Comments on the “Evaluation of the Genotoxicity of Cell Phone Radiofrequency Radiation in Male and Female Rats and Mice Following Subchronic Exposure” by Smith‐Roe et al.

Abstract

In the publication by Smith-Roe et al., the results from genetic damage tests in rats and mice that were conducted as part of a National Toxicology Program (NTP) bioassay of radiofrequency (RF) fields used in cell phones as a possible carcinogen were reported. In the study, Smith-Roe et al. exposed two rodent species (rats and mice) to RF energy at two frequencies (900 and 1800 MHz) with two modulations (CDMA and GSM) at three doses of specific absorption rates (SARs, 1.5, 3, and 6 W/kg for rats and 2.5, 5, and 10 W/kg for mice) for intermittent exposure of 10 min on/off cycles for 19 weeks (rats) and 14 weeks (mice). The genetic damage was assessed using the alkaline comet assay in five different tissues (frontal cortex, cerebellum, hippocampus, liver, and peripheral blood leukocytes) and a flow cytometer for micronuclei (MN) analysis in peripheral blood erythrocytes. Sham-exposed control animals were the same for both modulations. Necropsies were performed in two shifts and each completed in approximately 4.5 to 7 hr after termination of RF exposure. The study has serious weaknesses that compromised the interpretation of its results. We submit the following comments on the study. Our concerns pertain to both experimental methodological and statistical issues. METHODOLOGICAL ISSUESIt is well-known that the comet assay is very sensitive and it is also extremely sensitive to minor perturbations in handling and processing tissue samples. That is a matter of particular concern with this study, for which the effects reported from the comet assay in Tables I-VIII were quite small with 70% of the data showing an average of 10% tail DNA. Smith-Roe et al. stated "Animals were euthanized by CO 2 asphyxiation". In this context, it is important to mention the publication by Malyapa et al. (1998) in which rats were exposed to 2450 MHz RF energy at 1.2 W/kg SAR and compared the results from animal sacrifice by CO 2 asphyxiation or decapitation using guillotine. The results from the alkaline comet assay showed that the larger the delay between the death of the rat by CO 2 asphyxiation and the removal of the brain, the greater the DNA damage observed in brain cells. The authors stated "these results are indicative of a relationship between the presence of DNA damage detected by the alkaline comet assay and the length of time between death and brain dissection". "… brain cells are extremely sensitive to hypoxia", and "even a 2-or 3-min asphyxiation can cause irreversible damage". Even if Smith-Roe et al. study was otherwise well controlled, individual variations in the time required for an animal to die during euthanasia procedure and small (minutes) variations in the subsequent processing time would result in considerable variability in results, as Malyapa et al. (1998) reported. It is a potential source of variability unless meticulously controlled. Smith-Roe et al. did not describe precautions to control for such effects, and the NTP study may have confirmed (rediscovered) the euthanasia artifact effect described by Malyapa ...

Thermoregulatory Stress as Potential Mediating Factor in the NTP Cell Phone Tumor Study

“…DNA damage was also reported in the 14‐week interim evaluation of male (frontal cortex) and female (leukocytes) mice. However, at least for the frontal cortex data of male mice, an artifact introduced by the extraordinary low value of % tail DNA in the shared sham‐exposed group cannot be ruled out [Vijayalaxmi et al, 2020] (cf. supplemental Fig.…”