C Analysis of Biological Effects and Limits of Exposure to Weak Magnetic Fields Chathurika D. Abeyrathne ∗† , Peter M. Farrell † and Malka N. Halgamuge ∗† , Member, IEEE, Department of Civil and Environmental Engineering ∗ , Department of Electrical and Electronic Engineering † , The University of Melbourne, Parkville, VIC 3010, Australia. Email: c.abeyrathne@pgrad.unimelb.edu.au, {pfarrell,malka.nisha}@unimelb.edu.au Abstract—Adverse biological outcomes due to thermal effects of exposure to high power magnetic fields are well understood and are the basis for standards for limiting human exposure to such fields. Over the past few decades a controversy has arisen over possible adverse biological effects due to exposure to weak, low frequency magnetic fields. This paper involves a critical analysis of the voluminous literature with a view to a theoretical investigation and comparison of the most prominent limits of exposure to weak magnetic fields and geomagnetic field to elucidate the main points of contention. Most of the weak magnetic fields that have been used in these experiments are below international exposure limits and quite a few fields are below Adair’s minimum theoretical exposure limit. There is a large variation in the response of biological systems for various AC magnetic field strength to frequency ratio with no clear correlation. These results demonstrate that characterizing the biological effects by AC magnetic field strength to frequency ratio does not appear to be a reliable technique. Keywords—biological effects, biological systems, exposure limits, weak magnetic fields I. I NTRODUCTION ONSIDERABLE work has been done to date to determine the effects of magnetic fields. The influences of high power magnetic fields are known due to heat generated by those fields [1]. For example, biological effects such as nerve excitation and cardio stimulation can be caused due to the current induced in the body from high power fields [2]. The energy absorption rate of these high power magnetic fields is measured by the specific absorption rate (SAR). There is an ongoing controversy over possible health effects of weak, extremely low frequency magnetic fields since these effects are non thermal. Epidemiological evidence in support of the hypothesis has been published as well as laboratory based measurements of biological activity [3] - [19]. To explain the mechanisms involved in the interactions of biological systems with these fields, variety of mechanisms have been proposed such as Faraday Induction, Ion Cyclotron Resonance (ICR), Ion Parametric Resonance (IPR), magnetite coupling and Radical Pair Mechanism (RPM) [20] - [22]. Both the proposed mechanisms and the empirical evidence have been subjected to considerable criticism on the basis of thermal electrical noise interactions [23] - [26]. In order to analyze the experimental results on human body, the characteristics of tissues such as conductivity, exposed part of the body, sensitivity and exposed area should be compatible with the characteristics of biological systems (plants, animals) that are used in these experiments. Even though there is evidence for biological effects of weak magnetic fields it is not known whether these effects arise from induced electric fields or currents, sensitivity of the part of the body, threshold to the exposure to fields and response (cumulative, statistical, linear and nonlinear). In daily life exposure to 50 or 60 Hz electromagnetic fields is unavoidable because of highly utilized electricity. This draws an attention to the importance of the limits of exposure to weak electromagnetic fields. Adair’s theoretical limits of exposure to weak low frequency electromagnetic fields are basically based on the physical analysis of energy content in these weak fields and thermal electrical noise energy at cell level [23] - [25], [27]. The problem arises in the possibility of explaining the complex biology using these simple physics. The remainder of the paper is organized as follows. In Section II, natural limit of exposure to magnetic fields that is the geomagnetic field, Adair’s theoretical exposure limits and International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines are discussed. Some experimental evidence for biological effects of weak magnetic fields is compared with these exposure limits in Section III. In the discussion of the results (Section IV), the experiments that were done using weak magnetic fields below Adair’s minimum theoretical exposure limit are studied. The conclusions are given in Section V. II. EXPOSURE LIMITS A. Geomagnetic Field (GMF) The geomagnetic field has a number of sources both internal and external to the earth. Most of the fields generated by these sources are time dependent [28]. The geomagnetic field contains magnetic fields up to 3 Hz. The natural signals above this frequency mostly arise from geomagnetic pulsation such as thunderstorms and lightning [29]. The Schumann resonances which are resonants of electromagnetic waves also occur at 978-1-4244-8551-2/10/$26.00 ©2010IEEE 415 ICIAfS10