Banner by Dhara Patel

Overexposed

By Miranda Scarborough

The scene is set: a barren wasteland, empty cities that are too quiet. The camera pans over to a hoard of mindless zombies with bloody clothes and lifeless, gray skin. This is the apocalypse the horror industry has always warned us about. That apocalypse is happening now. This apocalypse, however, is invisible to the naked eye; mutations in our DNA, caused by exposure to solar radiation, are altering our genetic code permanently. But what exactly is creating these mutations and what can we do to prevent it? To answer these questions, we must first look to the stars, for man’s mission to explore the universe is dependent on limiting solar radiation and the study of genetics.

“The study of genetics is everything. It is the connection, at its simplest form, between phenotype and genotype,” explains Dr. Saoirse McSharry, a professor of genetics in the biology department at the University of Pittsburgh. “[It is] trying to understand and make causative arguments about how the sequence of bases in our genome gets to who we are.”

However fundamental the field of genetics is, solar radiation is key to answering questions about DNA damage, and our increasing cancer rates. When solar radiation from the sun hits the Earth, it travels through the atmosphere. When it reaches the Earth’s surface, it is converted into visible light and ultraviolet (UV) rays. UV radiation directly damages DNA by creating pyrimidine dimers, which may cause errors in DNA replication. Pyrimidine dimers form when two thymine bases pair with each other, instead of with adenine bases on the opposite strand of DNA. Typically, the dimers will create a deletion of an adenine base, causing a frameshift mutation that could interrupt a sequence of DNA. Most of the time, if there is enough time between the damage and the next round of DNA replication, the body can repair its own DNA. However, a problem arises when constant irradiation damage builds up, as with constant solar radiation exposure.

This is where pyrimidine dimers come in. “With a pyrimidine dimer, you have from when that dimer occurs and the next round of DNA replication to fix it. Some cells do not divide very often, so it might not become a fixed mutation every time,” Dr. McSharry describes. Over time, the increase in mutations will produce cancer by causing sequences in DNA to change. Genetics explains how mutations can alter a reading frame, which is the sequence of DNA that defines a gene. This shift in reading frame will cause mutant formations of proteins which no longer function, or a novel form that can cause cells to grow at unprecedented rates. Who is most at risk for UV radiation and where can we compare the effects? These are questions NASA has been trying to answer.

NASA has been studying the effects of solar radiation both here on Earth and in space. To see the difference, NASA conducted a human study involving identical twins, Scott and Mark Kelly, in which they placed one twin in space and the other on Earth. The point of the study was to expose one twin to spaceflight hazards and detect any changes in DNA structure by using the genetically identical blood that remained on Earth as a baseline. NASA’s twin study showed evidence that increases in solar radiation and sustained living in space conditions, such as microgravity, do in fact alter DNA sequences. More specifically, the twin in space saw a distinct lengthening in the telomere ends of his chromosomes, in comparison to his genetically identical twin. The lengthening of telomere ends is very important to protect important sequences of DNA from damage during DNA replication for the life of the cell, as they add long noncoding regions that can be removed without harming the cell.

For spacebound Scott, “mutations that arose as a result of UV, gamma rays, or other kinds of high energy light will more often experience deletions,” says Dr. McSharry, as she continues with her explanation of mutations. “If you have a deletion on telomeres, you get closer to the coding region or regulatory region that is required for life. As an astronaut, we would want the telomeres to be shorter, because we want them to have a finite lifetime.” If telomeres were to mutate and become longer, cells can accumulate more mutations and have more occurrences of disease like cancer. Due to the constant shortening of telomere ends during cellular replication, there is a limit on how many times a cell can replicate before cell death. Thus, due to the increased exposure of radiation and lack of protection from the atmosphere, astronauts are more likely to experience more mutations than someone on Earth. Therefore, it is not one mutation that is the problem; it is the effect of multiple replications of mutations that can lead to diseases like cancer. However, despite the safety net of our atmosphere, scientists know that everyday professions are still impacted on Earth.

