Utteridge TD, Gebski V, Finnie JW, Vernon-Roberts B, Kuchel TR.
In 1997 Repacholi and his colleagues reported that exposure of mice to radiofrequency (RF) radiation at 900 MHz for 18 months increased the incidence of lymphoma. These authors stated that there was a need to "replicate and extend" their study. Utteridge and co-authors carried out a replication study using the same strain of mice as in Repacholi's - one that is particularly prone to develop lymphoma. They included refinements designed to overcome perceived shortcomings in the original study:
The authors used a double-blind design. A total of 120 heterozygous (lymphoma-prone) and 120 wild-type mice were exposed at each of the exposure levels (SARs 0.25, 1.0, 2.0 and 4.0 W/kg); 120 mice of each strain were sham-exposed; and there were 120 freely moving negative control mice of each strain. Thirty heterozygotes and 30 wild-type mice were used as positive controls by injecting them with ethylnitrosurea and sham-exposing them. One hundred sentinel mice were also used for health monitoring purposes. Hence a total of 1600 mice were used in the study. The mice were exposed to RF radiation at 898.4 MHz or sham-exposed for 1 hour/day, 5 days/week for up to 24 months. The mice were restrained during exposure. The dosimetry was checked independently at regular intervals by staff of the Australian Radiation Protection and Nuclear Safety Agency and the Defence Science Technology Organization. The other shortcomings of the Repacholi study were addressed appropriately.
Utteridge and colleagues found that different types of lymphomas occurred - lymphoblastic lymphomas usually developed before age 10 months, and non-lymphoblastic at more than 10 months. A few other types of tumours were found in a small number of the animals. The tumour incidences were no higher in the exposed mice than in the sham-exposed, either for lymphoma or for total tumour incidence. There was no evidence of a dose-dependent trend. For lymphoblastic lymphoma there was actually a decreased incidence of tumours in the exposed mice, although this reached statistical significance only for the 0.25 W/kg group.
In summary, this study did not confirm the findings of the Repacholi study, in that there was no evidence of an increase in lymphoma incidence after RF-field exposure.
The study was funded
by the Australian National Health & Medical Research Council and
was carried out at the University of Adelaide.
Utteridge and colleagues
replied to these concerns.
Several researchers have said that the use of "days of exposure" rather than "absolute age" in the survival curve is highly unusual, according to "Microwave News" in the January/February 2003 issue.
Other attempts to replicate the Repacholi study are underway at the present time.