http://informahealthcare.com/ebm ISSN: 1536-8378 (print), 1536-8386 (electronic) Electromagn Biol Med, Early Online: 1–8 ! 2013 Informa Healthcare USA, Inc. DOI: 10.3109/15368378.2013.783846
ORIGINAL ARTICLE
Investigating short-term exposure to electromagnetic fields on reproductive capacity of invertebrates in the field situation Martina G. Vijver1, John F. B. Bolte2, Tracy R. Evans1,3, Wil L. M. Tamis1, Willie J. G. M. Peijnenburg1,2, C. J. M. Musters1, and Geert R. de Snoo1 Institute of Environmental Sciences (CML), Leiden University, Leiden, The Netherlands, 2National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands, and 3Illinois Department of Natural Resources, Springfield, Illinois, USA
Abstract
Keywords
Organisms are exposed to electromagnetic fields from the introduction of wireless networks that send information all over the world. In this study we examined the impact of exposure to the fields from mobile phone base stations (GSM 900 MHz) on the reproductive capacity of small, virgin, invertebrates. A field experiment was performed exposing four different invertebrate species at different distances from a radiofrequency electromagnetic fields (RF EMF) transmitter for a 48-h period. The control groups were isolated from EMF exposure by use of Faraday cages. The response variables as measured in the laboratory were fecundity and number of offspring. Results showed that distance was not an adequate proxy to explain doseresponse regressions. No significant impact of the exposure matrices, measures of central tendency and temporal variability of EMF, on reproductive endpoints was found. Finding no impact on reproductive capacity does not fully exclude the existence of EMF impact, since mechanistically models hypothesizing non-thermal-induced biological effects from RF exposure are still to be developed. The exposure to RF EMF is ubiquitous and is still increasing rapidly over large areas. We plea for more attention toward the possible impacts of EMF on biodiversity.
Ambient field exposure, electromagnetic field, invertebrates, reproduction
Introduction Until 30 years ago the exposure to radiofrequency electromagnetic fields (RF EMF), 10 MHz–300 GHz was mainly from occupational communication devices and fixed broadcast transmitters for radio and television. However, since the introduction of digitally enhanced telecommunications, mobile phones and wireless internet (WiFi), exposure is increasing. With the use of new wireless devices, there is increasing concern about health and safety of wireless communications (Bolte and Eikelboom, 2012; Infas, 2004). Articles on human health effects report changes in cognitive functions, brain tumors and excretion of pituitary hormones (a full overview can be found in Ahlbom et al., 2004). The International Commission on Non-Ionizing Radiation Protection (ICNIRP) published guidelines for the protection from short-term adverse health effects (ICNIRP, 1998). These guidelines define reference levels for frequency-dependent exposure limits outside the human body. For RF EMF these reference levels are based on the prevention of thermal effects, i.e. effects due to warming over 1 C.
Address correspondence to Martina G. Vijver, Institute of Environmental Sciences (CML), Leiden University, Leiden, The Netherlands. E-mail:
[email protected]
History Received 16 May 2012 Accepted 10 January 2013 Published online 10 June 2013
The reference levels for mobile phone communications in 900, 1800 and 2100 MHz frequency bands are 41, 59 and 63 V/m, respectively (Bolte et al., 2008). Although less consistent and less robust than thermal effects, non-thermal effects were reported at the ambient environmental exposure levels. Primary causes of biological responses that are nonthermal are difficult to find. Although the causes of nonthermal influence are uncertain, there seems to be consistency in the reported effects (Hyland, 2000). Apart from ongoing discussions of possible adverse effects of RF EMF on humans, the question is whether effects on animals and plants occur. Until now, ecological effects of EMF received very limited attention. Balmori (2009) gave an overview of papers that reported negative ecological effects. In that review two papers on fruitflies, three papers on birds and two on mammals showed negative impacts by EMF. A critical part of the review by Balmori (2009) was that hardly papers documenting non-detrimental ecological effects were included. Hence, at this stage we conclude that adverse ecological effects are at present not well-studied and poorly understood. Animal studies have been identified as a major research agenda point by the WHO (Van Deventer et al., 2011). The WHO has given high priorities for field research on the effects of RF-EMF on development, behaviour, aging and reproduction of animal subjects.
