Radiofrequency biological effects

• Pages: 10-14

5

Radiofrequency biological effects

The biological effects of exposure to RF and microwave radiation have been

studied extensively and have been well reviewed by several national and international

bodies (Saunders et al., 1991; UNEP, IRPA and WHO, 1993). The effects are

summarized here with reference to data relevant to exposure from RF heaters.

Currently, however, there are few data on the effects of exposure to RF in the range of

10 to 100 MHz. Most studies have been carried out using higher frequency radiation.

5.1. Whole-body response

Most of the biological effects of acute exposure to RF electromagnetic fields are

consistent with responses to induced heating, resulting either in a body temperature rise

of about 1 °C or more, or in a thermoregulatory response. Most responses have been

reported at specific absorption rates (SARs) above approximately 1-2 W/kg in different

animal species exposed under various environmental conditions. The animal

(particularly primate) data indicate the types of response that are likely to occur in

humans subjected to a sufficient heat load. However, direct quantitative extrapolation

to humans is difficult, given species differences in responses in general, and in

thermoregulatory ability in particular.

The most sensitive animal responses to heat loads are thermoregulatory

adjustments, such as reduced metabolic heat production and vasodilation, with

thresholds ranging between about 0.5 and 5 W/kg, depending on environmental

conditions. These reactions form part of the natural repertoire of thermoregulatory

responses that serve to maintain normal body temperatures.

Transient effects seen in exposed animals, which are consistent with responses to

increases in body temperature of 1 °C or more (and/or SARs in excess of about 2 W/kg

in primates and rats), include reduced performance of learned tasks and increased

plasma corticosteroid levels. Other heat-related phenomena include effects on the

blood-forming and immune systems, possibly due to elevated corticosteroid levels. The

most consistent effects observed are reduced levels of circulating lymphocytes,

increased levels of neutrophils and altered natural killer cell and macrophage function.

An increase in the primary antibody response of B lymphocytes has also been reported.

Cardiovascular changes consistent with increased heat load, such as an increased heart

rate and cardiac output, have been observed, together with a reduction in the effect of

drugs, such as barbiturates, the action of which can be altered by circulatory changes.

There are relatively few studies that directly address exposures of humans to RF

fields. When human volunteers are exposed at a frequency of 64 MHz to SARs of

4 W/kg for 15-20 minutes, their average body temperature rises by 0.2 to 0.5 °C, which

is quite acceptable in healthy people (Shellock, 1989). The impact that this added

10