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

irrelevant to the public health questions posed in thisarticle, which is related to PDA emissions in normalusage.

ELF has been classified as a Group 2B carcinogenfor all humans, not just children, as Jaffa and Herzcomment. The strongest evidence came from epide-miological studies on childhood leukemia, but thedesignation applies to all humans, both adults andchildren.

The suitability of the EMDEX Lite 60-Hzrecording gaussmeter for testing of PDA units has beendiscussed elsewhere at length; we agree that bettermeters would be desirable, but we are reassured by atleast three articles using various ELF meters to verifysignificantly elevated ELF levels [Linde and Mild,1997; Tuor et al., 2005].

REFERENCES

Armstrong B, Theriault G, Guenel P, Deadman J, Goldberg M,Heroux P. 1994. Association between exposure to pulsedelectromagnetic fields and cancer in electrical utility workersin Ontario and Quebec, Canada, and France 1970–1989. AmJ Epidemiol 140:805–820.

ICNIRPGuidelines. 1998. Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to300 GHz). Health Phys 74(4):494–522.

Kheifets L, Sahl JD, Shimkhada R, Repacholi MH. 2005.Developing policy in the face of scientific uncertainty:Interpreting 0.3 uT or 0.4 uT cutpoints from EMFepidemiologic studies. Risk Anal 25(4): DOI: 10.1111/j.1539-6924.2005.00635.x.

Lee GM, Neutra RR, Hristova L, Yost M, Hiatt RA. 2002. A nestedcase-control study of residential and personal magnetic fieldmeasures and miscarriages. Epidemiology 13(1):21–31.

Li KD, Oudouli R, Wi S, Janevic T, Golditch I, Bracken TD, SeniorR, Rankin R, Iriye R. 2002. A population-based prospectivecohort study of personal exposure to magnetic fields duringpregnancy and the risk of spontaneous abortion. Epidemiol-ogy 13:9–20.

Linde T, Mild KH. 1997. Measurement of low frequency magneticfields from digital cellular telephones. Bioelectromagnetics18:184–186.

SageC, JohanssonO, SageA. 2007. Personal digital assistant (PDA)cell phone units produce elevated extremely-low frequencyelectromagnetic field emissions. Bioelectromagnetics 28:386–392.

Theriault G, Goldberg M, Miller AB, Armstrong B, Guenel P,Deadman J, Imbernon E, To T, Chevalier A, Cyr D, Wall C.1994. Cancer risks associated with occupational exposure tomagnetic fields amongutilityworkers inOntario andQuebec,Canada and France: 1970–1989. Am J Epidemiol 139:550–572.

Tuor M, Ebert S, Schuderer J, Kuster N. 2005. Assessment of ELFmagnetic fields from five mobile handsets. ITIS Foundation,Conference Presentation, EMF Health Risk ResearchLessons Learned and Recommendations for the Future.Monte Verita, Switzerland, November 20–24, 2005.

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