Mobile phone radiation could be
detected by the human brain.
Denis L Henshaw, Emeritus Professor of Human Radiation Effects
School of Chemistry University of Bristol Cantocks Close, Bristol, BS8 1TS
Re: Use of mobile phones and risk of brain tumours: update of Danish cohort study. Frei, et al. 343:doi:10.1136/bmj.d6387
In their introduction, Frei et al.  state: "So far, the mechanism of potential non-thermal interaction between radio frequency electromagnetic fields (EMFs) and living systems is unknown." This statement does not concur with scientific knowledge.
Mobile phones typically have three types of EMF emissions associated with them: in the GSM system a 900 MHz radio frequency, a 217 Hz pulsing signal and an extremely low frequency magnetic field (ELF MF) associated with the battery . The ELF component has so far been ignored in all epidemiological studies of mobile phone exposure and cancer. During phone use, this ELF component exposures the whole brain to MFs ranging from a few to tens of micro-tesla, above the intensity of power frequency ELF-MFs that have been repeatedly associated with increased risk of brain tumours in adults [3,4].
Animals across a wide range of species detect small changes in the Earth's magnetic field, which is exploited for navigation. Homing pigeons and newts are estimated to have a limiting magnetic detection sensitivity of 0.01 micro-tesla and magnetic compass sensitivity below 0.2 degrees . Two types of magneto-receptor are widely discussed [6, 7], one based on structures of magnetite particles, the other on a chemical compass exploiting the radical pair mechanism, RPM in which low intensity MFs alter the quantum spin state of the unpaired electrons in a free radical pair. Both mechanisms are relevant to the interaction of mobile phone EMFs in humans.
Thus, the human brain contains magnetite particles , some up to 600 nm in size, capable at body temperature of transducing both low intensity ELF MFs and microwave EMFs [9, 10].
The RPM forms part of basic spin chemistry  in which low intensity MFs can increase the lifetime of free radical pairs by singlet- to-triplet, S-T, interconversion of their quantum spin states. The increased lifetime of free radicals allows increased availability to cause biological damage, for example to DNA. The energy levels involved are some ten million times below thermal energy, the action being of the nature of a quantum mechanical switch.
There is compelling evidence that the avian magnetic compass utilises the RPM acting in the eye on cryptochromes protein molecules , best known for their function in controlling circadian rhythms. The magnetic compass can be disrupted by radio frequency fields. In the American cockroach disruption was seen by 1.2 MHz fields at 0.018 micro-telsa , well below current ICNIRP public exposure guidelines . There is evidence that human cryptochromes are magneto-sensitive  and that ELF MFs disrupt circadian rhythms in man .
IARC has recently classifieds radio frequency EMFs as a 2B possible carcinogen, based on the main body of case-control epidemiology and accumulated exposure to mobile phone radiation and increased risk of brain tumours in heavy users . Research into the possible health effects of mobile phones should now concentrate on designing epidemiological studies with more relevant exposure metrics and at investigating further the mechanistic pathways by which exposure may increase the risk of brain tumours and other adverse health outcomes. Meanwhile, precaution against undue exposure is warranted and should be encouraged.