Biological Effects to Strong Magnetic Fields
Do static fields effect cardiac pacemakers?
Effects on cardiac pacemakers have been reported for fields as low as 1.7 mT. The most common effect was triggering of the asynchronous mode; the effect is very model and orientation dependent, and in the models tested normal operation resumed when the pacemaker was removed from the field. Some pacemakers also exhibited significant torque when exposed. For this reason current static field guidelines restrict exposures for wearers of cardiac pacemakers to 0.5 mT. It would be prudent to apply this restriction to other implanted electronic devices, and to prosthetic devices as well, although not all standards are explicit on this point.
In contrast to the above, a 2000 study found that MR imaging could be safely performed at 500 milliT in patients with cardiac pacemakers.
Do static fields decrease fertility, cause birth defects or increase miscarriage rates?
There is no consistent evidence for such effects.
Fertility: Mur et al, found no significant effects on the fertility of men exposed to 4-30 mT static fields in the aluminum industry; and Evans et al, found no effect of fertility in female MRI operators. One animal study reported evidence for decreased male fertility at 1500 mT, but two other studies at 500-700 mT found no such effect. A fourth animal study reported decreased female fertility at 80 mT, but not at 30 mT.
Miscarriages: Baker et al, found that MRIs done at 1500 mT in the second and third trimester did not increase the miscarriage rate; and Evens et al, found no significant effect on miscarriage rates in female MRI operators. Two animal studies reported decreased fetal viability at 30 mT and 80 mT, but other studies at 500-1000 mT and 6300 mT found no such effect.
Birth defects: Baker et al, found that MRIs done at 1500 mT in the second and third trimester did not produce birth defects; and Evans et al, found no increase in birth defects in children of female MRI operators. One animal study reported adverse effects on development at 1500 mT; but other studies found no increase in birth defects at 30 mT, 500-1000 mT or 6300 mT. Two animal MRI studies done at 1500 mT reported increases in birth defects, but heating due to the radiofrequency (RF) radiation used in MRI cannot be ruled out as a factor. A third MRI study at 1500 mT found no such effect.
References:
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Medical College of Wisconsin - General Clinical Research Center
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J.E. Moulder and K.R. Foster, "Biological Effects of Power-frequency Fields as They Relate to Carcinogenesis"; Proc Soc Exp Med Biol, 209:309-324 (1995).
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J.E. Moulder, "Biological Studies of Power-frequency Fields and Carcinogenesis"; IEEE Eng Med Biol, 15:31-49 (July/Aug 1996).
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K.R. Foster, L.S. Erdreich, J.E. Moulder, "Weak Electromagnetic Fields and Cancer in the Context of Risk Assessment"; Proc IEEE, 85:733-746 (1997).
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J.E. Moulder, "Power-frequency Fields and Cancer"; Crit Rev Biomed Engineering", 26:1-116 (1998).
