Lead toxicity was first recognized as early as 2000 BC. Nicander of Colophon wrote of lead-induced anemia and colic in 250 BC and as everyone knows by now, lead is thought to have played a part in the decline of the Roman Empire due to the popular use of lead pipes used to transport drinking water. However, this is thought to be a mistaken legend since heavy corrosion of lead pipes with calcium carbonate would have prevented lead from contaminating the drinking water. Today, most exposure in developed countries is the result of occupational hazards, leaded paint, and leaded gasoline (which continues to be phased out in most countries). Bullets lodged in the body rarely cause significant levels of lead poisoning but bullets lodged in the joints are the exception, as they deteriorate and release lead into the body over time.
Symptoms of Lead Toxicity
The symptoms of chronic lead poisoning include neurological problems (reduced cognitive abilities, nausea, abdominal pain, irritability, insomnia, metal taste in oral cavity, excess lethargy or hyperactivity, headache and, in extreme cases, seizure and coma). There are also gastrointestinal problems, such as constipation, diarrhea, vomiting, poor appetite, weight loss, which are common in acute poisoning. Other associated effects are anemia, kidney deterioration, and reproductive failure. Lead toxicity can result in the formation of a bluish line along the gums, which is known as the “Burton’s line,” although this is very uncommon in young children. Blood film examination may reveal “basophilic stippling” of red blood cells, as well as the changes normally associated with iron deficiency anemia (microcytosis and hypochromia). A direct link between early lead exposure and extreme learning disability has been confirmed by multiple researchers and may explain the variation in violent crime rates in the U.S. and other countries.
Lead has no known biological role in the body. The toxicity comes from its ability to mimic other biologically important metals, the most notable of which are calcium, iron and zinc. Lead is able to bind to and interact with the same proteins and molecules as these metals, but after displacement, those molecules function differently and fail to produce enzymes necessary for certain biological processes. Most lead poisoning symptoms are thought to occur by interfering with an essential enzyme (delta-aminolevulinic acid dehydratase, or ALAD). ALAD is a zinc-binding protein which is important in the biosynthesis of heme, the cofactor found in hemoglobin. Genetic mutations of ALAD cause the disease porphyria, a disease which was highlighted in the movie The Madness of King George about George III (who lost the American colonies in the Revolutionary War). Lead poisoning is sometimes mistaken for porphyria but the distinction is that lead poisoning usually causes anemia while porphyria does not.
Lead poisoning is widely considered to cause agressiveness, depression, and in extreme cases may contribute to schizophrenia. Although this is still an area of debate, the relationship between lead and ADHD is considered well established.
Incidence and Sources of Lead Poisoning
Outside of occupational hazards, the majority of lead poisoning occurs in children under age twelve with the main sources of poisoning coming from ingestion of lead contaminated soil (this is less of a problem in countries that no longer have leaded gasoline) and from ingestion of lead dust or chips from deteriorating lead-based paints. This is particularly a problem in older houses where the sweet-tasting lead paint is likely to chip, but deteriorating lead-based paint can also go to powder and be inhaled. Small children also tend to teethe and suck on painted windowsills. In most American states, landlords and those selling such houses are required to inform the potential residents of the danger. Lead has also been found in drinking water. It can come from plumbing and fixtures that are either made of lead or have trace amounts of lead in them. Exposure to metallic lead such as small lead objects, can lead to an increase in blood lead levels if the lead is retained in the gastrointestinal tract or appendix. Lead can also be found in some imported cosmetics. There are also risks of elevated blood lead levels caused by folk remedies like Azarcon which contains 95 percent lead and is used to “cure” empacho. Lead may be contracted through the mucous membranes through direct contact to mouth, nose, eyes, and breaks in skin.
Testing for Lead Toxicity
Because lead is esconced within cells, blood and urine levels are normal unless the person has been very recently exposed or is deathly ill from lead intoxication. Few doctors realize this simple fact. The only practical way to measure the body burden of lead is the “challenge test” in which an oral or intravenous chelating agent is administered followed by urine collection and analysis.
Treatment of Lead Toxicity
The chelating agents to remove lead are EDTA, Vitamin C, DMSA, DMPS, BAL, and there are a few other lesser known and used agents. Administration can be oral or intravenous and should only be done by a physician experienced in treatment of heavy metal toxicity as there are a handful of nuances to the use of these agents.