Lack of promoting effects of the electromagnetic near-field used for cellular phones (929.2 MHz) on rat liver carcinogenesis in a medium- term liver bioassay

Abstract

The possible cancer promotion potential of local exposure to a pulse modulated 929.2 MHz electromagnetic near-field on chemically-initiated rat liver carcinogenesis was investigated employing a medium-term bioassay. A 929.2-MHz electromagnetic near-field of time division multiple access (TDMA) signal for PDC (Personal Digital Cellular, Japanese cellular telephone standard) system was directed to rats through a quarter-wavelength monopole antenna. Maximum local specific absorption rates (SARs) on temporal average were 7.2-6.6 W/kg within the whole body and 2.0-1.7 W/kg within the liver, which was the target organ. The whole-body average SARs on temporal average were 0.80-0.58 W/kg. Temporal peak SARs had three times these values due to the duty ratio of the PDC signal. Exposure was for 90 min a day, 5 days a week, over 6 weeks. The exposure apparatus was specially designed for this experiment, to allow exposure of the lateral mid-section of the rat body to the electromagnetic near-field. Male F344 rats, 6 week-old, were initially (at week 0) given a single dose of diethylnitrosamine (DEN, 200 mg/kg body wt, i.p.). At 2 weeks later, exposure (48 rats) or sham-exposure (48 rats) was started. The exposure of electromagnetic near-fields was performed using the exposure apparatus mentioned above. At week 3, all rats were subjected to a 2/3 partial hepatectomy. At week 8 (i.e. after 6 weeks exposure or sham-exposure), the experiment was terminated and all rats were killed. Carcinogenic potential was scored by comparing the numbers and areas of the induced glutathione S-transferase placental form (GST-P) positive foci in the livers of the exposed and sham-exposed rats. A further group of 24 animals, given only DEN and partial hepatectomy, served as the controls. The numbers (no./cm2) of GST-P positive foci were 4.61 +/- 1.77, 5.21 +/- 1.92 (P < 0.05, versus control) and 4.09 +/- 1.47 and the areas (mm2/cm2) were 0.30 +/- 0.16, 0.36 +/- 0.21 and 0.28 +/- 0.15, for the exposed, sham-exposed and control groups, respectively. There were no significant differences between the exposed and sham-exposed groups. These findings clearly indicated that local body exposure to a 929.2-MHz field, modulated in a PDC waveform, has no significant effect on rat liver carcinogenesis under the experimental conditions employed.

The 1.5 GHz Electromagnetic Near‐field Used for Cellular Phones Does Not Promote Rat Liver Carcinogenesis in a Medium‐term Liver Bioassay

“…Comparison of numbers and areas of GST-P-positive liver foci in rats exposed to 929. using the same rat liver medium-term bioassay did not demonstrate any enhancement of preneoplastic lesion development. 16) In the present study, an EMF of 1.439 GHz pulse modulated microwaves also did not enhance the appearance of GST-P-positive liver foci, the numbers in the EMF-exposed group, in fact, being significantly lower than in the sham-exposed group. These data clearly showed that exposure to an EMF of either 929.2 MHz or 1.439 GHz as used in cellular phones in Japan does not have any promoting potential on rat liver preneoplastic lesion development.…”

“…In our previous experiment, 16) corticosterone and ACTH levels in serum were significantly increased in both EMFexposed and sham-exposed groups. The reason for this was speculated to be the elevation of body temperature of the rats in the exposure box.…”

“…The exposure apparatus was specially designed, 23) and fundamentally the same as that used in our previous study (929.2 MHz), 16) except that a cylinder was added from the center of the ceiling in order to provide better air ventilation. Fig.…”

“…We have already demonstrated that local exposure to a 929.2 MHz field (PDC-800 system), modulated in a PDC wave form, used for cellular phones, has no significant effect on rat liver carcinogenesis. 16) In the present study, the effects of a 1.439 GHz field (PDC-1500 system) were analyzed in the same system and the data obtained from the two experiments were compared.…”

Radio frequency electromagnetic fields: Cancer, mutagenesis, and genotoxicity

“…Survival analysis also showed no significant difference in cumulative percentage survival between them. Imaida et al [1998a] investigated whether exposure of F344A rats to near field, TDMA modulated 929.2 MHz RFEMF at 50 pulses/s, 0.33 duty cycle [the Japanese standard signal for Personal Digital Cellular (PDC) telephones] would promote liver cancer initiated by the carcinogen diethylnitrosamine. Each rat was exposed for 90 min/day, 5 days/week for 6 weeks.…”