The quality of life of a country's citizens is most significantly indicated by the country's energy per capita consumption, which is directly proportional to a country's gross national product.[1] The United States is one of the leading consumers of energy with electrical energy making up thirty-six percent of all energy consump tion.[2] Therefore, electrical energy contributes greatly to the quality of life of the citizens of the United States.

Electrical energy provides benefits and conveniences that society now deems necessities. These benefits and conveniences range from the ability to read a book or newspaper after dark on a sultry summer evening, while being cooled by an electrically powered air conditioner to the ability to have a life-threatening tumor diagnosed by magnetic resonance imaging (MRI). Without question, electrical energy is one of the "good" resources contributing to modern life and one on which society now depends. Certainly from the time Benjamin Franklin discovered electricity, the public has been aware of the danger of death or injury upon contact with electrical power. In the seventies, concern arose about the possible ill effects caused by invisible emanations from electrical wires and appliances, consisting of electric and magnetic fields, generally referred to as "electromagnetic fields" or "EMF."[3]

Electric and magnetic fields exist wherever electricity is present. Some scientists, especially epidemiologists, suggest that electric and magnetic fields may cause adverse health effects such as brain cancer, childhood leukemia, testicular cancer, birth defects, and mis carriages.[4] Other scientists disagree with the conclusion that electric and magnetic fields can cause adverse health effects. [5] The press has emphasized the suggestions of harm to health in recent years, causing a public fear of electromagnetic fields.[6] The perception that EMF can cause cancer or otherwise harm health has in some cases affected property values,[7] influenced some governmental bodies to adopt land use rules and regulations affecting power line siting,[8] caused landowners to protest power line siting,[9] and spawned personal injury tort litigation.[10]

In response to public perception and concern, the United States Congress passed the Energy Policy Act of 1992,[11] which established an electric and magnetic fields research and public information dis semination program. In addition to dissemination of information, this program determines whether the electric and magnetic fields produced by using electrical energy affect human health and conducting research to mitigate any potential adverse health effects.[12] The legislation provided that the United States Department of Energy (DOE) would be the agency responsible for electric and magnetic field research and directed the Secretary of Energy to arrange for the National Research Council of the National Academy of Sciences[13] to review and evaluate the research on possible health effects of electric and magnetic fields.[14] In late 1996,[15] the National Research Council reported the conclusion "that the current body of evidence does not show that exposure to these fields presents a human-health hazard."[16]

Part II of this article presents the effect that the controversy surrounding electric and magnetic fields has had on public perception along with some of the concomitant effects on property evaluation, land use, and tort litigation. Part III explains electric and magnetic fields. Part IV summarizes the National Research Council Committee's report of its conclusions after prolonged study of the available acceptable research[17] and the Conclusion, Part V, speculates on the likely effect of the National Research Council Committee's report on public perception.

When reports of suspected harmful health effects caused by exposure to electric and magnetic fields began to reach the public, the public's concern and fear impacted at least three areas of law. In the area of land valuations, public concern provided a reason for the devaluation of property located near power lines.[18] In the area of land use, public concern influenced some governmental bodies to adopt land use rules and regulations affecting power line siting and caused neighboring landowners to protest power line siting.[19] In the area of litigation, concern about the health effect of EMF radiation generated some tort litigation.[20]

Issues concerning the effect of power lines located on or near an owner's property arise when an electric utility attempts to acquire property rights in the land on which it intends to place a power line.[21] A utility may negotiate with the landowner to purchase the property right, either in fee simple or as an easement.[22] If the landowner refuses to negotiate or a price cannot be agreed upon, the utility can exercise the power of eminent domain in a condemnation action.[23]

The exercise of the right of eminent domain requires that just compensation be given for the property taken.[24] The determination of just compensation for the condemned property usually involves computing damages in the amount of compensation for the land actually taken and severance damages, which are those damages caused by a reduction in the value of the remaining property when the condemned property is severed.[25] The measure of damages for the property actually condemned is the fair market value of that property.[26] Since severance damages are based on the reduction in market value caused by the severance, evidence of factors effecting that reduction is relevant and admissible.[27]

When fear of harm caused by exposure to electric and magnetic fields emanating from power lines became widespread, landowners, in an effort to increase severance damages,[28] began to introduce evidence in condemnation cases relating to EMF and the fear of exposure to EMF.[29] Courts required expert testimony regarding biological effects of electric and magnetic fields,[30] and expert or non-expert evidence of the public fear. Evidence of personal fear was inadmissible.[31] One court excluded evidence of harmful effects of power lines because the landowner's proposed experts "could not testify within the reasonable degree of probability necessary to express an opinion concerning the actual physical effects of electromag netic field exposure on humans."[32] Other courts have excluded expert testimony regarding public fear of power lines because the witness failed to quantify any damage to the fair market value of the remaining property,[33] or to show how to calculate with reasonable certainty the effect of the public fear on the market value of the remaining property.[34] Another court found that issues concerning alleged health hazards created by the construction and operation of electric power transmission lines necessitated an action's dismissal because such issues should have been determined by the regulatory agency.[35]

An important case involving a jury's decision after hearing evidence on the fear of electromagnetic fields and the effect of EMF on property that had been condemned for the construction of high-voltage transmission lines is Houston Lighting & Power Co. v. Klein Independent School District.[36] Following the utility's condemnation of a strip of land owned by the school district, the school district was awarded $78,604 by the Public Utilities Commission (PUC).[37] The school district then filed objections with the trial court.[38] The utility deposited $78,604 with the court, took possession of the strip of land, and constructed the transmission lines, which were energized in 1984.[39] The school district's pleadings alleged that the callous deci sion to locate the line on the school property, disregarding the safety and health of the school children, made the condemnation void.[40]

At trial, several experts testified for the school district. An engineering professor testified that the children in the intermediate school located 300 feet from the transmission line were being exposed to magnetic fields between six and ten milligauss.[41] An epidemiologist testified about the studies she and other epidemiologists conducted that showed correlation between cancer and power lines.[42] She concluded that the children in the schools were at increased risk of cancer because of the electromagnetic fields.[43] An oncologist testified similarly.[44] A pharmacology department chairman testified that because the electromagnetic fields were not obstructed by buildings or anything else, the children would be exposed to them daily.[45] Testifying for the utility was an expert who critiqued the school district's expert studies.[46]

The jury awarded the school district $104,275 actual damages and $25 million punitive damages, finding that the utility had abused its discretion in condemning the line and that it erected the line in reckless disregard of the school district's use of its property.[47] The lower court permanently enjoined the utility from using the transmission lines and ordered possession of the property restored to the school district.[48]

The appellate court ultimately modified the trial court judgment, deleting the award of punitive damages, and affirming the actual damages.[49] At the time of the appellate decision, the utility had already received permission from the PUC to relocate the transmission lines in order to avoid the school district property.[50]

The Klein Independent School District case thus demonstrates a jury's response to evidence that electromagnetic fields emitted from power lines may be dangerous to public health and that a utility's condemnation of property for power lines may be overturned. The dangers to public health caused by power lines have also increasing ly become an issue in power line siting litigation.[51]

Perceived health hazards associated with electric and magnetic fields emitted from power lines, and the public fear of power lines caused thereby, have frequently been issues in power line siting and land use cases.[52] The siting of power lines is regulated by state agencies, which may be designated the "Public Service Commission" (PSC), the "Public Utility Commission" (PUC), or some similar designation. These regulatory agencies investigate the need for new power lines and study the effects on the public of locating or siting those lines.[53] Public hearings constitute a part of a regulatory agency's investigation, and at these hearings property owners, muni cipalities, and other entities affected by the siting of proposed lines may raise their concerns.[54]

