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* Article title: Measurement of urban environmental exposure to Extremely Low Frequency Magnetic Fields in several Spanish regionsTittle page
Aránzazu8
Sanchis-Otero1
RaquelRamirez-Vazquez2,3
M.Jesús8
Paniagua9
RicardoBajo4,7
Enrique8
Arribas3,5
FernandoGiacomone4
RebecaRamis1
MarínPilar8
Palacios4
Francisco1
VargasMarcos6
Bajo4✉,7Emailrbbreton@ucm.es
1Non-ionizing Radiation Unit, Radioprotection Area, National Centre of Environmental HealthInstitute of Health Carlos IIIMajadahonda, MadridSpain
2Department of Physics, Polytechnic School of CuencaUniversity of Castilla-La Mancha, University Campus16071CuencaSpain
3MORFEO Research GroupUniversity of Castilla-La ManchaAlbaceteSpain
4Institute of Applied MagnetismComplutense University of MadridMadridSpain
5Department of Physics, Faculty of Computer Science EngineeringUniversity of Castilla-La ManchaAvda. de España s/n, University Campus02071AlbaceteSpain
6Deputy Direction of Environmental Health and Occupational HealthMinistry of Health, General Directorate of Public HealthMadridSpain
7Faculty of Science and technologyValencia International University (VIU)ValenciaSpain
8h.- Cancer and Environmental Epidemiology Unit. Chronic Diseases Department, National Centre for EpidemiologyInstitute of Health, Carlos III (ISCIII)MadridSpain, Spain
9GRNIIU Research GroupUniversity of Extremadura10003CáceresSpain
* Author names: Aránzazu, Sanchis-Oteroa†; Raquel, Ramirez-Vazquezb,c†; Jesús M., Paniaguai†; Ricardo, Bajod,g†; Enrique, Arribasc,e; Fernando, Giacomoned; Rebeca, Ramish; Pilar, Marín Palaciosd; Francisco, Vargas Marcosf.
* Affiliations:
a.- Non-ionizing Radiation Unit, Radioprotection Area, National Centre of Environmental Health, Institute of Health Carlos III, Majadahonda, Madrid, Spain.
b.- University of Castilla-La Mancha, Department of Physics, Polytechnic School of Cuenca, University Campus, 16071 Cuenca, Spain.
c.- MORFEO Research Group, University of Castilla-La Mancha, Albacete, Spain.
d.- Institute of Applied Magnetism, Complutense University of Madrid, Madrid, Spain.
e.- University of Castilla-La Mancha, Department of Physics, Faculty of Computer Science Engineering, Avda. de España s/n, University Campus, 02071 Albacete, Spain.
f.- Ministry of Health, General Directorate of Public Health, Deputy Direction of Environmental Health and Occupational Health, Madrid, Spain
g.- Faculty of Science and technology, Valencia International University (VIU), Valencia, Spain
h.- Cancer and Environmental Epidemiology Unit. Chronic Diseases Department, National Centre for Epidemiology, Institute of Health, Spain Carlos III (ISCIII), Madrid, Spain.
i.- GRNIIU Research Group, University of Extremadura, 10003 Cáceres, Spain.
* Corresponding author:
Bajo, Ricardo. Institute of Applied Magnetism, Complutense University of Madrid, Madrid, Spain & Faculty of Science and technology, Valencia International University (VIU), Valencia, Spain
Email address: rbbreton@ucm.es
Abstract
This is an observational descriptive study carried out in three Spanish regions to identify typical environmental levels of extremely low frequency magnetic fields (ELF-MF) in diverse population settings as well as in the proximity to various electrical infrastructures. To achieve this, measurement protocols were previously established considering national and international reference standards. To describe the public exposure to ELF-MF, both immission and emission levels have been quantified in public spaces and close to the main infrastructure related to the transportation and distribution of electricity, but also to those related to electrified transport. Based on the collected data, the average environmental ELF-MF exposure level in public spaces is 0.095 µT, while it is 1.303 µT in the vicinity of emission sources. The observed levels of exposure to ELF-MF in Spain are very similar to those in other European countries, with values significantly below the maximum exposure limits recommended by the International Commission on Non-Ionizing Radiation Protection in 2010, which for the public are set for 50 Hz at 200 µT. This study, as a preliminary step, paves the way for further research that may encompass more Spanish’ regions and provide a data collection for future epidemiological studies, as well as a useful reference for the public. It could provide a foundation for establishing national regulatory frameworks on this matter, given the current absence of specific legislation in Spain.
