The Current Science
Wireless phones fall broadly into 2 categories: cellular phones and personal communication system (PCS) phones. Both technologies employ radio frequency radiation (RFR) at a specific wave frequency to transmit voice messages via an antenna located on the phone. Cellular phones operate at between 824-894 megahertz (MHz) and emit either analog or digital signals. Analog phones produce a signal whose strength or frequency can vary over a defined range, but whose wave is continuous. With analog phones, voice messages are sent by varying either the wave's height or the number of waves per second. Digital phones produce a signal whose strength or frequency can vary in discrete steps. With digital technology, voice messages are sent in a series of rapid bursts or pulses to enable a greater density of users. Digital waves are pulsed. PCS phones in the United States operate in the 1800-2000 MHz range, and are primarily digital. Global System Mobile (GSM) is the digital standard that operates worldwide outside of the United States. From a public health perspective, the signals from each of these technology types are more similar than different in terms of biological impact.[14]
The first questions about the potential for cellular phones to cause brain cancer were raised in 1993. The clinical observation by a Florida neurologist, Dr. David Perlmutter, that his patient's brain tumor was located in an area where RFR from her cellular phone's antenna would be deposited, made international news after he aired his hypothesis, on CNN's Larry King Live television show, that use of the phone caused the tumor (Perlmutter D, personal communication). Biological bases for Perlmutter's hypothesis were derived from studies conducted by Dr. Stephen Cleary of the Medical College of Virginia, Richmond, showing a proliferation of tumor cells cultured in vitro following exposure to radio frequency radiation (RFR).[15,16]
At that time, most scientists believed that the low power pushing cellular phone signals was insufficient to cause heating of biological tissue, the only known mechanistic underpinning of RFR damage. The combined observations of Perlmutter and Cleary were met with skepticism. Because Dr. Cleary was not able to quantify the degree of heating in his experimental system, scientists believed his findings were artifacts due to the uncontrolled heating of the tumor cells.[17] Without a biological basis, the observation by Dr. Perlmutter that the tumor in his patient was proximal to the area exposed to RFR from the cell phone antenna was considered by many to be an artifact as well. Nonetheless, these observations raised questions that confused the public and alarmed the Congress, and led to the ambitious $27 million dollar surveillance and research effort funded by the wireless industry, later known as the Wireless Technology Research (WTR) program.[13]
In late 1994, Lai and Singh reported on their observation that rats whose whole bodies were exposed to microwaves similar in intensity to those radiating from a cellular phone antenna appeared to experience single-strand DNA breakage as a result of the exposure. The following year they published a similar report suggesting double-strand DNA breaks in the same exposure scenario. Lai and Singh had adapted the traditionally in vitro single-cell gel (SCG) assay to an in vivo situation. This adaptation had not been validated in other laboratories, so interpretation of these findings with respect to scientific validity was difficult.[18,19,20,21,22,23,24,25,26,27] In addition; the whole body microwave (2450 MHz) exposure approach of the investigators was sufficiently different from actual human cell phone exposure (ie, head only) to render their results not interpretable with respect to human cell phone usage.[28,29,30,31,32,33,34] Further, studies of the dosimetry of cell phone emissions suggested that the antenna from a cellular phone would emit insufficient energy to break the base pair bonds holding DNA together, thus casting further doubt on the relevance of these findings to human cellular phone usage. During the ensuing 2 years, spurred on in part by the perceived shortcomings of these earlier studies, scientists pursuing biological effects focused on the development of both in vitro and in vivo exposure systems that were capable of providing information directly relevant to humans using wireless phones[35,36,37,38] (Lee PS. Evaluation of radiofrequency radiation (RFR) in the L5178Y mouse lymphoma cell tk+/--tk-/- gene mutation assay. Submitted for publication). These focused efforts included adaptations that provided for uniform fields of exposure and heating controls for in vitro experiments and head-concentrated exposures for experiments using animals. With these new and directly relevant exposure systems now available, subsequent findings had to be looked at more seriously with respect to human health risk.
In 1997, Adey and colleagues[21] were the first to report biological effects in rats exposed head first to cellular phone-mediated RFR. While these data did not indicate a hazard from the RFR exposure, indeed they suggested a protective effect against tumors; this represented the first well-controlled study showing biological effects from RFR exposure that were not heat induced.
Later in the same year, Repacholi[39] reported that genetically engineered mice (in this case, specific mice that are predisposed to malignant tumor formation at an increased rate) exposed whole body to RFR exhibited an increase in lymphoma. Repacholi's findings were met with skepticism because it was unclear what dose of RFR the mice in the experiment sustained, and thus, relevance to humans using wireless phones was unclear. In addition, the tumor excess he observed occurred near the end of the life expectancy of the mice, at around 18 months, and the transgenic model employed was traditionally used for only a 6-month exposure.[40,41]
Worldwide, several in vitro and in vivo experiments have been published addressing potential biological effects from wireless signals. Table 1 presents an overview of the most recent laboratory research and Table 2 summarizes the most recent epidemiology. One epidemiology study published after this table was created is a Motorola-funded study conducted by Morgan and associates.[42] This study does not support an association between occupational RF exposure and brain cancers or lymphoma/leukemia. Exposure was measured qualitatively through the use of job titles to create a job exposure matrix. While occupational studies are informative, this study could not address real-life exposure from cellular telephones and is thus limited in its generalizability.
It is important to note in reviewing these data that only the WTR-sponsored studies presented herein employed the exposure systems developed specifically to allow extrapolation of results from experimental systems to people using wireless phones.
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Cite this: Scientific Progress - Wireless Phones and Brain Cancer: Current State of the Science - Medscape - Jul 31, 2000.
