How lethal is high dose UV?

Question

I watched a Neil DeGrasse Tyson video about teraforming Mars where he goes over the topic of UV radiation and how our ozone layer protects us. He makes a statement that the UV on earth is actually only a small percentage, about 3%, and furthermore only 5% of that being the more harmful UV-B which causes sunburn and skin cancer.

My question is, what would happen to a human if they were to receive the full dosage of UV-B radiation from the sun, let us assume 500 times higher than that on earth, with no protection? Would it be fatal? And if so how fast would it kill you?

Answer 1

The answer is easier than you think. Have you ever had a sunburn so bad that it causes blisters? (I have, as a teen falling asleep on the beach.) Those sunburns are called second degree sunburns. With that amount of exposure, the least that would happen is a 2° sunburn over most of your body (some parts don't suffer this), which would lead to hypovolemic shock. Without treatment (which includes fluid resuscitation), you would probably die within 24 hours. If, by chance you survived the first 24 hours, the blisters that break open (and they would) would get infected because your immune system would be compromised by the damaged capillaries of the skin (that's one cause of the blisters in the first place.) Your lifespan would be a few days if you didn't die within the first 24 hours.

This is the best case scenario.

_{This is why burn units exist. Second degree burns over a certain percentage of your body are lethal.}

Answer 2

You wouldn't get something like radiation sickness but something can be so unhealthy that can then lead to increased mortality. Whether or not something kills you is the lowest bar that can be set for whether something is healthy or not.

I couldn't actually find high wavelength resolution graphs for the solar irradiance at sea level since the values are vanishingly small on normal graphs.

However, if you take the the UV irradiance at outside of the atmosphere at 250nm to be 0.25W/m^2/nm and use that as a baseline for the UVB range of 280-315nm, then the irradiance 8.75W/m^2. Five hundred times that is equivalent to a 4.375mW UV laser producing a 1mm x 1mm square pot. The first thing you would notice is that you would go blind.

https://www.e-education.psu.edu/meteo300/node/683

Answer 3

It depends on the wavelength. This paper¹ provides the numbers:

This study was conducted to determine the toxicological effects of different wavelengths (250, 270, 290, and 310 nm) and doses of UV radiation on cell viability, DNA structure, and DNA damage repair mechanisms in a PC12 cell system. For this, we evaluated cell viability and CPD formation. Cell survival rate was markedly decreased 24 h after UV irradiation in a dose-dependent manner at all wavelengths (except at 310 nm). Cell viability increased with increasing wavelength in the following order: 250 < 270 < 290 < 310 nm. UV radiation at 250 nm showed the highest cell killing ability, with a median lethal dose (LD50) of 120 mJ/cm2. The LD50 gradually increased with increase in wavelength. Among the 4 wavelengths tested, the highest LD50 (6000 mJ/cm2) was obtained for 310 nm. CPD formation decreased substantially with increasing wavelength. Among the 4 wavelengths, the proportion of CPD formation was highest at 250 nm and lowest at 310 nm. On the basis of LD50 values for each wavelength, PC12 cells irradiated with UV radiation of 290 nm showed maximum DNA repair ability, whereas those irradiated with the 310-nm radiation did not show any repair ability. Toxicity of UV radiation varied with wavelengths and exposure doses.

You can find more details on this topic in ref.2

References

1. Masuma R, Kashima S, Kurasaki M, Okuno T. Effects of UV wavelength on cell damages caused by UV irradiation in PC12 cells. J Photochem Photobiol B. 2013 Aug 5;125:202-8. doi: 10.1016/j.jphotobiol.2013.06.003
2. Lawrence, K.P., Douki, T., Sarkany, R.P.E. et al. The UV/Visible Radiation Boundary Region (385–405 nm) Damages Skin Cells and Induces “dark” Cyclobutane Pyrimidine Dimers in Human Skin in vivo. Sci Rep 8, 12722 (2018). DOI: 10.1038/s41598-018-30738-6