Understanding that even low levels of lead exposures can cause central nervous tissue damage, especially among children (lowered IQs), it may be helpful to review the nature of lead as one of the most serious environmental contaminants. All regulations pertaining to lead and other heavy metals will be based upon this issue of human risk.

In The Pharmaceutical Basis of Therapeutics, the "bible" of chemical therapeutics in medicine, lead is defined in Latin as, "materia non grata," or, an absolutely unwelcome compound, of absolutely no value and causing great harm to human health. Even in 1970, it was considered to cause serious health risk at almost all dose levels. The work by Herbert Needleman in Boston, which found that small doses were having an impact upon the reading ability and high school graduation levels of students, would have been no surprise to the physicians and toxicologists who wrote on lead at that time.

History of Lead and Disease

Physicians and observers of industrial disease have sensed the danger of lead for generations, but never quite understood the low-dose risk. Hippocrates, the ancient Greek considered to be the father of medicine, at one point described a serious attack of colic or gastrointestinal pain as being based on lead exposure. In 200 BC, Nicander wrote that lead exposure, specifically, caused abdominal pains, pale complexion and gastrointestinal problems (constipation). By the First Century AD, in the era of Roman medicine, lead risk was well recognized, at least in terms of chronic exposures. Even then, physicians felt that lead exposure from drinking vessels, and certainly occupationally, could create disease, and speculated about its causing mental degeneration.

Around the time of the Renaissance, forms of lead poisoning at lower doses, with less immediate impact, were identified. Later references are also noted:

• Benjamin Franklin, in a letter to Benjamin Vaughan, Philadelphia, July 31, 1786 (Washington, DC Library of Congress): "The opinion of this mischievous Effect from Lead, is at least above Sixty Years old; and you will observe with Concern how long a useful Truth may be known, and exist, before it is generally receiv'd and practis'd on."

• J. Lockhart Gibson, Australian physician, in a plea regarding Queensland children in the Australian Medical Gazette, 1904: "I advance a very strong plea for painted walls and railings as the source of the lead, and for the biting of fingernails or sucking of fingers as . . . means of conveyance of the lead to the patient."

• Orfila, a physician, wrote in 1814 of the first known medical assessment of low-level lead exposure.

• Thirty years later, Alfred S. Taylor, medical lecturer at Guy's Hospital and author of Taylor on Poisons, a leading medical tome of the American Civil War era, wrote: "It is to be regretted that a substance so pernicious to health as carbonated lead should be so extensively employed in the arts and manufacturers. Much is said concerning the preventable deaths from bad drainage and defective ventilation, but yearly deaths from unnecessary poisonings are wholly disregarded. Under a proper system of medical policy, precautions would be taken to prevent the widespreading of a secret source of disease and death (exposure to lead)."

In public health symposiums and conferences of the 1950s, '60s and '70s, risks from lead were described and regulations limiting gross exposures were implemented, i.e. thresholds for amounts of lead in paint, elimination of lead from petroleum products, and stricter OSHA standards for protecting workers. When Dr. Herbert Needleman found a clear relationship between lead retention in children's teeth and actual measures of lower intelligence at even extremely small doses, the absolute need for legal intervention could not be questioned.

The standards adopted in 1992 by the Centers for Disease Control and the OSHA worker standards in the Title X Act are among the series of regulations responding to the increased understanding of how lower doses of lead can create human risk. The power of federal law has been marshaled against property owners and managers who allow exposure.

About Lead and Disease

Lead is absorbed very slowly by the body, but the problem is that the body stores the lead for a longer period of time. It takes twice as long to excrete the lead than it did to absorb it. A week's exposure to lead-based paint, at a constant dose, would take two weeks to be excreted. The absorption rate and consequent danger becomes greater in direct relationship to how young the children are when exposed.

Lead is essentially ubiquitous; a certain amount is taken in daily by nearly everyone, even in a normal diet. Only 8%-12% of ingested lead is actually absorbed, however. Most industrial poisoning relates to inhalation of lead dust or lead fumes, and in those cases, the doses are much greater.

Lead is absorbed by erythrocytes (red blood cells) and then distributed throughout the body. The first impact, especially in heavy doses, is on soft tissue (kidneys, liver) and is eventually deposited by blood cells in bone, teeth and hair. The deposition of lead in bone resembles that of calcium. In fact, if one has an increase in calcium in food, lead will be more rapidly pulled out of the blood and deposited in bone tissue, imbedded along with the calcium. Over time, it will slowly be re-released into the body.

It's fairly easy to determine through x-rays if a child has had past heavy exposures to lead, as the bones will show rings of increased density.

Specific Diseases

Because of increased safety at worksites of the Western World in terms of working conditions and limited occupational exposures, most direct poisonings today are pediatric in nature, relating usually to pica (the tendency of children to put things in their mouth, to experience taste and touch orally). Lead has a sweet/salty taste, so is occasionally ingested by children in quantity. However, it is that fine, white dust from degrading, chalking paint that can adhere to toys, clothes and food that probably does the most harm. Workers who are exposed usually are located in small, unregulated factories and most commonly work with battery casings, acetylene torches or lead-paint coated materials. Historically, one of the most blatant sources of severe lead poisoning came during Prohibition, among those exposed to "moonshine whiskey." The distillation process for moonshine was often through lead-bearing parts (automobile radiators or some other lead-containing apparatus).

People living near freeways or in urban areas where there is substantial automobile exhaust also have higher base lead counts. A person will normally take in .03 mg daily, although that can vary widely depending upon diet and especially upon hygiene in the home, school or worksite.

Heavy doses of lead poisonings result in spasmodic pains in the abdomen, liver damage, retention of uric acid, headache and despondency. Central nervous system (CNS) damage can occur at far lower doses. The first observable clues to development of this syndrome include clumsiness, vertigo, headache, insomnia, irritability. Later stages, as the lead burden builds, can include delirium, convulsions and extreme lethargy.

The fatality rate for serious exposure is high. Researchers have estimated that where there is complete CNS syndrome, 25% fatality occurs. They also estimate that 40% of survivors have neurologic problems, definable mental retardation, EEG abnormalities, hypertension etc. Clearly, there is some form of consistent neurological damage with lead exposure, whether at high or low doses.

At a lower threshold of lead exposure, jaundice occurs, usually from latent lead poisoning. Some of the physiological signs of long-term, lower dose include ashen color, a pallor to the lips, what appears to be "premature aging," or a thin, dark line along the gums known as the "lead line," which probably relates to the periodontal definition of lead sulfide. When one has serious levels of lead exposure, the earliest symptoms involve insomnia and other sleeping problems, i.e. disturbing dreams, restlessness etc. As the burden builds, this is followed by nausea, vomiting, anorexia, diarrhea, headache, muscular weakness and unaccountable emotional instability. Incidences of residual central nervous system damage have been reported, but as the lead burden is reduced by either eliminating the source or through medication, visible recovery is achieved.

Treatment

Chelating agents, which grip and essentially wash the lead out of the system, are of no use with acute poisoning, but at lower dose exposures, they will rapidly remove lead and, over time, will speed up the purging of lead from body tissue. Recovery may be virtually complete. The issue is to stop the slow and gradual introduction of lead and, if necessary, speed up the purging of the lead.

Prevention: The Best Response to Lead Exposure

An overall prevention approach to lead poisoning includes increased blood testing, reduced exposures in the workplace, assurances that schools, daycare centers and homes are clean and wholesome, and teaching parents methods for keeping themselves and their children environmentally safe. These are easy, low-cost steps to a safer America in the 21^st century.