Keywords:
Extremely low frequency magnetic fields (ELF-MF)
exposure assessment
outdoor exposure
public spaces
ELF-MF emission sources
exposure assessment
Highlights
- Typical ambient ELF-MF levels in Spain were identified.
- Immission and emission levels in public areas and from diverse sources evaluated.
- The low ELF-EMF levels found in Spain are like those in developed countries.
- The mean outdoor immission value is 0.1 µT and the mean emissions level 1.3 µT.
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1. Introduction
Residential exposure to magnetic fields (MF) in the extremely low frequency range (1 Hz to 100 kHz) has raised some public concern due to the hypothetical relationship between low levels of MF of 50 Hz/60 Hz and childhood leukemia (CL). Since 1979, this possible association has been observed for years in epidemiological studies (Wertheimer and Leeper 1979; Ahlbom et al. 2000; Greenland et al. 2000; Malagoli et al. 2023) (Kheifets, Ahlbom, et al. 2010) (Kheifets et al. 2016), and other health effects, such as cancer and neurodegenerative diseases in adults, have also been studied in connection to this environmental physical agent(Kheifets et al. 2016)(Seomun 2021; Gervasi et al. 2019; Huss et al. 2009).
The regulation to limit the exposure to ELF-MF for public protection relies, in Europe, on the recommendation for health protection against exposure to electromagnetic fields throughout the frequency range (0 Hz to 300 GHz), the EU Council Recommendation ((BOE) 1999).
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This is based on the guidelines published by ICNIRP in 1998, in light of established evidence on the acute effects (short-term) of exposure to electromagnetic fields (Matthes et al. 1998). Concerning ELF-MF, the primary objective is to prevent effects on the nervous system resulting from the induction of electric currents within the body, as well as any perception and annoyance occurring at high ELF-MF levels. Following the establishment of various safety factors, ICNIRP recommended as a basic restriction to limit the induced electric current density in the head and trunk to 2 mA/m2. Then, theoretically calculated reference levels for the 50 Hz magnetic field were set at 100 µT.In 2002, the International Agency for Research on Cancer (IARC) classified the ELF-MF in Group 2B as possibly carcinogenic to humans. The scientific literature evaluation made by the IARC led to this classification due to limited and inadequate evidence in humans regarding CL and other cancers, respectively, and to inadequate evidence in experimental animals. Specifically, the classification responded to those epidemiological studies reporting a statistical relationship between acute lymphoblastic leukemia (ALL) and prolonged average exposure during childhood to ELF magnetic field levels of 0.3–0.4 µT (IARC 2002), in which random, biased, or confounding factors could not be ruled out. Later, the health risk assessment of exposure to ELF electric and magnetic fields addressed by the World Health Organization (WHO), and published in 2007, concluded that “new human, animal and in vitro studies, published since the 2002 IARC monograph, do not change the overall classification of ELF magnetic fields as a possible human carcinogen” (Organization 2007).
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Then, in 2010, ICNIRP reviewed the 1998 guidelines regarding electric and magnetic fields at ELF, establishing a new limit of 200 µT for the magnetic field of 50 Hz (Matthes et al. 1998). A
These updated guidelines were based solely on the scientific evidence available at the time, excluding as a criterion the observed increased risk of childhood leukaemia due to the lack of a causal relationship with the chronic exposure to ELF-MF.Conclusions from consecutive scientific reports by national and international agencies and committees (European Commission 2015; National Agency for Food, Environmental and Occupational Health and Safety (ANSES) 2019; Swedish Radiation Safety Authority’s Scientific Council on Electromagnetic Fields 2024) are consistent with previous findings that, to date, any potential health effect from chronic exposure to ELF-MF do not meet sufficient criteria to be deemed causal, and further research is needed (ICNIRP 2015). This is generally supported by international bodies, such as the UK Health Security Agency, the German Federal Office for Radiation Protection (BfS), the Irish Environmental Protection Agency (EPA), the Dutch National Institute for Public Health and the Environment (RIVM) or the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Besides, the relative risk over time in epidemiological studies has shown a slight decrease, i.e., a weaker association between childhood leukaemia and ELF-MF, but without fully understanding the possible causes of this trend (Kheifets, Ahlbom, et al. 2010) (Swanson, Kheifets, and Vergara 2019; Crespi et al. 2020) (Crespi et al. 2020) (Swanson, Kheifets, and Vergara 2019) (Kheifets, Ahlbom, et al. 2010). In a recent study, the diverse meta-analysis addressed considering the different approaches for assessing the magnetic field exposure, such as direct ELF-MF measurements, distances between dwelling and high-voltage power lines (HVPL) and wire coding configurations, pointed to a reduced risk found when studies were based on magnetic field measurements (Brabant et al. 2021). Also, a pooled analysis of individual data from 24,994 cases and 30,769 controls, obtained from four recent studies on ELF-MF and CL, concluded that there is no increased risk at exposure levels above 0.4 µT compared to levels below 0.1 µT (Amoon et al. 2022) unlike previous studies. According to the authors, methodological issues, chance or a true finding of disappearance of the association could respond to these new observations.
