Bioelectromagnetics 28:583^585 (2007)

Comment

Measuring ELF Fields Produced by MobilePhones and Personal Digital Assistants (PDAs)

K. Jaffa1* and M. Herz2

1PacifiCorp2Pacific Gas and Electric

ELF measurements of personal digital assistants(PDAs) were recently reported by Sage et al. [2007] torange from about 10 mT to as high as 90 mT. The authorsalso interpret the meaning of these measurements in thecontext of ELF health studies and standards. We wouldlike to comment on parts of this discussion.

The authors incorrectly imply that the ICNIRPstandards [ICNIRP, 1998a, b] are based on thermaleffects in the frequency bandwidth of the EMDEX Litemeters, 40–1000 Hz. The ICNIRP standard as well asthe IEEE standard [IEEE, 2002] limits are based onelectrostimulation effects and not thermal effects in thisfrequency range. These limits are such that the generalpublic would not feel any electrostimulation effects atthe reported PDA field exposures. Further, the authorscompare their measurements to the ICNIRP referencelevels at power frequencies. These reference levels arebased on uniform field exposure to the whole body andare, more specifically, based on induced currents in thebrain and spinal cord. It is unfortunate that the authorsdo not report on how the field drops off with distancefrom their test PDAs; however it is reasonable to assumethat the fields from these devices are non-uniform anddrop off significantly with distance, since the source issmall compared to the dimensions of a person. In thissituation, the comparison to the whole body referencelevels of ICNIRP is meaningless. The proper applica-tion of the ICNIRP standard is to use their basicrestrictions rather than their reference levels. Forcomparison to the ICNIRP’s basic restrictions, oneneeds to account for the non-uniformity of the field,estimate the induced current from their PDAs in thespinal cord or brain, and compare this to ICNIRP’s basicrestrictions. A proper evaluation would also take intoaccount all of the frequency components. Thisis, however, a complex process and may have beenoutside their study scope.

Similar concerns can be raised about theircomparisons of results to the health effects studies thatare based on whole body time-weighted averageexposures. It is unfortunate that they speculate that this

PDA exposure could dwarf whole body exposures thatpeople experience, when in all likelihood theymay onlycontribute little to the whole body time-weightedaverage exposures. Further, while the authors citestudies to support increased risks of various cancers inadults, IARC, a source they cite for childhood leukemia,did not find sufficient information to classify EMF as apossible carcinogen for adults. Thus, caution is alsowarranted when reading their interpretation of thescience for other diseases.

Finally, we have concern about the accuracy ofmeasurements in the presence of strong non-uniformradio frequency fields. It is known that ELFmetersmustbe shielded in strong radio frequency field environ-ments [IEEE, 1991, 1994]. Often higher frequencyfields can saturate the electronics and make themeasurements meaningless unless they are specificallydesigned for this type of environment.

REFERENCES

ICNIRP. 1998a. Guidelines limiting exposure to time-varyingelectric, magnetic, and electromagnetic fields (up to 300GHz). Health Phys 74(3):494–522.

ICNIRP. 1998b. Response to questions and comments on theguidelines for limiting exposure to time-varying electric,magnetic, and electromagnetic fields. Health Phys 75(4):438–439.

IEEE. 1991. Magnetic fields task force report, an evaluationof instrumentation used to measure AC power systemmagnetic fields. IEEE Trans Power Deliv 6:373–383. NewYork.

�2007Wiley-Liss, Inc.

——————*Correspondence to: K. Jaffa, 1407 W. North Temple St., Ste.NTO275, Salt Lake City, UT 84116.E-mail: kent.jaffa@pacificorp.com

Received for review 13 April 2007; Final revision received10 May 2007

DOI 10.1002/bem.20349Published online 9 July 2007 in Wiley InterScience(www.interscience.wiley.com).

IEEE. 1994. Recommended practice for instrumentation:Specifications for magnetic flux density and electricfield strength meters–10 Hz to 3 kHz. IEEE Std. 1308.New York.

IEEE. 2002. Standard for safety levels with respect to humanexposure to electromagnetic fields, 0 to 3 kHz. IEEE

Standard C95.6. New York: The Institute of Electrical andElectronic Engineers.

Sage C, Johansson O, Sage SA. 2007. Personal digital assistant(PDA) cell phone units produce elevated extremely-lowfrequency electromagnetic field emissions. Bioelectromag-netics Mar 13 [Epub ahead of print].

Response

Response to Comment on‘‘Measuring ELF Fields Produced by Mobile

PhonesandPersonal Digital Assistants (PDAs)’’

Cindy Sage1* and Olle Johansson2

1SageAsssociates, California2Karolinska Institute, Experimental DermatologyUnit, Stockholm, Sweden

Jaffa andHerz correctly point out that the ICNIRPlimits we cite are based on electrostimulation ratherthan thermal effects.

Table 7 of the ICNIRPGuidelines confirms for thefrequency range of 0.025–0.8 kHz that the generalpublic exposure limits for 50 Hz and 60 Hz ELF are83 uT and 100 uT, respectively [ICNIRP, 1998] andTable 1 of Kheifets et al. [2005] confirms these numbersare correct; but the basis on which they have beendeveloped is a limitation on induced current density (to2 mA/m2 for the general public) rather than on thermaleffects.

Jaffa andHerz comment that ‘‘these limits are suchthat the general public would not feel any electro-stimulation effects at the reported personal digitalassistant (PDA) field exposures.’’ This is a worrisomeobservation precisely because even excessively highELF exposures from PDAs cannot warn the user, if theyare not felt.

They object to comparisons of our results [Sageet al., 2007] to the health effects studies that are basedon whole body time-weighted average exposures, asopposed to partial-body exposures. Our discussionof health effects studies providing context for ELFexposures includes studies relevant to the subject of thisscientific article; i.e., studies reporting both positive andnegative findings of adverse health effects with all kindsof ELF exposure. In the context of repetitive, chronicexposure to significantly elevated ELF pulses fromPDAsworn on the body, relevant health studies pointingto a possible relationship between ELF exposure andcancer and pregnancy outcome have been appropriately

cited, particularly Lee et al. [2002], Li et al. [2002],Armstrong et al. [1994], and Theriault et al. [1994].

These ICNIRP and IEEE limits govern themaximum ELF fields to which the public may beexposed, and we have cited the relevant health effectsliterature on ELF and cancer, pregnancy outcome, andneurological diseases which reports increased risks ofdisease that may occur at far lower levels than thecurrent limits. If the public argues against involuntaryexposure to ELFat levels, say, above 0.2 uT, these limitsare used by industry to justify such exposures, even inlight of the growing body of scientific evidence pointingto the need for caution, and even though ELF has beenclassified as an IARC Group 2B (possible) carcinogen.

It is not relevant to dwell on how ELF fields dropoff quickly with distance from the PDAs, since whenthey are worn at or very near the body, the relevantemission level is where the PDA contacts the user. Infact, the focus of the article is to highlight that typicaluse of PDAs is in contact with the body, whenworn on abelt or pocket and not at some distance away. WhetherELF drops off in any meaningful way at a distance is

�2007Wiley-Liss, Inc.

*Correspondence to: Cindy Sage, Sage Associates, 1396 Dan-ielson Road, Santa Barbara, CA 93108. E-mail: sage@silcom.com

Received for review 7 May 2007; Final revision received 10 May2007

DOI 10.1002/bem.20348Published online 24 July 2007 in Wiley InterScience(www.interscience.wiley.com).

584 Jaffa and Herz