Courtney Ayling
The 1986 Chernobyl disaster is considered the worst nuclear disaster in history. It was caused by the explosion of a nuclear power plant reactor, spewing radioactive material into the atmosphere. The aftermath of the event caused the establishment of an uninhabitable 19-mile radius around the building. The predicted death toll for both direct and indirect deaths was over 4,000 and more than 130,000 people were evacuated. Local biodiversity dramatically declined due to the contamination of the food chain and groundwater systems, though there has been evidence of wildlife revival in the area. Despite this disaster, an abundance of radiotrophic fungi was discovered growing within and around the plant, only 5 years after the catastrophic accident.
(Fig 1.) The Chernobyl nuclear power plant post reactor explosion. Associated Press (1986). https://allthatsinteresting.com/wordpress/wp-content/uploads/2012/06/iconic-images-1980s-chernobyl-disaster.jpg
Radiotrophic fungi are a specific group of extremophile fungi that can convert radiation into an energy source to stimulate growth. They can do this using melanin (a natural pigment found in living organisms) as an active ‘shield’ against high levels of radiation, whilst simultaneously being able to harvest energy from the same radiation. In 2007, an Italian scientist named Davide Castelvecchi hypothesized that the harvesting of radiation via melanin occurs using a process similar to photosynthesis, where instead of photons being captured by chlorophyll and being used to generate ATP via photophosphorylation, energy from ionising radiation is captured by melanin and transformed into ‘useable’ energy for growth. This hypothesis was tested on three melanin-containing fungi, and the experimental results showed that fungal-melanin exposed to radiation was 4 times more effective in reducing NADH (showing that NADH was being ‘consumed’ during biological processes) compared to the control melanin which was not exposed to radiation. However, his hypothesis is still being tested, so the real mechanisms behind radiotrophism are yet to be proven.
(Fig 2.) Cladosporium sphaerospermum culture, one of the major species observed in the destroyed reactor at Chernobyl. Medmyco (2005). https://upload.wikimedia.org/wikipedia/commons/thumb/1/1f/Cladosporium_sphaerospermum_colony.jpg/1200px-Cladosporium_sphaerospermum_colony.jpg
From the Chernobyl disaster, there has been an ironic turn of events; the finding of this adaptable fungus has led to another realm of research – the removal of radioactive waste. Nuclear power is often considered a sustainable energy source due to the lack of greenhouse emissions, and 96% of its waste can be recycled back into uranium-based fuels. But, the 4% of waste that is not recyclable is highly radioactive and has to be securely stored before it is considered safe for disposal. Deep geological repository of the dangerous leftovers has been discussed as a long-term storage solution when facing high levels of waste, but there could be unknown impacts for future generations. The discovery of radiotrophic fungus has led scientists to explore utilising it as a means to permanently dispose of highly radioactive nuclear waste (which has been known to have devastating impacts on health and the environment when not properly contained), and perhaps aid nuclear power into becoming a renewable resource, as well as a sustainable one.
(Fig 3.) An example of materials required in low-level radioactive waste storage; placed in drums and surrounded by concrete, and will later be put in clay-lined landfill sites. Thailand Institute of Nuclear Technology, (2014). https://upload.wikimedia.org/wikipedia/commons/thumb/9/93/TINT_Radioactive_wastes%27_barrel.jpg/800px-TINT_Radioactive_wastes%27_barrel.jpg
Another field of research is being explored with radiotrophic fungus in deep-space exploration; the ISS (International Space Station) has taken C.sphaerospermum with it into space, to explore the possibilities of it acting as a shield to radiation, and perhaps be used to aid future ventures. One of the biggest risks astronauts face is the long-term implications to health that can arise from high-radiation exposure; on Earth, we experience 6.2 mSv6 of radiation within one year, whereas the average astronaut will experience around 144 mSv7. This can increase the risk of developing diseases such as cancer, so the time that astronauts can spend in space is limited. If radiotrophic fungus can be manipulated to ‘absorb’ the majority of radiation that astronauts will come into contact with, the short periods that astronauts would spend in space could be extended, allowing for more fruitful expeditions. It seems that nature can overcome even the deadliest of human consequences, but should we be focusing on cleaning up our messes on Earth before trying to start new ones on other planets?
(Fig 4.) The ISS orbiting planet Earth. Image taken by ISS crew member. NASA (2001). https://www.nasa.gov/centers/marshall/images/content/98870main_sts105-707-019_m.jpg
Where to find out more:
- Chernobyl disaster – https://www.nationalgeographic.co.uk/environment/2019/05/chernobyl-disaster-what-happened-and-long-term-impact
- Chernobyl wildlife – https://chernobylguide.com/chernobyl_wildlife/
- Castelvecchi research – Dark power: pigment seems to put radiation to good use. – Free Online Library (thefreelibrary.com)
- Example of radioactive waste spill – https://www.globalsecurity.org/wmd/world/russia/chelyabinsk-65_nuc.htm
- Deep-space experiment – https://www.biorxiv.org/content/10.1101/2020.07.16.205534v1.full.pdf
- Recycling nuclear waste – https://www.youtube.com/watch?v=V0UJSlKIy8g
- Geological disposal of radioactive waste – https://www.geolsoc.org.uk/gdrw
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