In all studies, experimental groups include animals exposed continuously for 18.5 hours per day to linearly polarized sinusoidal 60 Hz magnetic field strengths of 0 G, 20 mG, 2 G, or 10 G, or intermittently (1 hr on/1 hr off) to 10 G fields. The program includes the following in vivo bioassays: a) 8-week toxicity studies in F344 rats and B6C3F1 mice, in which any effects of subchronic exposure to magnetic fields on overall animal health, specific organ function (monitored by clinical chemistry assays), and hematologic parameters are identified; b) a developmental toxicity (teratology) study in Sprague-Dawley rats, in which animals are exposed to magnetic fields in utero to assess possible effects on prenatal development; c) a multigeneration reproductive toxicity study in Sprague-Dawley rats using the Reproductive Assessment by Continuous Breeding (RACB) protocol, to identify any effects of magnetic field exposure on reproductive function; d) lymphoma promotion studies in PIM and p53 knockout transgenic mice, in which the influence of magnetic field exposure on lymphoma induction is assessed in animals that are genetically predisposed to the disease; e) immunotoxicology studies in mice, in which the influence of magnetic field exposure on lymphoid organ weight and cellularity, T-cell number and function, B- cell number and function, NK-cell function, composition of T-lymphocyte subsets, and host resistance to infection is determined; f) pineal function studies in F344 rats and B6C3F1 mice, in which the influence of magnetic fields on serum and pineal melatonin levels and pineal N- acetyltransferase activity is determined; and g) 2-year chronic toxicity/oncogenicity evaluations in F344 rats and B6C3F1 mice, in which the toxicity and potential carcinogenicity of magnetic fields will be evaluated in animals exposed over the majority of their natural life span. Group sizes have been increased beyond those traditionally used in toxicity and carcinogenicity bioassays to increase statistical power, and to increase the likelihood of detecting small effects.

2. Experimental Endpoints -- The influence of exposure to 60 Hz magnetic fields on overall animal health (monitored by survival, body weight, clinical observations, clinical pathology, and histopathology evaluations), cancer incidence (monitored by clinical observation, gross pathology, and histopathology evaluations), reproductive function (monitored as number and frequency of successful matings, litter size and weight, and pup survival), developmental toxicity (monitored as fetal survival, weight, and incidence of birth defects), immune function (monitored by assessment of T-cell number and function, B-cell number and function, NK cell function, and host resistance to infectious challenge), and pineal function (monitored by quantitation of serum and pineal melatonin and pineal activity of N-acetyltransferase) is being determined in animals exposed to magnetic fields for periods of up to two years. Where available, appropriate positive control materials are included in experimental designs.

3. Magnetic Field Polarization, Frequency, and Harmonic Content -- Linearly polarized, sinusoidal 60 Hz fields with less than 3% total harmonic distortion. Fields are ramped on and off over 7 to 9 cycles to preclude the generation of magnetic field transients.

4. Magnetic Field Intensity -- 0 G (sham control), 20 mG continuous, 2 G continuous, 10 G continuous, and 10 G intermittent (1 hr on, 1 hr off).

5. Exposure Duration -- 18.5 hrs per day for up to 2 years.

6. Relative Orientation of AC and DC Magnetic Fields -- AC fields horizontal (perpendicular to primary component of DC field).

7. Associated Electric Fields -- less than 100 Volts/meter.

8. Field Spatial Homogeneity -- Uniform to + 10% throughout exposure volume.

9. Field Temporal Homogeneity -- Measured continuously throughout program; temporal variability is < 5% over nearly 2 years of exposure system operation.

10. Field Monitoring -- Continuous throughout program (during both exposures and field-off conditions); monitoring includes both field strength and waveform.

11. Geometry of Animal Exposure -- Animals are allowed unrestricted mobility at all times during exposures.

12. Environmental Conditions -- Environmental conditions in all animal exposure rooms are maintained in the ranges of 72 + 3 oF, 50% + 15% relative humidity, and > 10 air changes per hour. Activation of magnetic field exposure modules has no effect on any environmental parameter. Environmental conditions are monitored continuously; sensors are alarmed to alert project personnel in the event of deviations from environmental set points.

13. Other Environmental Cues -- Noise, vibration, and lighting in exposure rooms are monitored continuously. Noise levels vary by less than 1 dB in the 125 Hz octave band when system is energized. Vibration is undetectable in animal cage racks. Lighting is controlled by automatic timer; light levels are identical in all exposure rooms.

