Author(s):
Vilić M*, Žura Žaja I, Tkalec M, Tucak P, Malarić K, Popara N, Žura N, Pašić S, Gajger IT.
* Department of Physiology and Radiobiology, Faculty of Veterinary Medicine, University of Zagreb, 10000 Zagreb.
Croatia
Published in:
Insects 2024; 15 (5)
Published: 20.05.2024
on EMF:data since 11.11.2024
Further publications: Studie gefördert durch:

No external funding.

Medical/biological studies
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Oxidative Stress Response of Honey Bee Colonies (Apis mellifera L.) during Long-Term Exposure at a Frequency of 900 MHz under Field Conditions.

Original Abstract

In this study, oxidative stress and lipid peroxidation in honey bee larvae, pupae and the midguts of adult bees were investigated during a one-year exposure to radiofrequency electromagnetic fields (RF-EMFs) at a frequency of 900 MHz under field conditions. The experiment was carried out on honey bee colonies at three locations with electric field levels of 30 mV m−1, 70 mV m−1 and 1000 mV m−1. Antioxidant enzymes, glutathione-S-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS) as indicators of lipid peroxidation were measured spectrophotometrically. The GST activity within the same developmental stage showed no significant differences regardless of electric field level or sampling time. The highest GST activity was found in the pupae, followed by activity in the larvae and midguts. Both CAT activity and TBARS concentration were the highest in the midguts, regardless of field level and sampling time. The larvae showed a significantly higher TBARS concentration at the location with an electric field level of 1000 mV m−1 compared to the locations with lower levels. Our results show that RF-EMFs at a frequency of 900 MHz can cause oxidative stress in honey bees, with the larval stage being more sensitive than the pupal stage, but there was no linear relationship between electric field level and effect in any of the developmental stages.

Keywords

radiofrequency radiation | honey bee | antioxidants | field conditions

Exposure:

900 MHz
GSM

EMF:data assessment

Summary

In concert with the widespread use of cell phones and other sources that generate radiofrequency electromagnetic fields (RF-EMF), there is growing public concern about harmful effects on human and animal health. In fact, the results of numerous studies have shown that exposure to RF-EMF (cell phones, routers, base stations) has various non-thermal biological effects such as oxidative stress, immune system dysfunction, genotoxic effects as well as effects on reproduction and fertility. These biological effects have been demonstrated in vitro and in vivo in various animal species, including mammals and insects. The honeybee is one of the most important insects for maintaining balance in natural ecosystems. The honeybee is thought to play the most important role in pollination of all insect species in the Hymenoptera order, as it is involved in almost 80−85% of pollination of the world's crops. Previous studies on the effects of RF-EMF on honey bee colonies have mostly examined adult honey bees in the laboratory or under unnatural conditions. To date, there are many uncertainties about the effects of RF-EMF on honey bee colonies due to the lack of studies under field conditions. The aim of this study was to answer the following questions: (a) Could RF-EMF cause lipid peroxidation and changes in three vital antioxidant enzymes  at different stages of honey bee development under field conditions? (b) Is there a possibility of a chronic effect on oxidative stress after one year of exposure?

Source: ElektrosmogReport - Issue 4/2024

Study design and methods

The study was conducted on honey bees exposed to RF-EMFs from mobile phone base stations in their natural environment. A total of fifteen (15) honeybee colonies were randomly selected. The experiment was conducted at three different locations:

Five honey bee colonies were located near mobile phone base stations with a frequency of 900 MHz and an average electric field of 1000 mV/m or 2.65 mW/m², referred to as high intensity (HI) (67 and 160 m from two base stations, respectively). Five other honey bee colonies were located at a site with an average electric field of 30 mV/m or 0.002 mW/m², named low intensity (LI), about 800 m from the base stations. Five honeybee colonies were located at a site with a field strength of 70 mV/m or 0.013 mW/m², named medium intensity (MI), at a distance of about 1600 m from the base stations.

All colonies were exposed for one year and samples were taken three times (2 weeks, 5 months and 1 year) after the start of the monitoring. Five- to six-day-old larvae, pupae in the violet eye stage and the midgut of adult honey bees (forager bees) were collected from each colony.

The activity of glutathione S-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) as well as the degree of lipid peroxidation (TBARS) were determined in accordance with a previously published study by the same authors.

Results

When comparing the results of the same observation period, the GST activities in all honeybee samples at locations with different electric field strengths (30, 70 and 1000 mV/m) did not differ statistically significantly.

CAT activity in the larvae was statistically increased (p < 0.05) at the HI site (1000 mV/m) compared to the MI and LI sites with lower electric fields in the fifth month of exposure, while it was increased at the LI site (30 mV/m) compared to the MI (70 mV/m) and HI sites (1000 mV/m) after one year of exposure. CAT activity in the midgut of the adult honey bee colony was significantly higher (p < 0.05) at the HI site (1000 mV/m) compared to the MI site (70 mV/m) after the two-week exposure as well as after the one-year exposure. On the other hand, it decreased at the HI site (1000 mV/m) compared to the LI site (30 mV/m) after the 5-month exposure.

The SOD activities in all honey bee samples (larvae, pupae and midgut) did not differ significantly when the results were compared between the different sites over the same observation period.

In the larvae, the TBARS concentration (= lipid peroxidation) was significantly higher at the HI site (1000 mV/m) compared to the other two sites, MI (70 mV/m) and LI (30 mV/m), after the two-week exposure, while after the one-year exposure, TBARS were also higher at both the HI and LI sites compared to MI (70 mV/m). The TBARS in larvae of honey bees from the LI site were significantly increased after one year of exposure compared to after two weeks of exposure.

Conclusions

The authors of this study had previously reported that GSM 900 MHz radiation affects the antioxidant system of honey bee larvae after short-term exposure under laboratory conditions. The results obtained in this study are consistent with the previous study. Thus, the activity of antioxidant enzymes and the concentration of lipid peroxidation products depend on the developmental stage of honeybees, the ambient electric field strengths and the duration of exposure. The overproduction of reactive oxygen species (ROS) after exposure to GSM RF-EMFs is scavenged by SOD, CAT and GST, the main antioxidant enzymes in honey bees. One of the reasons for the observed antioxidant enzyme activity at certain developmental stages could be the physiological developmental profile of these enzymes and their function in honey bees. Indeed, it is known that the activities of SOD, CAT and GST in a larva increase slightly from the first to the sixth day and then decrease until the end of honeybee development, with CAT activity decreasing the most. Based on the results that TBARS levels (at two-week and one-year exposure) and CAT (at five-month and one-year exposure) were significantly increased in larvae, the authors hypothesize that larvae are more sensitive to RF-EMF exposure than pupae. The higher TBARS content could be explained by the lipid content of the larvae, which have a significantly higher fat content than the pupae and are therefore more sensitive to oxidative stress. In contrast, no statistical differences were found in the developmental stage of the pupae between different sites at all three sampling times. One possible reason for this is the fact that the pupal stage is able to overcome the potential cell damage caused by oxidative stress due to the higher physiological activity of the antioxidative enzymes. CAT, SOD and GST activity did not show linearity with respect to field strength and time of sampling. As the mechanisms of RF-EMF are not yet well understood, it is difficult to say what effects such radiation might have on the physiological characteristics of bees. (AT)