Yankee Swap: tritium contaminated water anyone?

First published in the Montague Reporter

First we hear about tens of thousands of picocuries* in the groundwater beneath Vermont Yankee Nuclear Power plant, next it’s over one hundred gallons of water contaminated with over 2 million picocuries in some sort of concrete trench. Oops. Besides sloppy practices, lax monitoring, shoddy construction, and obfuscation (what underground pipes?) what do these numbers mean? Should we worry about all that tritium? And what the heck is a picocurie anyway?

Tritium is a radioactive isotope of the element hydrogen. What sets apart the radioactive elements from the non-radioactive is their lack of stability. They can disintegrate spontaneously, sometimes changing into other elements over time. Uranium, for example, decays into lead (although it may take billions of years,) while it takes roughly a decade for tritium to decay into helium.

The difference between a radioactive element and a plain old element depends upon what’s in the nucleus. The nucleus of any atom consists of protons (positive elements), neutrons (neutral elements) and electrons (negative elements). While the chemical properties of an element mostly depend on the number of protons in the nucleus, the radioactive properties are determined by the number of neutrons and the balance amongst the protons, neutrons and electrons. An element like hydrogen and its radioactive twin, tritium, have the same number of protons (and so, the same chemical properties), but instead of a single neutron, tritium has three neutrons. Tritium occurs naturally in small amounts, in addition to being produced by man either purposefully for research and consumer products (ever wonder about that glowing watch dial or that luminous EXIT sign?), or as a by-product of the nuclear industry.

Because tritium is chemically similar to hydrogen it can and does take the place of hydrogen – when this happens in water tritiated water or radioactive water is formed.

The radiation released by tritium is referred to as a beta particle. Beta particles, or electrons, are a form of ionizing radiation capable stripping electrons from other atoms, causing a sort of chain reaction of destabilization, and breaking chemical bonds. Although the beta particles released by tritium are low energy, incapable of penetrating through barriers such as skin (unlike some other forms of radiation), should tritium enter the body through inhalation or umm…water, those emitted particles would then have full access to vulnerable tissues and molecules.

Tritiated water is particularly insidious. The tritiated water lurking below Vermont Yankee for example, could be absorbed by the root systems of nearby plants, or imbibed by unsuspecting animals. Once consumed, distributes rapidly throughout the body of plant or animal. Additionally, ingestion of tritiated water, can lead to incorporation of tritium into organic materials like DNA, proteins and amino acids. Only, unlike hydrogen, tritium will eventually decay, leaving behind an atom of helium and releasing a beta particle with enough energy to break nearby chemical bonds.

In the body, the making and breaking of the chemical bonds between atoms is a highly coordinated process, normal and essential to life. The “unscheduled” breaking of chemical bonds can cause permanent cell damage, damage to the cell’s DNA or cell death.

The human genome is contained within the DNA of our 46 chromosomes located in a cell’s nucleus. Replication of these chromosomes during cell division is a critical process, requiring a number of complex biochemical interactions including copying and construction of identical chromosomal pairs that are then split off into the newly divided cell. Because integrity of the genetic material is essential to life, not only are there biochemical systems involved in maintaining chromosomes during division, but there are also a number of mechanisms by which errors may be repaired.

Say a few molecules of tritium enter the cell and cozy up to nuclear DNA. At some point in their unstable life-time they will disintegrate, releasing their energized electrons. Should the cells’ chromosomes be in their pathway, the transfer of energy from electron to chromosome may be enough to break off a bit of chromosome. Sometimes, depending on conditions within the cell and location of the break, the broken pieces may rejoin the chromosome, leaving little or no evidence of damage; other times a broken piece remains separate, becoming a chromosomal deletion; or both the deleted piece and the damaged chromosome will be copied as if nothing happened, only it will be altered. Or, instead of direct interference with DNA, emitted electrons may interact with other molecules such as oxygen, causing “indirect” damage by creating highly reactive oxygen radicals.

Since DNA tends to be a target of ionizing radiation, tissues made up of cells that are rapidly dividing – such as blood forming organs constantly churning out cells – tend to be far more sensitive to radiation damage than say, brain cells. Similarly, embryos and fetal tissues are more susceptible to radiation damage than adult tissues.

