The possible role of contact current in cancer risk associated with residential magnetic fields

Residential electrical wiring safety practices in the US result in the poss ibility of a small voltage (up to a few tenths of a volt) on appliance surf aces with respect to water pipes or other grounded surfaces. This "open cir cuit voltage" (V-OC) will cause "contact current" to flow in a person who t ouches the appliance and completes an electrical circuit to ground. This pa per presents data suggesting that contact current due to V-OC is an exposur e that may explain the reported associations of residential magnetic fields with childhood leukemia. Our analysis is based on a computer model of a 40 house (single-unit, detached dwelling) neighborhood with electrical servic e that is representative of US grounding practices. The analysis was motiva ted by recent research suggesting that the physical location of power lines in the backyard, in contrast to the street, may be relevant to a relations hip of power lines with childhood leukemia. In the model, the highest magne tic field levels and V(OC)s were both associated with backyard lines, and t he highest V(OC)s were also associated with long ground paths in the reside nce. Across the entire neighborhood, magnetic field exposure was highly cor related with V-OC (r = 0.93). Dosimetric modeling indicates that, compared to a very high residential level of a uniform horizontal magnetic field (10 mu T) or a vertical electric field (100 V/m), a modest level of contact cu rrent (similar to 18 mu A) leads to considerably greater induced electric f ields (>1 mV/m) averaged across tissue, such as bone marrow and heart. The correlation of V-OC with magnetic fields in the model, combined with the do se estimates, lead us to conclude that V-OC is a potentially important expo sure with respect to childhood leukemia risks associated with residential m agnetic fields. These findings, nonetheless, may not apply to residential s ervice used in several European countries or to the Scandinavian studies co ncerned with populations exposed to magnetic fields from overhead transmiss ion lines. (C) 2000 Wiley-Liss, Inc.