20 13
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
1
2
M. G. Vijver et al.
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
In the present study we examined the impact of exposure to GSM base station signals (900 MHz) on different endpoints in the reproductive capacity of invertebrates. Reproduction was the selected relevant endpoint as in other ecological and ecotoxicological studies. Additionally Balmori (2009) showed this to be an endpoint in fruitflies affected by EMF. Four different species of small hexapodae – different insects and springtail species – were selected, all easy to maintain under controlled experimental conditions and with different life strategies. All species were virgins during exposure. Within the field, the four different hexapodae species were placed at different distances from a GSM base station for a short-term period of 48 h. Reproductive capacity of the exposed organisms was followed for three weeks in the laboratory. Our nullhypothesis was that the reproductive capacity of the four hexapodae species was not affected by the short-term exposure to ambient EMF levels in the field.
Methods Field and dose measurements The 48-h field experiment was run in August 2010, from Monday 16.00 till Wednesday 16.00. All test organisms were placed in covered pedestal containers within the radius of approximately 150 m of a 900 MHz mobile phone base station located near the city of Leiden, the Netherlands. At the selected 900 MHz mobile phone base station two antennae were permanently attached at a height of 7.5 m (beam direction 20 and 170 ). The distance to the middle of GSM 900 MHz transmitter was set in two transects, in order to have different exposure classes. The first transect was at 25 m (A) and 62 m (B) at 20 from north. The second transect was in the south-east direction, 170 at 16 m (C), 73 m (D), 143 m (E) and 151 m (F). Six control groups were placed in Faraday cages (gauze width 1 mm; type Biologa Adamantan10 (Vitalitool, Nijmegen, Netherlands); cage sizes 20 cm diameter, 23 cm height) at all six locations within 2 m of the treatment groups. The area was an open field with 50–80% bare soil and fallow vegetation of mainly grasses and pioneer species up to 20 cm. Equipment and invertebrates were placed in 12 plastic containers each on top of a pedestal container at 30 cm height and protected against rain and sun by a plastic roof. The sides of the containers were open to allow ventilation. Weather conditions and temperature were recorded. Exposure and effect recording was performed in blinded and a randomized design. Moreover, duplicate electric field strength measurements were performed by two different research groups. At three of the six locations, the field strength was measured with a sampling interval of 15 s over 48 h utilizing EMF RF exposimeters measuring 12 different frequency bands for communication. The exposimeter of type EME Spy 121 (Satimo, Cortaboeuf, France) measures the RF electric field in 12 frequency bands: FM radio (88–108 MHz), TV3 (174–223 MHz), TETRA (380–400 MHz), TV4&5 (470–830 MHz), GSM uplink (880–915 MHz), GSM downlink (925–960 MHz), DCS uplink (1710–1785 MHz), DCS downlink (1805–1880 MHz), DECT (1880–1900 MHz), UMTS uplink (1920–1980 MHz), UMTS downlink (2110–
Electromagn Biol Med, Early Online: 1–8
2170 MHz), WiFi (2400–2500 MHz). TV3 and TV4&5 were the bands originally for analogue TV broadcasts. However, in the Netherlands all broadcasts are Digital Video Broadcasting Terrestrial (DVB-T) in the TV4&5 frequency band. Also part of the radio broadcasts are in Terrestrial Digital Audio Broadcasting (T-DAB) at 174–230 MHz in the TV3 band. Concomitantly, three magnetic field meters Emdex Lite (40–1000 Hz, Enertech Consultants, Campbell, CA) were installed at the locations allowing correction of radiation fields. To determine spatially explicit exposure patterns at all six locations, field strength at each location was measured for 10 min with a Narda, type SRM3000/probe3501/01 (Narda, Pfullingen, Germany). The whole spectrum was recorded from 88 MHz–2.5 GHz; with a recording every 4 s. Reduction of the EMF signals within all six Faraday cages was measured. We used measures of central tendency (mean), standard deviation (sd), geometric standard deviation and temporal variability of EMF as exposure metrics. All the analyses were done on the power density of the EMF expressed as (W/m2). Since power density is a measure of energy, contributions from signals at different frequencies can be combined. After calculations power density can be translated to electric field strength (V/m) by multiplying by 377 and taking the square root. Temporal variability measures were expressed as rate of change metric (RCM), standardised rate of change metric (RCMS), and fractional difference metric (FDM) (Yost, 1999). The RCM is a measure for the short-term temporal variability, but depends also on the sampling interval and the magnitude of the signal. RCM is calculated as the root mean square of the difference between two sequential instantaneous measurements in the time series. The RCMS is highly affected by the long-term trend. If the long-term trend increases, the RCMS decreases (Kaune et al., 2001). RCMS is the RCM divided by the sd. The FDM is also a measure of short-term temporal variability, but is more susceptible to sudden field changes and only weakly susceptible to longterm trends. FDM is the mean of the local first derivative divided by the local mean. Reproduction tests and effect measurements Four different hexapod species were tested. Springtails (Folsomia candida) were cultured and provided by Vrije Universiteit, Amsterdam, The Netherlands. The predatory bugs (Orius laevigatus) were cultured and provided by Koppert, Berkel en Rodenrijs, The Netherlands. The parasitic wasps (Asobara japonica) and fruitflies (Drosophila melanogaster) were obtained from the cultures of the Leiden University, The Netherlands. The organisms were selected for short generation time, high fecundity and short life cycle. Exposed organisms were pre-adolescent and virgin. After 48 h exposure in the field, all organisms were brought to the laboratory to facilitate reproduction. Bugs, wasps and fruitflies were paired in order to mate; springtails are parthenogenetic organisms. After approximately one week parents were removed. Reproductive success of each species was scored according to standard guidelines. Mortality and
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
DOI: 10.3109/15368378.2013.783846
various reproductive endpoints were scored. Reproductive success of each of the hexapoda species was determined by counting total offspring as a sum of eggs/pupae and hatched juveniles; sexes were differentiated. Springtails were kept in a climate room at 17 C 0.8, with a day-night cycle of 16:8 h. The jars were 5 cm high and had a diameter of 2.5 cm, a perforated lid and a bottom coated with gypsum. Every other day water and food (baker’s yeast, Saccharomyces cerevisiae) were given ad libitum. Every other day mortality, egg production and juveniles were counted. After 21 d the test was terminated and water was added to the jar. Juveniles floated on the water and were counted. After removal of the juveniles, the gypsum was broken and eggs were counted. Bugs were kept in a climate room at 25 C 0.5, with a day-night cycle of 16:8 h. The jars were 8 cm high and had a diameter of 5 cm, covered with a plastic lid and taped closed to prevent escapes. One male and one female bug were placed together in a jar allowing for mating. In all jars a 5 cm fresh, organic, French bean was added as a substitute for plant leaves on which the eggs were laid. As a food source for the predatory bugs, Ephestia eggs were added. After 20 d the juvenile bugs were counted. Fruitflies were kept in a climate room at 25 C 0.5, with a day-night cycle of 16:8 h. The jars were 8 cm high and had a diameter of 5 cm. A sponge was used to close the jars. At the bottom of the jars agar mixed with food medium and some baker’s yeast was added. One male and one female fly were placed together in a jar to allow for mating. After 6 d the adults were removed from the jars. After 16 d the jars, including newly emerged fruitflies, were put in the freezer at 18 C. Juvenile flies were then counted and sex ratios determined. Full pupae that had not developed were also counted. Wasps were kept in a climate room at 25 C 0.5, with a day-night cycle of 16:8 h. The jars were 5 cm in diameter, and 8 cm high and sponge was used to close the jars. One male and one female wasp were placed together in a jar to allow mating. Fruitfly larvae, two days old, were added to allow the wasps to parasitize and lay their eggs. Agar was the medium and yeast
No impact of 900 MHz antennae on hexapodae reproduction
3
was added for the larvae of the fruitfly to develop. As a food source for the adult wasps, a drop of honey was placed on the sponge. After 20 d the jars including newly emerged wasps, were put in the freezer at 18 C. Juvenile wasps were then counted and sex ratios were determined. Statistics To test the effects of EMF on the reproduction of hexapods, we applied a generalised linear model using R software, version 2.13.0 (Vienna, Austria, http://www.R-project.org). The general form of this model is: Response þ e Exposed þ d Exposure metric þ ed Exposed Exposure metric Since exposed is either 0 (not exposed, i.e. in the Faraday cage) or 1 (exposed), the model for the non-exposed organisms becomes Response þ d Exposure metric and for the