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Bioelectromagnetism

7.2.2 Low-Frequency Fields

Many studies have investigated the biological efects of low frequency electromagnetic felds up to

100 kHz (IARC, 2002; ICNIRP, 2003; NIEHS, 1998; WHO, 1987, 2007).

Te coupling between the low-frequency magnetic feld and the body is summarized below from the

document of ICNIRP (ICNIRP, 2010). For magnetic felds, the permeability of tissue is the same as that

of air so the feld in tissues is the same as the external feld. In this frequency ranges, the main interac­

tion of magnetic feld with the body is the Faraday induction of electric felds and associated currents in

the tissues. Key features of dosimetry for exposure of humans to low frequency magnetic felds include:

(1) for a given magnetic feld strength and orientation, higher electric felds are induced in the bodies

of larger people because the possible conduction loops are larger. (2) Induced electric feld and current

depend on the orientation of the external magnetic feld to the body. Generally, induced felds in the

body are greatest when they feld is aligned from the front to the back of the body, but for some organs

the highest values are for diferent feld alignments. (3) Weakest electric felds are induced by a magnetic

feld oriented along the principal body axis. (4) Distribution of the induced electric feld is afected by

the conductivity of the various organs and tissues (Ueno and Sekino, 2016).

Te only established health efects from LF also occur at high levels and include electric shock and

magnetophosphenes in the eye. Some epidemiological studies have reported a possible association

between prolonged exposure to LF magnetic felds and increased rates of childhood leukemia. Tis

association is not supported by laboratory or animal studies, and no credible theoretical mechanism

has been proposed. Based largely on this evidence, IARC has classifed LF magnetic felds as possibly

carcinogenic to humans (Group 2B) (IARC, 2002). Overall, the evidence related to childhood leukemia

is not strong and research in this area is continuing.

From the defnition of ICNRIP, LF is used to describe the frequency range from 1 Hz to 100 kHz (ICNIRP,

2010a,b). In this frequency range, the interaction of electric and magnetic felds with the human body is

the induction of electric felds and currents in the tissues. Te established efect is the induction of mag­

netophosphenes, a perception of faint fickering light in the periphery of the visual feld. Tey are thought

to result from the interaction of the induced electric feld with electrically excitable cells in the retina.

Te threshold for induction of magnetophosphenes has been estimated to low between about 50 and 100

mV/m at 20 Hz. Epidemiological studies have suggested that long-term exposure to 50/60 Hz magnetic

felds might be associated with an increased risk of childhood leukemia. Two pooled analysis indicate that

an excess risk may exist for average exposures exceeding 0.3–0.4 μT. However, some degree of confound­

ing and chance could possibly explain these results. No biophysical mechanism has been identifed and

results from animal and cellular studies do not support the mention that exposure to 50/60 Hz magnetic

felds is a cause of childhood leukemia. Tere is no substantial evidence for an association between low

frequency magnetic feld exposure and Parkinson’s disease, multiple sclerosis, and cardiovascular dis­

eases. Te evidence for an association between low-frequency magnetic feld exposure and Alzheimer’s

disease and amyotrophic sclerosis is inconclusive. Overall research has not shown that long-term low-level

LF magnetic feld exposure has detrimental efects on health. ICNIRP’s view is that the currently existing

scientifc evidence that prolonged exposure to LF magnetic felds is causally related with an increased risk

of childhood leukemia is too weak to form the basis for exposure guidelines. Te perception of surface

electric charge, the direct stimulation of nerve and muscle tissue, and the induction of retinal phosphenes

are the only well-established adverse efects and serve as the basis for guidance (ICNIRP, 2010b).

7.2.3 Radiofrequency Fields

Sheppard quantitatively evaluated potential mechanisms of interaction between RF electromagnetic

felds and biological systems (Sheppard et al., 2008). First, the established mechanisms are dielectric

relaxation and ohmic loss, which lead to elevate the temperature in tissue though heating. On the other

hand, the proposed is the radical pair mechanism.