A Mini-Review of the Potential Health Impacts of Indoor Radiation Exposure in Companion Animals

Abstract

Poor indoor environmental quality is a major concern for both humans and companion animals—yet its impact on the latter is often overlooked. This mini review sheds light on indoor radiation sources that may affect the health of companion animals. Radon, primarily from the ground and possibly also from cat litter, naturally occurring radionuclides in feed, radiofrequency radiation from mobile and cordless phones, Wi-Fi networks, pet tracking devices, solar radiation, and various sources of extremely low frequency radiation are all common examples. Indoor radiation, an odorless and tasteless pollutant, may have the potential to negatively impact the health and well-being of companion animals, which are involuntarily exposed to this environmental health risk factor. Therefore, preventive and precautionary measures are necessary.

Introduction

Indoor environmental quality is one of the most important aspects of the concept of environmental health. On a daily basis, both the public and companion animals are exposed to a wide variety of indoor pollutants that may impact their health and well-being. This brief review article aims to raise awareness about the radiation exposure of companion animals, which is an often overlooked aspect of indoor environmental quality that provides no sensory cues, such as color or smell. For the purposes of this article, a literature search was conducted using the widely utilized search engines PubMed, Scopus, and Google Scholar.

Exposure to Ionizing Radiation

Radon, a well-known human carcinogen that certainly affects the lungs and potentially other organs as well, ¹ has also been implicated as a potential cause of cancer in dogs and cats. In particular, evidence suggests that exposure to household radon may increase the risk of primary pulmonary neoplasia in these animals. ² Even though radon from soil typically enters houses through various openings such as cracks in floors and walls, it may also be present in other natural materials, such as cat litter. ³

Since it is well established that the risk of developing lung cancer is substantially higher for smokers exposed to radon compared to non-smokers, ⁴ the situation may become even more complex when pets live in indoor environments where owners smoke. Pets may be exposed not only to second-hand smoke but also to third-hand smoke, that is, the tobacco-related agents that become “embedded” in common household materials such as carpets, furniture, and toys.^5,6

Moreover, exposure to ionizing radiation—due to the presence of radon—may substantially elevate the overall radiation burden in animals, including companion species such as cats, dogs, rabbits, birds, and fishes, whose feed may naturally contain radionuclides like potassium-40.^7,8

Exposure to Sunlight

Another parameter that pet owners should consider is the prolonged exposure of their pets to sunlight—for example, while on balconies/yards or indoors through balcony doors and windows. Ultraviolet solar radiation lies on the borderline between ionizing and non-ionizing radiation, as part of it exhibits ionizing properties.^9,10 Moreover, it is well known that cumulative exposure to solar ultraviolet radiation—that is, exposure accumulated over a lifetime—can lead to biological effects that manifest later in life. ¹¹

Companion animals with thin fur and/or pale skin are at an increased risk of developing skin damages related to solar radiation. ¹² For instance, cats appear to have particularly high skin sensitivity to sunlight. Dermal sclerosis, edema, and squamous cell carcinoma caused by UV solar radiation are among the possible health effects.^13,14 Moreover, regarding vitamin D, since cats (and dogs) are not able to synthesize it adequately in the skin, dietary intake should replace prolonged sun exposure, ¹⁵ in order to avoid unwanted skin photodamages.

Another potential impact of sunlight is its involvement in the development of ocular damages, such as cataracts.^16,17 This may be more evident in regions where the protective ozone layer is significantly depleted. ¹⁷

Exposure to Non-Ionizing Radiation

In typical indoor household environments, companion animals are exposed to the same radiofrequencies as humans (eg, from devices such as Wi-Fi routers, Bluetooth devices, mobile phones, cordless phones, baby monitors, etc.). For instance, microwaves are known for their potential to disrupt the normal behavior and health of birds. ¹⁸ Additionally, the use of tracking devices should be considered another source of exposure. Given the necessity of tracking devices in many cases, efforts should be made to reduce the overall radiofrequency exposure of companion animals—especially in juvenile pets. Placing radiofrequency-emitting devices away from areas where animals are typically active, choosing low-emission devices, and limiting their operating time are among the appropriate mitigation strategies. ¹⁹

Electromagnetic radiation in the radiofrequency spectrum has also been associated with ultrastructural changes in the auditory cortex of guinea pigs, attributed to induced oxidative stress. The overall damage—including oxidative stress, apoptosis induction, and ultrastructural alterations—has been shown to increase in a Specific Absorption Rate (SAR)-dependent manner. ²⁰ Notably, the auditory system appears to exhibit high sensitivity to radiofrequency radiation, as 2 additional studies have confirmed its potential to affect normal neurophysiological and electrophysiological functions in rabbits.^21,22 Moreover, there is evidence that exposure of rats to radiofrequencies may have tumorigenic potential—leading to malignant tumors in the heart and brain, as well as malignant and benign tumors in the adrenal glands—as demonstrated by comprehensive studies conducted by the United States National Toxicology Program. ²³

Another source of non-ionizing radiation is Extremely Low Frequency (ELF) fields, which are present near sources such as electrical wiring and various household appliances. ²⁴ ELF electromagnetic fields have been implicated in altering lipid metabolism patterns, ²⁵ and can, for instance, cause changes in brain lipid profiles, “mimicking” physiological stress. ²⁶ Other reported effects include changes in physiological and behavioral parameters,^27,28 as well as impacts on cellular and molecular parameters and normal endocrine function.^27,29,30 In companion animals, there is evidence that the exposure to ELF electric fields can reduce the respiration rate in cats. ³¹ Obviously, more research is needed in this wide scientific field concerning the impact of ELF fields on animals. Moreover, one particularly interesting aspect is the potential influence of certain low frequencies such as those emitted prior to earthquakes on animal behavior. ³²

Finally, the use of laser toys is another aspect that requires attention. In addition to their potential to induce compulsive behaviors attributed to laser light play (eg, chasing lights and/or shadows), ³³ such devices, as reported in human case studies, may pose a risk of ocular injuries. ³⁴

Discussion

The modern lifestyle has resulted in the extensive exposure of companion animals to anthropogenic sources of radiation, adding to the background levels from naturally occurring sources. The most common indoor sources of radiation exposure for companion animals are illustrated in Figure 1.

Figure 1.

Common sources of indoor radiation exposure for companion animals. Icons created with DALL·E (OpenAI). Central image and composition: own work.

As part of a precautionary approach, unnecessary exposure to radiation should be avoided, both for humans and for animals, the latter of which are always subject to involuntary exposure. For example, using radon detectors/monitors for home use (particularly in houses located in geographical areas with known high radon concentrations), proper ventilation of indoor spaces with potentially elevated radon concentrations (such as basements), turning off devices that emit radiofrequency radiation when not in use, maintaining a distance from sources such as routers, and avoiding direct exposure to sunlight—especially for fair-coated animals—can all be considered prudent preventive and/or precautionary measures. The synergistic exposure to a multitude of radiation sources, and/or the potential joint effects with other agents including known carcinogens, ³⁵ should not be overlooked, and it is the responsibility of pet owners to protect their companion animals. In any case, such radiation constitutes a significant indoor pollutant, adding to already burdened indoor environments that also contain common indoor contaminants such as particulate matter, volatile organic compounds, and biological pollutants. ³⁶

Conclusion

Companion animals are increasingly exposed to a wide range of both ionizing and non-ionizing radiation sources. The potential health effects of such exposure should not be underestimated. Precautionary measures are necessary. There is a clear need to raise awareness among pet owners and to promote further research—in strict compliance with the most up-to-date animal welfare criteria—in this area.