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However, the data collected by the International Agency for Research on Cancer (IARC) shows a worldwide increase in the incidence rate of childhood leukaemia from the 1980’s to the end of the 2000s, that might only in part be explained by an improvement in diagnosis and registration (Steliarova-foucher et al. 2017). Therefore, all these observations indicate that more multidisciplinary investigations are still needed to clarify the potential role of ELF-MF on CL and other suggested health effects, especially, experimental and mechanistic but also epidemiologic studies, all of them supported by improved exposure assessments of this environmental agent (ICNIRP 2015; Schmidt, Hornhardt, and Erdmann 2021).A
Despite the international effort made in the last years for an improvement in the assessment of the ELF-MF exposure (Bonato et al. 2023; Gajšek et al. 2016), in Spain there are still few studies devoted to this issue. Some relevant data about personal indoor and outdoor exposure to ELF-MF by children and pregnant women were registered in two Spanish provinces, Granada (south) and Guipuzcoa (north), from the INMA project population cohort (Calvente et al. 2014; Gallastegi 2017). Other studies of ELF-MF environmental characterization were addressed in different towns from the western region of Extremadura to estimate the outdoor exposure levels of their inhabitants (Paniagua et al. 2004). Thus, one of the main objectives of this preliminary study is to provide new information about the ELF-MF environmental exposure in the general Spanish population, defining in advance a measurement protocol, considering both immission (magnetic field reaching a location) levels in public spaces (outdoor and indoor) and emission levels in proximity to electrical infrastructure. Through this study quality data and procedures will be provided for addressing future measurement campaigns and epidemiological analysis, but also relevant information will be reported for national regulator agents and other stake holders for risk perception management. Besides, this study, initiated by the Spanish Ministry of Health, addresses key objectives outlined in the "Strategic Plan for Health and Environment 2022–2026" (PESMA). It serves as a crucial first step towards a comprehensive national assessment of ELF-MF exposure levels in Spain.As a first approach, three Spanish regions were considered (Albacete, Cáceres, and Community of Madrid), and diverse public places and ELF-MF emission sources included. Measurements were performed following previously established protocol based on international and national standards. The immission ELF-MF levels in outdoor and indoor public spaces were measured. The ELF-MF emission levels were assessed in proximity to primarily infrastructure related to the transportation and distribution of electricity, but also to electrified modes of transport. Moreover, in order to analyze the consistency of this environmental assessment with other countries, the ELF-MF levels measured near the HVPL have been compared to those obtained from a recent French study (Deshayes-Pinçon et al. 2023).
2. Materials and methods
2.1. Measurement equipment and test inter-comparison
All measurements were carried out using identical electromagnetic field meters SMP2 from WAVECONTROL which allow selective -up to 400 kHz- and broadband measurements. All systems were equipped with the WP400 probe (frequency range of 1 Hz to 400 kHz and a resolution of < 0.1 nT (at 50 Hz)) and GPS for geo-referencing the recorded data. The devices calibrated at the manufacturer were subjected to an inter-calibration process, carried out at the Institute of Applied Magnetism of the Complutense University of Madrid (IMA-UCM), before the measurement campaign.
An Kepco BOP 2050 MG power supply and Helmholtz coils were used to generate various levels of magnetic field (in the supplementary material we can see an image showing the Kepco BOP 2050 MG power supply and the Helmholtz coils used to generate various levels of magnetic field). The coils were fed with four different current intensities − 0.1 A; 0.15 A; 0.2 A and 1 A - and a background measurement was also made. SMP2 equipment was configured to measure in the frequency range of 10 Hz to 400 kHz, and the magnetic field levels were recorded during six minutes. All results obtained for each intensity and equipment, were quite similar. Differences among them were evaluated through the dimensionless z-score parameter, defined as follows (1):
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in accordance with the G-ENAC-14 guide (National Accreditation Entity (ENAC) 2008) where x is the measurement of each equipment, xa is the average of the results obtained by the different equipment, and σp is the target or appropriate standard deviation. Since the objective of this project is the measurement of environmental magnetic fields, the average of the relative standard deviations of the outdoor measurements corresponds to σp, taking a value of 12.3%. All the z-score obtained for the different equipment were satisfactory (|z|< 2).
