Exposure assessment of radiofrequency electromagnetic fields (RF-EMFs) in everyday environments : methodological approaches and issue-specific perspectives

摘要

Introduction and objectives:udThere was a substantial development and persistent introduction of new telecommunication devices in the past two decades. Mobile communication is nowadays ubiquitous reaching a number of mobile-cellular subscriptions of around 6.8 billion in 2013 – almost as many as the entire population worldwide. This widespread use of mobile telecommunication required an expansion of the network to meet the new technological requirements and end-user demands. In the meantime, a shift could be observed from text messaging and calls towards mobile internet access through mobile devices which will continue to grow strongly. All these developments led to a substantial change of the radiofrequency electromagnetic field (RF-EMF) exposure situation and to concerns about potential adverse health effects in the population. Countries thus started to introduce precautionary exposure limits in order to decrease the exposure of the population. However, there is no study so far scrutinizing what consequences such precautionary limits have on outdoor exposure levels. The Research Agenda of the World Health Organization (WHO) classified EMF research as a high research priority. Measurement devices allowing to quantify personal RF-EMF exposure became available only some years ago. Accordingly, several studies have been conducted using personal measurement devices (exposimeters). However, such measurements had typically been conducted through recruited study participants being allowed to use their own mobile phone during measurements. This can limit data interpretation if one is interested to differentiate between the exposure from the own mobile phone and from the exposure of other people’s mobile phone. Still, little is known about the exposure situation in our everyday life and how RF-EMF exposure changed over time. Exposure assessment has become challenging, due to the high spatial and temporal variability of RF-EMFs, questioning how reproducible personal exposure measurements are.ududObjectives:udIn the framework of this dissertation, methodological and issue-specific questions have been examined. From a methodological point of view, we aimed to investigate the effect of the own mobile phone on personal measurements. As our measurements based on a repetitive data collection procedure at defined time frames and with predetermined measurement sequences, we studied the reproducibility of personal RF-EMF measurements over time using an exposimeter. Furthermore, we aimed to inspect how the mobile station network affects exposure situations in outdoor areas. udIssue-specific research questions focussed on the characterization of RF-EMF exposure levels in typical everyday environments and how exposure changed over time.ududMethods:udMeasurements were conducted during different time periods between 3 weeks and 1 year in several environments and across several European cities, i.e. Basel (Switzerland), Amsterdam (the Netherlands), Ghent and Brussels (Belgium). We used an exposimeter of the type EME Spy 120 for quantifying RF-EMF exposure on different frequency bands ranging from FM (Frequency Modulation, 88 MHz) to WLAN (Wireless Local Area Network, 2.5 GHz), including all telecommunication signals: GSM 900 (Global System for Mobile Communications), GSM 1800 and UMTS (Universal Mobile Telecommunications System) in up- (UL, communication from mobile phone to base station) and downlink (DL, communication from base station to mobile phone) traffic. We included different typical everyday environments in outdoor areas, public transports, and indoor settings. ududResults:udPrimarily, results on methodological questions showed that the own mobile phone in stand-by mode reached exposure levels up to a factor of 100 compared to a mobile phone being turned off. These results were more pronounced during car rides whether during rides in public transports, as the background exposure, especially in trains, was relatively high. Analysis of variance (ANOVA) indicated that despite the high spatial variability which was best explained by the type of area (30%) in urban cities and the type of city (50%), mobile phone base station exposure in outdoor urban areas was highly reproducible. Typical mobile phone base station exposure levels in outdoor urban areas (all types of outdoor urban areas combined) across different European cities ranged between 0.22 V/m in Basel and 0.43 V/m in Amsterdam. Peak exposure levels reached values of up to 0.82 V/m (Amsterdam) for the 95th percentile and the highest percentage of exposure (99th percentile) showed values which were between 0.81 V/m (Basel) and 1.20 V/m (Brussels). udAnalyses relating to issue-specific questions showed consistently during all measurements that highest total average RF-EMF levels occurred in trains with exposure levels between 0.83 V/m (Ghent) and 1.06 V/m (Brussels) and in downtown areas: 0.32 V/m (Ghent) to 0.58 V/m (Brussels). The total RF-EMF exposure increased by 20% in Ghent, by 38% in Brussels and by 57% in Basel during the study period of one year between April 2011 and March 2012 in all outdoor areas in combination.ududDiscussion and Outlook:udCharacterizing RF-EMF exposure with personal exposimeters has shown to be feasible for quantifying exposure levels and to investigate temporal trends. They allow collecting large amounts of data with little effort and enable including a large variety of different environments. In addition, our study demonstrated that measurements were highly reproducible for mobile phone base station exposure in outdoor urban areas which is a strength when planning exposure assessment studies based on repeated measurements. However, when taking measurements it is recommended to turn off the own mobile phone, as our results showed a considerable impact of the own mobile phone on personal measurements. The contribution to total RF-EMF exposure was predominantly influenced by telecommunication technologies, i.e. mobile phones and mobile phone base stations, representing the most important sources of exposure in outdoor areas, public transports and indoor settings. All exposure levels were far below the frequency-dependent reference levels (41–61 V/m) proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) as well as below national imposed precautionary limits implemented in the different countries (on average ten times lower than ICNIRP levels). Furthermore, our study did not find any indications that lowering the regulatory limits result in higher mobile phone base station exposure levels so far; nevertheless, further studies including more cities with different regulatory limits are needed. A monitoring of the exposure to RF-EMFs is important nowadays, especially with the introduction and expansion of new technologies and the increased usage of mobile telecommunication. Monitoring studies should help to clarify how RF-EMF exposure levels change over time and allow identifying areas with critical exposure values. These studies may contribute to a better understanding of potential adverse health effects. Global research efforts are highly needed to translate findings in public policies. In the light udof current uncertainties regarding potential adverse health effects due to long-term low-dose exposure levels, minimizing exposure might be reasonable and requested.