We are very appreciative for the support of the Environmental Protection Agency to permit this project to go forward and to all of the authors and reviewers of the many chapters in this supplement to Pediatrics. We especially thank Ramona Trovato and Martha Berger of the Environmental Protection Agency’s Office of Children’s Health Protection for their encouragement and assistance.
We have dedicated this supplement to practicing pediatricians in the hope that the articles in this supplement will stimulate their interest in reading and understanding the rapidly enlarging literature dealing with pediatric environmental toxicology. A better understanding of epidemiology and toxicology publications will permit the physician to be able to read the literature more critically. This should enable pediatricians to better counsel their patients about the risk or lack of risk of environmental exposures. The readership of this supplement will also realize that some scientists have taken positions that many environmental toxicants are a major child health problem whereas others have minimized the risks of children’s environmental exposures. Objectively, there are environmental toxicant exposures for which we have substantial evidence of serious effects at levels frequently experienced by children, and there are others for which there are either inadequate data or the data do not support danger to children. For some, there is clear evidence that the fetus and the child has increased sensitivity and vulnerability; for other toxicants, there is evidence of increased resilience and decreased vulnerability. For most chemicals, however, we do not yet have the actual exposure level of the nation’s children or adequate data concerning the no observable adverse effect level (NOAEL). This is why the most important conclusion of this supplement is the request for significantly increased and improved pediatric environmental toxicology research.
Important terms used in this monograph include the NOAEL, which is the highest exposure at which no adverse effect is seen. The threshold exposure is the lowest exposure at which deleterious effects can be produced or observed. These 2 exposures are very similar, with the threshold exposure being slightly higher. Another term is the maximum permissible exposure or maximum permissible level (MPL), which refers to a level of exposure that is established by regulatory agencies to protect the public. Clinicians frequently confuse this term with the NOAEL. This means that 2- to 10-fold increases above the MPL or even higher exposures may still not have any demonstrable adverse effect on the embryo, child, adolescent, or adult. However, to be cautious so that the public is not at increased risk, MPLs are usually set very low. There frequently is honest debate about the level at which the MPL should be set, with the need to regulate exposure despite limited data.
Throughout this supplement, pediatricians have been complimented for their contributions to discoveries of environmental risks and for educating their patients about these risks. Perhaps their greatest contribution has been the recognition of clusters of patients with relatively acute, or “toxic,” exposures, usually those that have led to overt signs and symptoms and often distinct clinical problems. This supplement illustrates that illnesses, diseases, and subtle but serious alterations or decrements in functioning that occur at low exposure levels of environmental toxicants are more difficult to identify when observing small clusters of patients with illness or disease or those with no readily apparent signs or symptoms but with low-level exposure. With low exposures, sophisticated epidemiology and toxicology tools must be introduced. It is difficult to conclude definitively a causal association from low exposures of environmental toxicants without appropriate studies, many of which require large numbers of children followed over extended periods of time. Several such studies are discussed in detail in this supplement. A serious problem occurs when physicians or scientists are willing to conclude a causal association when adequate data are not available or not to conclude a causal relationship in the face of extensive data supporting such a relationship. Although most pediatricians have been responsible in this area of medicine, there have been those who have taken positions that were not in the best interest of children. For example, the few physicians who mounted campaigns against immunization in the media and in the courts, or, more recently, the decision to remove ethyl mercury (in the preservative thimerosal) from vaccines that was not based on scientific evidence of adverse effects. In 2001 the Centers for Disease Control and Prevention convened a panel of >100 scientists, who reviewed the epidemiologic data, animal studies, and the pharmacokinetics of ethyl mercury and concluded that the vaccines with ethyl mercury, at the levels being used, were without risk to children, yet the ethyl mercury was removed, resulting in a period of vaccine shortage, and the necessity to handle the vaccines differently, thus raising their costs.
The most important message of this supplement is this: you cannot reach definitive conclusions about cause and effect of environmental toxicants without quality epidemiology, toxicology, and basic science research studies.
To make certain that the pediatrician maintains his or her global view of environmental risks, we have added an appendix entitled “Prioritizing Environmental Risks.” It is something that pediatricians do every day in their office when they interact with patients and their families. We hope that this supplement will be of interest and use to pediatricians as the field of pediatric environmental health continues to grow and to provide vitally important new information about the effects of environmental exposures on our nation’s children and ways to protect them from these exposures.NOAEL, no observable adverse effect level, MPL, maximum permissible level
- Copyright © 2004 by the American Academy of Pediatrics