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Bioelectromagnetism

questions about the possible human health risks in relation to exposures to electromagnetic felds in

bioelectromagnetism.

Te following section discusses the history of the human health evaluations related to exposures to

three diferent electromagnetic felds: static (DC; 0 Hz) electric and magnetic felds, extremely low fre­

quency (ELF) felds focused on power frequency (50/60 Hz), and RF (100 kHz–300 GHz) electromagnetic

feld.

2.6.1 Static Fields

When large amounts of power need to be transmitted over long-distances, DC transmission line are

cheaper to construct and are suitable for long-distance overhead and submarine cable transmission. In

the past, DC systems were limited to shorter distances because it was difcult to convert voltages between

high transmission lines and low distribution lines. Te frst DC transmission line system in the world

was for the supply of electricity to the island of Godland in Sweden (HVDC Godland). At that time, the

transmission distance was about 100 km. Over 600–900 km for overhead lines and 30–60 km for sub­

marine cable transmission were considered economical. In the 1930s, economically available converters

between DC and AC voltages were constructed. Tereafer, DC lines were constructed frst in New York,

and transmission of Extra High Voltage (EHV) DC transmission lines in the USA started in the 1970s.

Te electrical environment of HVDC transmission line is more complex than that of the HVAC

transmission line. Te coupling of electric feld to organism is entirely diferent. For the HVAC case, the

coupling is capacitive and induced currents are generated inside organisms as a result of the changing

electric felds. For the HVDC case, the electric feld coupling is resistive. To characterize the DC electri­

cal environment, three measures are used: (1) ion current density, (2) ion concentration, and (3) electric

felds. In addition, a current produces a static magnetic feld. It is generally accepted that people cannot

perceived the electric feld from the HVDC transmission line, with no harmful efects. Advantages of

DC transmission lines include lower power losses and low cost of construction.

In 1973, the construction of a ± 400 kV HVDC transmission line was planned from the Coal Creek

generation station near Underwood in North Dakota to the Dickinson converter station near the Twin

Cities (Minneapolis and St. Paul) in Minnesota. Tis line extends 708 km. It is inverted to HVAC for

further transmission to a local distribution system. In the planning stage and during construction pro­

cesses, public opposition to high transmission lines and the use of new technology of DC transmission

was voiced in diferent counties of Minnesota. At the time when the power line was constructed, the

health and safety issues related to air ions, DC electric feld, and ozone remained (Mains 1983; Wellstone

and Casper, 2003). In 1975, the Minnesota Environmental Quality Board (MEQB) ordered environmen­

tal reports on the project, and formed a citizen’s route-evaluation committee, which held 21 information

meetings and 23 days of public hearings. A testimony report of over 3,000 pages was published, from

which the farmers and landowners voiced the following concerns: (1) the use of eminent domain by the

cooperatives to take over private land, (2) the fnancial compensation due to them for the land, (3) the

loss of prime farmland for a large energy project, including interference with mechanical irrigation of

the felds and with aerial application of agricultural chemicals, (4) the amount of ozone generated by the

transmission lines and its efects on crops, animals, and people, (5) the hazards of working with large

farming equipment under the lines, (6) the direct efects of the electric and magnetic felds caused by the

lines on people and animals, (7) the relationship between this line and emerging controversies concern­

ing exposure to the felds from AC high-voltage lines, (8) the lack of notice to the landowners from the

counties, the state, and the cooperatives, (9) preemption of county authority by the state, (10) the fear

that the project was mainly to provide power for a large metropolitan area and not for the farms, as they

originally had been promised (Mains, 1983). Te report presented that there were increasing concerns

about compensation for private property, the efects of ozone on crops, animals, and people, the safety of

farming under power lines, and the direct efects of electric and magnetic felds on animals and people.