2.2. Measurement Locations
Across the three Spanish provinces involved, Albacete (Castilla-La Mancha), Cáceres (Extremadura) and Madrid, specific locations were selected within two distinct categories: public spaces (group A) and emission sources (group B). Thus, on the one hand, we will measure the ELF-MF immission levels in public spaces considering the following environments: A.1) streets in urban and single-family residential areas, A.2) parks and gardens, A.3) public buildings, A.4) public buildings (interior), A.5) public transport stations and A.6) underground. And, on the other, the emission levels were measured in proximity to ELF-MF infrastructure, which may present higher magnetic field values, considering the following sources: B.1) overhead 220 kV high-voltage power lines (HVPL), B.2) overhead 400 kV HVPL, B.3) underground 220 kV HVPL, B.4) electrical substations, B.5) transformer stations, B.6) electrical service entrances of buildings, B.7) photovoltaic solar panel installations, and B.8) electric vehicle charging points. Based on the information provided by the Spanish company responsible for electricity transportation, Red Eléctrica de España (REE), a preliminary selection of locations was conducted on-site regarding the corresponding infrastructure.
2.3. Measurement protocol
The measurement protocol was established in accordance with both international and national standards concerning the measurement of magnetic fields at industrial frequency in relation to human exposure (IEC 62110, n.d.; IEC 2014; Spanish standard UNE 215001 2004). In addition, the technical document TR 170 from Australian Radiation Protection and Nuclear Safety Agency was considered (ARPANSA (Australian Radiation Protection and Nuclear Safety Agency) 2023). A brief description of the protocol followed at each location is detailed below.
Configuration parameters used in all SMP2 devices for measurements in the project are the following: unit of measurement: Micro-Teslas (µT), filter applied (High Pass Filter): 10 Hz, measurement range: 10 Hz a 400 kHz, sampling frequency: 0.5 seconds.
2.3.1. High-Voltage Power Lines (HVPL)
Both longitudinal and transversal profiles of the ELF-MF were registered for each HVPL selected. All measurements were recorded 1 m above the ground, georeferenced, and for 1 minute. Once located the maximum magnetic field intensity, Bmax, under the HVPL axis line between two pylons, or along the path located perpendicularly above the underground line, longitudinal measurements were taken at least at 5 equidistant points, following the lateral lines (or above the line in underground lines). If the HVPL had three lines, the central one was disregarded. For the transversal characterization of the line, from the Bmax point and moving in the normal direction and outward from each of the two lateral lines, the field was recorded at the minimum recommended intervals: 0 m, 5 m, 10 m, 15 m, 20 m and 30 m, if no obstacle prevents it. In the supplementary material, we can see a photograph of the SMP2 equipment located under a 400 kV high voltage-power line in the city of Trujillo (Cáceres).
2.3.2. Electrical substations
First, the highest field Bmax is searched walking around the perimeter of the substation, measuring at 1 m height with the SMP2. From the Bmax point, at 0.2 m from the adjacent wall, the field is measured at 0.5 m, 1 m, and 1.5 m heights and the resulting mean value will correspond to the exposure level at that point. Again, from the same Bmax point, the field levels are measured at 1 m height and 1 m, 5 m, 10 m, and 20 m away from the wall. In the supplementary material, we can see a photograph of the SMP2 equipment placed in front of the entrance to La Pinilla substation in the city of Albacete (Spain).
2.3.3. Streets
On streets, field levels are recorded georeferenced by walking between two selected points in the center of the sidewalk, for 6 to 20 minutes, keeping the SMP2 at 1m height and avoiding sudden movements. At the beginning and end of the route, the field level was statically recorded for one minute as reference values to validate the dynamic registration. The possible magnetic field peaks that appear during the journey (number of them, magnitude and location) are identified and noted for further analysis.