exposed organisms Response þ e þ d Exposure metric þ ed Exposure metric or Response ð þ e Þ þ ð d þ ed Þ Exposure metric In case the exposure to EMF would negatively affect the reproduction of a species, we would expect to find results as in Figure 1. For the exposure metrics we would expect both d and e to be zero, while e*d would be negative. For distance, d would be zero again, but e would now be negative and e*d would be positive. Our null-hypotheses are therefore, in all case that e*d is zero. Our alternative hypothesis is for the exposure metrics that e*d is less than zero and for distance that e*d is higher than zero. Note that we do not formulate a null-hypothesis concerning the other regression coefficients of the model. This is because these parameters may deviate from zero because of reasons not related to an effect of EMF: e may be non-zero because of the Faraday cages themselves
Figure 1. Expected relationship between the exposure metrics or distance and reproduction in case that the EMF affects hexapod reproduction.
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
4
M. G. Vijver et al.
have an effect on reproduction and d may be non-zero because an environmental gradient that is affecting reproduction, such as temperature or humidity, is correlated with the exposure metrics or distance. To test our null-hypotheses we applied the GLM’s to estimate the regression coefficients and test whether these deviate significantly from zero by using a one tailed t-test. The response variables were fecundity and number of offspring. Fecundity is a binary variable measuring whether a pair or individual had offspring or not. It was assumed to have a quasi-binominal distribution. For the models this means that the intercept a is actually Ln(p/(1 p)), where p is the probability of having offspring. This is zero when p ¼ 0.5, which makes testing for deviation from zero irrelevant. Number of offspring was only tested for those pairs or individuals that had offspring. The number of offspring showed differences in distribution between the species, making it necessary to apply a different transformation per species. Offspring numbers of wasps and fruitflies showed normal distribution. Based on residual analyses it was decided to log-transform the number of offspring in the case of springtails and bugs. Dose variables were central tendency measures as calculated from the power density and rates of change metrics at the location. For central tendency the mean power density (MPD) was taken. It was log-transformed to get a better distribution of the data along the power gradient. The exposure metric of the rate of changes was RCMS.
Results Weather conditions during the 48 h of exposure in the field were optimal with only 30 min of drizzle. The average temperature recorded was 17 C, with night time low 5.0 C and day time high 23.2 C.
Electromagn Biol Med, Early Online: 1–8
Table 1), that is approximately a factor of 4000 attenuation, subsequently giving exposure measurements that are below detection limit. Effects Some organisms died directly after the transfer from the field to the laboratory. In total six out of 120 springtails F. candida died; two of 98 bugs O. laevigatus died. Of the fruitflies D. melanogaster, 108 useable pairs were formed after exposure. Of the wasps Asobara japonica 23 males and 16 females died and 70 useable pairs could be formed. These mortality data were not used in the analysis (Figure 3). The average reproduction of the springtails was 11.7 3.9 juveniles per springtail in the non-exposed (n ¼ 53). Variability of the reproductive success of each single springtail was large, zero reproduction was found and included. These values are commonly found (personal communication Vrije University) when animals are exposed individually in a jar. The average reproduction of bugs, was 6.7 1.4 juveniles per pair in the non-exposed group (n ¼ 34); eight pairs of bugs had zero reproduction. The average reproduction of fruitflies was 128 7 juveniles per pair in the non-exposed group (n ¼ 61); five fruitfly pairs had zero reproduction in the nonexposed group. The average reproduction of wasps was 75.4 6.0 juveniles per pair in the non-exposed group (n ¼ 37); three wasps pairs gave zero reproduction. With the wasps fertility testing was complicated by mating failure in all pairs which resulted in only male offspring. Disruption in mating was almost certainly due to the cold shock that the exposed males experienced from the short storage (up to max 20 min) in the fridge at 8 C. That was done to slow down the mobility of the wasps in order to make the transfer from the exposure jars into the mating jars possible. It turned out, however, that females did not mate with the males and had parthogenetic reproduction.
