A case-control study was conducted in the USA to investigate the association between contact current exposure and the risk of childhood leukemia. Furthermore the relationship between residential contact currents and magnetic fields should be examined.
The hypothesis whether exposure to contact currents might act as a confounder in the reported associations between magnetic fields and childhood leukemia should be tested. Contact currents occur when a person touches conductive surfaces at different potentials and completes a path through which electric current flows within the body. The voltage on a residential water line can produce contact currents in young children while they are bathing provided that they are in contact with a metallic fixture and that the drain is made of conductive material.
Exposure to contact currents and magnetic fields were assessed by 30-minutes measurements inside and outside the homes of the children.
|Reference group 1||indoor contact voltage: quartile 1-2 (0.00 - 0.25 mV)|
|Group 2||indoor contact voltage: quartile 3 (0.25 - 1.50 mV)|
|Group 3||indoor contact voltage: quartile 4 (≥ 1.50 mV)|
|Reference group 4||indoor contact voltage: unexposed (90. percentile, < 10.5 mV)|
|Group 5||indoor contact voltage: exposed (≥ 10.5 mV)|
|Reference group 6||outdoor contact voltage: quartile 1 (0.00 - 35.8 mV)|
|Group 7||outdoor contact voltage: quartile 2 (35.8 - 89.7 mV)|
|Group 8||outdoor contact voltage: quartile 3 (89.7 - 166.8 mV)|
|Group 9||outdoor contact voltage: quartile 4 (≥ 166.8 mV)|
|Reference group 10||outdoor contact voltage: unexposed (90. percentile, < 291.2 mV)|
|Group 11||outdoor contact voltage: exposed (≥ 291.2 mV)|
|Reference group 12||indoor magnetic field exposure: quartile 1 ( 0 - 0.01 µT)|
|Group 13||indoor magnetic field exposure: quartile 2 ( 0.01 - 0.02 µT)|
|Group 14||indoor magnetic field exposure: quartile 3 ( 0.02 - 0.05 µT)|
|Group 15||indoor magnetic field exposure: quartile 4 (≥ 0.05 µT)|
|Reference group 16||indoor magnetic field exposure: unexposed (90. percentile, < 0.09 µT)|
|Group 17||indoor magnetic field exposure: exposed (≥ 0.09 µT)|
|Reference group 18||indoor magnetic field exposure, a priori cutpoint: ≤ 0.10 µT|
|Group 19||indoor magnetic field exposure, a priori cutpoint: > 0.10 - ≤ 0.20 µT|
|Group 20||indoor magnetic field exposure, a priori cutpoint: >0.20 - ≤ 0.30 µT|
|Group 21||indoor magnetic field exposure, a priori cutpoint: > 0.30 µT|
No statistically significant associations were observed between childhood leukemia and indoor or outdoor contact voltage levels and indoor magnetic fields. Contact voltage was weakly correlated with magnetic field (correlation coefficients r = 0.10 (P = 0.02) for indoor contact voltage and r = 0.15 (P = 0.001) for outdoor contact voltage).
The authors concluded that in this Califoria population, there was no evidence of an association between childhood leukemia and exposure to contact currents or magnetic fields and a weak correlation between measures of contact current and magnetic fields.