2.3.4. Inside and outside public buildings
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The community sensitive spaces or public buildings (kindergartens, schools, nursing homes, health centers, among others) were inspected to identify the emitting sources. To begin, we positioned ourselves at the entrance of the building to be measured, noting down the location. Outside the entrance, we set up the equipment (SMP2) to record in "continuous" mode. Next, we started walking around the building, aiming to avoid sudden movements with the equipment, and keeping it consistently at a height of one meter. During this tour, we identified the location where the peak of the magnetic field was highest. Once the peak was identified, we conducted at least three “static” measurements (spot measurement) on the equipment positioned one meter high, without any movement, for 1 minute each. In some buildings where access was allowed, additional measurements were carried out. This same procedure was applied to the measurements conducted within the train and bus station building.With respect to the measurements in public buildings, the field levels are also recorded georeferenced while walking, keeping the SMP2 at 1m height and avoiding sudden movements. Where a magnetic field peak is identified, one to three additional measurements are recorded at that point for 1 minute. The measurements carry out in public transport stations follow the same procedure.
3. Results
The environmental average levels of ELF-MF obtained from the total data collected in both public spaces - immission levels - and in proximity to the selected field-generating sources - emission levels - are graphically represented in Fig. 1. Specifically, in total, throughout the three Spanish regions, 39 different locations were measured as public spaces, meanwhile for emission sources 46 items were considered. The averaged time for data registration was around 20 min, resulting in around 2,400 recordings of the magnetic field per site.
Fig. 1
Average environmental levels of magnetic field (ELF-MF), both in public spaces (black) and in vicinity of emission sources (gray), based on the total data. In total, n = 39 locations were measured as public spaces, and n = 46 for emission sources. Magnetic fields were measured in microTeslas (µT).
3.1. Public spaces
Average of the total ELF-MF records carried out in the so-called public spaces (A) resulting a mean value of 0.095 µT for the magnetic field B, with a median of 0.068 µT. The distribution of magnetic field levels found is represented in the histogram of Fig. 2. Subsequently, results are broken down and shown in Table 1, categorized as previously mentioned. For each type of public area, the number of different locations sampled is as follows: A.1) 10 urban areas, A.2) 4 parks and gardens, A.3) 17 surroundings of public buildings, A.4) inside of 5 public buildings, A.5) 5 public transport stations, and, finally, A.6) 3 records in the underground (urban transport).
Fig. 2
Bar plot of the average ELF-MF values in public spaces. Magnetic fields were measured in microTeslas (µT).
Mean | Median | Minimum | Maximum | % of the limit value (200uT) | |||
|---|---|---|---|---|---|---|---|
A.1 Streets in urban & single-family residential areas | 0.083 | 0.062 | 0.010 | 1.430 | 0.042% | ||
A.2 Parks and gardens | 0.078 | 0.058 | 0.012 | 0.906 | 0.039% | ||
A.3 Public buildings | 0.096 | 0.065 | 0.001 | 11.700 | 0.048% | ||
A.4 Public buildings (interior) | 0.129 | 0.086 | 0.011 | 0.870 | 0.065% | ||
A.5 Public transport stations | 0.089 | 0.071 | 0.001 | 0.460 | 0.044% | ||
A.6 Underground | 0.152 | 0.096 | 0.041 | 3.514 | 0.076% | ||
* Magnetic field units: microTeslas | |||||||
3.2. Emission sources
The quantification of ELF-MF environmental emission levels near various sources has shown, as expected, higher values than those in public spaces. The average values of ELF-MF in the vicinity of the so-called emission sources, derived from all recordings across the various locations analyzed in the study, resulted in a mean value of 1.303 µT, with a median of 1.154 µT. The corresponding histogram of these values is depicted in Fig. 3.
Fig. 3
Bar plot of the average magnetic field values recorded at the 46 locations around ELF-MF emission sources. Magnetic fields were measured in microTeslas (µT).
Mean | Median | Minimun | Maximun | % of the limit value (200uT) | |
|---|---|---|---|---|---|
B.1 Overhead 220 kV hifh-voltage power lines | 0.733 | 0.674 | 0.065 | 3.334 | 0.366% |
B.2 Overhead 400 kV | 2.140 | 2.298 | 0.130 | 6.700 | 1.070% |
B.3 Underground 220 kV | 1.069 | 0.954 | 0.245 | 2.751 | 0.535% |
B.4 Electrical substations | 0.669 | 0.522 | 0.019 | 8.995 | 0.335% |
B.5 Transformer stations | 2.083 | 1.294 | 0.001 | 13.452 | 1.042% |
B.6 Electrical service entrances of buildings | 3.284 | 3.097 | 0.104 | 6.540 | 1.642% |
B.7 Photovoltaic solar panel installations | 0.066 | 0.060 | 0.042 | 0.180 | 0.033% |
B.8 Electric vehicle charging points | 0.382 | 0.331 | 0.207 | 0.615 | 0.191% |
* Magnetic field units: microTeslas | |||||
Table 2. ELF-MF (µT) values recorded in overhead 220 kV high-voltage power lines, overhead 400 kV, underground 220 kV, electrical substations, transformer stations, electrical service entrances of buildings, photovoltaic solar panel installations and electric vehicle charging points.