EMF measurements Exposure at GSM900 frequency was detected during the 48 h measurements. These typical exposure patterns over 48 h (Figure 2) showed variations in field strengths. During day-light hours, intensities showed more peaks and higher amplitudes due to mobile phone communication. During the night, intensity pattern showed lower amplitudes and fewer peaks in the field strength. To characterize exposure levels in the field, descriptive statistics of the locations calculated on the power density of the signals in W/m2 are given in Table 1. The results show that in our field study most of the measures were highly correlated to each other, MPD and RCM was 0.996, power density and FDM gave a correlation of 0.784. A low correlation was found between MPD and RCMS, 0.0469. Hence, most focus in the analysis of the doseresponse regressions was given to these measures. The power density had a maximum difference by a factor 33.5, with A being highest and F being the location with lowest power density. The standardized rate of change had highest value at B and lowest value recorded at F. The fractional difference metric was highest detected at B and lowest at A. Exposure measurements within the Faraday cages were between 36 and more than 40 dB lower (not shown in
Dose-response regressions Dose response regressions were derived between exposure measures and fecundity endpoints (Supplementary table). Fecundity was determined in terms of reproduction or zero reproduction for each of the species. The exposure measures as used were power density (MPD) and rate of change metrics. Regressions were also calculated using distance being a proxy. Since none of the interaction coefficients e*d were significantly different from zero in the expected direction, fecundity of the organisms, i.e. whether a pair or individual had offspring or not, seemed not significantly affected by exposure to the EMF. For the fruitflies, d exposure metric was significant. Dose response regressions were derived between exposure measures and total number of offspring (Table 2). The exposure measures as used were power density (MPD) and rate of change metrics (e.g. RCMS). Regressions were also calculated using distance as a proxy. Total reproduction was determined in terms of total number of offspring either eggs, unhatched pupae or juveniles for each of the species. The results in Table 2 shown one interaction coefficient e*d that is significantly lower than zero (p ¼ 0.031), viz. in
No impact of 900 MHz antennae on hexapodae reproduction
DOI: 10.3109/15368378.2013.783846
5
location C 1.0
0.8
0.6
0.4
location B Electric Field Strength (V/m)
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
0.2
1.0
0.8
0.6
0.4
0.2
location A 1.0
0.8
0.6
0.4
0.2
aug 31 00:00
aug 31 12:00
sep 01 00:00
sep 01 12:00
Time Figure 2. Exposure pattern of the locations A (top), C (middle) and B (bottom) over 48 h. A and B were located in the transect of North direction, C was placed in the transect of South-East direction.
case of the number of wasps offspring and power density. However, we performed 24 tests on interaction coefficients. When applying a Bonferoni correction this significant p value loses its significance. In almost all cases a was shown to have
a significant regression with reproduction, meaning that for all those species reproduction occurred. Regressions of a with RCMS were not significant. Most likely this was caused by the low variances in RCMS.
6
M. G. Vijver et al.
Electromagn Biol Med, Early Online: 1–8
Table 1. Descriptive analysis of the exposure measurements made using the Narda meter.
Transect Code N N SE SE SE SE
A B D F C E
MPD (W/m2)
RCM
RCMS
FDM
Time record
4.344 103 0.295 103 0.266 103 0.130 103 0.403 103 0.495 103
0.000755 0.000112 0.000111 3.99E-05 9.22E-05 0.000157
1.11 1.17 1.16 1.02 1.09 1.09
0.139395 0.269889 0.25775 0.232007 0.178625 0.256613
14:37–14:47 15:04–15:14 14:00–14:10 13:30–13:40 15:24–15:34 13:43–13:53
Legend: N ¼ north direction, 20 degrees from north; SE ¼ south-east direction, 170 degrees from north. MPD ¼ mean power density, RCM ¼ rate of change metric, RCMS ¼ standardised rate of change metric, FDM ¼ fractional difference metric, are all calculated from the power density.