Among the issues considered by a regulatory agency in an evidentiary hearing are the effects of electromagnetic fields on health and safety.[55] Though science has not confirmed the adverse health effects of electromagnetic fields, in an attempt to control the risks of exposure to electromagnetic fields the regulatory agencies have tried to regulate the level of exposure by adopting simple field strength safety standards.[56] Some state regulatory agencies have adopted a strategy of "prudent avoidance" as a means of risk management.[57] A strategy of prudent avoidance means taking steps that would prevent the public from being exposed to electromagnetic fields, but taking only those steps involving modest costs.[58] Some possibilities for prudent avoidance include attempting to route new transmission lines so that they avoid people; widening transmission line rights-of-way; developing designs for distribution systems, including new grounding procedures, which minimize associated fields; developing new approaches to house wiring that minimize associated fields; and redesigning appliances to minimize or eliminate fields.[59]

In addition to the cases involving regulatory agencies and proposed power line sitings or proposed upgrades of existing lines, at least one case involved a pre-existing line and the public perception of health hazards caused by the line. In Borenkind v. Consolidated Edison Co.,[60] plaintiffs, who were vendors of residential property located near the power line, sued the utility seeking consequential damages because of the alleged decrease in value caused by the public's perception of a health risk associated with living near the line.[61] However, the court dismissed the complaint.[62]

Electric and magnetic fields and the fear of health hazards associated with power lines have also been issues in cases involving zoning ordinances, zoning changes, and land use ordinances regulating power lines.[63] The town of East Greenwich, Rhode Island, is a party in two such cases: East Greenwich v. O'Neill[6]4 and East Greenwich v. Narragansett Electric Co.[65] Because the citizens of East Greenwich expressed concern about the possible harmful effects of electromagnetic fields emanating from power lines, the town adopted an ordinance creating a three-year moratorium on the construction of transmission lines exceeding sixty kilovolts.[66] The ordinance prevented the utility from constructing its proposed transmission line through the town and the utility appealed to the state Public Utilities Commission (PUC), which scheduled a hearing to follow the determination of the outcome of the town's suit challenging the PUC's jurisdiction in the matter.[67] The appellate court invalidated the ordinance and held that the PUC had jurisdiction of the matter.[68]

The Narragansett Electric Co. case resulted from the town's suit to quash a PUC order invalidating amendments to the town's comprehensive plan.[69] Implementing its concern about the possible harmful effects of electromagnetic fields emanating from high-voltage power lines, the town council approved five amendments to its comprehen sive plan.[70] On appeal, the court affirmed the PUC's invalidation of the amendments because they invaded the "field of public utilities regulation, which the General Assembly had expressly preempted from town and city intrusion."[71]

Other land use related cases raising electromagnetic field issues[72] include those where landowners challenged a zoning change that would allow construction of a power substation because of the risk of health hazards[73] and where a town challenged the regulatory agency's decision to grant a utility an exemption from the town's zoning restriction.[74] Interestingly, in one case, the party petitioning the PUC to invalidate the town's rezoning of its lot from heavy industrial to residential was the utility, the party that usually tries to refute the existence of health hazards associated with electromagnetic fields.[75] At the PUC hearing, the utility argued that the rezoning would adversely affect its utility operations.[76] If the utility were to construct power lines on its re-zoned lot and connect them to a substation on its adjoining property, the utility "could be potentially liable for the putative harmful effects of the electromagnetic fields (EMF) from such lines on residents on those lots."[77]

Liability for the putative effects of electric and magnetic fields emanating from power lines and facilities has been alleged in tort litigation.[78] However, because of the failure of science to definitively link causation of cancer and other alleged personal injuries to electric and magnetic fields, there has been no recovery based on the allegations and few reported cases.[79] When the reports of an association between cancer and the electric and magnetic fields around power lines and electricity became known to the public, the suggestion was that electromagnetic field litigation would be the next asbestos.[80] One source predicts that litigation over health problems allegedly caused by electromagnetic fields will continue despite the National Research Council Committee's report finding no conclusive evidence linking electric and magnetic field radiation exposure with cancer and other diseases.[81]

Health issues related to electromagnetic field exposure have produced litigation in which liability was claimed against utilities for purportedly causing non-Hodgkin's lymphoma,[82] emotional distress,[83] and chronic myelogenous leukemia.[84] However, no definitive scientific proof exists linking the alleged injuries and electromagnetic fields and in none of these personal injury cases did plaintiffs recover.[85] Since electric and magnetic fields have caused litigation and controversy, a discussion of these fields is helpful.

Power delivery systems begin with the generation of power, which is measured by "voltage." Voltage is a measure of electric potential energy that makes electric charges flow through a circuit.[92] The power is generated at about 20,000 volts (twenty kilovolts or twenty kV), but because power is more efficiently transferred over long distances at a higher voltage, large transformers increase or "step-up" this voltage to a level measuring from 65 to 765 kilovolts for transmission over high voltage transmission lines.[93] The high voltage transmission lines deliver the power to substations, where it is transferred through step-down transformers to lower-voltage distribution lines in which the voltage measures from five to twenty-five kilovolts.[94] The power then is transferred through a distribution step-down transformer (the large "cans" hanging on the power poles in neighborhoods and along streets) to the customer.[95] The power in homes is measured at 115/230 volts.[96] Just as electrical potential energy causing electric charges to flow through a circuit is called "voltage" and is measured in units called "volts," this flow of charges is called "current" and is measured in units called "amperes" (amps), describing the rate at which the electrical charges flow in a power line or wire.[97] The 115/230 volt wiring in houses is designed to carry currents of up to thirty amps.[98]

Over 370,000 miles of transmission line and over two million miles of distribution line exist in the United States today.[99] One would have to look long and hard to find dwellings in the United States that are not wired for electricity. Therefore, because of the universal exposure of people to sources of electric power and electric devices, the primary area of investigation for the National Research Council (NRC) Committee was the low-frequency electric and magnetic fields associated with electric power and electric devices.[100]

Electric power is either alternating current (AC) or direct current (DC).[101] Batteries produce direct current; power used in homes and workplaces is alternating current.[102] Power line fields alternate from positive voltage to negative voltage.[103] The number of times per second that the variation occurs is called the "frequency" of the current.[104] One cycle per second is measured as one Hertz (Hz), an internationally accepted unit of frequency.[105] For example, a power field that alternates sixty times per second is said to have a frequency of sixty Hz.[106] The frequency of electric power produced in the United States is sixty Hz, while countries in Europe and other places generally produce power at a frequency of fifty Hz.[107]

Associated with the characteristic of frequency of electromagnetic energy is the characteristic of "wavelength."[108] The relationship between frequency and wavelength is that higher frequencies have shorter wavelengths.[109] Frequency and wavelength of electromagnetic energy are related to the electromagnetic spectrum because the spectrum is a classification of electromagnetic energy by frequency and wavelength ranging from extremely low frequencies (ELF) with longer wavelengths to very high frequencies with shorter wave lengths.[110] The frequencies are commonly expressed as powers of ten; for example, a frequency of 10[9] is one gigahertz (Ghz) and is 1,000,000,000 Hz.[111] The range of the electromagnetic spectrum[112] frequencies is from zero to 10[22113] The extremely low frequencies or extra-low frequencies (ELF)[114] include the fifty to sixty Hertz power associated with electric current in homes.[115] In increasing frequencies, the spectrum includes radio waves at 10[6] to 10[10] Hz, microwaves at 10[10] to 10[12] Hz, infrared radiation at 10[12] to 10[14] Hz, visible light at 10[14] Hz , ultraviolet radiation at 10[15] Hz , and at greater than 10[17] Hz, X-rays and gamma rays, which have very high frequencies and very short wavelengths.[116]

