The study comprised four campaigns dedicated to measuring the electric field (E-field) in HUC. The primary focus of these measurements was to evaluate wireless signals and determine their adherence to legally established exposure thresholds at mobile frequencies. The observed E-field background served as crucial data for assessing potential health effects and interactions with neighboring wireless networks, including devices emitting within the same frequency band. To ensure comprehensive coverage, 11 measurement locations were strategically chosen, taking into account base station information within a 500-m radius around HUC. These locations were identified based on data collected and documented by the Ministry of Digital Transformation (2023) (Figure 1). Measurement locations inside HUC are shown in Figure 2.

The measurements were conducted utilizing the MVG EME SPY 200 Personal E-field Exposimeter, which is a type of radiofrequency (RFR) frequency-selective exposure meter commonly called an exposimeter or PEM (personal E-field exposimeter). Measurements were taken every 5 s with a three-axial E-field probe that measures E-field V/m and calculates total exposures based on recorded samples in 20 predefined frequency bands in the 88 MHz—5850 MHz range. The measurement protocol differentiates uplink (UL) and downlink (DL) for mobile communications. The upper detection limit of measurement instrumentation is 6 V/m, while the sensitivity varies for different bands and is 0.005 V/m for most, excluding WiFi5G with a sensitivity of 0.01 V/m.

The PEMs utilized in this study were specifically designed for environmental surveillance, enabling the execution of radiofrequency (RFR) static measurement campaigns at designated locations. These devices monitor electromagnetic field (EMF) exposure over time in complex and heterogeneous environments. Numerous epidemiological studies (Gotsis et al., 2008; Troisi et al., 2008; Grigoriev et al., 2019; Grigoriev et al., 2020; International Commission on Non-Ionizing Radiation Protection ICNIRP, 2020) have utilized PEMs to assess and evaluate EMF exposure in such environments. To measure the multi-spectral distribution of radiofrequency (RF) energy and determine the signal strength of specific frequencies, an experimental protocol was employed with the PEM. Figure 3 illustrates the PEM’s capacity to measure 20 frequency bands, including both DL and UL communications. It is notable that this study excluded consideration of exposure from wireless handsets and UL communications [LTE B12 (UL), LTE B13 (UL), LTE B4 (UL), and LTE B7 (UL)] as discerning the E-field due to UL from individuals’ phones proves challenging. The analysis focuses on the DL measures of various communication systems, including LTE B20 DL, GSM+UMTS 900 DL, GSM 1800 DL, UMTS 2100 DL, LTE B7 DL, WIFI 2G, WIFI 5G, and DECT 6.0. The measurements were conducted in February 2022, June 2022, December 2022, and June 2023.

A multi-band scenario setup was chosen, employing an E-field sampling rate of 4 s in the SPY 200 PEM. The procedure encompasses five primary steps. Initially, the locations of base stations for each campaign were determined (Ramos et al., 2021). Subsequently, specific measurement locations within the HUC contour were identified. The PEM data were then collected from the 11 selected locations. Following data collection, the fourth step involved the analysis and presentation of four locations with higher E-levels registered in both campaigns. The frequency exhibiting the highest observed level was utilized as the E-field level for organoid exposure. A significant portion of the measurements fell below the lower detection limit of the PEM (0.005 V/m) in each individual frequency band, leading to censorship. The placement of the PEM hardware device aimed to mitigate underestimation by locating it away from the staff member’s body, minimizing body-shielding effect underestimation (only 1 V/m of body-shielding effect when another user/scatterer is located between the radiating antenna and the receiver) (de Miguel-Bilbao et al., 2019). After sample collection, the dosimeter generated graphics depicting the electric field vs. time (Figure 4A) and frequency (Figure 4B). Approximately 400 realistic exposure samples were generated in 30 min to ensure statistically relevant results.

The analysis utilized median and maximum values extracted from specific datasets of E-field strength, denoted in volts per meter (V/m). This approach aimed to assess the impact of exposure for each measured frequency band outlined in Table 1, including LTE B20 (DL), GSM+UMTS 900 (DL), GSM 1800 (DL), UMTS 2100 (DL), and LTE B7 (DL).