A recent study at Harvard University showed that pilots and flight attendants are regularly exposed to high levels of ionizing radiation. However, unlike for career astronauts, there are no regulations or testing for the adverse effects of high level radiation exposure. Typically, radiation risks are taken by the standard unit of measurement, the sievert (Sv). This unit represents the average background radiation dose in one year. On Earth, the average exposure to radiation is about 4 mSv per year. However, air crew may be exposed to rates as high as 20 mSv per year due to their proximity to space. In contrast, for astronauts, NASA recommends doses no higher than 400 mSv per career term. Yet, aircrew may experience as high as 400 mSv per 20 years of career, meaning, a pilot flying for 20 years will easily exceed the limit set by NASA. As further precaution, health outcomes for astronauts are carefully monitored over the course of their careers, even years after they are Earthbound, whereas flight crew are currently unmonitored for cancer rates or risk. And for many of us, solar radiation is not only a question for those in the skies or space, but also an important aspect of everyday life here on Earth — more integral than we may think.

Solar radiation is required to sustain life here on Earth. Plants have accumulated specific adaptations to the amount of solar radiation that reaches the Earth’s surface. For example, plants use photons, which come as packets of energy from the sun, to elicit photosynthetic processes, providing us with oxygen as a result. However, over the last 60 years, there has been a substantial increase in solar radiation on Earth due to climate change and depletion of the ozone layer. As these changes have not occurred over millions of years, adaptations to increasing solar radiation have not yet emerged and as the amount of solar radiation increases, so do our chances of adverse health effects like skin cancer. In studies on cancer-causing effects, researchers found that higher exposure to solar radiation in adults substantially increases the risk of developing skin cancers. These researchers followed adult women for 12 years in varying degrees of solar radiation exposure; their results described that women who were exposed to high levels of radiation in childhood through adulthood had a 19% increased risk to develop cancer. Their study also showed that high childhood exposure and low adulthood exposure to UV radiation showed no significant increase in risk for cancer, once again suggesting that extended doses of radiation are fatal. However, despite higher levels of radiation in the modern world, there are currently no standardized tests or methodologies in place to scan for cancers in adults or children. This results in most adults waiting until the onset of two or three symptoms before scheduling a doctor's visit. The increase of cancer can also be linked to other chemical mutagens. However, this is a cyclic process because such mutagens are greatly contributing to the climate crisis here on Earth.

Since the industrial revolution, the activities of humans have drastically changed the world and the climate. Global carbon emissions from everyday practices, such as the burning of fossil fuels, has created a greenhouse effect in Earth’s atmosphere. The increasing temperature of the oceans globally results in the melting of ice caps. Earth’s ice caps are responsible for reflecting a large percentage of solar radiation. With rising sea levels and increased absorption of solar radiation, the Earth’s climate has already begun to change for the worse. 

Yet, “life can adapt,” Dr. McSharry offers. “The planet has life forms that can and have adapted. That is why we want ‘errors’ in our DNA, so we can adapt to new environmental situations.” This change will not occur in our lifetime and it may not even occur within the human race. However, evolution and adaptation takes time, more time than our planet has if current conditions do not improve dramatically.

The apocalypse we have watched play out in movie scenes may be the creation of Hollywood producers but, in some ways, it is happening in real time and we are our own worst enemies. Can we save ourselves from the coming apocalypse? We have made steps in the right direction before. Take chlorofluorocarbons (CFCs), a man-made product which created a hole in the atmosphere by disrupting the bonds between ozone particles. Since banning CFCs from production, the ozone layer has begun to repair itself which has decreased the amount of solar radiation reaching the Earth. The banning of CFCs globally is an example of the power the human race wields to fix our biggest mistakes and save our planet from further destruction. But, climate change is still rapidly affecting the globe and causing irreparable damage to the polar ice caps. Professions such as pilots and stewardesses, as well as air travel in general, may cease to exist if radiation rates continue to increase. It is time to take a look at human activities on a global scale and reduce climate change as much as possible, as soon as possible.