14. Stray Fields -- Laboratory site has been fully mapped for ambient 60 Hz and geomagnetic (dc) fields; temporal characteristics of ambient magnetic fields have been determined. Ambient magnetic fields in all animal exposure rooms are less than 1 mG. No DC field cancellation is used. Ambient fields are monitored continuously in sham control room, and during field shutdown periods in all other rooms.

15. Sham Exposure Conditions -- Ambient 60 Hz fields are monitored continuously in sham control room; ambient fields are uniformly less than 1 mG.

16. Crosstalk -- less than 1 mG between rooms in worst-case room rotation scenario.

2. Ambient 60 Hz and Static Magnetic Fields -- Fully mapped by IITRI engineers prior to installation of exposure system and incubators. No DC field cancellation.

3. Magnetic Field Monitoring -- Field strength and waveform monitored continuously throughout program (both during exposure periods and periods of module shutdown).

4. Control for Positional Effects -- A regular schedule of animal rotation (from top to bottom within a rack, from bay to bay within each exposure room, and between exposure rooms) is maintained to preclude the possibility that data may be confounded by positional effects within animal racks, animal rack bays, or animal exposure rooms.

5. Positive Controls -- Where available, appropriate positive control agents have been included in study designs.

6. Peer Review -- All histopathologic findings will be reviewed by a National Toxicology Program Pathology Working Group.

2. Developmental Toxicity Studies -- The conduct of gross external, visceral, cephalic, and skeletal evaluations on more than 3,000 Sprague-Dawley rat fetuses revealed no evidence of magnetic field teratogenicity. Fetal survival, fetal body weights, and maternal body weights in EMF-exposed groups did not differ from sham controls.

3. Reproductive Toxicity Studies -- The conduct of a multi-generation reproductive toxicity study in Sprague-Dawley rats using the Reproductive Assessment by Continuous Breeding (RACB) design revealed no adverse effect of magnetic field exposure on reproductive performance in either sex.

4. Lymphoma Promotion Studies -- Studies conducted in two strains of transgenic mice [PIM mice carrying the pim-1 oncogene and TSG-p53 mice, in which the tumor suppressor gene, p53, has been deleted] revealed no activity of 60 Hz magnetic field exposure as a promoter of hematopoietic neoplasia.

5. Pineal Function Studies -- Neither amplitude studies (in which pineal function is assessed at a single time point) in F344 rats or B6C3F1 mice nor time course studies (in which pineal function is characterized throughout the dark cycle) in B6C3F1 mice revealed any biologically significant effect of subchronic magnetic field exposure on serum or pineal melatonin content or pineal activity of N-acetyltransferase, the rate-limiting enzymatic step in melatonin biosynthesis.

6. Immunotoxicology Studies -- Subchronic exposure to magnetic fields had no effect on: a) lymphoid organ weight or cellularity in B6C3F1 mice; b) B-cell function in B6C3F1 mice measured by the antibody plaque-forming assay; c) T-cell function in BALB/c mice measured by delayed- type hypersensitivity responses; d) lymphocyte subsets in B6C3F1 mice, as enumerated via FACS analysis; or e) host resistance to infection with Listeria monocytogenes. Decreases in NK cell activity in B6C3F1 mice (assessed by YAC-1 cytolysis) have been observed in some studies. However, the influence of EMF on NK cell function is variable between experiments, and no clear pattern has emerged from a total of 4 replicates of the NK study design.

7. Two-Year Chronic Toxicity/Oncogenicity Studies -- Two year studies are currently in progress to evaluate the influence of chronic exposure to magnetic fields in F344 rats and B6C3F1 mice. Group sizes of 100 animals per sex per group are being used to increase the statistical power of the bioassays, and to increase the likelihood of detecting small effects. Complete histopathologic evaluation (approximately 50 tissues per animal) will be performed on all study animals at the conclusion of the two-year exposure period.

Studies to evaluate the toxic and carcinogenic potential of 60 Hz magnetic fields in rats and mice. Proc. Ann. Rev. Res. Biol. Effects of Elect. Magnet. Fields from the Generation, Delivery, and Use of Energy, 1992. G.A. Boorman, D.L. McCormick, and J.H. Roycroft.

Studies to evaluate the toxic and carcinogenic potential of 60 Hz magnetic fields in laboratory animals: Progress report on the National Toxicology Program (NTP) project. Proc. Ann. Rev. Res. Biol. Effects of Elect. Magnet. Fields from the Generation, Delivery, and Use of Energy, 1993. D.L. McCormick, J.R. Gauger, T.R. Johnson, B.M. Ryan, J.C. Findlay, J.B. Harder, and G.A. Boorman.

