exposure in the future. In 1971, Congress passed the Lead Paint Act, limiting the use of lead in paints. This will also help, but not for many years to come, since many older homes still contain leaded paints. As they deteriorate, lead gets into the soil and does not degrade. In 1979, a law was passed decreasing the use of lead in food storage cans, though it is still present in some solders.
Bone analysis of very old skeletons indicates that modern humans have nearly 500-1,000 times more lead in our bones than did our ancient ancestors. Our total body content of lead nowadays is estimated at 125-200 mg. We can handle nearly 1-2 mg. daily with normal functioning, but the margin of safety is narrow. Luckily, most people’s daily exposure is less than that, about 300-400 mcg.
Lead is a neurotoxin and commonly generates abnormal brain and nerve function. It passes into the brain and can also contaminate the in-utero fetus and breast milk. Most lead, though, is stored in the bones. With lead intoxication, “lead lines” are visible in the bones on X-rays. Some is also stored in the liver and soft tissues. Infants have very little lead, but our body concentrations usually increase with age.
Luckily, lead is not very well absorbed, usually less than 5 percent, though children absorb it at a higher rate. Many minerals, such as calcium and iron, interfere with further lead absorption. When lead gets into the blood, it does not stay long, either going into the bones and other tissues or being eliminated. Most ingested lead leaves via the feces; that which is absorbed or inhaled will usually be cleared by the kidneys, through perspiration.
Evaluating lead exposure and measuring lead levels in humans is not easy. Blood and urine tests are not very good indicators, because lead is cleared fairly rapidly. With acute toxicity, both of these body fluids may have high measurements, but most exposure is chronic. Hair analysis is the simplest and best test for evaluating chronic lead poisoning, which has become much more common with long-term exposure. Hair-test screening for lead is fairly reliable and can be done on both adults and children. Hair (and urine) levels can be remeasured to follow the progress of treatment. Increased body burdens of lead can be shown by testing with an intravenous dose of a chelating drug such as EDTA. A high level of urinary lead elimination suggests increased levels of body stores, especially in the bones. Also, since lead interferes with many red blood cell enzymes such as delta-aminolevulinic acid dehydratase, an increase in delta-aminolevulinic acid in the urine, as well as zinc protoporphyrin and erythrocyte protoporphyrin, suggests problems of lead toxicity. A blood level of zinc protoporphyrin is currently the best way to assess lead toxicity.
Sources: Lead exposure and body lead levels are higher in North America than anywhere else in the world. In the United States alone, it is estimated that approximately 1.3 million tons of lead are used yearly in batteries, solder, pottery, pigments, gasoline, paint, and many other useful substances. Somewhere between 400,000 and 600,000 tons per year go into our atmosphere, onto our earth, into our food, and into our body and tissues. So there is a lot of lead around. The following are some of the common contaminants:
Leaded gasoline. Tetraethyl lead was previously added to all gasoline; it is now used only for older vehicles. After combustion, this lead goes directly into the atmosphere as air pollution and is inhaled by us and other living, breathing entities. It also settles into the earth and its living vegetation; heavily traveled roadways show higher concentrations of lead in the air, soil, and nearby vegetation.
Paint. Though, by law, the amount of lead in paints must be reduced, some still contain lead. Many homes retain lead paints, so this change may not affect us in environmental lead exposure for a couple of decades.
Food. Lead is contained in many foods, especially in those grown near industrial areas or busy cities or roadways. Grains, legumes, commercial and garden fruit, and most meat products pick up some lead. Liver and lunch meats are usually higher. Liverwurst and other sausages may contain more lead than other foods. Roadside vegetation, such as herbs, fruits, and vegetables, has higher concentrations of lead than vegetation growing in more secluded areas. Measurements of lead in trees growing along roads show much more than was present in the 1930s. Bonemeal, a source of calcium and magnesium, is usually made from cattle bones and may contain high amounts of lead. Dolomite, an earth rock source of calcium and magnesium, is usually lower in lead. Pet foods may also be high.
Water. Drinking water may be contaminated with lead. Lead solder in pipes or lead plumbing in older homes and drinking fountains, can leach into the water, especially soft water. A more acid water will also pull lead and other toxic and nontoxic minerals from the piping.
Pottery. “Earthenware” in general has potential for lead exposure. Though some potters refrain from using much lead, it is hard to avoid. When the glazing is inefficient, lead containers can contaminate food stored in them. Fruit juices or acidic foods, such as tomatoes, will tend to pull out more minerals. Glazed coffee mugs should be avoided.
