"Animal Facility

The animal cages were contained in a room (6.10 m 􏰄 4.57 m) with independent temperature, humidity, ventilation and lighting control. Room temperature was maintained at 24 􏰆 1􏰇C, with relative humidity at 50 􏰆 10%. The air flow rate was constant at 18 exchanges/h. A time- controlled lighting system provided a 12 h/12 h light/dark cycle (lights on at 0600). An illumination level of 325 lux at 1.0 m above the floor was provided by fluorescent fixtures.

Animal Housing

Each cage housed two mice and allowed both animals free access to food and water. The cages were constructed entirely of Plexiglas􏰁 with a center partition to separate the mice and with 5.0-mm rods on the floor, spaced 0.75 cm apart. The rods provided adequate animal support and allowed feces and urine to fall into a disposal tray beneath the cage. The cages provided a floor area of 143 cm2 per animal, which is significantly greater than that required by the Guide for the Care and Use of Labo- ratory Animals. Observations twice a day indicated no preferred position of animals within the cages.

Animal Husbandry

The mice were provided with certified Purina Rodent Chow and water ad libitum. A stairway attached to the center partition of each cage al- lowed the mice to share a common water source. No evaluation of food and water consumption was performed during this project.

On each day, Monday through Friday, a set of 20 cages were changed. On those days, 40 mice were removed from their cages, weighed, pal- pated, visually inspected and returned to clean cages. Water bottles were changed biweekly. Waste disposal trays underneath each cage were changed weekly along with the cages. All soiled cages, trays and watering

been discussed previously (6, 7). Smith and Oughstun (8), however, recently stated that UWB pulses could have im- portant biological effects. Such effects were postulated by those authors to be due to the emergence of precursor elec- tric fields associated with UWB propagation through tissue, thereby generating extra heat at certain depths (where none would be generated by the main UWB signal). Studies of the effects of UWB pulses on a wide range of biological systems have been summarized elsewhere (9–11).

It has been suggested that chronic, low-level exposure to RF radiation induces or promotes tumorigenesis in mam- mals. There have been few well-controlled epidemiological studies relative to this topic, as reviewed previously (12). These results provide only limited information on cancer risk. In the absence of adequate data from epidemiological studies, long-term investigations using laboratory animals may help to identify potential carcinogens. The great ma- jority of known human carcinogens are also carcinogenic in long-term rodent bioassays (13). Most studies of RF ra- diation have found no significant genotoxicity (14). Con- sequently, most investigators believe that, if electromag- netic fields (including RF radiation) do increase cancer in- cidence, the result is due to promotion rather than initiation (e.g. ref. 15). Indeed, Moulder et al. (14) noted that, on the basis of biophysical aspects, there is no reason to even sus- pect causation of cancer by RF radiation.

A few previous studies investigated RF radiation and mammary tumor incidence. In a study by Szmigielski et al. (16), mammary tumor-prone mice (C3H/HeA) were ex- posed to 2450 MHz RF radiation at 5 or 15 mW/cm2 for 2 h/day, 6 days/week, for various numbers of months. Mice irradiated for 3 months developed mammary tumors sig- nificantly earlier and in slightly greater numbers than did sham controls. In several other recently completed studies of chronic exposure to RF radiation, however, there were no significant effects on mammary tumor incidence (17– 20). Although the frequencies, power densities and expo- sure conditions used in these experiments were different, the animal model was the same, the end points were essen- tially the same, and all three studies achieved similar re- sults. Long-term, low-level exposure to microwaves did not affect mammary tumor incidence, latency to mammary tu- mor onset, mammary tumor growth rate, or animal surviv- al, when compared to sham controls. Another study showed no significant effects of chronic RF irradiation on the de- velopment of 7,12-dimethylbenz[a]anthracene-induced mammary tumors in Sprague-Dawley rats (20).

The latter studies mentioned above (17–20) involved ex- posure to discrete single frequencies of RF radiation (435, 900 or 2450 MHz). The current study was designed to in- vestigate potential mammary tumor-promoting effects of repeated exposure to UWB pulses with a rise time of 176 ps and a peak E field of 40 kV/m. Unlike previous studies of the biological effects of conventional RF energy (in which hundreds of animals could be exposed continuously in circular wave guides), only two animals at a time could devices were sanitized in a commercial cage and bottle washer (wash and rinse cycles 􏰃82.2􏰇C). Animal weights were obtained with a computer- ized, automated animal weight recording system used in previous studies (18, 19). All animals were inspected visually twice daily, once between 0800 and 0900 and again between 1400 and 1500."

C3H/HeJ mice, female

HAWC