3.3. Statistical Analysis
Several statistical analyses are presented below, including hypothesis testing for group comparison, percentile calculation, variability analysis of the records, and confidence interval calculation.
3.3.1. Statistical comparison between groups
Based on the two exposure scenarios, namely public spaces and emission sources, considering that both data groups do not follow a normal distribution, a non-parametric (Mann-Whitney test) for two samples was conducted with a significance level of 5%. The probability p value obtained for the hypothesis test was 1.81 x 10− 5, and therefore, the null hypothesis can be rejected, indicating that both groups of values are statistically different. The mean field value in public spaces is 0.095 µT compared to 1.303 µT in proximity to ELF-MF emission sources. Nevertheless, as previously mentioned, this highest average value resulting from the contribution of all emission sources represents 0.65% of the recommended 200 µT reference level.
3.3.2. Percentile calculation
In all the cases presented, the average value of the measured magnetic field, resulting from the emission sources, corresponds to the highest values, which represents 0.65% of the limit recommended by the ICNIRP (200 µT). .
It is noteworthy that 95% of the recorded values are below 0.17 µT in public spaces and 4.12 µT for emission sources. This exposure level represents only 2% of the recommended 200 µT reference level.
3.3.3. Variability of the recorded data and confidence Intervals for the means
The variability of the measured field levels is described by the standard deviation calculated for both groups. In public spaces, the standard deviation is 43%, whereas for emission sources it is 149%. Consequently, it is evident that there is a greater dispersion of values among the ELF-MF records in the emission source group.
By definition, the confidence interval for the mean provides both a maximum and a minimum value within which the population mean is estimated to lie, with a certain margin of error. Calculated at 95% confidence level, the confidence interval for each of the two data groups turns out to be [0.072 µT- 0.10 µT] for public spaces and [0.73 µT − 1.71 µT] for emission sources. As expected, the wider dispersion of the data collected around the emission sources results in a significantly broader range of values for the mean of this group.
3.3.4. Analysis focused on emission sources
When initially categorizing the data into public spaces and emission sources, it was assumed that the ELF-MF sources were consistently distant from the public areas. However, upon recognizing that three types of emission sources – electrical transformation centers, building electrical connections, and electric vehicle charging points – can be present in public spaces, data have been reorganized. Then, the field levels recorded for these three sources were included in the group of public spaces and excluded from the emission sources, and the comparative study was carried out again. Both data subsets follow a normal distribution and exhibit equal variances, as indicated by Snedecor's Test (p = 0.67). The analysis of exposure levels in public spaces now includes electric transformation centers, building electrical connections, and electric vehicle charging points, comprising a total amount of 48 locations, while the emission sources group has been reduced to 28 locations. Subsequently, a t-test for two samples with equal variances was conducted once again (alpha = 5%), yielding a probability p value of 0.06 for the hypothesis test. Given that p > 0.05, we conclude that both sets of values are not statistically different. Therefore, significant disparities between the field values measured in public spaces and those recorded in the proximity to emission sources are no longer evident.
3.4. Study of the magnetic field around HVPL
The results obtained during the environmental characterization of ELF-MF levels near the HVPL outline the cross-sectional profile of magnetic field that decreases with distance from the midpoint of the line, as shown in Fig. 4 (a and b) for voltages of 220 kV and 400 kV, respectively.
Extrapolating values obtained through an exponential function (with equation:
and R2-value: 0.98, for 220 kV, and equation:
and R2-value: 0.99, for 400 kV), as observed from the solid lines in both graphs (Fig. 4), the magnetic field values at 50 m distance from the power lines are like the average ELF-MF values in any of the public spaces within the urban environment, nearing 0.1 µT.
A recently published study evaluating the French population's exposure to ELF-MF from HVPL (Deshayes-Pinçon et al. 2023) follows a similar protocol for measuring the magnetic field and analyses the records from 731 HVPL sites of 225 kV and 306 of 400 kV, characterized longitudinally and transversally. Despite the different sample sizes, considering the similarities with the present study, a comparison has been made between both studies. Figure 4 (c and d) shows the ELF-MF levels on the transverse axis of the HVPL in France and Spain.
