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Chemistry of Lake Karachay
Episode 1817th June 2021 • Chemistry Connections • Hopewell Valley Student Publication Network
00:00:00 00:10:33

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Chemistry Connections

Episode #18  

Welcome to Chemistry Connections, my name is JACQUELINE SUN and I am your host for episode #18 called The Chemistry of Lake Karachay. Today I will be discussing what is arguably the most polluted and undoubtedly the most radioactively contaminated lake in the world, Lake Karachay, as well as the chemistry behind what made it that way in the first place.

Segment 1: Introduction to Lake Karachay

The history behind why Lake Karachay earned its name as the most polluted place on earth is convoluted and widely unknown.

  • Karachay is a small lake less than 1 square mile in area located in Central Russia in the Ural Mountains. 
  • In 1951, near the beginning of the Cold War, the Soviet Union dumped radioactive waste from the nearby, secret nuclear facility Mayak into Lake Karachay.
  • The Mayak reactor was built between 1946 and 1948 in total secrecy from the outerworld. Its purpose was to create radioactive material, primarily plutonium, that would allow the Soviets to build up a nuclear arsenal matching that of the US. 
  • The results of this reactor and many other’s efforts could be seen in the Soviet’s successful detonation of their first atomic bomb in 1949.
  • However, afterward, there was much toxic nuclear waste remaining. Without regulation or regard for safety, the Soviet government directed for the radioactive waste either to be stored in underground tanks or to be disposed of in nearby water reservoirs.
  • Lake Karachay was the closest lake to Mayak, making it the primary dumping point.
  • From this point on, Lake Karachay’s radioactive levels rose sharply.
  • Lake Karachay accumulated 4.4 exabecquerels of radiation after the dumping. That is about 4 quintillion (which is 10^18) becquerels, or 10 billion curies of radiation. For reference, the Chernobyl disaster released over 5 exabecquerels of radiation. However, Karachay was theoretically more dangerous because of the type of radiation it released, Caesium-137, which had a greater radioactive impact on its surroundings.
  • In 1990, it was reported that standing by the shore of Lake Karachay for just less than an hour would provide enough radiation to kill you.

Segment 2: The Chemistry Behind Lake Karachay


  • Radiation is clearly a highly deadly and complex process. It all centers around nuclear chemistry, or chemical modifications made directly to the nucleus of an atom. 
  • Nuclear reactions are different from chemical reactions in that chemical reactions really only involve changes and transfers in electrons, causing chemical compounds to be formed or rearranged. Nuclear reactions center around changes in the protons and neutrons located in the nucleus, which have the potential to release significant amounts of energy.
  • When the number of protons is changed, the element is changed from one to another. When the number of neutrons is changed, the element remains the same, but an isotope is created. These changes are called transmutations.
  • Transmutation is often spontaneous, or thermodynamically favorable, because nuclei naturally seek stability, or lower levels of potential energy. This is a similar concept to the octet rule in chemical reactions, or how atoms seek a full valence shell of electrons to reach their most stable state. Nuclear reactions will occur so that atoms may achieve a certain combination of protons and neutrons that stabilize the nucleus. 
  • Therefore, an unstable nuclei may release protons and neutrons, leading to its decomposition and the formation of a different nucleus. This process is known as radioactive decay, or radioactivity. The often large quantities of energy released during this time is called ionizing radiation, and it is in the form of alpha and beta particles and gamma rays, with the degree of penetration and strength increasing from alpha to gamma.
  • It is important to note that radioactive decay reactions are first order reactions. This means that the reaction rate is directly dependent on the concentration of the reactant, or the radioactive substance. This also means that the rate of decrease in the concentration of the substance also decreases over time, because the reaction rate decreases as the concentration decreases. Due to this phenomenon, radioactive decay reactions have constant half-lives, which is the amount of time it takes for one-half of the number of nuclei in a sample of a radioactive substance to decay. However, different nuclear substances have different half-lives. For example, 100g of plutonium-239, with a half life of 24,100 years, will take that amount of time to deteriorate to 50g of plutonium-239. It will then take another 24,100 years to deteriorate to 25g of plutonium-239. In the case of Lake Karachay, Caesium-137 was the main radioactive substance accumulated, which has a half-life of 30.17 years. After 30.17 years, half of the Caesium-137 decays into metastable barium-137, which has a half life of around 2.6 minutes. After 2.6 minutes, metastable barium-137 decays to ground state barium-137, where it is stable and no longer decays.
  • During this decay period, large amounts of ionizing radiation in the form of beta particles and gamma rays were emitted. 
  • Certain combinations of half-lives and amounts of ionizing radiation are what makes nuclear substances so dangerous.
  • This is because a shorter half-life means a higher rate of decomposition, which means more energy is being released in a shorter period of time. When combined with a high level of ionizing radiation, dangerous, potentially lethal amounts of energy could be produced, bombarding the surroundings. This was the case with Karachay, whose high energy beta particles and gamma rays easily penetrated their surroundings and disrupted the internal functions of nearby organisms.


