Interactions between electromagnetic radiation and biological systems

Abstract

Even though the bioeffects of electromagnetic radiation (EMR) have been extensively investigated during the past several decades, our understandings of the bioeffects of EMR and the mechanisms of the interactions between the biological systems and the EMRs are still far from satisfactory. In this article, we introduce and summarize the consensus, controversy, limitations, and unsolved issues. The published works have investigated the EMR effects on different biological systems including humans, animals, cells, and biochemical reactions. Alternative methodologies also include dielectric spectroscopy, detection of bioelectromagnetic emissions, and theoretical predictions. In many studies, the thermal effects of the EMR are not properly controlled or considered. The frequency of the EMR investigated is limited to the commonly used bands, particularly the frequencies of the power line and the wireless communications; far fewer studies were performed for other EMR frequencies. In addition, the bioeffects of the complex EM environment were rarely discussed. In summary, our understanding of the bioeffects of the EMR is quite restrictive and further investigations are needed to answer the unsolved questions.

Keywords: Biological sciences; Electromagnetics; Physics.

Scheme 1

Investigations of the bioeffects of the EMR

Scheme 2

Current theories for explaining the bioeffects of EMR (A) Ion cyclotron resonance model applied to EMR effects on calcium influx and downstream signaling pathways (adapted from^204,236); (B and C) Radical pair theory. (B) Energy diagram of electronic spin states (S, T₀, T₊, and T₋) of a radical pair in a magnetic field B. The vector representation corresponding to each spin state were shown by the cartoon next to the curve. The triplet spin states (T₀, T₊, and T₋) are energy degenerate at B = 0, but T₊ and T₋ are split to higher and lower energy from T₀ at B > 0. Meanwhile, the energy level of the spin states S and T₀ are unaffected by the magnetic field B (adapted from²¹¹). (C) Reaction scheme for a radical pair reaction with magnetic field-dependent reaction products. The radical pair is generated by an electron transfer from a donor molecule D, which is excited by light, to an acceptor molecule A. The external magnetic field affects the interconversion between the singlet and triplet states of the radical pair (adapted from^207,208). (D) Radical pair reaction of Cry. A flavin adenine dinucleotide (FAD) bounded with cryptochrome (Cry) is excited by a photon (FAD→FAD∗) and then protonated (FAD∗→(FADH⁺)∗). Three electron transfers occur sequentially: the first one is from the tryptophan residue (W_A) of the Cry to (FADH⁺)∗, the second from tryptophan residue W_B to W_A, and the third from tryptophan residue W_C to W_B, generating magnetosensitive singlet and triplet radical pairs (^S[FADH⋅ W_A/B/C⋅⁺] and ^T[FADH⋅ W_A/B/C⋅⁺]). The different spin states of the radical pairs act differently in the reaction cascade (adapted from^212,220,237). (E) Magnetosensitive radical pair reactions involving radical pairs of enzyme-bound neutral flavin FADH and superoxide (singlet state ^S[FADH⋅ O₂⋅⁻] and triplet state ^T[FADH⋅ O₂⋅⁻]) (adapted from¹⁴⁴).