There is some good news amidst all this havoc and destruction. That is, most if not all cells have some capacity for DNA repair. These include an array of enzymes and proteins that find and correct damaged DNA in addition to a number of antioxidants capable of disarming those reactive oxygen radicals. The presence of such repair mechanisms have led some to speculate that exposures to very low amounts of radiation may be a good thing, “priming” these repair systems and leading to greater protection with low levels of exposure – a phenomenon referred to as hormesis. However, a National Academy of Science report on The Health Effects of Low Level Ionizing Radiation, published in 2007, found no available evidence of radiation induced hormesis in mammals, and concluded that any single track of ionizing radiation (for example by a single ejected electron in the case of tritium) has the potential to cause cellular damage.

And, despite the capacity for repair, sometimes the system is overwhelmed, or sometimes the repair itself introduces a new error (think sloppy auto mechanic.) At this point the genetic damage has the potential to become permanent, or “fixed.” Permanent damage to DNA can result in the eventual development of cancerous cells, or a defect in an exposed fetus or as a mutation passed on to the next generation. While the evidence for carcinogenicity in human populations is strong for some radioactive isotopes like strontium-90, plutonium and radium, the health effects of tritium, a weak beta emitter are less clear.

Which brings us to concentration. How much is too much? What does it mean that the groundwater has over 200,000 picocuries of tritium per liter of water, or that there are “troughs” with over 2 million picocuries per liter? A curie (named in honor of radiation pioneers Pierre and Marie Curie) is a quantity of radionuclide in which there are 37 billion disintegrations a second. That’s a lot of disintegration and in the case of tritium would be a lot of beta particles whizzing about. But the amounts drawn from the ground water were measured in picocuries per liter – or one millionth of a millionth of a curie. So, every second, until all the tritium has disintegrated to helium (the half-life for tritium is 12.5 years) there would be roughly 7,400 electrons winging about in a liter of Vermont Yankee groundwater.

As a result of the current hypothesis that exposure to any amount of ionizing radiation carries with it some risk of cancer, the U.S. EPA’s Maximum Contaminant Level Goal for all radionuclides in drinking water, a goal which aims for “zero-risk” to public health, is zero picocuries per liter. Unfortunately, achieving “zero risk” is not only wishful thinking but currently unenforceable and, because there is some naturally occurring tritium impracticable. Instead, EPA has developed Maximum Contaminant Levels (MCL) for drinking water. While the MCLs are enforceable, they are calculated considering best available technology and economic feasibility. For tritium, the derived** MCL is 20,000 picocuries per liter, while the derived MCL for strontium 90, a more powerful beta emitter associated with bone cancer and leukemia, is 8 picocuries.

Here’s the thing. Right now we’re talking two wells and a trench (where, incidentally, a small amount of radioactive cobalt has turned up as well.) While current concentrations in the ground water (the trench is another story) may not present an immediate health risk, who knows what a more comprehensive analysis - currently underway - might reveal?

*As of Feb 10, 2010 over 2 million pCi was measured in test wells around the plant.

For more see: http://www.rutlandherald.com/article/20100205/NEWS04/2050349/1003/NEWS02

**The MCL for beta emitters is based on a dose of 4mrem/year to the total body and assumes ingestion of 2L a day – the picocurie concentrations are derived for each specific beta emitting isotope depending on their strength. Over the years, there has been discussing of using different calculations for tritium that would dramatically reduce the MCL.

Plutonium, By the Way.....

I had been working on a project about the development of nuclear power plants in this country and through a list-serve of scientists and engineers found a few who were willing to educate me on the early days of nuclear power. They’d spent most of their lives working either for the industry or for government regulatory agencies, and had a lot to say about the early days. This provided some pretty interesting reading. It was one of my last questions however, about worker health, which clearly revealed the bias of one respondent.

“By the way,” he wrote, “plutonium is not toxic when eaten. You can eat it with a spoon if you want to.” To his credit he did concede that if you happen to inhale plutonium, there is a long-term risk of cancer, “just like naturally occurring polonium in tobacco smoke.”

He’s right of course. You could eat plutonium if you wanted to. You could also eat dioxin or arsenic if you wanted. But why would you?

Plutonium, like some forms of strontium, uranium and the now famous polonium-210 is a radioactive metal or element, although plutonium and radioactive strontium differ from uranium in that they do not occur naturally in our environment (for the most part) but are by-products of our “tinkering” with natural elements. Human activities like uranium mining, nuclear weapons production and testing, and nuclear energy production, are the primary human activities which have lead to environmental releases of plutonium, radioactive strontium, and other radioactive elements.

What sets apart the radioactive elements from the non-radioactive elements is their lack of stability. They can disintegrate spontaneously, sometimes even changing into other elements over time. Uranium, for example, will eventually decay into lead (although it may take billions of years.)