Cans. Solder in tin cans, usually used to hold the seam together, contains lead; some are nearly 100 percent lead. Some can manufacturers are changing this, but progress is slow. Avoid lead-lined containers or cans whose seams have a shiny, metallic solder appearance. Many imported cans contain lead. The leaded plugs in evaporated milk cans may contaminate the milk.
Cosmetics. Many pigments and other substances used for makeup and other cosmetics contain lead. Historically, lead has been part of face paints and other beauty creams.
Cigarettes. Lead is occasionally a contaminant in cigarettes. Lead arsenate may be used as an insecticide in tobacco growing.
Pesticides. Many pesticides and insecticides contain some lead, mainly as the lead-arsenate base.
Methods of toxicity: Though this is not completely clear, lead most likely interferes with functions performed by essential minerals such as calcium, iron, copper, and zinc. Lead does interrupt several red blood cell enzyme systems, including delta-aminolevulinic dehydratase and ferrochelatase. Especially in brain chemistry, lead may create abnormal function by inactivating important zinc-, copper-, and iron-dependent enzymes. (When body levels of these three minerals are high, there is first less absorption of lead and then more competition with lead for enzyme-binding sites.) Lead affects both the brain and the peripheral nerves. It may also diminish hemoglobin synthesis and can react with cell membranes. This may cause increased permeability of the cells and damage or even death of those cells. Lead can displace calcium in bone, deposit there, and form softer, denser spots that can be seen on X-rays as “lead lines.”
Lead also binds with the sulfhydryl bonds and inactivates the cysteine-containing enzymes, thus allowing more internal toxicity from free radicals, chemicals, and other heavy metals.
Lead is also an immunosuppressant; it lowers host resistance to bacteria and viruses, and thus allows an increase in infections. It may also influence our cancer risk. How lead affects the gastrointestinal tract causing symptoms, including a coliclike pain, is still uncertain.
Symptoms of toxicity: An estimated nearly 20 percent of men and 10 percent of women have problems with lead toxicity, though it is not clear what levels of chronic lead toxicity, which is most common, will produce symptoms. Lead in the body subtly interferes with optimum function and general health, and other toxicity factors may affect this. Lead accumulation may also cause shifts in important body minerals, such as zinc, calcium, and manganese.
Early signs of lead toxicity may be overlooked, as they are fairly vague: headache, fatigue, muscle pains, anorexia, constipation, vomiting, pallor, anemia. These can be followed by agitation, irritability, restlessness, memory loss, poor coordination and vertigo, and depression.
Acute lead toxicity symptoms include abdominal pain similar to colic, nausea and vomiting, anemia, muscle weakness, and encephalopathy. Lead encephalopathy is a brain syndrome that can arise also from advanced chronic toxicity. It is characterized by poor balance, confusion, vertigo, hallucinations, and speech and hearing problems.
A low level of lead intoxication may affect brain function and activity more subtly, influencing intelligence, attention span, language, and memory. Insomnia and nightmares may be experienced. Hyperactivity and even retardation and senility may also result. Moderate levels of lead may reduce immune and kidney function and increase risk of infection, and may be another factor in increasing blood pressure. There is some suggestion that lead intoxication may correlate with cancer rates. Further research is needed in this area. With heavy lead intoxication, death may result.
In children, lead is a special cause for concern. Hyperactivity and learning disorders have been correlated with lead intoxication; children with these problems should be checked. Several studies have shown a relationship between lead levels and learning defects, including daydreaming, being easily frustrated or distracted, a decreased ability to follow instruction or a low persistence in learning, and general excitability and hyperactivity. There is also a recent correlation between sudden infant death syndrome (SIDS) and increased lead levels. This needs further research to implicate lead intoxication as a cause of death.
Amounts leading to toxicity: The average daily intake of lead, as estimated by weveral researchers, ranges from 200-400 mcg. Most of that, 80-90 percent, comes from food or contamination from car exhaust. Average absorption is about 5-10 percent, so most of us should be able to eliminate most of what we get. Actually, with proper function we can excrete many times more lead than that daily.
It is not clear what exposures or body levels of lead will actually produce functional difficulties or specific symptoms; this probably varies from person to person. In measurements of any nutrient or chemical in the body, there is an estimated normal, or reference, range, above which some problems or symptoms may appear. For the level of lead in hair, the reference range of the lab that my office uses is 0-30 ppm. Many authorities set lower levels, perhaps below 15-20 ppm, as a concern; Doctor’s Data in Chicago uses 10 ppm. Even lower amounts, especially in children, may be a body burden and interfere with optimum brain and metabolic functions. For whole blood measurements, below .40 ppm is usually considered within the normal range; less than .20 ppm is probably ideal. In children, lower levels than that, even .10 ppm may be a concern.