Bugs
20
exposed faraday
15
10
5
0 A
B
C
D
E
Fruitflies
200
F exposed
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
faraday
Marginal significant regressions were found for fruitflies related to RCMS, e for the exposed organisms. For the exposed bugs, e, showed marginal significances when correlated to the distance.
Discussion Distance is often used to create a gradient in energy exposure in the EMF perspective. However, it is reported that the intensity of the transmitter and the direction of transmitting is more relevant (Bolte and Eikelboom, 2012; ICNIRP, 1998). Our results also show that distance is not a good proxy for the exposure to the EMF; since apart from distance to the transmitter, the direction and tilt of the transmitter will determine whether the location of interest is in the main beam. In other words ‘‘the antenna may ‘shine’ over a location’’. Therefore, closer to the transmitter the exposure may be lower than further away from it, but in the direction of the beam. This was found when comparing location D which was closer to the transmitter than location E, but the power density is lower for D than for E. The correlation of distance with MPD was 0.468 (p value ¼ 0.349). Within our study, only one location (A) showed large variation compared to the five other locations; hence the difference in exposure was a factor of 33. In the other five selected locations, exposure measure based on field strength as determined did not show much variation, only a factor of 4. Also the signals of the base stations used in this study did not show large variances in RCM and RCMs values, therefore all sites where the exposures took place did not give distinct patterns in rate of change metrics. Having a larger rate of change modulations may be related to more noticeable effects. Although RF electromagnetic energy is distributed over large areas around rural areas, many contradictory results can be found in literature on if and to what extent negative effects can occur induced by GSM 900 MHz frequencies. Among invertebrates, fruitflies are the most widely studied organisms, and an overview is given in Balmori (2009). He quoted adverse effects causing fragmentation of DNA in the gonads, resulting in a decrease of fruitflies’ reproductive capacity of 50–60% (Panagopoulos et al., 2004). In contrast to these results, a greater number of fruitfly adults (22% to 50% higher) were found by Weisbrot et al. (2003). However, the same author also found that 900 MHz increases the level of heat shock protein 70 (a stress protein). Drosophila salivary
150
100
50
0 A
B
C
D
E
Springtails
30
F exposed faraday
25
20
15
10
5
0 A
B
C
D
E
Wasps
120
F exposed faraday
100
80
60
40
20
0 A
B
C
D
E
F
Figure 3. Average total reproduction for each species.
gland chromosomes exposed to low EMF showed an increase in the transcriptional activity in 73 of the 200 investigated chromosomal regions (Goodman et al., 1992) including housekeeping genes. This could be a reason for the increased number of offspring. From these studies, Balmori (2009) stated that severe adverse effects to this group of organisms were reported. In our study we used the reproductive capacity
No impact of 900 MHz antennae on hexapodae reproduction
DOI: 10.3109/15368378.2013.783846
7
Table 2. Number of offspring: GLM of Gaussian family with identity link; the interaction coefficient is one-tailed tested (in bold), all other coefficients are two-tailed tests. Ln(Springtails)
n ¼ 81
Estimate
SE
t Value
p Value
Ln(MPD)
a e d e*d a e d e*d a e d e*d n ¼ 53 a e d e*d a e d e*d a e d e*d n ¼ 100 a e d e*d a e d e*d a e d e*d n ¼ 66 a e d e*d a e d e*d a e d e*d