  • The radioactive substances, primarily Caesium-137, in the lakebed of Lake Karachay irradiated over half a million people in the nearby vicinity. Many came into contact with it through everyday use, such as drinking or watering crops. There was also a catastrophe when a windstorm blew radioactive sediment dust over a wide radius, affecting many residents.
  • Radiation can cause much surface-level damage such as burns, sores, and nausea. More ominously, however, radiation can permanently alter the chemical composition of DNA, leading to mutations, cancer, and death.
  • DNA consists of two helical strands.
  • An individual strand is supported by a sugar-phosphate backbone. Within this backbone are phosphodiester bonds, which are intramolecular covalent bonds that bind together the sugars and phosphate groups. Covalent bonds are formed by a relatively even sharing of electrons between two nonmetals: in the case of DNA, a carbon from the sugar is linked to an oxygen in the phosphate group.
  • The two strands of DNA are held together by intermolecular hydrogen bonds between nitrogenous base pairs in DNA. Pairs can only form between a pyrimidine and purine base. Hydrogen bonds are formed between a hydrogen atom and a fluorine, oxygen, or nitrogen atom. However, the hydrogen atom must be bonded covalently to either a fluorine, oxygen, or nitrogen atom as well. In the case of base pairings, there will be two hydrogen bonds formed between an oxygen and a hydrogen atom and one hydrogen bond formed between a nitrogen and hydrogen atom.
  • The Caesium-137 radiation emitted by Karachay damaged the local residents’ DNA by disrupting these bonds. The ionizing radiation first randomly knocked valence electrons out of their atomic shells. The valence electrons could be more easily removed, or ionized, because they were a further distance from the positive charged nucleus and experienced more shielding, decreasing coulombic attractions. As a result, the atoms became highly unstable ions. At such high levels of potential energy, ions underwent thermodynamically favorable reactions that disrupted the hydrogen and covalent bonds in DNA, inducing single and double stranded breaks. This derailed the vital structure of DNA, leading to mutations, which then often lead to cancer due to failure to undergo apoptosis, or programmed cell death. 
  • At the time of irradiation, there had been a 41% increase in the rate of leukemia, 21% increase in the rate of cancers, and 25% increase in the rate of birth defects.
  • Even today, the effects of the radiation can still be seen. In the city of Ozersk near Lake Karachay, the life expectancy is around 50 years, which is exceedingly low compared to the world average of 72 years.

Segment 3: Personal Connections

Even though its threat level was comparable with other well-known nuclear disasters such as Chernobyl and Fukushima, Lake Karachay is not widely known. In fact, information on it remained classified by the Russian Government until the late 80s. The local residents of the lake had been in the dark about the so-called “mysterious illness” that had been afflicting them, not knowing that it was radiation poisoning. Lake Karachay shows just how impactful nuclear warfare can be even in “non-war” times and environments and why steps should be taken to rid the world of nuclear threats and influence. Today, Lake Karachay is covered by cement blocks in an effort to prevent the further irradiation of the environment and nearby residents. Even if the incident is quietly literally buried in the past, it is imperative to bring it to light to make sure the same mistakes are never made again. 

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Music Credits

Warm Nights by @LakeyInspired