## 1 Introduction  
It is very difficult to imagine the modern world without electricity. Over the past decades, the electromagnetic field (EMF) has become the main moderator between primary sources of energy and their final utilization on the public side as well as the main information agent. Economic growth resulted in significantly increased demand for modern technologies that make our lives easier. However, this demand multiplies the natural occurrence of EMF within the environment, leading to daily exposure of living beings to increasing values of electromagnetic quantities, which is documented by growing interest [1; 2; 3; 4] in the assessment of such exposure. Modern appliances are almost exclusively driven by EMF at a frequency of 50 or 60 Hz, which falls within the range of an extremely low-frequency electromagnetic field (ELF-EMF), according to WHO (1-300 Hz). ELF EMFs are present wherever electricity is generated and used (appliances or power lines), but also can be found within the EMF spectrum used in wireless technologies. It should be highlighted that the ELF EMF is not isolated in the wires. The wires shape the path of EMF in space, and EMF is widely distributed around them. Energy of the artificial ELF EMF is irretrievable for technologies, but it can have an impact on living organisms [5; 6; 7; 8; 9; 10; 11; 12], where the biophysical and physiological processes have also the electromagnetic nature. Public health concerns have been underlined since 2002, when the International Agency for Research on Cancer (IARC) classified these fields as Group 3, corresponding to insufficient evidence of harmful effects, but later, based on growing scientific evidence [13; 14; 15], the IARC changed the classification of ELF EMF to Group 2B, corresponding to the possibly carcinogenic group for people. This classification originates from conclusions applied to ELF MF, stating that:  
_\"There is limited evidence in humans for the carcinogenicity of extremely low-frequency magnetic fields in relation to childhood leukaemia._  
_There is inadequate evidence in humans for the carcinogenicity of extremely low- frequency magnetic fields in relation to all other cancers._  
_There is inadequate evidence in experimental animals for the carcinogenicity of extremely low-frequency magnetic fields.\"_[13]. If the effects of these weak fields were confirmed, it would have an adverse and at the same time economic impact on the general public. The exposure to EMF can be investigated from various perspectives, commonly taking into account the electric and magnetic parts separately considering corresponding physical quantities and properties--mainly electric intensity, magnetic flux density, frequency and exposure duration. Assessment of biological reactions to external EMF is usually bound to energy absorption resulting in so-called thermal effects, which are relatively known and well described [16; 17; 18]. However, under certain circumstances and EMF levels, the thermal effects are insufficient to describe the behavior of biological objects exposed to EMF [19]. This is very common in the area of ELF EMF, where the wavelength is simply too long in comparison with biological objects to cause any significant thermal effect. To address this problem, the nonthermal description of EMF action needs to be considered, especially when the magnetic component of ELF EMF is investigated. At the molecular level, several theories describing the biological effects of an extremely low-frequency magnetic field (ELF MF) have already been proposed, among which the theory about reactive oxygen species (ROS) and free radical pairs [20; 21; 22; 23] is one of the most popular explanations of ELF MF nonthermal effects, postulating that it is the increase in the amount of ROS that causes various pathological processes and diseases in the body.