2.68694 0.10526 0.06634 0.07376 1.0914 0.9977 3.3312 0.9027 2.5938885 0.0402045 0.0001918 0.0003705 Estimate 1.2849 0.1904 0.2144 0.1859 3.839 6.050 4.903 5.876 1.910742 0.754729 0.004284 0.004018 Estimate 149.861 9.368 5.181 2.250 202.19 296.86 54.43 271.50 134.75339 12.97056 0.07728 0.09467 Estimate 75.105 13.214 6.551 14.930 72.14 62.78 11.23 63.49 90.95083 10.88816 0.08438 0.05158
0.20683 0.28011 0.10179 0.14519 2.6844 3.5879 2.4343 3.2477 0.2202172 0.2943149 0.0022533 0.0031217 SE 0.2984 0.4208 0.1819 0.2392 3.645 5.368 3.304 4.865 0.329978 0.439548 0.003411 0.004810 SE 8.316 12.860 4.548 6.617 106.35 170.76 96.17 153.95 10.01230 13.69789 0.09310 0.13629 SE 9.216 12.970 5.321 7.811 120.36 166.29 108.83 150.44 9.03916 13.46512 0.09716 0.13864
12.991 0.376 0.652 0.508 0.407 0.278 1.368 0.278 11.779 0.137 0.085 0.119 t Value 4.306 0.453 1.179 0.777 1.053 1.127 1.484 1.208 5.791 1.717 1.256 0.835 t Value 18.022 0.728 1.139 0.340 1.901 1.738 0.566 1.764 13.459 0.947 0.830 0.695 t Value 8.149 1.019 1.231 1.911 0.599 0.378 0.103 0.422 10.062 0.809 0.868 0.372
50.001*** 0.708 0.517 0.694 0.685 0.782 0.175 0.391 50.001*** 0.892 0.932 0.547 p Value 50.001*** 0.653 0.244 0.221 0.297 0.265 0.144 0.117 50.001*** 0.092 (*) 0.215 0.204 p Value 50.001*** 0.468 0.257 0.368 0.060 (*) 0.085 (*) 0.5727 0.960 50.001*** 0.346 0.409 0.756 p Value 50.001*** 0.312 0.223 0.031* 0.551 0.707 0.918 0.337 50.001*** 0.422 0.388 0.356
RCMS
Distance
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
Ln(Bugs) Ln(MPD)
RCMS
Distance
Fruitflies Ln(MPD)
RCMS
Distance
Wasps Ln(MPD)
RCMS
Distance
Legend: MPD ¼ mean power density multiplied by 10.000, *** ¼ high significance, * ¼ significance p50.05, (*) ¼ marginal significance p40.05 and p50.10.
being a response parameter, similar to the studies as mentioned above, but not the more sensitive endpoints as DNA fragmentation. Another difference that might explain the differences is the dose, as many studies in Balmori’s review were performed in controlled laboratory settings. The results of our study at ambient relevant field exposure doses gave no clear significant effects of RF EMF on reproduction at the treated organisms. In our study we used linear regressions, although it is known that biological effects are often non-linear. Finding no distinct
and clear effects does not exclude the existence of physiological changes. It should be noted that Vecchia et al. (2009) state that mechanisms giving rise to non-thermal induced biological effects from RF exposure are complex and remain undiscovered and unidentified. The set-up of our field experiment can be seen as a black box. Causality is difficult to assess: no physiological or physical models exist (Vecchia et al., 2009). The organisms selected in this study had all a rather small size. The springtails have a body length of on average 2 mm, wasps are about 3 mm,
8
M. G. Vijver et al.
Electromagn Biol Med Downloaded from informahealthcare.com by 213.46.107.14 on 06/19/13 For personal use only.
the bug sizes from 1.4 to 2.4 mm, and the largest organisms tested are the female fruitflies that are about 2.5 mm length and the males are slightly smaller. Organisms of this size are not strong antennae for 900 MHz waves with a wavelength of approximately 33 cm, due to limited adsorption and little energy uptake capacity. We assume that we exposed all organisms at their most sensitive life stages. The transition from juvenile to adult is a crucial step in the life history of organisms. In the life stages we selected, virgins just before the first reproduction, reproductive organs are rapidly developing. Furthermore, reproduction is an important sub-lethal endpoint in itself, as it is the closest approximation to total fitness (Stearns, 1989). In order to increase the possibility of measuring effects, we suggest that in further research longer exposure times should be used.