The electromagnetic spectrum ranges from "non-ionizing" radiation at the low end of the spectrum to "ionizing" radiation at the high end.[117] Energy is ionizing if it is capable of causing an atom or a molecule to gain or lose one or more electrons, thus producing charged particles when it interacts with the atoms or molecules.[118] Gamma rays, X-rays, and some types of ultraviolet lights are ionizing radiation.[119]

Ionizing radiation has been long-studied and known to damage biological systems[120] because it is able to break chemical bonds, thereby adversely affecting health.[121] Lower on the spectrum than the ionizing radiation bands are bands of high frequency non-ionizing radiation that do not break chemical bonds. These include visible light, microwaves, and radio and television waves.[122] Microwaves do have the capacity to cause water molecules to vibrate, which produces heat; therefore, microwaves can also adversely affect human health because of the capacity to heat human tissue.[123]

As the lowest bands on the spectrum, ELF energy is non-ionizing and is not able to break chemical bonds, nor can it vibrate water molecules or heat human tissue.[124] The manner in which ELF energy interacts with biological systems is "speculative;"[125] however, ELF effects have been reported to "include effects on cell metabolism and growth, gene expression, hormones, learning and behavior, and promotion of tumors."[126] Scientists have debated the validity of the above effects, leading to the National Research Council Committee's study and report discussing the possible health effects of exposure to electric and magnetic fields.[127]

Humans are affected by electric and magnetic fields, which are generated from both external and internal sources. Until about 125 years ago, external human exposure was limited to those fields emanating naturally from atmospheric electricity and geomagnetism.[128] Since the discovery of electricity and its ever-increasing use to power all the modern conveniences, the electric and magnetic fields to which humans are exposed have greatly multiplied.[129] Internal sources also exist because humans and all other organisms have within them "endogenous electric fields and currents that play a role in the complex mechanisms of physiological control such as neural and neuromuscular activity, tissue growth and repair, glandular secretion, and cell membrane function."[130] Given the role that electric and magnetic fields play internally in the biology of humans, a natural inquiry concerns the effect that the external electric and magnetic fields have on that biology.

Studies have shown that electric and magnetic fields, by the processes of induction, can affect humans by producing currents in the body[131] as well as charges on the surface of the body.[132] When a person's body is exposed to an electrical field, induced fields within the body are extremely weak because the conductivity of the body tissue weakens the electrical field.[133] However, the same is not true for magnetic fields. The conductivity of the body tissue does not affect the magnetic fields, so magnetic fields pass through the body inducing electric currents within the body.[134] Nor do most common building materials weaken magnetic fields, which can pass through thin sheets of metal; however, iron and other magnetic materials that serve as paths of conduction of magnetic fields can sometimes be used as shields from magnetic fields exposure.[135] Because most materials have enough conductivity to sufficiently weaken electric fields, most materials can easily shield people from exposure to electric fields.[136]

The electric power used in homes and workplaces produces both electric and magnetic fields because when electric charges move to create a current, magnetic fields are created.[137] Even if an electric appliance plugged into an electrical outlet is turned off, it might have an electric field present. If the appliance is turned on and operating, a magnetic field will also be present.[138] When the two fields, which are quite different in character, are "coupled" in this manner, they are referred to in the NRC Report as "electromagnetic fields" (EMF).[139] However, because coupling at the low frequencies of fifty and sixty Hz is extremely weak, considering the electric and magnetic fields as independent and not substantially linked is more appropriate. For this reason the NRC Report reserves the use of the term "electromagnetic field" for high frequency fields where the electric and magnetic fields are substantially linked.[140]

The fields to which people are exposed can be measured. The intensity of an electric field is measured in units of volts per meter (V/m).[141] Since a thousand volts equals a kilovolt, a thousand volts per meter is a kilovolt per meter (kV/m).[142] The intensity of an electric field decreases rapidly as distance from the source increases.[143] Several different units are used to measure strength and intensity of a magnetic field. For instance, the ampere per meter (A/m) properly measures magnetic field intensity and corresponds to the V/m for electric fields.[144]

Magnetic flux density is a related quantity indicating magnetic field strength and comprises the number of field lines (lines representing graphically either an electric or magnetic field) that cross a unit of surface area.[145] The unit measuring magnetic flux density is the gauss (G), with 10,000 gauss making a unit called a "tesla."[146] The magnetic field intensity measured in A/m is eighty times as great as the measurement of the magnetic flux density in gauss, though both the gauss and the tesla are considered large units.[147] When measurements of magnetic fields are reported, they are usually in thousandths of a gauss or milligauss (1mG = 0.001 G). For example, the magnetic fields produced underneath the commonly observed neighborhood distribution power lines generally measure around five mG, though densely populated areas may produce fields measuring as high as fifty mG.[148] The strength of magnetic fields produced by electric appliances varies from very few milligauss to several hundred milligauss.[149] The intensity of the magnetic field decreases rapidly as the distance from the source increases.[150]

Though electric fields and magnetic fields at the power line frequency of sixty Hz can each be measured or calculated in most any environment,[151] the determination of human exposure is more diffi cult.[152] Some of the difficulties include the many varieties of electric and magnetic field environments that the average person encounters in a day, the lack of knowledge of the specific characteristic of electric and magnetic fields that interact with biological systems, and whether a specific characteristic does indeed interact with the biological system.[153]

Other problems of measurement and calculation are caused by the perturbation of electric fields by conducting objects.[154] If people and animals are in a measured field, their presence affects the field. Consequently, a significant difference occurs in the measurement of a field without a person present and the measurement of a field with a person present.[155] The measured field of an ELF magnetic field, being unaffected by the presence of humans and animals, represents the actual exposure field.[156]

Given all the above-mentioned problems, typical exposures to electric and magnetic fields have been investigated. Devices to measure the electric and magnetic fields have been designed to determine the average root mean square (rms) field strength, which is either magnetic flux density for magnetic fields or electric field strength, for a specific time period.[157] The usual minimum time period that the instruments average is about one second.[158]

The electric equipment used in the workplace and the home is responsible for exposure to electric fields in those environments. However, electric fields have not been satisfactorily categorized because of the ease of shielding sixty Hz electric fields. When attempts to measure personal exposure to electric fields have been made, the measurements have depended greatly on several factors, including where the exposure meter was worn, the orientation of the meter, and the presence of any conductors near the exposure.[159] One study found the range of the mean personal exposure to sixty Hz electric fields in home or office to be from five to ten V/m.[160]

While workplace and home electric fields have not been well characterized, power line electric fields have. Ground-level electric fields under a line depend on the line voltage and may be as high as ten kV/m. A field of ten kV/m is strong enough to shock a person touching a vehicle parked under the high-voltage line and can also cause a fluorescent tube to glow when held under the line. The study mentioned above showed that electrical substation, distribution line, and transmission line workers experience a mean personal exposure ranging from fifty to 5,000 V/m.[161]

Exposure to residential magnetic fields is most commonly caused by electric appliances in the home, the grounding system (usually the water pipes), and nearby low voltage distribution power lines.[162] The internal wiring usually is not a significant source of magnetic field exposure unless a problem with the wiring exists.[163] Nor are high voltage transmission lines at a distance of more than one hundred meters from the residence considered a significant source of exposure.[164] However, transmission lines can be a source of magnetic fields if the home is near the line, especially during the time of peak power usage.[165] In addition, substations, while usually not an important source of magnetic fields, do provide a greater possibility of exposure to residences near those facilities because power lines converge at the substations and may be closer to the ground as they approach the substation.[166]

