The air inside Chernobyl’s New Safe Confinement, which now houses Reactor 4, is damp and cool, with a subtle metallic smell of decaying concrete. The interior, a cathedral of catastrophe cut off from the outside world, has temperatures and radiation levels that change from room to room and floor to floor.
Something was growing on the walls of the containment structure when scientists were exploring its interior in the late 1990s. It’s not corrosion or simple weathering, but rather a dark, persistent mold that grows thickest in the regions with the highest radiation readings. The moment of realization was moving in the direction of the source rather than away from it, as one researcher subsequently explained.
One of the more subtly remarkable discoveries in contemporary biology resulted from that observation. The organisms were determined to be radiotrophic fungi, which include species from the genera Cladosporium, Cryptococcus, and Wangiella. What distinguished them was not only their ability to withstand radiation but also their seeming desire for it. The findings of the Chernobyl surveys were validated by laboratory tests: these fungi are resistant to more than just ionizing radiation.
When exposed to it, their growth improves. Highly melanized fungal species grew noticeably more quickly after being exposed to ionizing radiation at levels about 500 times higher than the typical background, according to a study published in PLOS One. Melanin, the same dark pigment that gives human skin and hair their color, emerged as the solution when researchers broke down the mechanism.
| Category | Details |
|---|---|
| Subject | Radiotrophic fungi discovered at Chernobyl — organisms that absorb and convert ionizing radiation into energy |
| Primary Species | Cladosporium sphaerospermum, Cryptococcus neoformans, Wangiella dermatitidis |
| Discovery Location | Inner walls of Unit Four (Reactor 4), Chernobyl Nuclear Power Plant, Ukraine — the epicenter of the 1986 explosion |
| First Documented | Late 1990s — scientists found 37 fungal species including C. sphaerospermum clinging to walls in highest-radiation areas |
| Key Mechanism | Radiosynthesis — melanin in fungal cells absorbs ionizing radiation (gamma rays) and converts it to chemical energy, analogous to photosynthesis |
| Key Pigment | Melanin — same pigment responsible for dark skin and hair coloring in humans |
| Key Finding | Fungi grew toward radiation sources rather than away; ionizing radiation boosted growth of melanized cells significantly |
| Space Application | C. sphaerospermum grown on the International Space Station (2018–2019); 1.7mm thick layer blocked over 2% of cosmic radiation |
| Mars Relevance | One year on Mars = ~400 mSv radiation exposure (60x+ average Earth levels); these fungi may offer biological shielding |
| Bioremediation Potential | Some species decompose radioactive graphite “hot particles” by moving toward and engulfing them |
| Scientific Reference | Studies in Mycological Research, Current Opinion in Microbiology, Journal of Environmental Radioactivity, PLOS One, Frontiers in Microbiology |
| Reference Website | Discover Magazine — Mold Is Feasting on Radiation in Chernobyl’s Abandoned Nuclear Plants |
Melanin in human skin acts as a passive UV light barrier, absorbing enough UV radiation to lessen cellular damage. The process seems to be essentially more active in radiotrophic fungi. The electron structure of melanin, which is tightly packed into the fungal cell walls, is changed by gamma radiation in a way that permits the energy to be transferred into the metabolic processes of the fungus.
This process, which is similar to photosynthesis but uses ionizing radiation instead of sunlight as the energy source, has been dubbed radiosynthesis by researchers. The comparison is flawed because radiosynthesis is not yet thought to be as effective at capturing energy as photosynthesis. However, it works well enough for these fungi to flourish in a setting that could kill an unprotected person in a matter of minutes.
There have been reports of some species at Chernobyl going even farther. According to research published in the Journal of Environmental Radioactivity and Mycological Research, some fungal species can physically approach and engulf radioactive graphite, which is the dense, radioactive material found in “hot particles” dispersed throughout the site.
Passive absorption is not what this is. This is more akin to feeding behavior aimed at one of the exclusion zone’s most dangerous materials. Researchers have been cautious not to overstate whether this amounts to significant bioremediation at scale, but it has sparked curiosity about whether targeted fungal deployment could eventually aid in cleanup efforts at contaminated sites like Fukushima or Chernobyl.
However, space might be the more immediately useful application. Any future long-term crew on Mars will be exposed to about 400 millisieverts of radiation per year, which is more than 60 times the average annual dose for Earthlings. The heavy materials used in current radiation shielding solutions for spacecraft—mostly metals—add mass and expense to each mission.
In order to investigate whether a fungal layer could offer biological shielding in the microgravity and radiation environment of low Earth orbit, researchers cultivated Cladosporium sphaerospermum on board the International Space Station in 2018 and 2019. Cosmic radiation was reduced by more than 2% by a layer that was 1.7 millimeters thick. That may be modest in absolute terms, but it was accomplished using a thin biological film that is low-mass, self-replicating, and possibly growable locally as opposed to being transported from Earth.
It’s still unclear if any of these applications will advance from lab curiosity to real-world implementation in the timeframes that researchers anticipate. Fungi-based bioremediation raises difficult issues regarding ecological impact and erratic interactions with contaminated environments. The early ISS experiments showed that much thicker and more dependable coverage would be needed for space shielding using C. sphaerospermum. Furthermore, even though radiosynthesis is real and well-documented, the exact mechanism by which captured radiation is converted to metabolic energy has not yet been thoroughly mapped, unlike photosynthesis.
The biological fact itself is already established, and it has an intriguing quality. A type of life that views the site’s most persistent hazard as a resource has been developing in the ruins of Chernobyl’s Reactor 4 for almost forty years. Observing that develop from a distance, via robotic surveys and peer-reviewed publications, carries a particular kind of weight. Life did not merely endure the catastrophe. Life found a way out and continued to exist in the specific corner of the building that took in the worst of it.