Neural stem cell organoid exposure was performed in GTEM exposure cell GTEM ETS-LINDGREN 5402 coupled with RF Signal Generator Rohde & Schwarz SMBV 100B (8 kHz–6 GHz) to obtain the GSM 1840 MHz (DL) signal with 2.1 V/m during exposure. The generator is connected to a power amplifier ZHL-42 W (10 MHz–4200 MHz). This set up is presented in Figure 5. Control organoids were located outside the chamber and were evaluated for background exposure using a MVG EME SPY 200 Dosimeter. Temperature was maintained at 25 °C both inside and outside the GTEM during the whole exposure period.

The purpose of this cell was to create a uniform electromagnetic field that is the most important factor in a GTEM cell. To verify its field uniformity, it was measured by Isotropic Probe (IP) ETS-Lindgren HI-6105 (100 kHz—6 GHz). The exposure chamber was designed based on a field uniformity check based on planar measurements. The field conditions of uniformity inside GTEM are defined for the different frequencies as per Annex B of IEC standard 61000-4-20:2022 (IEC Standard, 2022). This process has been presented in in-depth in previous publications by authors Ramos et al. (2021); IEC Standard, 2022.

To select the exposure level, a field value 2.15 V/m at a frequency of 1840 MHz was selected inside the uniformity volume. The level of the RF generator to obtain a field level of 2.15 V/m was −32.6 dBm.

Biological-model control samples were assessed under baseline exposure conditions outside the GTEM. This evaluation was conducted using the MVG EME SPY 200 Dosimeter covering a frequency range of 88–5850 MHz. The dosimeter allowed for the isotropic recording of the electric field across various preselected frequency sub-bands. Additionally, it captured the total electric field for the entire measurement range, exemplified by wideband recordings spanning 27 MHz–6 GHz (Figures 5, 6).

In total, our measurement campaign collected around 7500 RF-EMF samples. In this section, we present the comparative analysis based on frequency-selective measurement of the E-field in the 88 MHz–6 GHz frequency range. To better understand the impact of each technology and their contribution to the total exposure, this section presents the most significant bands that caused relatively higher V/m values: LTE B20 (DL), GSM+UMTS 900 (DL), GSM 1800 (DL), UMTS 2100 (DL), and LTE B7 (DL). All presented higher levels in the fourth campaign and did not in any case exceed the ICNIRP reference levels, remaining significantly lower.

A PEM generates numerical datasheets in Excel format (MS Office). Initial visual inspection of the measurement results (Figure 4) indicated that certain frequency bands did not significantly contribute to the evaluated exposure, with cellular phones being the most prominent contributors, along with DECT frequency bands. Wi-Fi 2G and 5G bands were excluded from consideration due to their consistently low registered levels. It is worth noting that PEMs were positioned at a distance from routers and that no individuals were in proximity during measurements. Measurement results that fell within the sensitivity range of the employed devices are omitted. The distinctive features of the experimental results are then compared to total E-field measurements for RF systems during Campaign A in February 2022, Campaign B in June 2022, Campaign C in December 2022, and Campaign D in June 2023, respectively.

Figures 7–10 depict the consideration of distances to electromagnetic radiation (EMR) sources and the evolving landscape of radiocommunication services along with their physical infrastructure.

Consistent with earlier research findings, similar conclusions emerge. Generally, radiofrequency electromagnetic field (RF-EMF) exposure levels across a wide frequency spectrum remain very low in typical daily life situations. These exposure levels consistently fall well below 1 V/m when compared to the existing international limits for RF-EMF exposure (Grigoriev et al., 2020).

As can be observed in Figures 7–10, the location that registered the highest E-field level was Location 6. The frequency with the highest contribution GSM 1800 (DL) and 2.174 V/m observed (1840 MHz) was selected for biological effects evaluation.

The radiation levels to which the control samples were exposed never exceeded 0.36 V/m. In the 1840-MHz frequency band, the maximum value recorded throughout all exposures was 0.005 V/m and so did not exceed the PEM detection threshold.

