Is the radical pair mechanism relevant for radiation protection?

What is the issue?

In general, molecules are set in motion as soon as a body has a certain temperature. This is referred to as thermal motion and exerts strong forces on molecules – even at ambient temperature. Likewise, magnetic fields have a direct force effect on charged molecules in motion. However, below the limit values, this effect on the movement of the molecules is considerably less than the thermal movement and thus negligible. A relevant mechanism of action of magnetic fields is thus highly likely non-thermal in nature. The most well known non-thermal effect of weak magnetic fields on biological systems is the radical pair mechanism, which has been intensively researched as the sense of orientation of migratory birds.

Electrons have an intrinsic angular momentum (i.e. spin). In a magnetic field, the intrinsic angular momentum of an electron begins to precess between its possible configurations. Similar to a spinning top, this refers to the change in direction of the axis of rotation. If a pair of radicals (i.e. unpaired electrons in molecules) is created in a chemical reaction, the magnetic field of the surrounding particles leads to a fluctuation between the two possible spin states. Radical pair reactions can have different end products depending on which spin state is present. External magnetic fields influence the fluctuation of the possible spin states and thus the outcome of the corresponding chemical reactions.

What is the current situation?

The alteration of chemical reactions by magnetic fields via the radical pair mechanism has been demonstrated at low field strengths (down to fields in the microtesla range). This is below the legal limits. It has been proven that migratory birds use this mechanism to orient themselves to the Earth’s magnetic field. They use certain proteins that generate radical pairs through light. It has not yet been clarified whether similar processes also play a role in humans and whether radical pairs are also generated by processes other than light. In general, the effect of artificial magnetic fields on biological systems via the radical pair mechanism is an open research question.

What are the objectives of the BfS research project?

The aim of the research project is to evaluate the relevance of the radical pair mechanism for radiation protection. In concrete terms, this means determining frequency-dependent threshold values for the magnetic field strength below which a considerable influence on the radical pair mechanism can be ruled out.