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Approfondimento

Cancerogenesis: animal studies

 

Recently, several animal studies investigating the carcinogenic potential of radiofrequency radiation have been carried out.

 

The main goal is to determine if RF fields can act as carcinonegic process promoter, alone , or combined with other chemical and physical agents known for their carcinogenic proprieties.

 

Carcinogenic substances can be classified into two different categories, depending on their mechanisms of action: substances determining by themselves tumors formation, called “initiators”, and substances that in combination with other agents induce tumors formation, called “promoters”.

 

Overall, the experiments consist in the animal exposure to a RF field, possibly with a known dosimetry, followed by an examination of the action based on different tumors typologies installation or malignant transformation.

 

 

An important advantage of animal studies is that they provide information concerning interactions between RF radiation and living systems, referring to the full repertoire of body functions, such as immune response, cardiovascular changes and behavior, in a way that cannot be achieved with cellular studies.

Evaluating carcinogenicity in laboratory rodents has remained a cornerstone in identifying agents likely to cause cancer in humans. Agents for which there is sufficient evidence of carcinogenicity in experimental animals are considered to pose carcinogenic hazard to humans. However, extrapolation to humans is not straightforward since there are obvious differences in physiology and metabolism between species as well as differences in life expectancy and many other variables.

In addiction, despite the similarities in many cancer characteristics between humans and laboratory rodents, interspecies differences need to be taken into account when extrapolating data from rodents to humans: many agents that are carcinogenic in rodents (often only at very high doses) are not carcinogenic to humans, and some human carcinogens do not affect rodents.

The research has been effectuated both on healthy animals and on tumour-prone animal strains in order to verify if RF field exposure can induce tumours alone or combined with a known genotoxic/carcinogenic agent.


RF radiation alone


Several groups of research carried out studies investigating if radiofrequencies can induce tumours, both on healthy laboratory animals through ordinary tests on biological parameters; and on transgenic animals in order to increase, thanks to their predisposition, the probability that a highest number of animals develop the investigated pathology.

The research focused mostly on the induction of brain tumours due to RF exposure since electromagnetic fields from cellular phones have head as main target.

These investigations intended to simulate cronical condition exposure to electromagnetic fields from mobile phones, for this reason the animals had been exposed for most of their lifetime and some investigations also included in utero exposure.

The research has been carried out on rodents using electromagnetic fields with variable frequency between 835 MHz and 1.62 GHz; the results did not show any effect either on Central Nervous System (CNS) or on brain tumours incidence, both on animals whose exposure started in utero and for those animals with only a postnatal exposure. Moreover, no effects were found on lifetime duration or carcinogenic effects in other organs.

Studies on transgenic animals have been conducted in order to verify a possible association between exposure and development of multiple tumours. The main aim of transgenic lines is to increase statistic power.

In particular, studies on Patched1 mice, transgenic for the development of brain tumours (medulloblastoma and rhabdomyosarcomas) have been carried out. Patched1 transgenic mice and their wild-type siblings were exposed to GSM 900 signals, SAR 0.4 W/kg. No statistically significant differences in survival were found between exposed and sham-exposed animals. Medulloblastomas and rhabdomyosarcomas were found in the Patched1 mice but not in the wild-type animals. The incidence of rhabdomyosarcoma was higher in the exposed group than in the sham-exposed group, but this difference was not statistically significant. The incidences of medulloblastomas, other tumours or preneoplastic skin lesions did not differ between the exposed and sham-exposed groups.

 

Other studies finalized to verify a possible promoter effect of brain tumours due to a RF exposure of 1950 MHz did not show any difference among exposed, sham-exposed and control animals.

 

In order to conduct a complete research about tumours, some experiments have been carried out with a RF exposure of healthy mice and transgenic B6C3F1 rats with frequency variable between 900 MHz and 2.45 GHz and SAR between 0.15 and 4.0 W/kg.

 

Studies on healthy strains rats exposed to 2.45 GHz radar-type pulsed RF radiations showed that the organ-specific tumour incidences were low (except those in some endocrine organs). The incidence of any single type of primary malignant or benign neoplasm, the combined incidence of benign neoplasms or survival were not statistically significantly affected, and the authors concluded that, overall, the study did not show any definite biologically significant effects.

In conclusion, the results showed no conclusive scientific evidence of a carcinogenic effect of RF fields as far as tumors development is concerned, both single and multiple, and therefore further analysis and research on the subject are required.

