Berkeley Radiological Air and Water Monitoring -- Frequently Asked Questions
Frequently Asked Questions
Thank you for visiting our FAQ page! We have prepared answers to many of the most common questions we are hearing from visitors to our site. For the questions pertaining to health effects, we have even brought in the expertise of Berkeley health physicists in forming our answers. If you have a question that is not addressed here, please post it on our public forum.
- What compelled you to make these measurements?
- Are other groups making measurements like this?
- How long will you be making these measurements?
- Will you be testing other things, like milk and tap water?
- Can your methods detect Uranium and Plutonium?
- How long will these isotopes be in our environment?
- What does radiation do to your body?
- What steps would you recommend members of the public take to avoid the radiation?
- How do your measurements compare to regulatory limits from the EPA or other government agencies?
- Is there a health risk from low doses of radiation, such as the levels you are measuring?
- Which risk model do you assume in your calculations?
- Is it valid to compare doses from these radionuclides to a cross-country plane flight?
- What is total effective dose equivalent (TEDE)?
- Can you point me to some resources that discuss radiation dose and its effects on health?
What compelled you to make these measurements?
We are undergraduates, graduate students, and scientists from the research group of Professor Kai Vetter at the University of California Berkeley. As responsible scientists and members of a public university, we have a duty to make these measurements and communicate them to you, our local community and members of the public at large. Since March 16, we have been working full-time to ensure accurate and useful information about the quantity of the radiation from Japan in the Bay Area. You can learn more about individual members at our team website. And we also really appreciate your feedback on our forum page so that we can better communicate our results to you.
Are other groups making measurements like this?
There are other academic groups around the country measuring radiation from Fukushima:
- University of Washington Physics Department Air Radioactivity Monitoring: You can see their spectra for I-131, I-132, Te-132, Cs-134, and Cs-137.
- University of Nevada Las Vegas Air Monitoring: They are posting measured activities for I-131 and Cs-137.
- Taylor Wilson at University of Nevada, Reno: he's detecting I-131, Te-132, Cs-134, and Cs-137 in air and water samples
In addition, there are US government agencies posting results:
- The US Department of Energy has been posting data from Japan. This includes aerial surveys of the area around Fukushima.
- The Environmental Protection Agency's RadNet Program is monitoring radiation from Japan. They are keeping a log of daily updates and are posting air filter results. At this point (early April), they are only detecting I-131 in their air filters.
- The California Department of Public Health is releasing air monitoring updates, including detections of I-131
- The State of Arizona's Emergency Information Network is posting measured activities for I-131.
- The Community Environmental Monitoring Program in Las Vegas, NV is measuring I-131, Cs-137, Te-132, and Xe-133.
There are also ongoing monitoring efforts in other countries:
- The Radiological Protection Institute of Ireland is monitoring air, rainwater, and milk in Ireland
If you know of other institutions putting out similar measurements, please let us know on the forum page and we will link them from here.
Important note: We are most qualified to comment on our own instruments, not those of other people. We can give you detailed information on our own measurements and make comparisons to these other groups, but we are limited in what we can interpret from other people's data.
How long will you be making these measurements?
We plan to make measurements of the local air and rainwater until the isotopes cannot be detected anymore, which could be by mid-April. Keep watching our site for updates.
Will you be testing other things, like milk and tap water?
The short answer is yes. We have plans to do these measurements in the coming days and weeks. The problem is that we have recently had several days of heavy rains, and we are trying to measure samples rainwater at least daily, since that is where the highest concentration of radioisotopes should be. Since we are only able to dedicate one germanium detector system to liquid measurements at this time, there is a bottleneck in our testing.
With regard to tap water, we plan to quantify the rainwater run-off pathway dilution soon by analyzing local creek water and tap water. We can compare the signatures we see in the rain water with these other points in the run-off. There is some chemistry that may occur between the rain water and the soils. This means we expect a lower signature in the run-off. Additionally, since we have had a lot of rain in the Bay Area this season, the recent rain with radiation from Japan will be greatly diluted in local reservoirs and the signature in tap water should be very low. This is obviously an important issue to the public and we will make these measurements and publish our numbers soon.