The neighborhood power lines are usually lower voltage distribution lines, not the transmission lines discussed above. As mentioned earlier, the distribution lines produce magnetic fields that are usually about five mG with densely populated areas sometimes measuring up to fifty mG.[167] Burying distribution lines does not necessarily decrease the magnetic field associated with the lines unless the lines are buried in a single metal pipe.[168] The other method of burying the lines is called direct burial, a method that can produce ground-level magnetic fields equal to overhead lines.[169]

Typical exposures to magnetic fields in the home and in the workplace have been studied.[170] While electric appliances cause the strongest magnetic fields in homes, grounding systems, power lines, or a combination of the two, produce fields referred to as "background magnetic fields" in the center of rooms away from most appliances.[171] One study of 992 homes showed that only five percent of the homes had average background magnetic fields greater than 2.9 mG.[172]

The strong magnetic fields produced in homes by electric appliances usually decrease rapidly with distance from the appliance. For example, one study reporting the range of magnetic field strengths of common household appliances showed that the magnetic fields of microwave ovens range from 100 to 300 mG at a distance of six inches and from one to 200 mG at a distance of one foot.[173] The study used measurements of rms fields that were averaged over one second or more for spot measurements and up to twenty-four hours for long-term and personal exposure measurements.[174] Another study showed that ninety-five percent of all of the 485 microwave ovens measured emitted magnetic fields less than seventeen mG at fifty-six centimeters (twenty-two and one-half inches).[175] Differences in design of appliances of the same type can cause different magnetic fields to be produced. Electric blankets have been a cause for concern about exposure to magnetic fields because when blankets are in use they are very close to internal organs, which lie about five centimeters from the surface of the blanket. When magnetic fields associated with conventional electric blankets are measured at that distance, the field strengths average about twenty-two mG.[176]

When personal exposure is measured, the fact that a person moves around the house or workplace means that the measurement is a combination of exposures to electric appliances, power lines, and grounding systems.[177] The office environment magnetic field measurements are similar to those for the home, however, personal exposure measurements are somewhat higher. This is probably caused by the more constant use of electric equipment and the proximity to that equipment at the workplace.[178]

The foregoing discussion of measuring exposure has been based on direct measurement by instruments of the electric and magnetic fields. Epidemiological studies use indirect methods of measuring magnetic fields and will be considered in the following section discussing the National Research Council Committee Report.[179]

The National Research Council is an agency of the National Academy of Sciences (NAS), granted a charter by Congress in 1863 with the mandate to advise the federal government on scientific and technical matters.[180] Under the charter of the NAS, the National Academy of Engineering was established in 1964 to share responsibility for advising the federal government.[181] In 1916 the NAS organized the National Research Council (NRC) for the purpose of associating the science and technology community with the Academy's purposes.[182] Since its establishment, the NRC has become the chief operating agency of both the NAS and the National Academy of Engineering. The NRC provides services to the government, the public, and the scientific and engineering communities.[183]

When the United States Department of Energy (DOE) requested that the NAS review the scientific evidence of potential health risk from exposure to the electric and magnetic fields generated by electric devices, the Committee on Possible Effects of Electromagnetic Fields on Biologic Systems (NRC Committee) was convened.[184] The charge to the NRC Committee from the DOE included: reviewing and evaluating the existing scientific information on the potential effects of exposure to electric and magnetic fields on cancer incidence, reproduction and development, and learning and behavior; critically examining epidemiological and laboratory data relating to those topics and assess potential health effects; focusing on electric- and magnetic-field frequencies and exposure modalities found in residential settings; and producing a report that contains a review of pertinent information on the effects of electric and magnetic fields; identification of research areas in which data are needed to better understand any potential health hazard; and recommendations for research in those areas and strategies for implementing research that would enhance understanding.[185] If data of appropriate quality is available, the NRC Committee should include a health risk assessment of power-frequency electric-field and magnetic-field exposures.[186]

As the charge reflects, the NRC Committee was to evaluate three categories of health hazards: carcinogenic effects, neurobehavioral effects, and reproductive effects.[187] After almost three years of study, the NRC Committee released its Report.

The NRC Report consists of an Executive Summary, an Introduction, and chapters on Exposure and Physical Interactions, Cellular and Molecular Effects, Animal and Tissue Effects, Epidemiology, Risk Assessment, and Research Needs and Agenda. Appended to the Report are tables summarizing various studies discussed in the Report and a discussion on "wire codes," or wiring configurations, used in some epidemiological studies instead of direct measurement of exposure.[188] The Executive Summary, Introduction, and the Exposure and Physical Interaction chapter are reflected in the materials above. The other chapters are discussed below.

The NRC Report discussed the published scientific studies of the effects on cells and molecules "in vitro" (in glass) of exposure to power frequency electric and magnetic fields.[189] Concluding that residential strength magnetic field exposures do not produce significant in vitro effects,[190] the NRC Report also specifically discussed effects on genotoxicity, signal-transduction pathways, intracellular calcium concentrations, and general patterns of gene expression.[191]

1. Heritable Changes in Cells Exposed In Vitro

Scientists often study the ill effects that certain environmental agents have on genes, or genotoxicity, by using cultured cells. Genotoxicity can be indicated by direct heritable changes such as mutation or chromosomal aberrations, or indications of heritable changes such as DNA damage or repair.[192] After reviewing twenty-nine published articles reporting effects of exposure to residential power, twenty-four of which used frequency of sinusoidal form, the NRC Committee concluded that power frequency electric and magnetic fields are not directly a genotoxic agent.[193]

2. Transient Changes to Cells Exposed In Vitro

Whereas the NRC Committee found no direct heritable changes, that is, no genotoxicity, in cells exposed in vitro to electric and magnetic fields, it did discuss the evidence that magnetic fields can induce transient changes in cell expression in three categories: signal transduction pathway changes, gene expression changes, and intracellular calcium level changes.[194]

a. Signal Transduction Changes

Signal transduction processes, in which molecular systems inside the cell and at the cell membrane receive signals from the environment and from other cells, provide a mechanism by which cell functions may be influenced by electric and magnetic fields.[195] Metabolic activities, gene expression, cell proliferation, and other intracellular processes are regulated by the signals received, therefore, if the electric and magnetic fields affect or change the path of the communication of signals (signal transduction changes), the function of the cell might be changed.[196] Signal transduction changes are a common result in experiments and such changes alone do not indicate an adverse effect.[197] Studies indicate that changes in membrane-transduction pathways are caused by low frequency electric and magnetic fields.[198] However, most of the studies have not been independently replicated, a requirement given great weight in reaching conclusions about the result of studies and experiments.[199]

One study that has been independently replicated by at least two laboratories[200] observed that magnetic field exposure produces changes in ornithine decarboxylase (ODC) activity, an enzyme involved as a cell membrane signal transduction pathway.[201] The significance of this observation is that ODC activity is associated with mitogen activity and the various activities of tumor-promoting agents during carcinogenesis. The observation led to the hypothesis that low strength electric fields acting on the cell membrane, while not causing cancer, might be a copromoter and act with another tumor-promoting agent to cause more growth of an existing cancer than the agent acting alone.[202]