 

A recent investigation evaluated carcinogenicity of both GSM signal at 902 MHz and DCS signal at 1.8 GHz in B6C3F1 mice with SAR levels ranging among 0 W/kg (sham exposure), 0.4 W/kg and 4 W/kg. The study produced no evidence that EMF exposure for whole body SARs up to 4.0 W/kg increased the incidence or severity of neoplastic or non-neoplastic lesions, or resulted in any other adverse health effects.

 

Other studies have been conducted with the aim to investigate the association between exposure to RF fields and the development of severe and frequent tumor types such as, lymphomas, breast cancers, and some families of brain tumors.

 

The interest in the investigation of possible associations between RF fields exposure to and development of lymphoma, started by the results of a study carried out by Repacholi at the end of the 90’s who used RF Eμ-Pim1 mice (prone to malignant lymphoma) exposed to 900 MHz GSM-type RF radiation.

 

A replication and extension of the Repacholi study has been conducted by exposing Eμ-Pim1 mice to pulsed GSM 900 RF at a whole-body SAR of 0.5, 1.4 or 4.0 W/kg and to a generic UMTS test signal at a SAR of 0.4 W/kg.

 

Compared to the sham-exposed controls, survival was reduced in the animals exposed to RF radiation and no increase in lymphoma incidence or in other types of tumours was observed in the RF exposed groups. The same results were found for UMTS test signals; in this case no life shortening has been recorded.

However, based on the data reported, a different analysis strategy (comparison to the sham-exposed group only) would not essentially change the interpretation that there was no effect of RF exposure on tumour incidence at any site. The reduced survival in RF-field-exposed animals is not thoroughly discussed; this finding remains unexplained and difficult to interpret without detailed information about the causes of death.

The studies which investigate possible interactions between RF fields exposure and development of mammary tumors started in the 80s with the exposure of genetically predisposed C3H/HeA mice to 2.45 GHz fields and SAR between 2 and 8 W / kg.

After the exposure an increase of tumor formation rate and a consequent decrease of survival were found, even if high SAR values may have caused a heat stress in animals and therefore influenced the results of the research which were not confirmed in following experiments carried out exposing

C3H/HeJ mice to lower SAR signals for longer periods of time.

The results observed showed no increase in the development of mammary tumors and no decrease in survival, leading to the conclusion that exposure to RF fields does not affect these two parameters.

 

Combined RF and known genotoxic/carcinogenic agents – Promoter effect

 

There has been considerable interest in testing RF radiation as a co-carcinogen that enhances the effects of known carcinogenic agents. Animal studies on co-carcinogenic effects have usually been designed based on the concepts of “initiation” and “promotion”. Such studies involve a short-term exposure to “an initiator” (known DNA-damaging agent) followed by long-term exposure to the putative “cancer promoter”.

 

Investigations have been carried out evaluating the combined effect of electromagnetic fields and known carcinogens, both physical and chemical, such as etilnitrosurea, MX, x-rays, DBMA and benzopyrene.

 

Several animal studies have evaluated the effects of RF radiation on tumorigenesis initiated by transplacental administration of a known genotoxic agent, n-ethylnitrosourea (ENU) in rats.

Using a carousel exposure set-up (with frequency between 836 MHz and 1439 GHz; and SARs localized at the head between 0.3 and 1.4 W/kg) to ensure well defined dosimetry, these studies have provided no evidence that RF radiation can promote the development of central nervous system tumours in this model.

RF exposure did not increase the incidence of brain tumours induced by transplacental administration of ENU in rats.

 

Recent studies evaluated possible effects of RF radiation on tumorigenesis induced by the mutagen and multisite carcinogen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX). Rats were exposed to GSM 900 RF at 0.3 or 0.9 W/kg.

RF radiation did not statistically significantly affect mortality or organspecific incidence of any tumour type. The only statistically significant difference was an increase in the combined frequency of vascular tumours of the mesenteric lymph nodes in the high-RF group compared to the sham-RF group. However, comparison to cage-control animals suggested that this difference was due to an unusually low frequency of this type of tumours in the sham-RF group, rather than high frequency in the high-RF group.

 

Several studies have investigated effects of RF field on mammary gland tumorigenesis induced by the carcinogen dimethylbenz(a)anthracene (DMBA) in rodents.