Who is susceptible? There is a long list (hundreds) of industrial and other workers who have a higher than average potential for exposure to lead. Obviously, anyone who works directly with lead has more exposure. Working in zinc or vanadium mining can also increase lead exposure.
As stated, children are especially at risk for lead toxicity. For instance, teething children
|Lead miners and other lead workers|
Insecticide makers and users
|Glass makers and polishers|
|Dye makers and dyers|
|Vehicle tunnel workers|
|Police and fire fighters|
|Linoleum and tile makers|
|Solder makers and solderers|
|Shellac, varnish, and lacquer makers|
|Pottery glaze workers|
|Paint makers and painters|
|Wallpaper makers and hangers|
|TV picture tube makers|
|Metal workers and refiners|
|Toll booth collectors|
|Dentists and dental technicians|
may be exposed to lead; it is especially true for children living in older or low-income housing or who live and play near busy streets. Much less exposure than would affect adults can lead to problems in children, because their absorption is better and their bodies are smaller. A small amount of leaded paint can increase body levels enough to create symptoms of toxicity. Children showing signs of hyperactivity or poor learning should be screened for lead levels.
Pregnant women and even the fetus are at risk of lead exposure. Anyone who works around car exhaust or in any of the many industries in which lead is used, from printing to painting to plumbing, should be aware of lead problems and probably get checked for lead levels every few years, until we as a society are able to lower our lead use and environmental exposure.
Treatment: EDTA, a synthetic amino acid, is the standard intravenous medical treatment for lead poisoning. It is a strong chelating agent, as it “claws” or latches onto metals and increases their urinary excretion. This treatment for lead intoxication led to use of the newer “chelation therapy” for other problems as well, as some of the patients treated for lead poisoning also experienced improvement of cardiovascular symptoms. This benefit may be a result of pulling out extra calcium and other metals that may be clogging arteries. Though chelation therapy is a controversial treatment that warrants further research, EDTA does much for lead and most heavy metal intoxication. This intravenous treatment, is administered by a doctor, often in a hospital setting. Other medical treatments for lead intoxication include Dimercaprol (British antilewisite, BAL), given intramuscularly, and oral D-penicillamine. Treatment by any of these pharmaceutical agents has risks, so the level of lead intoxication should be accurately assessed.
To reduce lead toxicity, a high-calcium diet or supplemental calcium will inhibit further lead absorption. Injections of calcium chloride and extra vitamin D will increase body levels of calcium, which may even displace some lead stored in the tissues, particularly the bones. Vitamin C also helps improve elimination of lead and other metals. The amino acids cysteine and methionine have some effect in detoxifying lead and other toxins, and foods such as eggs and beans, which contain these sulfhydryl-group amino acids, may also help bind and clear additional lead.
Prevention: Obviously, the number one prevention is to restrict lead exposure. That involves awareness of increased lead contamination potential. The following are some ways to practice this prevention:
- Do not exercise along freeways or in heavy traffic.
- Do not allow children to play near busy streets.
- Do not store food in pottery.
- Avoid soldered cans, which are mostly the tin cans.
- Evaluate for lead levels any questionable substances, such as water or bone meal, that are used regularly.
More positive things we can do to reduce lead problems in our body include eating a wholesome diet with plenty of fresh fruits, vegetables, and whole grains to obtain adequate minerals, avoiding refined foods, and possibly taking a mineral supplement so as to competitively reduce lead absorption. Calcium and magnesium do this well, so a good level of these minerals in our diet, as well as supplements, can reduce lead contamination. Iron, copper, and zinc also do this. With low mineral intake, lead absorption and potential toxicity are increased.
Algin in the diet, as from kelp (seaweed) or the supplement sodium alginate, helps to bind lead and other heavy metals in the gastrointestinal tract and carry them to elimination. Pectin and other fiber foods in the diet will also tend to bind the heavier metals and reduce absorption. With this, though, we need to take more of our essential vitamins and minerals, such as the Bs, vitamin C, iron, calcium, zinc, copper, and chromium, to help decrease lead absorption. As mentioned, L-cysteine, 250 mg. twice daily, is a sulfur-containing, detoxifying amino acid that will help bind and eliminate lead.
Children can be somewhat protected by getting adequate iron, calcium, and vitamins C and E in their diet and as supplements in appropriate amounts for their age. This program may also help get a little of that lead out and keep them clear thinking, more balanced, and active (but not hyperactive).
Our understanding of lead is just beginning. Better prevention and treatments for lead intoxication, along with reduced lead use by industry in fuels, cars, paints, and so on, should enable us to control the problems associated with this widespread contaminant.