Studies to evaluate the toxic and carcinogenic potential of 60 Hz magnetic fields in laboratory animals. Proc. 4th Annual IEEE Dual-Use Technologies Conference, Vol. 1, pp. 553-560, 1994. D.L. McCormick, J.R. Gauger, and G.A. Boorman.

Design, construction, validation, and operation of a dedicated magnetic field animal exposure facility. Proc. Bioelectromagnet. Soc., 160, 1994. J.R. Gauger, T.R. Johnson, D.A. Williams, and D.L. McCormick.

Eight week toxicity study of 60 Hz magnetic fields in F344 rats and B6C3F1 mice. Proc. Bioelectromagnet. Soc., 83, 1994. D.L. McCormick, B.M. Ryan, J.C. Findlay, J.B. Harder, J.R. Gauger, T.R. Johnson, M.J. Tomlinson, L.H. Brennecke, and G.A. Boorman.

Pineal function assessment in F344 rats and B6C3F1 mice exposed to 60 Hz magnetic fields. Proc. Bioelectromagnet. Soc., 50, 1994. D.L. McCormick, M.A. Cahill, J.B. Harder, B.M. Ryan, J.C. Findlay, L.E. Pomeranz, R.R. Symanski, and G.A. Boorman.

Developmental toxicity (teratology) study of 60 Hz magnetic fields in Sprague-Dawley rats. Proc. Bioelectromagnet. Soc., 127, 1994. B.M. Ryan, E. Mallett, Jr., T.L. Bryan, M.A. Cahill, J.C. Findlay, L.C. Moore, L.E. Pomeranz, R.R. Symanski, J.D. Ter Molen, and D.L. McCormick.

Exposure to 60 Hz magnetic fields and lymphoma development in PIM transgenic mice. Proc. Ann. Rev. Res. Biol. Effects of Elect. Magnet. Fields from the Generation, Delivery, and Use of Energy, 1994. D.L. McCormick, B.M. Ryan, J.C. Findlay, and G.A. Boorman.

Multigeneration reproductive assessment of 60 Hz magnetic fields in rats using the continuous breeding protocol. Proc. Ann. Rev. Res. Biol. Effects of Elect. Magnet. Fields from the Generation, Delivery, and Use of Energy, 1994. B.M. Ryan, R.R. Symanski, J.C. Findlay, L. Pomeranz, E. Mallett, Jr., T.L. Bryant, and D.L. McCormick.

Evaluation of the subchronic, developmental, and reproductive toxicity of 60 Hz magnetic fields. Toxicologist, 15, 166, 1995. D.L. McCormick, B.M. Ryan, J.C. Findlay, J.B. Harder, and G.A. Boorman.

Two-year chronic toxicity/oncogenicity studies of 60 Hz magnetic fields in F344 rats and B6C3F1 mice: 6 month interim progress report. Proc. Bioelectromagnet. Soc., 173, 1995. D.L. McCormick, B.M. Ryan, J.C. Findlay, T.R. Johnson, J.R. Gauger, and G.A. Boorman. Pineal function in B6C3F1 mice exposed to 60 Hz magnetic fields: time course studies. Proc. Bioelectromagnet. Soc., 81, 1995. D.L. McCormick, M.A. Cahill, B.M. Ryan, J.C. Findlay, and G.A. Boorman.

Immunotoxicology evaluation of 60 Hz magnetic fields in mice. Proc. Bioelectromagnet.Soc., 212, 1995. R.V. House, H.V. Ratajczak, P.W. Barbera, P.T. Thomas, T.R. Johnson, J.R. Gauger, and D.L. McCormick. Natural killer (NK) cell function in F344 rats receiving subchronic exposure to 60 Hz magnetic fields. Proc. Bioelectromagnet. Soc., 78, 1995. R.V. House, J. Kozak, A.S. Guy, P.T. Thomas, and D.L. McCormick.

Developmental toxicity (teratology) study of 60 Hz (power frequency) magnetic fields in Sprague-Dawley rats. Teratology, 51, 196, 1995. B.M. Ryan, E. Mallett, Jr., T.L. Bryan, M.A. Cahill, J.C. Findlay, L.C. Moore, L.E. Pomeranz, R.R. Symanski, J.D. Ter Molen, and D.L. McCormick.