Among the unreplicated studies examining the effects of magnetic fields on signal transduction pathways is a study suggesting a possible correlation between magnetic field exposure and the growth of cancer cells.[203] The cancer cells exposed to a twelve mG sinusoidal magnetic field at sixty Hz were human estrogen-responsive breast cancer cells, which grow rapidly in the presence of normal concentrations of estrogen, a female sex hormone.[204] The study confirmed that the growth rate decreases in the presence of normal concentrations of melatonin, a hormone produced by the pineal gland, but that exposure to the sixty Hz magnetic field at twelve mG prevented the melatonin's effect of decreasing the cancer cell growth rate.[205] No significant effect was observed when the strength of the magnetic field was lowered to two mG, leading to the suggestion that a threshold for effect might exist between two and twenty mG.[206]

The NRC Committee noted that if other laboratories replicated the above effects, an exception to the observation that cells in tissue culture are not significantly affected by residential strength magnetic fields would exist.[207] Stressing the need for independent replication of most of the studies in the area of signal transduction, the NRC Committee concluded that while evidence exists that fields of strengths greater than residential strength fields[208] probably do have an effect on signal-transduction-related pathways in cells, essentially no evidence exists for such effects at residential field strengths.[209]

b. Gene Expression Changes

Whether exposure to residential strength electric and magnetic fields might change DNA[210] structure or function has been studied. Most studies show that such a change is unlikely, however, a 1991 study[211] reported results showing an increase in transcription activity after brief exposures to fields at higher than residential strengths.[212] Other studies showing changes in gene expression followed,[213] but like the 1991 study, they were highly criticized because of a lack of method precision and a lack of consistent con trols, both external and internal.[214] The criticisms led two groups to attempt replication studies using improved experimental techniques and elaborate precautions.[215] Despite those efforts, the groups failed to replicate the gene expression effects that had been previously reported.[216] The NRC Committee concluded, "[e]vidence for electric- and magnetic-field effects on gene expression at residential field strengths is completely lacking."[217]

c. Calcium Changes

Calcium, as an inorganic ion that serves as a biochemical event messenger, is important in biological processes such as bone formation, muscle contraction, and synaptic transmission.[218] The concentration of calcium inside a cell regulates enzyme catalysts, thus serving as a second messenger in neural function.[219] Because calcium is so important in biological processes, any external agent causing calcium ions to flow into or out of the cell could have a significant effect on biological function.[220]

During the past two decades many studies have sought the effect that power frequency electric and magnetic fields have on calcium. The NRC Report summarized only such studies that had appeared in peer-reviewed journals from 1990 to October 15, 1994 in Table A3-2 in Appendix A.[221] The NRC Committee notes that, though most of the studies show some sort of positive association between calcium concentration changes and exposure to electric and magnetic fields, problems exist relating to explaining the results,[222] difficulty in observing the effects,[223] and inadequate replication.[224] Only three of the Table A3-2 studies have been replicated by independent laboratories, published in peer-reviewed journals, and have identified explicitly the exposure strengths used.[225] Having met those exacting requirements, the three studies, involving experiments showing an increase in calcium transport when thymic lymphocytes were exposed to pulsed magnetic fields having flux densities that were about 10,000 times greater than the average environmental flux densities, can be given more weight.[226]

The NRC Committee cautioned that results observed when the field strengths are higher than residential and workplace field strengths cannot be extrapolated to the lower field strengths since it is not known whether the mechanisms inducing the high field strength effects are the same as those at the lower strengths.[227] Therefore, based on its analysis of the in vitro experiments, the NRC Committee concluded that fifty to sixty Hz magnetic field exposures induce changes in cultured cells only when the field strengths are 1000 to 100,000 times that experienced at residential levels.[228]

Focusing on three areas of principal interest (carcinogenesis, reproduction and development, and neurobehavioral and neuro endocrine responses), the NRC Committee evaluated the published literature on the exposure of animals and tissues to power frequency electric and magnetic fields.[229] In considering this literature, the NRC Committee's criteria for the reported experiments included the following: the literature must be peer-reviewed; results must be exposure related; and results must be statistically significant; with the greatest weight being given to blinded studies[230] that were confirmed in peer-reviewed literature.[231]

The NRC Committee concluded that no convincing evidence exists that adverse health effects such as cancer, harm to reproduction and development, or behavior distortion are caused by exposure to power frequency electric and magnetic fields.[232] However, the NRC Committee did report evidence of a positive health effect associated with the healing of bones when the broken bones were exposed to higher-than-residential field strengths.[233]

Before summarizing more specifically the NRC Committee's conclusions in the areas mentioned above, a background discussion of the use of animals in studies evaluating risk to humans is appropriate. Animal studies, which are important in evaluating risk to humans from suspected toxic agents, are based on two principles: that the effects produced in the laboratory on animals apply to humans; and that exposing animals to the toxic agent in high doses is a valid method to discover possible hazards to humans.[234]

Other important assumptions in animal studies concern the "dose-response" relationship, a relationship forming the basis for toxicology that allows scientists to predict adverse health effects because of the expected predictable interactions between organisms and the toxic agent.[235] The assumptions regarding dose-response relationships include the following: the agent administered caused the response;[236] a relationship exists between the measurement of the dose and the response;[237] and means are available to measure and express toxicity precisely.[238] The foregoing assumptions are presumed to hold true for ELF fields if they indeed are found to be toxic agents.[239]

1. Carcinogenic and Mutagenic Effects

After presenting its conclusion that no convincing evidence exists that exposure to power frequency electric and magnetic fields causes cancer in animals,[240] the NRC Committee discussed the few peer-reviewed laboratory animal studies examining the issue of magnetic fields and cancer, summarized in the Report at Appendix A, Table A4-1.[241]

The experiments on animals examining the carcinogenic effects of exposure to power frequency electric or magnetic fields are either complete carcinogen studies, tumor-initiation studies, or tumor-promotion studies.[242] If an electric or magnetic field's potential to cause cancer development is being tested, then the field is being tested for its potential to be a complete carcinogen.[243] Such a study would need one and a half to two years of exposure of rats or mice to the field.[244] This would allow the animals to be observed for most of their life-spans, during which time exposure to confounding agents[245] must be minimized, and would require a large number of animals because several dosage groups should be included. The number of animals and the length of time involved cause complete carcinogenicity studies to be expensive; therefore, few such studies have been completed. Of three studies, which were studies of control groups exposed to magnetic fields without being exposed to a chemical initiator, and which were criticized by the NRC Committee for having inadequate group sizes, one found an increase in tumors while two found no increase in tumors.[246]

Along with the complete carcinogen approach to studying carcinogenicity, another approach is to assume that the suspected carcinogenic agent acts as either a cancer initiator or a cancer pro moter. Because carcinogenesis is considered a multi-step process, studies of two phases of the process, initiation and promotion, may be performed.[247] Initiation is a genotoxic event where a carcinogen affects the DNA directly.[248] Promotion is responsible for initiated cells changing to cancerous cells.[249] Initiation and promotion studies use less time, fewer animals, and are less expensive than complete carcinogenesis studies.[250] However, because the energies involved in power frequency electric and magnetic fields are too weak to break chemical bonds, and because the in vitro studies provide no evidence of DNA damage from exposure to residential strength fields, no tumor-initiation studies have been reported and few animal studies of tumor promotion have been completed.[251]

A few recent studies have investigated promotion of mammary tumors by exposure to magnetic fields.[252] In theses studies a chemical initiated the tumors, then the tumors were exposed to the magnetic field.[253] Though the studies have yet to be replicated and their results are inconsistent,[254] they seem to suggest a positive relationship between breast cancer in animals treated with a carcinogen and exposure to magnetic fields of about one Gauss.[255]