Fig. 4
Representation (in a and b) of the transverse profile of the magnetic field with the distance from the axis of the line, resulting from the average values recorded in the environment of 220 kV and 400 kV high-voltage lines, and values obtained through extrapolation (blue line). Comparison (c and d) of the transverse profile of the ELF-MF obtained in proximity to 225 kV and 220 kV HVPL in France and Spain, respectively, and in 400 kV lines, along with the result of the extrapolation in each case (blue and red lines). Magnetic fields were measured in microTeslas (µT).
4. Discussion and conclusions
From the present study, based on the ELF-MF data recorded at the different locations in Albacete, Cáceres, and Madrid, with over 85 sites and more than 28 hours of total measurement, several conclusions can be drawn. Firstly, upon analyzing the categorized groups of public spaces and emission sources, it is observed that 95% of the environmental ELF-MF recorded in public spaces are below 0.17 µT, while in proximity to the emission sources, 95% of the measured emission levels are lower than 4.12 µT, constituting this higher value a mere 2% of the recommended limit value of 200 µT. Secondly, statistically comparing public spaces and emission sources or, respectively, immission and emission levels, the resulting average magnetic fields from public spaces, 0.095 µT, is significantly lower than those from the so-called emission sources, 1.303 µT. However, considering that some of these emission sources may be within public spaces contributing to immission levels, as occurs with transformation centers, building electrical connections and electric vehicle charging points, then, in this case, the conclusion is that there would be no significant differences between the environmental ELF-MF values in public spaces and in proximity to emission sources.
Specifically, in relation to the ELF-MF immission levels in public spaces, the median value of 0.068 µT is around 30% lower than the mean value of this same group. Since the median is a much more robust parameter to extreme values than the mean, it can be considered that 0.068 µT better reflects the environmental magnetic field level in public spaces. Furthermore, comparing the ELF-MF levels observed in streets of denser urban centers to those in streets of residential areas -single-family homes-, the average field value in less populated residential areas is around 25% lower. Another aspect to highlight is the difference found between the magnetic field levels in the vicinity of public buildings, 0.096 µT, and the levels inside them, 0.129 µT, with the latter being approximately 26% higher. This discrepancy may be due, among other reasons, to the significant contribution from electrical installations inside the buildings. Among all the data in public spaces, the highest magnetic field value of 11.69 µT was recorded in the vicinity of a shopping center, probably due to proximity to some unnoticed internal transformer station in the building. It is followed by the maximum of 3.51 µT recorded during the journeys made in the underground, in any case representing less than the 6% of the reference level.
In relation to the emission sources, three subgroups contribute to higher ELF-MF exposure levels: 400 kV HVPL, averaging 2.14 µT, transformer stations, with an average of 2.08 µT, and building electrical connections, averaging 3.28 µT. Among these subgroups, building electrical connections exhibit the highest emission levels and could, therefore, strongly contribute to the residential exposure levels as do interior transformer rooms in buildings (Röösli et al. 2011; Okokon 2014; Navarro-camba 2018). They should be then considered for future exposure assessment in residential settings. Regarding HVPL, the decreasing transverse profile of the magnetic field with the distance to the central point of the axis line was verified. Extrapolating the obtained values, it is noteworthy that the contribution of overhead HVPL to the ELF-MF exposure levels at 50 m distance from the axis line, approximating 0.1 µT, is like the field levels found in a typical urban environment, away from this electrical infrastructure. With respect to the installations of photovoltaic panels, more and more used for energy supply of diverse public services like electric bikes stations, and the electric vehicle charging points, the lowest values were registered as expected far from transformer devices and due to safety design of charging infrastructure networks.
As the main conclusion of the present study, with the data available to date, the ambient ELF-MF levels of the population in Spain are very similar to those in other developed countries (Bonato et al. 2023; Gajšek et al. 2016), remaining well below the 200 µT limit recommended by ICNIRP. The exposure levels in public spaces are within a range of 0.05 to 0.2 µT, with values of few µT in proximity to the emission sources, which in any case represent only the 1.64% of the ICNIRP reference level, in the worst-case scenario near the building electrical connections.
