The comprehensive electrification of modern societies has created conditions where living organisms are exposed to 50 or 60 Hz power frequency electric and magnetic fields which are, although usually weak, clearly considerably above the naturally occurring ambient fields of about 10− 4 V m− 1 (electric field) and up to 10− 4 T (magnetic fields). To demonstrate the size of the fields concerned, Table 1 summarises both the field strengths of electric fields and the flux densities of magnetic fields that are found near power lines (NRPB, 1992a). However, both electric and magnetic fields are encountered wherever electric current is either produced or distributed. To illustrate the situation, a number of examples of magnetic flux densities measured at various distances from commonly used domestic appliances are summarised in Table 2 (NRPB, 1992b). The electric field strengths close to domestic appliances are in the range of about 200–300 V m− 1.

A series of epidemiological studies including residents who live close to high voltage power lines has shown a possible link between the exposure to weak electromagnetic fields (EMF) and an increased risk for the development of leukaemia, in particular leukaemia in children (Wertheimer & Leeper, 1979; Savitz et al., 1988; Coleman et al., 1989; London et al., 1991; Feychting & Ahlbom, 1992). However, the calculated risk factor obtained from those studies is quite small (in the range of about 1.5–3.0). In general, however, the whole spectrum of epidemiological studies dealing with the exposure to EMF seems to obtain rather contradictory results.