2. Reproductive and Developmental Effects

The NRC Committee next discussed the biological effects of residential strength electric and magnetic fields on reproduction and development. The NRC Committee considered the following types of studies: effects of electric fields on non-mammals such as fish[256] and chicken;[257] effects of electric fields on mammals such as mice,[258] rats,25[9] swine,26[0] and cattle;[261] effects of magnetic fields on non-mammals such as chicken;[262] and effects of magnetic fields on mammals such as mice[263] and rats.[264] Based on the studies, which are summarized in Appendix A, Table A4-2, the NRC Committee concluded that ELF electric or magnetic fields have not been shown to affect reproduction and development in animals, especially mammals.[265]

3. Neurobehavioral and Neuroendocrine Effects

The third area of concern to the NRC Committee is whether exposure to ELF electric and magnetic fields cause neurobehavioral effects or neuroendocrine effects. These effects were considered separately in the NRC Report.

a. Neurobehavioral Effects

The studies of neurobehavioral effects caused by exposure of animals to ELF electric and magnetic fields that meet the NRC Committee's requirements of publication in peer-reviewed journals and descriptions of methods adequate for replication are summarized in Appendix A, Tables A4-3 through A4-6.[266] Of those studies, only repeatable and reliable reports were discussed by the NRC Committee.[267] The NRC Committee considered the effect on animal detection of electric fields[268] and magnetic fields,[269] and whether animals would exhibit aversion to those fields.[270] The review of these studies produced two conclusions: although animals can detect and respond to electric fields, the behavioral response is not one of aversion nor are the effects adverse neurobehavioral ones; and little evidence exists of neurobehavioral response in animals to magnetic fields and neither aversive nor adverse behavioral effects have been shown.[271]

b. Neuroendocrine[272] Effects

Neuroendocrines consist of various glands in the body that produce hormones which influence nerve activity.[273] Most of the reported studies of the relationship between exposure to electric and magnetic fields and neuroendocrine effects have concerned pineal melatonin production and are summarized in Appendix A, Table A4-7 through Table A4-11.[274] Melatonin is a hormone in humans, and possibly all animals, produced mainly by the pineal gland.[275] The pineal gland, an end-organ of the visual system, has nerves whose activity is determined by light perception at the retina.[276] More melatonin is present during the night than during the day because more is produced in darkness than in light.[277] Melatonin is associated with circadian or biological rhythms of organisms.[278]

Visible light, as well as some ultraviolet wavelengths and some infrared wavelengths, have been shown to alter pineal melatonin production.[279] Residential strength electric and magnetic fields are of extremely low frequency, have long wavelengths, and are below the visible light range.[280] Studies considering the effects of electric fields on melatonin production in animals report suppression of melatonin concentrations,[281] as do studies considering the effects of magnetic fields[282] and studies considering the effects of combined electric and magnetic fields.[283] Humans have been found to have melatonin rhythms that are similar to those in other mammals.[284] However, two reports showed no significant change in blood mela tonin concentrations when adult males were exposed to the electric and magnetic fields of magnetic resonance imaging (MRI).[285]

Understanding how ELF fields affect melatonin production in humans is important because suppression of melatonin levels may be related to the higher cancer incidence reported by some epidemiological studies. The NRC Committee presents two theories that describe a link between the alleged increase in cancer and ELF field exposure:

[R]educed melatonin concentrations lead to an increased secretion of prolactin and gonadal steroids. That increase causes prolifera tion of cell division in breast or prostate tissue and stimulates growth of initiated cancer cells . . . . [M]elatonin suppression reduced the total antioxidative potential of the organism, thereby increasing the likelihood of damage by a carcinogen to the DNA of any cell. DNA damage can increase the risk of cancer particularly if electric- and magnetic-field exposure also increases the half-life production of free radicals.[286]

c. Bone Healing and Stimulated Cell Growth

Experiments considering the effects on bone tissue exposed to electric and magnetic fields have been conducted in vivo on animals[288] and humans.[289] In vitro studies of those effects have also been performed.[290] The studies show that normal functions of the bone and the healing processes in bone are influenced by exposure to electric and magnetic fields. Bone fracture healing in response to this exposure has been well documented,[291] but the mechanism by which this healing occurs is not clearly established.[292]

Bone in living organisms is known to possess an electric component,[293] and several hormones are known to regulate activities of the bone cells that synthesize and calcify bone matrix (osteoblasts) and the cells that reabsorb bone mineral and matrix (osteoclasts).[294] Bone growth has long been hypothesized to be influenced by endogenously generated electric fields; consequently, externally generated electric fields applied to bone fractures or defects have been hypothesized to be therapeutic.[295] Upon a review of the experiments testing the hypotheses, the NRC Committee concluded that convinc ing evidence exists of an association between bone-healing in animals and exposures to pulsed magnetic fields with strengths greater than five Gauss.[296] This field strength is much higher than that ordinarily encountered in residential environments.[297]

Few of the laboratory experiments considering the effects of electric and magnetic field exposure on animals were studies of humans.[298] Humans, however, are the subjects of all epidemiological studies because epidemiology is "the study of patterns of health and disease in human populations to understand causes and identify methods of prevention."[299] Since 1979 when Nancy Wertheimer and Edward Leeper first reported an association between childhood leukemia and electric power distribution line configurations,[300] the question most frequently asked by the public and one that has caused the greatest concern relative to electric and magnetic fields is: "Do they cause cancer?" DOE's charge to the NRC Committee included the mandate to review and evaluate existing evidence on the effect of exposure to residential ELF on the incidence of cancer.[301] Consequently, the NRC Committee reviewed and evaluated more than fifteen years of epidemiological research providing data on cancer in its Report.[302]

Determining whether exposure to electric and magnetic fields causes cancer based on the results of epidemiological studies is a problem because epidemiological research involves studies of observations to which statistical methods are applied, but which lack the ability to assign exposure in a random manner. As the NRC Committee Report explains:

Without randomly assigning the potential causes of interest (e.g., magnetic-field exposure) and observing the resulting health event (e.g., a change in cancer incidence), a mistaken inference that a given exposure causes a specific disease can result from a number of potential errors or misinterpretations. Conversely, even when a true causal relationship is present, it will not always be discerned easily. Ultimately, causal inference is enhanced when a number of non-causal explanations have been carefully postulated, tested, and refuted.[303]

When epidemiological studies report an association between exposure and disease, as indicated above, a judgment must be made that sufficient evidence exists to justify the acceptance of a causal association. Several criteria have been suggested that bear on the question of causality and also relate to whether errors described above have affected the study. The criteria are:

Strength of association: If a given exposure and disease are strongly associated (i.e., a large relative risk), then unrecognized confounders are less likely to be responsible for the association;

Consistency: If the association is observed in different populations under different circumstances, it is more likely to be a causal relationship and not a product of some methodologic artifact in the study;

Specificity: A cause should lead to a single effect rather than multiple effects; if multiple diseases are associated with a suspected agent, the associations are more likely to be spurious;

Temporality: The exposure must logically precede the disease in time if the association is causal;

Biologic gradient: A dose-response gradient, in which risk of disease rises with increasing exposure level, is generally more likely to indicate causality than some other pattern of association between exposure and disease;

Plausibility: Plausibility refers to whether the association is supported by scientific studies or information from disciplines other than epidemiology;

Coherence: A causal interpretation should not be in conflict with current knowledge about the natural history of the disease. This criterion is virtually the same as plausibility;

