Why do you compare cross country flight doses to air and water (internal) doses?

EPA states this it is fact inhalation is the worst form of exposure...

This topic deserves debate and study.thanks to the brawn team for publishing there findings.the major concern I have is I really have no choice of avoiding these internal emitters as I do have some limited control over external radiation .

Please add my voice to those who find the comparison between the radiation dose from food ingestion and a cross-country flight invalid. I posted my angst on my blog recently. It broadens the subject a bit. I am not a physician or scientist, but an educator,disaster preparedness specialist and nurse. Comments would be appreciated. My original blogpost follows.

From the Department of Nuclear Engineering, UC Berkeley. See link at the bottom of the post.

Notes from your editor: The numbers in parentheses after the radiation activity level indicate the number of kilograms "that one would need to consume to equal the radiation exposure on one round trip flight from San Francisco to Washington, D.C. (0.05 mSV)."

For example, one would have to consume 2, 570 kg of spinach contaminated with Cesium-134, purchased on 4/7/11, to absorb the equivalent radiation from making one SF to DC flight. One kg equals 2.2 pounds. So, for that batch of spinach, one would have to eat 5654 pounds to equal the radiation exposure from one flight.

But is it reasonable to compare the dose from a round-trip airline flight to the amount in particular contaminated foods? Here are some reasons why this comparison may not be valid:

For an airline flight, the radiation source diminishes rapidly with altitude so that the dose effectively vanishes (to background level)at low altitudes.

For food, soil (and also milk, water and other sources) that have been contaminated, radioactivity persists. Once radioactive materials are taken into our bodies, they stay there for varying periods of time, until they decay or are excreted. Meanwhile, our cells, tissues and organs are being bombarded by radioactivity according to the energy of each type of radioisotope and its effective half-life.

The physical half of Iodine-131 is relatively short, but Cesium-137, which accumulates in muscles and other tissues, has a half-life of 30 years. The effective half-life of Cesium-137 is 110 days, still a long time.

We eat several types of food at each meal and we drink beverages, several times a day, day in and day out. Since each type of food we eat and each liquid we drink is contaminated with radioactivity, each time we eat or drink it, the cumulative dose should be taken into account for all the foods and liquids we ingest for every day they are taken into our bodies. (Note: water from covered wells, springs and reservoirs may not be contaminated.

Neither UC Berkeley nor any other entity is testing for all radioactive materials arriving via the jet stream from the Fukushima plant in Japan. Berkeley is testing only for Cesium-124, Cesium-137 and Iodine-131, Iodine -132, and Tellurium-132. The EPA tests for far fewer types. Other unidentified radioactive particles are also getting into our food, water, soil, animals, homes and businesses.

Radioactive particles from Japan have been scattered over the earth for five weeks (at the time of this post), with no end in sight. These radioisotopes are accumulating in our bodies, soil, water, crops, animals, oceans and atmosphere faster than they are being removed through decay and other processes.

Due to the large amount of contaminated grasses and contaminated water consumed by grazing animals and the concentration of radioactivity in milk, milk and other products of grazing animals contain more elevated levels of radionuclides than other foods.

We cannot shield ourselves from radiation in food and water (or air). We must take these substances into our bodies to survive. Most of us have a choice about taking cross country trips; whether to take them at all or to travel by train or car.

There are many more sources of radioactive particles from Fukushima and routes of entrance into our bodies than are noted above or tallied.

In addition to eating and drinking them, we are inhaling these same radioactive particles, adding to the internal radiation dose. Hot showers aerosolize the particles, so they are inhaled from this source as well. Sweeping and vacuuming redistributes settled particles into the air adding to the particles that are inhaled. Vacuums with HEPA filters may filter out some particles.
Some types of radioactivity penetrate our skin, or enter our bodies through cuts or other skin openings
The continuing contamination from Fukushima effectively distributes radioactive particles onto every surface and object in our lives, either directly or indirectly. For example, we track these particles into our homes, businesses and other destinations on our shoes. Our pets are contaminated. We take showers and wash our clothes and dishes with contaminated water. We touch contaminated items with our hands and then put our fingers or the contaminated items into our mouths. Contaminated objects themselves may emit radiation, albeit tiny amounts.

Excerpt from UC Berkeley testing report:

Radionuclides, once deposited by rainwater or air onto the ground, will find their way through the ecosystem. We are already tracking its path from rainwater to creek runoff to tap water, but we would also like to monitor how much these isotopes that make their way into our food. For example, how much gets taken up by the grass and eventually winds up in our milk?

We have been collecting produce that is as local as possible to test for the radioactive isotopes. We might expect different kinds of plants to take up different quantities of cesium and iodine, so we are trying to measure as many different plants and fruits as we are able to. So far, we have measured grass, wild mushrooms, spinach, strawberries, cilantro, kale, and arugula. We have also measured local topsoil.

Link

if you do not have the info on the actual risks from ingesting, say, three 1/2 liter glasses of radioactive iodine in milk a day for a year , then please try to find links so there is no more of this banality about flying cross country etc and external dosing.

WHAT thresholds are we looking to avoid altogether and cumulatively?

Maybe you can find some premed students to join your project and dig up the studies or some MDs with experience in the actual effects of radiation internally at the doses we are receiving or may expect to recieve if these rates of exposure continue for months and years (given the hlaf lives of cesium getting into our soil and plants etc)