Monday, 5 December 2016

Brief history of radiation protection. What does it mean?

People are prone to jump on moral crusades. We see it today with global warming. Back in the day, radiation and cancer were a moral crusade.

In the early days of radiation it was the Wild West. No radiation limits. Marie Curie died of radiation induced cancer. Radium girls often caught mouth cancer. By the 1920s it was clear that high radiation doses presented a serious health risk. Dose limits were imposed in the early 1930s. OMG! - how did humanity survive before we had environmentalists to protect us? Easy. Sensible folks noticed something was wrong and proposed regulation to stop bad things. Yet even back then I bet we had the equivalent of SJWs; crusaders who pushed regulation too far.

No widespread major illnesses developed among radiation workers after maximum dose limits were imposed in the early 1930s. Consider the following timeline. In response the development of the atomic bomb radiation protection standards were increased. Later in response to the threat of nuclear power, radiation protection standards were ratcheted tight.

  • 1931: National Council on Radiation Protection establish first formal dose limit = 1 mGy/day
  • 1934: International X-ray and Radium Protection Committee (later to become ICRP) set limit = 2 mGy/day, ~ 730 mGy/year.
  • 1945 Aug: first atom bombs dropped.
  • 1948: Radiation protection group (US, Canada and UK) reduce permissible human radiation dose by half (to ½ mGy/day, ~ 183 mGy/year)
  • 1950: ICRP reduce recommended limit to 3 mGy/week, ~ 150 mGy/year.
  • 1953 Dec: Eisenhower's atoms for peace UN speech calls for civilian nuclear power
  • 1954 Mar: Rockefeller foundation meet to discuss radiation. Presumably in response to the threat of plentiful atomic power promised by Eisenhower just months earlier. Probably not in response to the Atomic bomb threat; although nuclear tests were increasing during the 1950s, peaking, by number, in 1958 and 1961. In 1954 atomic bomb testing was not huge. 8 tests during the whole year. Rockefeller sponsor NAS BEAR [Biological Effects of Atomic Radiation] committee, pick its membership. Help set its agenda.
  • 1955 Apr: NAS BEAR begin work.
  • 1956 Jun: NAS BEAR publish in NYT calling for no safe radiation dose. Excluding evidence by Ernst Caspari which contradicted no safe dose).
  • 1961: AEC tighten dose limits for occupational exposure to an average of 50 mGy per year after the age of 18 while continuing to suggest that general population exposure levels be restricted to 10% of the occupational levels (5 mGy per year) for individuals. [average U.S. natural exposure from background radiation ~ 4 mGy per year]
  • 1963 Aug: Countries sign global atomic bomb test ban treaty. BEAR scientists congratulate themselves on a job well done: "We made the world a safer place".
  • 1975: I'm told in undergraduate physics class there is "no safe dose" for radiation. That scientists are certain of this. All the evidence tells us. Ernst Caspari is apparently a non person. Real Science says his research never happened. [ I remember so well because I questioned the lecturer on it immediately as it contradicted everything I knew about the response of biological systems to stress ]

PS: All radiation units above were converted to mGy (milli-Gray) to give approximate values for comparison. In reality some limits were set as REMs some as milli-Gray, most as roentgens.

High/medium dose radiation causes cancer

No safe dose: Is not peculiar to radiation. It was decreed that there was "no safe dose" for all carcinogenic substances. From what I can gather, this was a theory first approach to regulation. Better safe than sorry. It is a bit of a nonsense because it cannot be enforced. E.g. Oxygen, which essential to human life. is a DNA mutagen. Some substances are thousands of times more carcinogenic than others. E.g. Aflotoxin made by fungi growing on badly stored nuts or grain is about the most carcinogenic substance known. It may indeed have "no safe dose". Yet that does not mean you get cancer eating some. I loved nuts when I was a child. I must've accidentally eaten bad nuts at least 50 times. Mostly spitting it out but I'm sure some of the "no safe dose" deadliest carcinogen slipped by. I'm still alive and cancer free. DNA mutation and cancer is a complex thing. To cause cancer several mutations are needed and they must be the right ones: leading to a cell growing out-of-control, dividing into new cancerous cells, undetected by our body's immune system. Our body thinks it is still a normal body cell. The wrong mutation will lead to the immune system identifying a bad cell and killing it. Most mutations will be detected and destroyed by our immune system. Unfortunately we have a lot of cells (~ 70 trillion). Each undergoes up to 1 million DNA damage events per day. To start a cancer, it only takes one cell to slip by with the right set of DNA mutations which fool the body's immune system into thinking it's kosher. Most DNA damage events can be repaired by the cell itself, so do not lead to mutations. Single-strand DNA damage is basically repaired. Double-strand DNA damage is also repaired but may not be done so well.

Hormesis to the rescue

In addition there is a hormetic effect. A low dose of a carcinogen may stimulate the immune system to protect the body against cancer. E.g. by increasing autolysis of suspect or damaged cells. This hormetic effect of radiation is thought to kick in at a dose much lower than the 1930s maximum limit. There are a lot of carcinogenic substances about. Oxygen is a DNA mutagen, as well being essential to animal life. We breath in about 500 gram per day of it. It's estimated that up to 3% goes astray in that it is not all used by the right metabolic pathway. That's about a third of a mole per day of wayward oxygen our body must deal with. 2 × 10²³ rogue molecules of oxygen for about 70 trillion human cells; about 3 billion rogue oxygen molecules per human cell. Every day. That must be causing some cancer, some of the time. If the immune system can be stimulated by a hormetic effect, radiation can actually reduce the effect of cancer. Perhaps protecting against harm done by more common / chronic carcinogens as well. It's difficult for me to imagine how oxygen could induce such a (hormetic) effect!, since oxygen is so common. Yet:

Hyperbaric oxygen therapy of humans (100% O2 at 2.5 atm), for instance, induces significant oxidative DNA damage to peripheral blood cells on the first day of therapy but fails to cause damage on subsequent days
-- Oxidative Decay of DNA, by Kenneth B. Beckman and Bruce N. Ames

At moderate to low radiation doses (below 730 mGy/year) the harmful effect of radiation is increased cancer risk. It is a carcinogen. Yet no major illnesses developed among workers after maximum dose limits were imposed in the early 1930s. Because at this level < 2 mGy/day, the hormetic effect of radiation protecting us out-weights the additional harm done by mild radiation exposure. In 1948 / 1950 this exposure level was cut to just a quarter of the 1930s. Then it was cut again to "no safe dose". No scientific studies conclusively show either the lower limit (~ 150 mGy/year) or the zero limit are safer. Scientific studies are inconclusive. Some show barely perceptible increased risk. Some show a clear hormetic effect of less cancer risk.

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