A new study by the U.S. National Toxicology Program found that high exposure to radiation similar to that emitted by cellphones caused cancerous tumors in the brain and heart of male rats. This finding is the outcome of a two-year study by the government organization, which led to the classification of the radio frequencies emitted by cellphones in the same category as other cancer-causing substances.

The rats in the study were exposed to frequency bands in the 900 MHz ranges, which is the same as what is generally used in the US. The rats used in the study were exposed to the radiation in cycles of 10 minutes on and off, totaling about 9 hours of exposure daily.

“Under the conditions of these 2-year studies, the hyperplastic lesions and glial cell neoplasms of the heart and brain observed in male rats are considered likely the result of whole-body exposures to GSM- or CDMA-modulated RFR,” said the report.

“Given the widespread global usage of mobile communications among users of all ages, even a very small increase in the incidence of disease resulting from exposure to RFR could have broad implications for public health.”

A recent survey by CTIA (The Wireless Association) revealed the most popular wireless device in the US is the smartphone, with more than 228 million smartphones.