The appearance and morphology of the BOs were not altered by the applied radiation (Figure 11A). The molecular analysis by quantitative real-time PCR detected no significant variations in gene expression associated with apoptosis (BAX, BCL-2) or cellular senescence (CDKN1A). However, a significant decrease in the modulation of genes involved in proliferation and cellular cycle (MKI67 and CCND1) and cellular activity (C-FOS) was observed in radiated BOs with respect to the control group during the differentiation stage, with no changes in the other stages presented in (Figures 11B–G). This suggests that more attention should be given to the potential effects of RF exposure on early brain development.

The most notable frequency bands contributing to relatively higher E/m values were LTE B20 (DL), GSM+UMTS 900 (DL), GSM 1800 (DL), UMTS 2100 (DL), and LTE B7 (DL). Among these, GSM 1800 (DL) exhibited the most significant radiation exposure in all measured locations, with higher levels observed during the third campaign. It is important to note that, as explained in Section 2, the measurements presented here do not account for the impact of radiation exposure from individual cell handsets. These findings align with the existing literature, including a recent study across five EU countries (Birks et al. 2018), research in five different urban areas in Belgium (Velghe et al., 2019), work presented in (Ramos et al., 2023) in outdoor healthcare environment, and a study conducted in public shopping malls (Celaya-Echarri et al., 2021).

Table 2 provides a summary of the RF-EMF exposure levels obtained from the six selected locations, presenting percentage values compared to the lowest reference level outlined by ICNIRP guidelines for the respective frequency band (ranging from 36.37 V/m to 61 V/m). Additionally, it includes percentage values for medium and maximum exposures.

For the user category, the location exhibiting the highest peaks is Location 6, registering a maximum of 2.2 V/m (equivalent to 0.029% of the ICNIRP reference level). Notably, all maximum peaks were observed within LTE (DL) frequency bands across the four campaigns.

The evolution of the infrastructures observed by the Ministery of Digital Transformation (2023) is the provision of service in 5G technology at frequencies of 700, 3500, and 3400 MHz. As 4G services decreased over time, there was an increase in 5G. At the time of this study, there were 43 3700 MHz stations, 54 700 MHz stations, and four 3500 MHz stations. The 3500-MHz band is not registered in the SPY 200 and is one of the 5G bands in increasing use. The cells were adjusted depending on usage and the distance of users. Lower levels may indicate network optimization.

The progression and densification of base stations (BS) can potentially elevate exposure levels. However, it is crucial to emphasize that, in any scenario, these levels do not surpass 0.5% of the ICNIRP reference levels compared to the threshold values established by prevailing standards and guidelines. This observation is significant in preventing electromagnetic interference to medical equipment, mitigating potential harm to workers, monitoring exposure levels within the workforce and the public at large, and ensuring that emission levels remain below recommended thresholds.

The effects of the level of cell proliferation, apoptotic cell death, and senescence were analyzed, which is useful for preventing potential damage to the general public (including workers) and biological effects by means of organoid evaluation. This study presents a novel approach to wireless technology effects produced at frequencies where radiation absorption by tissues is higher and the assessment of non-thermal effects or system alterations.

Here, we used human BOs as a model to study some of the possible molecular effects of RF exposure during brain development. We found that an 1840-MHz RF—widely used in mobile phone communication—has no effect on senescence or the apoptosis of developing BOs, with no changes in the expression of the apoptosis- (BAX, BCL-2) or senescence (CDKN1A)-related genes. These data are from studies in different types of NSCs (Eghlidospour et al., 2017; Chen et al., 2021; Velghe et al., 2019; Ramos et al., 2023).

On the other hand, the cell cycle and proliferation of NSCs is related to the self-renewal capacity of the cells, which is of great importance in maintaining the total number of NSCs for generating various types of neurons and glia during brain development. Our data show that RF exposure decreases the expression of genes related to proliferation and cell cycle (MKI67 and CCND1) and activity (C-FOS) in differentiating BOs without changes in the other stages of induction and maturation/maintenance of these cultures. This suggests that the effects of RF on BOs depend on the developmental stage of the BOs. These data differ from those by (Eghlidospour et al., 2017; Chen et al., 2021; An et al., 2023; Cruz-Mendoza et al., 2022) in NSCs. This discrepancy may be due to the different cell models and the durations and frequencies of exposure.