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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.
|参照集団 1||indoor contact voltage: quartile 1-2 (0.00 - 0.25 mV)|
|集団 2||indoor contact voltage: quartile 3 (0.25 - 1.50 mV)|
|集団 3||indoor contact voltage: quartile 4 (≥ 1.50 mV)|
|参照集団 4||indoor contact voltage: unexposed (90. percentile, < 10.5 mV)|
|集団 5||indoor contact voltage: exposed (≥ 10.5 mV)|
|参照集団 6||outdoor contact voltage: quartile 1 (0.00 - 35.8 mV)|
|集団 7||outdoor contact voltage: quartile 2 (35.8 - 89.7 mV)|
|集団 8||outdoor contact voltage: quartile 3 (89.7 - 166.8 mV)|
|集団 9||outdoor contact voltage: quartile 4 (≥ 166.8 mV)|
|参照集団 10||outdoor contact voltage: unexposed (90. percentile, < 291.2 mV)|
|集団 11||outdoor contact voltage: exposed (≥ 291.2 mV)|
|参照集団 12||indoor magnetic field exposure: quartile 1 ( 0 - 0.01 µT)|
|集団 13||indoor magnetic field exposure: quartile 2 ( 0.01 - 0.02 µT)|
|集団 14||indoor magnetic field exposure: quartile 3 ( 0.02 - 0.05 µT)|
|集団 15||indoor magnetic field exposure: quartile 4 (≥ 0.05 µT)|
|参照集団 16||indoor magnetic field exposure: unexposed (90. percentile, < 0.09 µT)|
|集団 17||indoor magnetic field exposure: exposed (≥ 0.09 µT)|
|参照集団 18||indoor magnetic field exposure, a priori cutpoint: ≤ 0.10 µT|
|集団 19||indoor magnetic field exposure, a priori cutpoint: > 0.10 - ≤ 0.20 µT|
|集団 20||indoor magnetic field exposure, a priori cutpoint: >0.20 - ≤ 0.30 µT|
|集団 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.