The research consisted of three experiments started exactly at the same time of the year and carried on for three consecutive years in which female rats treated with DMBA and mammary cancer were exposed to 900 MHz RF fields with SAR between 0.03 and 0.13 W/kg.

In one of the three experiments an increase in progression and development of mammarian tumors

was statistically significantly extended in the RF field-exposed group. This finding was not supported by the two other experiments. The overall conclusion was that long-term exposure to RF radiation had no significant effect on the development of DMBA-induced mammary tumours in rats.

 

A more recent research evaluated RF field effects on rodents treated with DMBA for a 6 month cronical exposure to a 900 MHz field (SAR between 0.4 and 4 W/kg).

All RF-exposed groups had significantly more palpable mammary gland tissue masses than the sham-exposed group, but there were no differences between the three RF-exposed groups. However, the incidence of benign tumours was significantly lower in the three RF exposed groups than in the sham-exposed group. The number of animals with benign or malign neoplasms was similar in the sham-exposed group and in the three RF-exposed groups. The cage control group had the highest incidence and malignancy of neoplasms among all groups.

 

Given that the DMBA mammary tumour model is known to be prone to high variations in the results, the authors’ interpretation was that the differences between the groups were co-incidental.

A significant acceleration of the development of benzo(a)pyrene(B(a)P)-induced tumours was found in mice irradiated with 2.45 GHz RF at SAR about 6-8 W/kg.

Exposure to RF fields has accelerated the development of skin tumors causing a decrease in survival. However, the data obtained were difficult to interpret because of the lack of protocols that describe in detail the methodology used.

 

Few years later some studies reported that low-level RF field exposures had no effects on tumour appearance or survival in B(a)P-treated female rats. Similarly, the RF field exposures had no effects on the levels of antiphosphatidylinositol auto-antibodies, a suggested marker of malignant transformation.

 

Finally, some investigations aimed at verifing whether the combination of RF fields and ionizing radiation (X rays), may increase the risk of cancer (lymphoma) after x-ray exposure have been carried out.

 

Rats treated with x-ray for three weeks were chronically exposed to RF fields at 900 MHz and SAR of 1.5 W/kg for one year and a half. The results from this study have shown, however, no effect of electromagnetic fields either in the development of lymphoma or in other neoplastic diseases.

 

In several experiments, especially in the field of physiology and pathology, man is replaced by animals: knowledge derived from experiments on animals such as rodents could be applied to humans, especially in the toxicology field and in the study of carcinogenesis.

 

There is a good correlation (84%) between agents that cause cancer in humans and those that cause cancer in rodents, for instance, the most of the chemical factors that cause leukemia in humans also cause leukemia in rodents.

 

Mechanisms of interaction in mice and humans follow the same metabolic process and the same way of cell repair, and it is sufficient, thanks to mathematical models, to apply doses to human size.

 

It is important, however, in this context to take into account interspecies differences. In fact, although many tumors present similar characteristics in humans and laboratory animals, it is necessary to extrapolate the data correctly, and relate them to man.

 

Furthermore, as far as RF fields exposure is concerned, it is also important to make complex dosimetric evaluations. In fact, SAR reaches its peak at the resonant frequency, this parameter is related to body size. Therefore, for some specific frequencies, it may happen that, for the same incident power density, SAR and exposure are greater in small animals (mice, rats) than humans.

 

Conclusions

 

Possible carcinogenic effects (cancer induction and promotion) of RF fields have been extensively studied, both through classical experiments on healthy animals, and by using genetically modified lines for induction of multiple tumors, or analyzing the effects of RF exposure combined with physical and chemical agents of known genotoxicity.

Excluding some exceptions, these investigations have not shown a carcinogenic effect due to RF fields exposure, even with at high SAR levels, alone or in combination with other agents.

Exceptions correspond to very old studies about incidence of lymphoma after RF exposure in mice genetically modified at 900 MHz and no replication was found.

 

More recent studies, all characterized by a better quality of dosimetry protocols, in fact, did not report any effects of induction or promotion of cancer in animals, both in prenatal and postnatal exposure. These recent results lead to the conclusion that there is no association between RF exposure and induction or promotion of cancer in animals, for SAR up to 4 W/kg.

 

 

Bibliography


[1] Adey WR, Byus CV, Cain CD, Higgins RJ, Jones RA, Kean CJ, Kuster N, MacMurray A, Stagg RB, Zimmerman G, Phillips JL, Haggren W. Spontaneous and nitrosourea-induced primary tumors of the central nervous system in Fischer 344 rats chronically exposed to 836 MHz modulated microwaves. Radiat Res 152:293-302; 1999.

