Upper bound on the biological effects of 50/60 Hz magnetic fields mediated by radical pairs

Abstract

Prolonged exposure to weak (~1 T) extremely-low-frequency (ELF, 50/60 Hz) magnetic fields has been associated with an increased risk of childhood leukaemia. One of the few biophysical mechanisms that might account for this link involves short-lived chemical reaction intermediates known as radical pairs. In this report, we use spin dynamics simulations to derive an upper bound of 10 parts per million on the effect of a 1 T ELF magnetic field on the yield of a radical pair reaction. By comparing this figure with the corresponding effects of changes in the strength of the Earth's magnetic field, we conclude that if exposure to such weak 50/60 Hz magnetic fields has any effect on human biology, and results from a radical pair mechanism, then the risk should be no greater than travelling a few kilometres towards or away from the geomagnetic north or south pole.

On the optimal relative orientation of radicals in the cryptochrome magnetic compass

“…(1) for realistic radical pairs manageable without resorting to semi-classical approximations. In a recent paper, Hore provides a detailed assessment of these approximations in the context of cryptochrome [66]. For the parameter ranges typically expected, these omissions are considered tolerable.…”

“…The current approach facilitates the fast evaluation of all relative orientations for complex spin systems by assuming the absence of inter-radical interactions, as well as identical lifetimes for the singlet and triplet state. While it is clear that these assumptions do not apply in reality, deviations from this ideal are considered small enough to avoid qualitatively different results [39,66]. As a consequence, this approximate approach has been widely employed to calculate reaction yields [37,39,58,59,78].…”

“…Again, this is not expected to change the conclusions, but one needs to keep in mind that in reality the effects will likely be smaller. Detailed discussions of the assumptions made and their consequences can be seen in [39] and more recently in [66]. Semiclassical approximations have been suggested as alternative means to approach large spin systems for symmetric and asymmetric reactivity [57,81,82].…”

Could radical pairs play a role in xenon-induced general anesthesia?

“…Eventually, the coherent oscillation of the RP between singlet and triplet states ceases and the electrons may recombine (for the singlet component of the state) or diffuse apart to form various triplet products 13 . In order for significant interconversion between singlet and triplet states to occur, the RP lifetime and the RP spin-coherence lifetime should be comparable to the electron Larmor precession period, which in the case of the geomagnetic field of the Earth (B ≈ 50µT) is approximately 700 ns [13][14][15] . The coherent spin dynamics and spin-dependent reactivity of radical pairs allow magnetic interactions which are 6 orders of magnitude smaller than the thermal energy, k B T , to have predictable and reproducible effects on chemical reaction yields 14,16 .…”

“…In particular, it has been studied in detail for the cryptochrome protein as a potential explanation for avian magnetoreception 16,[18][19][20][21][22][23] . In the present work we apply the principles and methods used to investigate cryptochrome 14 to xenon-induced anesthesia.…”