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Radio frequency (RF) and microwave (MW) field intensities are usually measured in milliwatts per square centimeter (mW/cm2). However, the intensity provides little information on the biological consequence unless the amount of energy absorbed by the irradiated object is known. This is generally given as the specific absorption rate (SAR), which is the rate of energy absorbed by a unit mass (e.g., one kg or one g of tissue) of the object. The unit of measurement for the SAR is watts per kg (W/kg).
The rate of absorption and distribution of RF/MW energies depend on many factors like type and shape of tissue, orientation relative to the radiation, type and parameters of the radiation, etc. The distribution of absorbed energy in an irradiated organism is extremely complex and non-uniform, and may lead to the formation of so called "hot spots" of concentrated energy in the tissue.
Present US safety standards related to RF/MW EMF are based on thermal (heating) effects. The first standard adopted was derived largely from the work of the engineer Herman Schwan who, although not a biologist, assumed that heating was the only effect EMFs would have on living tissue. In the 1950s Schwan worked for the US Department of Defense, estimating danger levels based on how much radar MW energy was needed to measurably heat metal balls and beakers of salt water, which he used to represent the size and presumed electrical characteristics of various animals.
Appreciable heating occurred in these models only at levels of 100 mW/cm2 or above, so, incorporating a safety factor of ten, Schwan in 1953 proposed an exposure limit of 10 mW/cm2 for humans. No one ever tested for subtler effects, and the 10 mW/cm2 level was uncritically accepted on an informal basis by industry and the military. In 1966 the American National Standards Institute (ANSI) recommended it as a guideline for worker safety [ref. 5].
Later, in the late 1980s and the early 1990s, the models used for establishing safety standards became more sophisticated, but the safety limits did not change much. In the UK, the 10 mW/cm2 still applies at a distance of 5 cm from the source for up to 2 minutes in any one hour – or a short term exposure of 25 mW/cm2. In the US, the following power density standards have been defined: around 0.579 mW/cm2 for 800-900 MHz cell phones, 1 mW/cm2 for PCS (public exposure), and 5 mW/cm2 for PCS (occupational exposure). The US ANSI/IEEE applicable standard measured in SAR is, for one gram of tissue, 1.6 W/Kg for "uncontrolled" (general public) environments, and 8 W/Kg for "controlled" (workplace) environments. In Europe the standard limit is 2 W/kg for the general public. In Japan the standard is 8 W/kg for the general public.
Although it may be more relevant to use SAR, it is much more difficult to measure and control, requiring the use of "phantom-heads", models of human heads. Of course, these can never be identical to "real" human heads.
Also for RF/MW exposures, research has demonstrated significant RF/MW induced effects on cells and animals at exposure intensities thousands of times below the various standard safety limits. Some examples: in 1997 the Danish scientists Kwee and Raskmark [ref. 6] reported changes in human cell proliferation rates at SARs of 0.000021-0.0021 W/kg; Magras and Xenos in 1997 reported a decrease in reproductive functions in mice exposed to RF/MW of intensity at 0.00016-0.001053 mW/cm2 [ref. 7]; Ray and Behari (1990) reported decrease in eating and drinking behavior in rats exposed to 0.0317 W/kg [ref. 8]; Dutta et al. (1989) reported changes in calcium metabolism in cells exposed to 0.05-0.005 W/kg [ref. 9]; and Phillips et al. (1998) observed DNA damage at 0.024-0.0024 W/Kg [ref. 10].
In December 1998, Dr. Hyland of the University of Warwick, UK, at the International Institute of Biophysics, Neuss-Holzheim, Germany, [ref.11] presented an attempt to draw attention to "a multitude of frequency-specific, non-thermal bioeffects – induced in living systems by ultra-low-intensity microwave radiation – the existence of which is not currently taken into account in the formulation of the safety limits to which microwave devices must conform".
Other scientists representing decades of practical experience within the field of RF/MW induced biological effects, Dr. Henry Lai of University of Washington, Seattle and Dr. Neil Cherry of Lincoln University, New Zealand, have found low-level effects and have reviewed the scientific literature, addressing a multitude of scientific evidence of low-level RF/MW induced bioeffects in cells and animals, neurological effects in humans and elevated risks of cancer in humans. The scientists setting the standard safety limits have chosen to disregard such evidence, showing that EMF induced effects may be cumulative, (DNA damage).
The primary sources of RF/MW exposures are mobile phones, personal communication systems (PCS), mobile phone and PCS antenna towers, TV and radio broadcasting antennas, radar equipment, and two-way radios.
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