 

[2] Adey WR, Byus CV, Cain CD, Higgins RJ, Jones RA, Kean CJ, Kuster N, MacMurray A, Stagg RB, Zimmerman G. Spontaneous and nitrosourea-induced primary tumors of the central nervous system in Fischer 344 rats exposed to frequency-modulated microwave fields. Cancer Res 60:1857-1863; 2000.

 

[3] Anderson LE, Sheen DM, Wilson BW, Grumbein SL, Creim JA, Sasser LB. Two-year chronic bioassay study of rats exposed to a 1.6 GHz radiofrequency signal. Radiat Res 162:201-210; 2004.

 

[4] Bartsch H, Bartsch C, Seebald E, Deerberg F, Dietz K, Vollrath L, Mecke D. Chronic exposure to a GSM-like signal (mobile phone) does not stimulate the development of DMBA-induced mammary tumors in rats: results of three consecutive studies. Radiat Res 157:183-190; 2002.

 

[5] Chagnaud JL, Moreau JM, Veyret B. No effect of short-term exposure to GSM-modulated low-power microwaves on benzo(a)pyrene-induced tumors in rat. Int J Radiat Biol 75:1251-1256; 1999.

 

[6] Chou C-K, Guy AW, Kunz LL, Johnson RB, Crowley JJ, Krupp JH. Long-term, low level microwave irradiation of rats. Bioelectromagnetics 13:469-496; 1992.

 

[7] Frei MR, Jauchem JR, Dusch SJ, Merritt JH, Berger RE, Stedham MA. Chronic, low-level (1.0 W/kg) exposure of mice prone to mammary cancer to 2450 MHz microwaves. Radiat Res 150:568 576; 1998b.

 

[8] Heikkinen P, Kosma VM, Hongisto T, Huuskonen H, Hyysalo P, Komulainen H, Kumlin T, Lahtinen T, Lang S, Puranen L, Juutilainen J. Effects of mobile phone radiation on X-ray-induced tumorigenesis in mice. Radiat Res 156:775-785; 2001.

 

[9] Heikkinen P, Ernst H, Huuskonen H, Komulainen H, Kumlin T, Maki-Paakkanen J, Puranen L, Juutilainen J. No effects of radiofrequency radiation on 3-chloro-4-(dichloromethyl)-5-hydroxy- 2(5H)-furanone-induced tumorigenesis in female Wistar rats. Radiat Res 166:397-408; 2006.

 

[10] Hruby R, Neubauer G, Kuster N, Frauscher M. Study on potential effects of "902-MHz GSM-type Wireless Communication Signals" on DMBA-induced mammary tumors in Sprague-Dawley rats. Mutat Res 649:34-44; 2008.

 

[11] Jauchem JR, Ryan KL, Frei MR, Dusch SJ, Lehnert HM, Kovatch RM. Repeated exposure of C3H/HeJ mice to ultra-wideband electromagnetic pulses: lack of effects on mammary tumors. Radiat Res 155:369-377; 2001.

 

[12] La Regina M, Moros EG, Pickard WF, Straube WL, Baty J, Roti Roti JL. The effect of chronic exposure to 835.62 MHz FDMA or 847.74 MHz CDMA radiofrequency radiation on the incidence of spontaneous tumors in rats. Radiat Res 160:143-151; 2003.

 

[13] Oberto G, Rolfo K, Yu P, Carbonatto M, Peano S, Kuster N, Ebert S, Tofani S. Carcinogenicity study of 217 Hz pulsed 900 MHz electromagnetic fields in Pim1 transgenic mice. Radiat Res 168:316-326; 2007.

 

[14] Shirai T, Kawabe M, Ichihara T, Fujiwara O, Taki M, Watanabe S, Wake K, Yamanaka Y, Imaida K, Asamoto M, Tamano S. Chronic exposure to a 1.439 GHz electromagnetic field used for cellular phones does not promote N-ethylnitrosourea induced central nervous system tumors in F344 rats. Bioelectromagnetics 26:59-68; 2005.

 

[15] Sommer AM, Bitz AK, Streckert J, Hansen VW, Lerchl A. Lymphoma development in mice chronically exposed to UMTS-modulated radiofrequency electromagnetic fields. Radiat Res 168:72-80; 2007.