Present study has several limitations that should be acknowledged. First, the observational and descriptive nature of the research precludes the establishment of causal relationships between electromagnetic field exposure levels and potential health effects. Second, the geographic scope was limited to specific regions, which may not be representative of exposure patterns in other urban or rural settings, thereby limiting the generalizability of our findings. Third, measurement conditions were subject to inherent variability, including temporal fluctuations, time-of-day variations in emission sources, and spatial heterogeneity. Finally, the measurements represent environmental exposure levels rather than personal exposure, and no correlation was established between the recorded electromagnetic field levels and individual exposure patterns or health outcomes. Future research should address these limitations through longitudinal designs, personal dosimetry, and integration with epidemiological health data to better characterize the relationship between electromagnetic field exposure and potential biological effects.
Overall, the results of this study in Spain can guide to address a broader evaluation of environmental exposure to ELF-MF through an established protocol, bringing relevant data for future epidemiological studies, as well as useful tool for management of risk communication to the Spanish population. The identified ambient levels of ELF-MF can be also relevant information for the implementation of the requested national regulation to limit the exposure levels to this range of magnetic fields. It is a first steppingstone, bridging the gap between scientific inquiry and practical policy implementation in the realm of ELF-MF regulation.
Glossary
- Extremely low frequency magnetic fields (ELF-MF)
Magnetic fields with frequencies below 300 Hz, typically associated with power lines and electrical appliances
- Electrical infrastructures
Systems and facilities for the generation, transmission, and distribution of electrical power
- Emission (magnetic fields): Refers to the generation or release of magnetic fields from a source. It is the process by which a device or infrastructure produces and radiates magnetic fields into the surrounding environment.
- Immission (magnetic fields): Refers to the presence and intensity of magnetic fields at a specific location. It is the result of emissions from one or more sources after they have propagated through the environment.
- International Commission on Non-Ionizing Radiation Protection (ICNIRP): An independent organization that provides scientific advice and guidance on health and environmental effects of non-ionizing radiation.
- Induced electric current density: The amount of electric current flowing through a unit area of a conductor, induced by a changing magnetic field.
- International Agency for Research on Cancer (IARC): An intergovernmental agency part of the World Health Organization, focusing on cancer research.
- High-voltage power lines (HVPL): Electrical transmission lines that carry high voltages (typically above 100 kV) over long distances.
- G-ENAC-14 guide: Spanish technical guide issued by the National Accreditation Entity (ENAC)
- Z-score: A statistical measure that indicates how many standard deviations an element is from the mean of a data set.
- Georeferenced measurements: Measurements or data associated with specific geographic locations or coordinates.
- Median value: The middle value in a sorted list of numbers, separating the higher half from the lower half of a data set.
Electronic Supplementary Material
Below is the link to the electronic supplementary material
Additional Files
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Acknowledgements
We would like to express our sincere gratitude to Rodrigo San Millán and Enrique López from Redeia’ company, for their invaluable assistance and support in conducting this study. Their contributions were instrumental in the successful completion of our research.
We are also deeply indebted to Dr. Miguel Ángel Cobos from the Institute of Applied Magnetism (UCM) for his selfless help in carrying out the measurements in the Community of Madrid.
The authors gratefully acknowledge the support of all those who contributed to this research.
Funding
Funding: This work was partially supported by the Environmental Department of the company Redeia (Spain).
RR-V and EA gratefully acknowledge financial support from the Junta de Comunidades de Castilla-La Mancha of Spain (Project SBPLY/23/180225/00089) and from University of Castilla-La Mancha grant number 2022-GRIN-34356.
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Authors’ contributions
- Sanchis-Otero, Aránzazu: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Writing – original draft and Writing – review and editing.
- Ramírez-Vázquez, Raquel: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Supervision, Validation, Visualization and Writing – review.
- Paniagua, Jesús M.: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Supervision, Validation, Visualization and Writing – review.
- Bajo, Ricardo: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – original draft and Writing – review and editing.
- Arribas, Enrique: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, and Writing – review.
- Giacomone, Fernando: Conceptualization, Data curation, Investigation, Methodology, Validation.
- Ramis, Rebeca: Conceptualization, Formal analysis, Investigation, Methodology, Resources, Supervision and Writing – review.
- Marín Palacios, Pilar: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, and Writing – review.
- Vargas Marcos, Francisco: Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, and Writing – review.
Ethical Approval
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Consent to Participate
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Consent to Publish
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Competing InterestsNo competing interests
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Data availability statements
All data corresponding to the present study are available in the following free repository (GitHub):
https://github.com/Ric-count/Spain-ELF-MF-data-
Clinical trial number: not applicable
