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

The possible cancer promotion potential of local exposure to a pulse m odulated 929.2 MHz electromagnetic near-held on chemically-initiated r at liver carcinogenesis was investigated employing a medium-term bioas say. A 929.2-MHz electromagnetic near-field of time division multiple access (TDMA) signal for PDC (Personal Digital Cellular, Japanese cell ular 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 pe ak 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. Th e exposure apparatus was specially designed for this experiment, to al low exposure of the lateral mid-section of the rat body to the electro magnetic near-field. Male F344 rats, 6 week-old, were initially (at we ek 0) given a single dose of diethylnitrosamine (DEN, 200 mg/kg body w t, i.p.). At 2 weeks later, exposure (48 rats) or sham-exposure (48 ra ts) was started. The exposure of electromagnetic near-fields was perfo rmed 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 w eeks 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 f orm (GST-P) positive foci in the livers of the exposed and sham-expose d rats. A further group of 24 animals, given only DEN and partial hepa tectomy, served as the controls. The numbers (no./cm(2)) of GST-P posi tive foci were 4.61 +/- 1.77, 5.21 +/- 1.92 (P < 0.05, versus control) and 4.09 +/- 1.47 and the areas (mm(2)/cm(2)) were 0.30 +/- 0.16, 0.3 6 +/- 0.21 and 0.28 +/- 0.15, for the exposed, sham-exposed and contro l 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 wave form, has no significant effect on rat liver carcinogenesis under the experimental conditions employed.