## 1 Introduction  
Non-ionizing electromagnetic fields (EMFs) are widely used in everyday life, because a lot of electronic devices (mobile phones, cordless phones, computers, etc.) work by emitting and receiving EMF radiations. As such, people are continuously exposed to such non-ionizing radiation: although it cannot produce charged ions when passing through human body, it can induce charge movements which can affect active transport across cell membranes, cause oxidative stress and interfere with DNA [1; 2; 3; 4; 5]. Although the scientific debate concerning adverse health effects of EMFs has been developed for many years, today controversial results still occur [6; 7; 8]. Among biological tissues, peripheral blood is one of the most involved in environmental EMF exposure, because it circulates throughout the human body and passes just below the skin, i.e., very close to the external environment where EMFs are present. Blood consists of many components, which play the functions of nutrition and defense of the human body. In particular, monocyte and lymphocyte cells play the fundamental role of immune defense against infections of pathogens. Therefore, it is worth investigating the effects consequent to exposure of peripheral blood lympho-monocyte (PBLM) cells to non-ionizing EMFs, in order to better establish measures to protect the population against adverse effects due to proliferation of source of EMFs. Many results have been recently reported about the induction of changes in cells extracted from peripheral blood and exposed to EMFs. In particular, [PERSON] et al. [9] demonstrates that radiofrequency (RF) signals with specific absorption rate (SAR) larger than 5.0 W/kg can induce chromosomal damage in long-term exposed human lymphocytes. [PERSON] et al. [10] reported chromosomal instability in human peripheral blood lymphocytes exposed to 830 MHz EMFs (SAR 1.6-8.8 W/Kg). [PERSON] et al. [11] showed a significant increase of reactive oxygen species (ROS) production in monocytes extracted from peripheral blood after exposure of blood samples to 900 MHz EMFs, whereas it was not significant in lymphocytes. [PERSON] et al. [12] investigated the blood from people living in the vicinity of tower antennas for mobile phones and they found that some blood parameters, such as the percent of monocyte cells, were altered by exposure. This latter study raised an alert for health safety of people involved in long-term exposure to EMFs. Recently, we reported on morphological modifications, biochemical changes, increase of the oxygen consumption rate and damage of the oxidative phosphorylation system occurring in lympho-monocyte cells extracted from peripheral blood exposed to 1.8 GHz EMFs (with an SAR value of 0.21 W/Kg) for several times ranging from 1 h to 20 h [13]. In particular, we measured and compared, for each exposure time, unexposed and exposed PBLM cells isolated from the blood obtained by single human donors. Significant biochemical differences for 5, 12 and 20 h exposure times were found. Such biochemical modifications were detected by means of Raman microspectroscopy measurements of single PBLM cells. Raman spectroscopy is an analytical technique based on the measurement of the energy of vibrational modes of functional groups inside the investigated cells. This technique has been largely applied to obtain information about biochemical changes induced by exogenous agents at single cell level [14; 15; 16]. Multivariate statistical methods, such as principal component analysis (PCA), can be used to analyze Raman spectra dataset including cells of different type: in fact, PCA allows to discriminate them according to differences in their biochemical content and identify the spectral features with large variability [16; 17; 18].