Generally speaking, elements are defined by what is in their nucleus. The nucleus of any atom consists of protons (positive elements), neutrons (neutral elements) and electrons (negative elements). While the chemical properties of an element are primarily dependent on the number of protons in the nucleus, the radioactive properties generally depend on the number of neutrons, and the balance among the protons, neutrons and electrons. An element can have several different stable forms, or forms in which the number of protons remains the same (thereby imparting the chemical properties), yet the number of neutrons might vary. Water, for example consists of two hydrogen atoms and one oxygen atom. Most often, the hydrogen in water contains just one proton and one neutron in its nucleus. This form of hydrogen is stable and does not undergo radioactive decay. But some hydrogen atoms exist that have two or even three neutrons. Those with two are called deuterium and those with three are referred to as tritium. Both deuterium and tritium can combine with oxygen forming heavy water which, for the most part, behaves chemically just like normal water. Deuterium atoms are stable. Tritium atoms however are not stable and at some point in time they will disintegrate, eventually leading to the production of helium (although in a much shorter period of time than it takes uranium to decay to lead - something in the order of decades rather than billions of years).

When atomic disintegration occurs radiation is released and depending on the element, may occur as alpha particles, beta particles or gamma rays. Although each one of these radioactive emissions has their own characteristics (see box), all three types are known as ionizing radiation, a powerful form of radiation capable of stripping electrons from other atoms and molecules (causing them to become either unstable or reactive) and breaking chemical bonds. The displaced electrons become free energetic electrons, and in turn are capable of imparting their energy to electrons of other molecules, either exciting them or knocking them out, continuing the process of bond breaking, excitation, and ionization.

In the body, the making and breaking of the chemical bonds between atoms is a highly coordinated process, normal and essential to life, and the “unscheduled” breaking of chemical bonds can cause cell death, permanent cell damage, or damage to the cell’s DNA.

Human DNA is contained within the 46 chromosomes (making up 23 pairs) that carry our genetic code. Replication of these chromosomes during cell division is a critical process, requiring an immense number of complex biochemical interactions, which involve copying and construction of identical chromosomal pairs that are split off into the newly divided cell. Since integrity of the genetic material is essential to life, there are biochemical systems involved in maintaining chromosomes during division, including mechanisms by which errors may be repaired.

As discussed above, ionizing radiation results in highly energized electrons that are capable of breaking any chemical bond in the body. Likewise, the track of an energized electron is capable of breaking chromosomal bonds, thereby breaking off pieces of the chromosome. Once a break occurs, depending on conditions within the cell and location of the break, the broken pieces may rejoin the chromosome, leaving little or no evidence of damage; the broken piece may remain separate, becoming a chromosomal deletion; or the deleted piece may continue to copy itself, as will the chromosome that is now lacking a portion of genetic information. It is generally agreed that the critical genetic damage from ionizing radiation is most likely the result of chromosome breaks, although other types of genetic damage can occur as well.

If the genetic damage becomes permanant, or “fixed”, and begins to propagate within the cell, the change can lead to the development of cancer, or to mutations that may be either genetic (capable of being passed on to offspring) or teratogenic (impacting only the exposed fetus) in nature.

So, when an element like plutonium disintegrates, it releases alpha particles and though these particles don’t travel vary far, once inside the body (say, from ingestion or inhalation), they are capable of interacting with, and potentially harming any bodily tissue along their path.

In other words, wherever the plutonium ends up, be it in the stomach, or the liver, or the bones, where it’s most likely to travel once it leaves the stomach, it has the potential to emit alpha particles, and cause tissue damage for as long as it remains in the tissue, which in the case of plutonium can be decades.

There is a great deal of information on the health impacts of radiation available on the web. Here are a just few sites that may be of interest if you wish to learn more:

The Institute for Energy and Environmental Research: http://www.ieer.org/

The US EPA: http://www.epa.gov/radiation/topics.html

And, if you really want to read the details there is the National Research Council’s latest report on “Health Risks from Exposure to Low Levels of Ionizing Radiation,” which is available online (and for purchase) at http://www.nap.edu/books/030909156X/html/R1.html

BOX:

Radiation Type	Emission	Distance traveled in air	Health threat from external exposure (penetration)	Health hreat from internal exposure	Emitted by:
Alpha (a)	2 protons, 2 neutrons	Centimeters	Low	High	Plutonium-236; uranium-238, radium-226
Beta (b)	Electron	Meters	High	High	Strontium-90; tritium, Iodine 131; Cesium 137
Gamma (g)	Photon (electromagnetic radiation)	Thousands of meters	High	High	Cobalt-60; Cesium-137