Conclusions Synthesizing our results it was seen that the reproductive capacity of the hexapodae species was not affected by the short-term EMF exposure. For the particular levels of power density and RCMS as determined in our field no relationship could be found between exposure and responses. Hence, our null-hypothesis that the reproductive capacity is not impacted by the EMF levels in the field could not be rejected. As the exposure to RF EMF is ubiquitous and is still increasing rapidly over large areas, we strongly agree with the WHO statements and hence plea for more attention to this and the possible impacts of EMF on biodiversity.
Acknowledgements We are grateful to Jos Kamer of the Ministry of Economic Affairs for verifying the exposure measurements. We thank our colleagues Suzanne Kos, Eric Gertenaar and Kees Koops from the Leiden University for their assistance in collecting the reproduction data. We thank Rudo Verweij, Vrije Universiteit, for providing the springtails. Declaration of interest The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
Electromagn Biol Med, Early Online: 1–8
References Ahlbom, A., Green, A., Kheifets, L., et al. ICNIRP (International Commission for Non-Ionizing Radiation Protection) Standing Committee on Epidemiology. (2004). Epidemiology of health effects of radiofrequency exposure. Environ. Health Persp. 112: 1714–1754. Balmori, A. (2009). Electromagnetic pollution from phone masts, effects on wildlife. Pathophysiology. 16:191–199. Bolte, J.F., Eikelboom, T. (2012). Personal radiofrequency electromagnetic field measurements in the Netherlands: Exposure level and variability for everyday activities, times of day and types of area. Env. Internat. 48:133–142. Bolte, J., Pruppers, M., Kamer, J., et al. (2008). The Dutch exposimeter study: Developing an activity exposure matrix. Epidemiology 19: 78–79. Goodman, R., Weisbrot, D., Uluc, A., Henderson, A. (1992). Transcription in Drosophila melanogaster salivary gland cells is altered following exposure to low frequency electromagnetic fields: Analysis of chromosome 3R. Bioelectromagnetics. 13:111–118. Hyland, G. (2000). Physics and biology of mobile telephony. The Lancet. 356:1833–1836. Infas (Institut fu¨r angewandte Sozialwissenschaft GmbH) (2004). ¨ ngste der breiten O ¨ ffenlichkeit Ermittlung der Befu¨rchtungen und A hinsichtlich mo¨glicher Gefahren der hoch frequenten elektromagnetischen Felder des Mobilfunks – ja¨hrliche Umfragen. – Abschlussbericht u¨ber die Befragung im Jahr 2003 – Bundesamt fu¨r Strahlenschutz: Salzgitter. International Commission on Non-Ionizing Radiation Protection. (1998). Guidelines for limiting exposure to time-varying electric and magnetic fields and electromagnetic fields (up to 300 GHz). Health Phys. 74: 494–522. Kaune, W. T., Davis, S., Stevens, R. G., et al. (2001). Measuring temporal variability in residential magnetic field exposures. Bioelectromagnetics. 22:232–245. Panagopoulos, D. J., Karabarbounis, A., Margaritis, L. H. (2004). Effect of GSM900-MHz mobile phone radiation on the reproductive capacity of Drosophila melanogaster. Electromagn. Biol. Med. 23: 29–43. Stearns, S. C. (1989). Trade-off in life-history evolution. Funct. Ecol. 3: 259–268. Van Deventer, E., van Rongen, E., Saunders, R. (2011). WHO research agenda for radiofrequency fields. Bioelectromagnetics. 32: 417–442. Vecchia, P., Matthes, R., Ziegelberger, G., et al. (2009). Exposure to high frequency electromagnetic fields, biological effects and health consequences (100 kHz–300 GHz). ICNIRP 16/2009. Weisbrot, D., Lin, H., Ye, L., et al. (2003). Effects of mobile phone radiation on reproduction and development in Drosophila melanogaster. J. Cell Biochem. 89:48–55. Yost, M. G. (1999). Alternative magnetic field exposure metrics: Occupational measurements in trolley workers. Radiat. Prot. Dosimetry. 85:99–106.