Experimental evidence: When possible, experimental evidence in the form of randomized trials with prescribed exposures is highly desirable;

Analogy: If other known and accepted causal agents have been found that are similar to the one under evaluation in their manner of action on the biologic system, then the one under evaluation is more likely to be causal.[309]

Epidemiological studies have persistently reported an association between the incidence of childhood leukemia and "wire codes," a hypothetical estimate of electric and magnetic field exposure.[311] Wire codes are external wire configurations that are used to classify houses according to the amount of magnetic flux density expected to be inside the house.[312] Wire codes are used as substitutes to estimate the size of the magnetic field rather than actually measuring magnetic flux density inside the house.[313] Because the studies are of homes over a period of years retrospectively, actually measuring the magnetic fields inside the homes is too difficult, too expensive, and too time consuming.[314] Wire codes of various classifications,[315] consisting of outdoor factors such as the distance of the home from the power line and the size of the wire near the home, were first used by Wertheimer and Leeper[316] in their study of childhood cancer occurring in Denver, Colorado between 1950 and 1973. The results of that study, which showed an association between electric power distribution lines and childhood cancers, were published in 1979.[317] The 1979 Wertheimer and Leeper study was of 344 cases (children with a Colorado birth certificate who lived in the area most of their lives and who also died of cancer under the age of nineteen between 1950 and 1973) in 491 homes compared to 344 controls (children whose birth certificate was placed next in the birth certificate files unless the next birth certificate was that of a sibling of a case child) in 472 homes.[318] The homes were classified according to two wire codes, High Current Configuration (HCC) and Low Current Configuration (LCC).[319] The results of the study showed that children in HCC homes had a 1.6 to 2.2 times higher incidence of cancer than did the controls.[320] One study has shown that the expected number of cases of childhood leukemia in children up to the age of fourteen is about ten in 100,000.[321] The results in the 1979 Wertheimer and Leeper study mean that the risk to children exposed to HCC wiring configurations is about doubled, or twenty in 100,000. The study accounted for the possible confounders of socioeconomic class, family pattern, and traffic congestion near the homes, but not other possible confounders or bias-causing factors.[322] Consequently, the study has been widely criticized,[323] among other reasons, for its use of wire codes to measure exposure, for its consideration of cancer deaths only and not all diagnosed cancers, and for failing to conduct the study "blind."[324]

Since the 1979 Wertheimer and Leeper study, other researchers have examined the possible association between residential exposure to electric and magnetic fields and the incidence of cancer.[325] The NRC Report organized the results of these studies into tables in Appendix A thus: Table A5-1 summarizes the structures of the studies; Table A5-2 summarizes the methods of control selection in case-control studies; Table A5-3 summarizes exposure assessment approaches; Table A5-4 focuses on childhood leukemia; Table A5-5 focuses on childhood brain tumors; Table A5-6 focuses on childhood lymphoma; Table A5-7 focuses on other childhood cancers; Table A5-8 focuses on childhood cancers in the aggregate; Table A5-9 focuses on cohort studies of residential exposure and cancer including all ages; Table A5-10 focuses on adult leukemia; and Table A5-11 focuses on adult cancers generally.[326] The NRC Committee noted its recognition that increasingly sophisticated study designs have replicated the association between location near power lines and childhood leukemia and its determination to concentrate on studies concerning exposure to magnetic fields and the occurrence of childhood leukemia.[327]

The NRC Committee reviewed the studies of the association between exposure to magnetic fields and the incidence of childhood leukemia by undertaking a "meta-analysis," which is "a statistical method used to provide a single risk estimate that summarizes the results of a set of similar studies."[328] Of the twelve studies focusing on childhood leukemia, results have been conflicting with some reporting an association between childhood leukemia and residential exposure and some reporting no association.[329] The reaction of scientists examining the evidence has also been conflicting; the disagreements concerning quality, bias, accuracy, and uncertainties have resulted in varying interpretations. Some find evidence of an overall association;[330] others consider the positive results to be caused by bias, either systematic or random with no proper adjustment made for multiple comparisons, with most concluding that no consistent pattern of association has been shown by the results.[331] The NRC Committee's goal in using the meta-analysis included the following:

(1) to examine quantitatively the consistency of the existing epidemiologic studies; (2) to analyze the influence of any single study on the combined effect measures; and (3) to estimate the sample size or number of studies needed to balance the combined results of previous studies. In short, the purpose of this meta-analysis is to consider the possible role of bias due to random error as an explanation for the observed results in a set of such studies.[332]

The magnitude of the possible risk was also uncertain, however, the overall conclusion was that the studies do show an association of childhood leukemia with wire codes, proximity to source, and magnetic fields calculated from power consumption records.[335] The NRC Committee remained puzzled by the inconsistent results of the various studies and also by the lack of a positive association when the exposure was assessed by spot measurements.[336]

The only exposure assessment strategy of the epidemiological studies analyzed that failed to show an association with childhood leukemia was that of spot measurements of magnetic field strength.[337] Another contradiction was the failure of the data to indicate a consistent dose-response relationship.[338] The NRC Committee noted two possible explanations for the spot measurement contradiction if the associations shown by the other exposure assessment strategies were reliable. One explanation is that the other ways to measure exposure might somehow indicate the true risk factor, which might not be related to magnetic field strength.[339] The other explanation is that measurement methods might better represent some element of magnetic field strength that is related to the cause of leukemia.[340] The inconsistent dose-response relationship pattern might be caused by an imperfect correlation with the true risk factor.[341] The NRC Committee suggested that future studies should try to understand these inconsistencies and stressed that "strong and consistent" data suggests "a relatively weak increased risk of leukemia for children living in close proximity to power lines."[342]

The NRC Committee summarized its analysis of the research linking electrical wires near homes to childhood cancer as falling "short of providing definitive evidence that an association exists, and even if an association were proved, the causal agent has not been identified."[343] They also recognized suggestions of bias caused by control selection or too small a number of subjects in some studies.[344] The NRC Committee based its overall conclusion of no association between exposure to magnetic fields and childhood cancer (which seems to be in conflict with its recognition of a link between wire codes and childhood leukemia), on the fact that those epidemiological studies estimating exposure to magnetic fields by measuring present-day average magnetic fields found no association between exposure and childhood leukemia and on the weak association between measured residential magnetic fields and wire code ratings.[345]

A further conclusion of the NRC Committee was that associations between magnetic fields and adult cancers, pregnancy outcome, and neurobehavioral disorders were not supported by epidemiological studies.[346] After examining the epidemiological studies, the studies of animal and tissue effects, and those of cellular and molecular effects, the NRC Committee assessed the risk to human health from exposure to electric and magnetic fields.

