Strong Electric Fields Implicated in Major Leukemia Risk for Workers

Long term employees of Ontario Hydro who worked in strong electric fields had much higher risks of leukemia, Canadian researchers have found. Significant risks were also found for non Hodgkin’s lymphoma (NHL) in a related study.

The elevated risks were seen among workers who spent the most time in electric fields above certain thresholds, in the range of 10 to 40 V/m. The largest increases occurred among those with more than 20 years on the job. Senior workers with the greatest time above the thresholds had an eight to tenfold increase in the risk of leukemia—much higher than in past epidemiological studies of electromagnetic fields (EMFs).

THE SWEDISH STANDARD

Sweden has been a leader in developing recommended visual ergonomic and electromagnetic emission standards for computer displays. In 1987 the Swedish National Board for Measurement and Testing (MPR) introduced the first, non-mandatory testing procedures for VDTs. The test methods, called MPR 1, specified a maximum of 50 nT (.5 mG) of peak VLF magnetic field strength in the 1 kHz to 400 kHz range at 50 cm (19.7 inches) from the front of the screen. The full test procedure called for 16 measurements taken on 5 horizontal planes at 22.5 degree intervals all around the display F for a total of 80 measurements in all. No ELF requirements were included in the MPR 1 standard, because widespread concern over ELF radiation was just developing.

On July 1, 1991, new guidelines became effective. The new test methods, called MPR 2, specify less than 2.5 mG rms (root mean square) of ELF magnetic emissions in the 5 Hz to 2 kHz range (Band 1) and less than .25 mG rms of VLF magnetic emissions in the 2 kHz to 400 kHz range (Band 2). The number of measurements was reduced to 48 for each band F taken at 50 cm (19.7 inches) starting from the front of the screen and every 22.5 degrees all around the display (16 points) on each of three horizontal planes 25 cm apart.

The change in the VLF standard from the previous .5 mG peak to .25 mG rms, as explained by Lars-Erik Paulsson of Sweden's National Institute of Radiation Protection, is not a tightening of the standard, but rather a change in the method of measurement. "The two limits are essentially the same," Paulsson stated, because "the peak value is the maximum reading during each cycle, while the rms value is a time-weighted average." Commenting on this, electrical engineer Mark Kettering says that "using an oscilloscope to study the wave forms from VDTs shows that the two limits are not 'essentially the same.' The shape of the wave form (mG vs time) varies, depending upon the manufacturer. Some VDTs have sharp spikes in their wave form, but the rms value essentially ignores these spikes." Based on current knowledge, it is not known which method of measurement is most appropriate.

MPR 2 also includes guidelines for visual ergonomics (such as focus, jitter and character distortion), X-ray radiation (which is not a problem), electrostatic potential, electrostatic discharge, and AC electric fields. The source of the electric fields are the power supply and deflection coils. These components can also create a surface potential of several kilovolts, depending upon humidity, temperature, air velocity and ion concentration in the air. Reduction of the electrostatic potential and the electric fields is normally achieved by a conductive surface coating on the screen, which is connected to the power ground, together with metallic shielding of the power supply. Sometimes a CRT-style VDT will include a metal cage around all the components, or metal foil on the inside of the cabinet, to help shield the electric field.

The Swedish guidelines have received a formal embrace from many major manufacturers of computer displays. Yet even in Sweden there is not a complete consensus on the limits. A major Swedish union (the Swedish Confederation of Professional Employees, or TCO) is seeking more stringent limits and test protocols F as low as 2 mG for ELF magnetic fields at 30 cm (12 inches) from the front of the screen. Their reasoning is that levels above 2 mG have been linked to increased risks of cancer, and that many VDT users' heads, hands and/or breasts are often closer than 50 cm from the screen. Some experts have also questioned the validity of .25 mG for VLF, pointing out that the higher frequency VLF field contains more energy than ELF. These experts say that if induction levels are used to measure the amount of energy in the radiation, then 2.5 mG of ELF is equal to .01 mG of VLF. MPR's response is that "there are no proven biological reasons" for limiting VDT EMFs, and that the guidelines are not based on health risks. Rather, the recommended limits are based on what is technically feasible to measure and on what is achievable "today or within the near future."

July/August 2001

ELF EMFs (electromagnetic fields) are now classified in the same category as DDT, lead, Carbon Tetrachloride and Chloroform, Category 2B possible carcinogens.

IARC Finds ELF EMFs Are Possible Human Carcinogens

A working group assembled by the International Agency for Research on Cancer (IARC) has unanimously concluded that power-frequency magnetic fields are possible human carcinogens. This finding, announced on June 27 in Lyon, France, is based on the consistent association between childhood leukemia and residential exposure to extremely-low-frequency electromagnetic fields (ELF EMFs).

Category 2B: Possible Carcinogen
Evidence: limited in humans and less than sufficient in animals
Chemical and physical agents:
Carbon tetrachloride, chloroform, DDT, ELF EMFs, lead, PBBs. Total number of agents: 236

June, 2001

Maximum EMF Exposure EmergesAs Strong Miscarriage Risk

A new and innovative epidemiological study has found an up to six fold increased risk of spontaneous abortions among women exposed to magnetic fields of 16 mG or greater. The results “should have wide implications,” concludes Dr. DeKun Li, who led the study team at Kaiser Permanente’s research division in Oakland, CA.