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even federal agencies whose mission coincided with public health activists were under attack and stymied in their attempts to regulate the environment, identify and remedy unhealthy working conditions, and provide services to the poor. New publicly built housing virtually ceased in these years. In the face of this broad assault, largely at the behest of conservative critics of the Great Society programs of the 1960s, public health activism waned.²⁴

      A strategy of avoiding confrontation with the political and economic institutions that impede the solutions for public health problems—and indeed may have given rise to them—has led to avoiding confrontation with the structural impediments to improving public health. This is the dilemma of public health today: For generations, many in the public health field have depended on the laboratory, on the development of the next magic bullet, on new technologies and diagnostic and therapeutic interventions to deal with public health problems. But, like lead, other ubiquitous environmental poisons now raise fundamental problems that cannot easily be addressed by these methods. If detection of endocrine disruption is truly a new frontier in the understanding of reproductive problems or other biological changes, for example, a medical intervention may not be adequate; and even were it possible, dealing with the consequences individual by individual would overwhelm any health system.

      If public health professionals are to effectively address the problems of chronic conditions, subtle neurological damage, obesity, and childhood developmental anomalies, they will be forced to confront huge industries that profit from, for example, the production of fast foods, high-calorie drinks, and tobacco. These health difficulties are not simply an issue for public health professionals; they are of course an issue for society as a whole. Public health individuals and institutions can press, but ultimately their success depends on political and economic forces larger than themselves. From the guarantee of an adequate water supply and sewer system to the passage of Medicare and Medicaid, successful public health reforms of the past have depended on social movements and legislative and/or executive action, and the same is likely to be true for effective action on a broad array of toxins, lead included.

      THE SCIENCE AND POLITICS OF LOW DOSES

      As the character of the lead-poisoning epidemic has changed over the past half century, especially with the elimination of lead from the manufacture of paint and from gasoline, and as the harm to children of nonfatal doses of lead has become more apparent, the focus of research has shifted to the effects of these smaller doses. Results indicate that, though the level of lead exposure may be low compared to what brings on acute episodes of lead poisoning, the effects are far from minor.

      Children with even relatively low levels of lead in their blood (even below 5 micrograms per deciliter) have been shown to suffer disproportionately from behavioral problems in school, school failure, hyperactivity, trouble concentrating, difficulty with impulse control, lowered intelligence scores on standardized tests, higher rates of juvenile delinquency and arrests, and ultimately unemployment and failures in life. Further, children with lead exposure are more likely as adults to have physical problems like kidney and heart disorders. The scientific community and many political leaders now recognize that lead poisoning has been among the most important epidemics affecting children in the United States in the last century.

      A particular tragedy of low-level lead poisoning is that its “symptoms” are easily confused with myriad other insults suffered by children who grow up in poor communities, whose housing is substandard and whose lives are shaped by poor education, social marginalization, and, in some instances, racism. In a 1990 article Herbert Needleman noted a stunning statistic that brings this issue home: more than half of all “poor black children have elevated blood lead levels,” estimated at the time as exceeding 25 μg/dl.²⁵

      Consider, for example, Sam T., the youngest of his family’s nine children, born in June 1990, just as the Kennedy Krieger Institute study was beginning in Baltimore.²⁶ The family lived in an apartment located in one of Milwaukee’s poorest and most lead-polluted neighborhoods, but according to his medical record, Sam “thrived as a baby” and was developmentally normal at the ages at which he started to crawl, walk, and babble.²⁷ Like many lead-poisoned children, his problems began as a toddler, when he began to move more freely around the apartment, mouthing or sucking his fingers after touching the walls, windowsills, or other objects covered with lead paint or dust.²⁸ When Sam was fourteen months old, a routine check found his blood lead level to be 18 μg/dl, at that time almost twice the Centers for Disease Control’s acceptable exposure limit, which had been reduced from 25 to 10 μg/dl in 1991. A few months later, his blood lead level had almost doubled, to 40 μg/dl, and it did not fall below 25 μg/dl at any time tested over the next two and a half years.²⁹ The family moved to a house nearby in an attempt to escape such a heavily leaded environment, but conditions there were no better. In the summer of 1993, when Sam turned three, his lead levels jumped significantly and he was hospitalized for five days while he received chelation treatments, the in-hospital chemotherapeutic blood treatment aimed at leaching lead from the body.³⁰ But by then it was too late to forestall damage.

      When Sam entered kindergarten, teachers immediately noticed that he had problems. Within weeks, he was referred for speech and language therapy and was soon, according to the court record, “transferred to a different school because he needed a small, structured classroom.”³¹ In first and second grades, he had difficulties with reading, writing, and arithmetic and he suffered various language delays.³² In his teenage years, a battery of neuropsychological exams indicated that Sam “had a number of deficiencies in various areas of brain function . . . : problem solving, planning, executive function, fine motor function, expressive language, aspects of visual-spatial construction, visual working memory, visual-spatial memory and verbal concept formation”³³—an array of deficits consistent with what is known about damage from lead ingestion. “[Sam]’s injuries are permanent and irreversible,” the examining physician concluded.³⁴ By his midteens Sam, who had been described as a normal, happy infant, had become a failure in school, a troubled young man who lacked the skills to escape the dangerous neighborhood in which he was raised.³⁵

      The lessons of America’s continuing lead-poisoning epidemic are not confined to the tragedies of a few specific children like Sam T. Nor are its lessons limited to lead alone. Discovery by lead researchers of the impacts of early low-level lead exposure has been instrumental in revolutionizing our understanding of environmental danger and how we define what is a risk. As a result, our concerns regarding environmental dangers can no longer be confined to worries over cancer, heart disease, and the like. Researchers have identified that low-level exposures can result in biological changes with measurable and important consequences for individuals. Behavioral changes such as hyperactivity, attention deficit disorders, and even antisocial behaviors have been linked to low-level exposures to lead, mercury, and other heavy metals in infancy and even in utero. Morphological changes such as premature puberty and an increased proportion of female births have been linked to the rise in the use of plastics and bisphenol A and other “endocrine disruptors.”³⁶

      Researchers into low-level exposures to a variety of substances have also challenged, even transformed, our understanding of what is toxic and what is toxicology. We can no longer take solace in believing that any substance can be used if a “safe” level of exposure is officially identified. Researchers have shown that for many synthetic materials introduced yearly into our environment, the developmental moment at which a fetus or child is exposed to a toxin is every bit as important as the amount to which he or she is exposed.³⁷ Many of these issues that challenge us today were first identified while studying lead and lead exposures. The modern history of this unfolding understanding and corresponding attempts to regulate lead may thus give us insight applicable to current debates over other toxic substances.

      Sam T.’s story is similar to that of countless others, often who have ingested far less lead. In fact, from the 1970s to the 1990s a growing body of research indicated that as each lower “safe level” was agreed upon by the federal government, deleterious effects were found at a still lower level. Investigators such as Philip Landrigan at Mount Sinai Medical Center in New York, Herbert Needleman at the University of Pittsburgh, and Kim Dietrich and Bruce Lanphear, both then at the University of Cincinnati, showed that even

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