The NRC Committee used a method called "risk assessment" to evaluate the risk to human health from exposure to residential electric and magnetic fields. When some hazard is thought to exist because of results observed in a study, for example, rats developing more cancerous tumors when fed a large amount of saccharin, the risk assessor attempts to estimate the risk to human health by extrapolation. Risk assessment is based on the principle that health effect data obtained from studying a small number of subjects that have been exposed to a high concentration of a suspected hazardous agent can by extrapolation predict the health effects in a large number of subjects that have been exposed to a lesser concentration of that agent.[347] In the example above, the estimate might be that some specific number of persons ingesting a specific quantity of saccharin will develop cancer.[348]

The four stages of risk assessment are hazard identification,[349] dose-response assessment,[350] exposure assessment,[351] and risk char acterization.[352] Risk characterization is quantitative in that it results in an estimate of the number or proportion (for example, one in one million) of the population that might be adversely affected.[353] The assessor "weighs" the evidence at each stage of the process, with well-designed studies being given more weight than studies with weaknesses in some areas.[354] At the conclusion of the assessment process, all evidence is weighed together to produce an overall conclusion about risk assessment.[355] If all four stages of a risk assessment are used ending in a quantitative risk estimate, the risk assessment is a complete one.[356] If only some of the stages are used, the assessment is said to be a partial one.[357] Whether the assessment is complete or partial depends upon the available data and the purpose of the risk assessment.[358]

The NRC Committee did not perform a complete assessment of the risks of exposure to residential power frequency electric and magnetic fields because of uncertain data.[359] The NRC Committee did use the framework of risk assessment to perform a limited assessment because it recognized the public concern over the possible risks of exposure to residential electric and magnetic fields.[360]

Within the risk assessment framework and concentrating primarily on the risk of childhood cancer, the NRC Committee reviewed its previous conclusions. Under "Hazard Identification," the conclusions included the following: "no consistent or convincing evidence exists of effects" of typical residential electric- and magnetic-field exposure on cultured cells implying a human health effect at that exposure level;[361] "no consistent or convincing evidence" exists of that typical exposure on whole animals implying a human health effect, though neurobehavioral and neuroendocrine changes not considered evidence of adverse health effects on humans have occurred in response to much higher exposure levels;[362] and "a moderately consistent, statistically significant association between wire codes, . . . and childhood leukemia" exists.[363] Under "Dose-Response Assessment," the NRC Committee concluded that the data did not furnish evidence of a dose-response relationship convincing enough for development of a mathematical model.[364]

Under "Exposure Assessment," the NRC Committee acknowledged the universal and unavoidable daily exposure of the popula tion to electric and magnetic fields.[365] This universal exposure would mandate the consideration of how even a very small proven adverse effect would affect public health.[366] Under "Risk Charac terization," the NRC Committee concluded that "the effects of exposure to electric and magnetic fields on biologic systems are either negative or so uncertain that making such an estimate would be injudicious and misleading."[367] Furthermore, the relationship that is assumed to exist between electric and magnetic field exposure and adverse health effects has not been explained in a biologically plausible manner.[368]

Finally under "Overall Conclusions of Risk Assessment," the NRC Committee concluded that the evidence examined by it did not demonstrate that ELF electric and magnetic field exposure constitutes a human health hazard.[369] Only the epidemiological studies of humans suggest adverse health effects with the results of those studies indicating relatively small risks as compared to other harmful exposures studied by epidemiologists.[370] However, uncertainty about the validity of using wire codes as a surrogate for magnetic ex posure, as well as other unresolved questions about epidemiological and laboratory findings, suggest a need for further research.[371]

The NRC Committee proposed areas of research needed to resolve the remaining uncertainties. The epidemiological studies' findings of an association between exposure to electric and magnetic fields and cancer, especially childhood leukemia, are the primary reason the public became concerned about the possible adverse health effects. Thus, epidemiological studies using wire codes should be conducted in a manner designed to eliminate control-selection bias and imprecision.[372] Possible confounders relating to wire codes and other risk factors for childhood cancer should be tested. In addition, more knowledge about sources of magnetic fields is needed, especially how outside wires relate to magnetic fields inside the homes and whether wire codes are representing some other source of exposure. The NRC Committee recommended improved studies of measured residential magnetic fields and sources of magnetic fields other than power lines.[373]

In addition to proposing epidemiological research, the NRC Committee recommended additional laboratory research. While recommending improved engineering techniques for measuring exposure, the NRC Committee stressed the need for a plausible biological explanation to account for an association between expo sure to electric and magnetic fields and adverse health effects.[374] Among the possible productive areas of research for laboratories suggested were studies of bone-healing, studies of in vitro dose-response, and studies of the role that magnetic fields play as a promoter of initiated cancers or when combined with chemical carcinogens.[375]

Finally, the NRC Committee recognized that its work and all the other work supported by the Energy Policy Act of 1992 is not expected to answer all questions relating to the possible health effects of ELF electric and magnetic field exposure. The five-year program ended in 1997. Beyond that time, continued research is important.[376]

The long-awaited National Research Council Report on the possible health effects of exposure to the electric and magnetic fields which people encounter daily in their homes and places of work concludes that the current evidence does not show that such exposure presents a health hazard. The report also stresses the importance of continued research in this area of possible health effects. The law has been affected by public alarm at the possibility of electric and magnetic fields causing dreaded illnesses such as cancer, and in the devaluation of property in condemnation cases; power line siting controversies; and the causation of ill health effects as the basis of tort litigation. The NRC Report cautions that causation of health hazards has not been demonstrated in any study; even epidemiological studies reporting an association are not reporting causation.

The bottom line of the report appears to reflect an evolutionary point of the law in these areas. Rare damage awards in tort litigation reflect the lack of causal proof between EMF and adverse health effects.[377] Since land value is affected by public opinion, and the public perception is that EMF is a risk to health, damages for property devaluation have been awarded in some cases. Power line siting controversies are often driven by public opinion of risk, and the law has sometimes responded to that public opinion. Given this, society must to assess the NRC Report's potential impact on public perception of EMF and its relative health risks.

Although the report reflects a comprehensive study of the issue and is the latest scientific consensus on the issue, the NRC Report is not likely to have a great effect on the public perception that EMF is a health hazard because public perception is driven by emotion and often varies from reality. Even if electric and magnetic fields do not present a substantial risk to public health, land values near power lines will be affected because the public is unlikely to believe the report.

Public perception of risk is influenced by several factors including: voluntariness, control, fairness, process, morality, familiarity, memorability, dread, and diffusion in time and space.[378] If a person acts voluntarily, such as smoking a cigarette or using a cellular telephone, that person is less likely to perceive a risk from those acts. Related to voluntariness is control. A person is less likely to perceive risk from sources of exposure over which that person exercises control.

When a result seems unfair, a person is likely to associate it with risk. For example, having the air that the public breathes polluted by a factory seems unfair, so the air pollution is more likely perceived as a risk. When morality is involved, as in child abuse, the action is more likely perceived as a risk. Familiarity also influences risk per ception. The mysterious and complex nature of electric and magnetic fields make them more likely viewed as a risk because people tend to fear what they do not understand.

The memorability of an event, such as Three Mile Island or Chernobyl, causes a greater perception of risk. These memorable events heightened the public's fear of nuclear fallout. Dread of something also causes an increased perception of risk. The dread of contracting cancer underlies the public perception of the risk EMF cause. Moreover, electric and magnetic fields are here today. Unlike risks occurring in the past or at a distant place, the exposure to these fields is ongoing, increasing the perception of risk.[379]

Ultimately, as long as the public believes that electric and magnetic fields are a health risk, effects of that perception will remain. The devaluation of land located near electric and magnetic fields will likely continue because the perception makes the land less desirable. Controversies over power line siting will continue because of the public perception of risk associated with the EMF emanating from them. Moreover, the conclusions of the NRC Report tend to make proof of causation even more difficult.[380] This will keep the number of damage awards in EMF-based tort litigation at a minimum.

Public perception about the risk of EMF exposure will change only when the public's underlying beliefs are changed. Power companies, health departments, and other entities with an interest in changing the public perception of risk must undertake information dissemination programs to educate the public about the true risks of electric and magnetic fields. Of course, no meaningful education programs can occur until further research is done to ascertain the true risk of electric and magnetic fields. Until research can prove conclusively that electric and magnetic fields pose no real threat to human health, fear, in all of its manifestations, will remain.