Single exposure to near-threshold 5G millimeter wave modifies restraint stress responses in rats

Abstract

Category: Toxicology Tags: 5G, millimeter wave, stress response, SAR, corticosterone, noradrenaline, rat study DOI: 10.1265/ehpm.24-00321 URL: pmc.ncbi.nlm.nih.gov Background Concerns have risen regarding the health effects of quasi-millimeter waves (qMMW) utilized in 5th-generation wireless communication systems. Guidelines have conservatively set a whole-body average specific absorption rate (WBA-SAR) of 4 W/kg—equivalent to a 1°C increase in core temperature—as the operational threshold for adverse effects. However, direct biological evidence for these thresholds has been lacking. Previous experiments showed a 1°C core temperature increase following 30 minutes of qMMW exposure at 4.6 W/kg in rats, highlighting the need for further investigation into biological stress responses near this threshold. Methods - Fifty-nine young Sprague-Dawley rats (240-322 g) were exposed to 28 GHz for 40 minutes at WBA-SARs of 0, 3.7, and 7.2 W/kg. - Experiments were conducted under normal (22.5°C, 45-55% humidity) and heat (32°C, 70% humidity) conditions, with rats restrained in acrylic holders. - Serum and urinary biomarkers of stress were repeatedly measured and analyzed using mixed models, accounting for sham exposure and between-subject variation. Key Findings - Sham exposure induced stress responses, primarily due to restraint stress. - After adjusting for sham effects, 28 GHz exposure elevated serum-free corticosterone 1 or 3 days post-exposure, especially in animals with >1°C rectal temperature change. - Urinary-free catecholamines indicated that 28 GHz exposure has an inhibitory effect on the stress response (notably noradrenaline) immediately after exposure. - Heat exposure amplified the effect, with a correlation between noradrenaline and tail surface temperature, supporting the role of noradrenaline in heat dissipation. Conclusions This study provides the first direct evidence that qMMW whole-body exposure near threshold values can modify the stress response in rats, as indicated by changes in corticosterone and noradrenaline. These findings offer biological insight into whole-body exposure thresholds specified by international safety guidelines and underscore the potential stress-related health risks associated with near-threshold 5G millimeter wave exposures.

AI evidence extraction

Main findings

In restrained rats, sham exposure induced stress responses. After adjusting for sham effects, 28 GHz whole-body exposure was associated with elevated serum-free corticosterone 1 or 3 days post-exposure, particularly in animals with >1°C rectal temperature change. Urinary catecholamines suggested an inhibitory effect on the immediate post-exposure stress response, notably noradrenaline, with heat conditions amplifying effects and noradrenaline correlating with tail surface temperature.

Outcomes measured

• Serum-free corticosterone
• Urinary-free catecholamines (including noradrenaline)
• Rectal temperature change
• Tail surface temperature

Limitations

• Sham exposure itself induced stress responses due to restraint stress
• Findings are from an animal model (rats), limiting direct generalization to humans
• Effects depended on temperature change (>1°C rectal temperature change) and environmental heat conditions

Suggested hubs

• 5g-policy (0.78)
  Study evaluates biological effects of near-threshold 5G (28 GHz) whole-body exposure relevant to safety thresholds/guidelines.
• who-icnirp (0.62)
  Abstract explicitly discusses international safety guideline thresholds (WBA-SAR 4 W/kg) and provides biological evidence near those values.

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    "study_type": "animal",
    "exposure": {
        "band": "mmWave",
        "source": "5G",
        "frequency_mhz": 28000,
        "sar_wkg": null,
        "duration": "40 minutes (single exposure)"
    },
    "population": "Young Sprague-Dawley rats (240–322 g)",
    "sample_size": 59,
    "outcomes": [
        "Serum-free corticosterone",
        "Urinary-free catecholamines (including noradrenaline)",
        "Rectal temperature change",
        "Tail surface temperature"
    ],
    "main_findings": "In restrained rats, sham exposure induced stress responses. After adjusting for sham effects, 28 GHz whole-body exposure was associated with elevated serum-free corticosterone 1 or 3 days post-exposure, particularly in animals with >1°C rectal temperature change. Urinary catecholamines suggested an inhibitory effect on the immediate post-exposure stress response, notably noradrenaline, with heat conditions amplifying effects and noradrenaline correlating with tail surface temperature.",
    "effect_direction": "mixed",
    "limitations": [
        "Sham exposure itself induced stress responses due to restraint stress",
        "Findings are from an animal model (rats), limiting direct generalization to humans",
        "Effects depended on temperature change (>1°C rectal temperature change) and environmental heat conditions"
    ],
    "evidence_strength": "low",
    "confidence": 0.7800000000000000266453525910037569701671600341796875,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "5G",
        "millimeter wave",
        "qMMW",
        "28 GHz",
        "whole-body average SAR",
        "WBA-SAR",
        "restraint stress",
        "corticosterone",
        "catecholamines",
        "noradrenaline",
        "heat exposure",
        "rat"
    ],
    "suggested_hubs": [
        {
            "slug": "5g-policy",
            "weight": 0.7800000000000000266453525910037569701671600341796875,
            "reason": "Study evaluates biological effects of near-threshold 5G (28 GHz) whole-body exposure relevant to safety thresholds/guidelines."
        },
        {
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}

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