 

[16] Szmigielski S, Szudzinski A, Pietraszek A, Bielec M, Janiak M, Wrembel JK. Accelerated development of spontaneous and benzopyrene-induced skin cancer in mice exposed to 2450-MHz microwave radiation. Bioelectromagnetics 3:179-191; 1982.

 

[17] Szudzinski A, Pietraszek A, Janiak M, Wrembel J, Kalczak M, Szmigielski S. Acceleration of the development of benzopyrene-induced skin cancer in mice by microwave radiation. Arch Dermatol Res 274:303-312; 1982.

 

[18] Tillmann T, Ernst H, Ebert S, Kuster N, Behnke W, Rittinghausen S, Dasenbrock C. Carcinogenicity study of GSM and DCS wireless communication signals in B6C3F1 mice. Bioelectromagnetics 28:173-187; 2007.

 

[19] Toler JC, Shelton WW, Frei MR, Merritt JH, Stedham MA. Long-term, low-level exposure of mice prone to mammary tumors to 435 MHz radiofrequency radiation. Radiat Res 148:227-234; 1997.

 

[20] Zook BC, Simmens SJ. The effects of 860 MHz radiofrequency radiation on the induction or promotion of brain tumors and other neoplasms in rats. Radiat Res 155:572-583; 2001.


Glossary


Benzo (a) pyrene: polycyclic aromatic hydrocarbon class of benzpyrenes; an oxidized form produced by living organisms (benzo (a) pyrene-7,8-dihydrodiol-7 .8 9 .10-diidrooxide) is able to bind to DNA and interfering with its replication mechanism. Benzo (a) pyrene is classified in category 1 by the IARC: substances carcinogenic to humans.


Dimethylbenzanthracene (DMBA): immunosuppressant and potent carcinogenic promoter, is used in laboratories as a tumor initiator due to its mutagenic activity. It also has an accelerating effect on the growth of tumors already in situ.


Etilnitrousurea (ENU): powerful mutagenic agent capable of transferring an ethyl group within the nucleic acid (generally a thymine) in the DNA chain by inducing a bases transversion. At high doses is toxic

 

MX: high mutagenicity compound formed by chlorination and oxidation of the degradation products of the organic material.


X-rays: high frequency ionizing electromagnetic radiation. X-rays are produced by the impact of electrons very fast with a target material (usually a heavy metal). X-rays are penetrating radiation and bodies, cannot fully absorb them. As gamma rays also x-rays can be hazardous to living cells, in particular can cause mutations, both direct through direct breaking of chemical bonds, both indirect through free radicals production 

 

Sham exposure: simulation of exposure conditions without proceeding to the administration of the physical agent

Elenco riviste

 

Di seguito viene riportato un elenco delle principali riviste internazionali peer reviewed che spesso ospitano articoli rilevanti sul tela effetti dei campi elettromagnetici sulla salute umana.

 

 

 

 

 

 

 

 

 

 

 

 

Effetti della esposizione ai campi elettromagnetici

La sezione contiene una raccolta di documenti scientifici riguardo gli effetti della esposizione ai campi elettromagnetici a frequenza compresa tra 100 kHz e 3 GHz. Gli articoli sono stati scritti sulla base dei risultati di una revisione completa della letteratura scientifica pubblicata nel corso degli ultimi anni e coprono una grande varietà di situazioni, prendendo in considerazione sia gli effetti acuti (o a breve termine) sia gli effetti a lungo termine che possono eventualmente essere conseguenza di esposizioni prolungate, anche della durata di anni, a livelli di campo molto inferiori a quelli caratterizzanti la comparsa degli effetti acuti.
Ogni articolo viene presentato corredato di un glossario dei termini per una migliore comprensione ed a una bibliografia dettagliata ad uso dei lettori che desiderano approfondire ulteriormente l'argomento.

Elenco argomenti:

  • Effetti della esposizione ai campi elettromagnetici a bassa frequenza (1 Hz - 100 kHz)
  • Effetti della esposizione ai campi elettromagnetici a radiofrequenza (100 kHz - 3 GHz)

Anomalie comportamentali derivanti da esposizione a campi a radiofrequenza

 

Numerosi studi sono stati effettuati su animali o su volontari al fine di verificare un eventuale effetto della esposizione acuta e cronica a campi a radiofrequenza sul comportamento e sulle funzioni cognitive.

Read more: Anomalie comportamentali derivanti da esposizione a campi a radiofrequenza

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