Biological Effects of the Atomic Bomb (Level 4)

Level 4: Development of Cancer in Victims of Atomic Bomb Blast

Cancer in victims of the atomic bomb blast is mainly caused by beta, gamma and x-rays. Beta radiation can contaminate food and water which are consumed frequently by victims. Caesium and strontium, which are elements that emit beta particles, possess compounds which are soluble. This means that they can be taken up into plants via the roots if these elements get into the soil, and are eventually consumed by humans and animals. Victims that eat contaminated animals will thus ingest these beta particles.

A nuclear fallout (refer to Level 2 of Biology for information on nuclear fallout) after the explosion also leads to victims ingesting the irradiated materials via breathing the contaminated air. When gamma and x-rays get into the human body via penetration or beta particles via mostly ingestion, they emit ionizing radiation which can produce molecular-bond-breaking energy. It alters the molecular structure of the molecules exposed to radiation, damaging chromosomes and impacting the epigenetic factors which regulate the gene expression. Gene expression is the process in which information in a gene is used in synthesis of a new gene. This results in abnormalities in the tissue, or mutations that result in losses in the cell’s function.

One of the most damaging alterations are the double-strand breaks to the DNA. Double-strand breaks removes a portion of the epigenetic markers of the DNA, and although there are cellular mechanisms that attempt to repair the damage, some of these repairs will be incorrect and the chromosome abnormalities will become irreversible. Cells suffering from major damages die and lose their ability to reproduce, while those suffering from lesser damages remain partly functional and stable. These functional cells can proliferate and create many copies of the abnormalities, and the mutations eventually lead to the development of cancer.

This mutation process is sped up if tumor suppressor genes are damaged. Tumor suppressor genes play a role in stopping a cell from becoming cancerous. They sieve out cells which contain damaged DNA, which in this case is caused by the ionizing radiation, to ensure that the cells do not divide and result into increased chances of mutations in future generations. The tumor suppressor genes then attempt to repair the DNA and if the damage can be repaired, the cells’ reproduction cycle can continue. However, if the damage cannot be repaired, they will program the cell to die in a process called apoptosis. However, if these tumor suppressor genes are mutated or deactivated due to the radiation emitted from the atomic explosion, it results in a loss of function and the genes lose its ability to inhibit cell growth. This causes cells which contain damaged DNA to sometimes undergo uncontrollable cell division, accumulating the DNA damage over time.

The cells then undergo neoplastic transformation, which is the conversion of a tissue with a normal growth pattern into malignant tumors where cells invade nearby tissues. This causes the spread of cancer to different parts of the body.

Free radicals, which are atoms with unpaired electrons, are also created in large amounts by these types of ionizing radiation. They are created when the radiation strikes an atom or molecules, or when it ionizes the water, forming free radicals of hydrogen atoms. A large proportion of the human body contains water, and a lot of damage is caused by free radicals produced from water, also known as the reactive oxygen species. The free radicals are highly reactive and damage the biomolecules which form the various structures of the cells.

This results in oxidative stress, where our body cannot detoxify the huge number of reactive oxygen species or repair the subsequent damage caused by them. This either causes cell deaths or sometimes damages to the DNA, which will then play a role in the development of cancer as stated earlier.