Design, construction, and validation of a large capacity rodent magnetic field exposure laboratory

A magnetic field exposure laboratory has been constructed to support Nation al Toxicology Program studies for the evaluation of the toxicity and carcin ogenicity bf pure, linearly polarized, 60 Hz magnetic fields in rodents. Th is dual corridor, controlled access facility can support the simultaneous e xposure of 1200 rats and 1200 mice. The facility contains fully redundant e lectrical and environmental control systems and was constructed using non-m etallic materials to maintain low levels of background (ambient), stray, an d cross-talk magnetic fields. The exposure module design provides for large uniform exposure volumes with good control of stray and cross-talk fields, while allowing the use of roll-around cage racks for simplified animal hus bandry. Stray fields and cross-talk have been further reduced by the inclus ion of "steering coils" in each exposure module. Ambient 60 Hz fields (less cross-talk) in all exposure rooms are <0.1 mu T (1 mG), and static magneti c fields have been mapped extensively. Magnetic field strength, waveform, t emperature, relative humidity, light intensity, noise level, vibration, and air flow in all animal holding areas are tightly regulated, and are monito red continuously during all studies. Field uniformity in the animal exposur e volumes is better than +/-10%; a systematic program of cage, rack, and ro om rotation controls for possible positional effects within the exposure sy stem. Magnetic fields are turned on and off over multiple cycles to prevent the induction of transients associated with abrupt field level changes. To tal harmonic distortion is <3% at all field strengths. The facility has bee n used to study magnetic field bioeffects in rodent model systems in experi ments ranging in duration from 8 weeks to 2 years. (C) 1999 Wiley-Liss,Inc.