With regard to milk, the reason milk is of interest is that it may be a point in the chain of rainwater-->soil-->plants-->animals-->humans where iodine-131 becomes reconcentrated (it should in general be filtered and diluted). We will be testing milk soon. Two caveats to this -- first, from some of our research it appears most cows in California are fed grass from other areas of the country. Secondly, iodine-131 has a half-life of 8 days, meaning that it rapidly disappears from the environment.
Can your methods detect Uranium and Plutonium?
The short answer: Technically yes, but in reality no.
The long answer: The isotopes in nuclear fuel (U-235, U-238, Pu-239) undergo alpha decay, in which they emit a helium nucleus during their decay. Our detectors cannot see alpha particles. These isotopes also emit small numbers of gamma-rays, which our detectors are sensitive to, but it would take large amounts of U or Pu for us to detect their gamma-rays at the same levels at which we are detecting isotopes like I-131 and Cs-137.
Another issue is that the chemical properties of U and Pu constrain how they would be transported across the ocean. These elements tend to form oxides and are not easily transported in water or air. On the other hand, elements like iodine, tellurium, and cesium are more reactive and volatile, and thus they are more readily transported through air, which is why we are able to detect them.
How long will these isotopes be in our environment?
The short answer: the radioactive isotopes from Japan may no longer be strong enough for us to measure by approximately mid-April, depending on atmospheric transport. They are already at safe levels for the public.
The long answer: As soon as the earthquake hit Japan, their reactors were scrammed or shut down. This means that the nuclear fuel was no longer burning and the isotopes we are measuring were no longer being produced by the fission process. All radioactive isotopes decay, which means that they eventually die away into non-radioactive nuclei. This decay rate is different for different isotopes, quantified by the so-called half-life. After waiting one half-life, half of the radioactive nuclei will have decayed away, often into stable (non-radioactive) nuclei. The half-lives of the radioactive isotopes we are measuring from the Japanese reactors are listed in the table below:
Isotope Half-life I-132 2.3 hours* Te-132 3.2 days I-131 8.0 days Cs-134 2.06 years Cs-137 30.07 years
* I-132 has a very short half-life (2.3 hours). We are able to measure it because it is the decay product of Te-132, so its presence is tied to the presence of Te-132.
So by considering the effect of radioactive decay alone, after waiting a few weeks the only isotopes we should be able to measure are Cs-134 and Cs-137. However, these are both already very close to our minimum detectable levels. Effects other than radioactive decay will also come into play -- namely, the dilution of these isotopes in the soil and groundwater. We expect this to happen in the course of days to weeks. Please continue checking the levels on our website for current information.
What does radiation do to your body?
Radiation, whether it comes as sunlight, radio waves, X-rays or gamma rays, transfers heat to the cells of our bodies. Sometimes this heat causes immediate damage -- a sunburn from sunlight -- and sometimes it can cause chronic damage to cells and the cell components. Extended exposures to sunlight, ultraviolet light, X-rays and gamma rays have been linked to increased rates of cancer. This research shows that the more intense radiations including X-rays and gamma rays along with alpha and beta particles can be more damaging because they are able to remove electrons from atoms in your body. If an electron is removed from one of your atoms, the atom will become an ion and attempt to chemically reconfigure itself with nearby atoms. The most common effect of this ionization is the formation of reactive oxygen, which can kill cells or damage cells. If the ionized atom is in your DNA, this reconfiguration can cause single strand breaks in your DNA. These types of single strand breaks already happen millions of times a day due to things like exposure to sun/chemicals and the process of cell division that constantly occurs in our bodies. In addition to this there are single strand breaks being caused by radiation from potassium-40 and other naturally occurring radioisotopes. These single strand breaks are repaired correctly something like 99.99% of the time. The other 0.01% of the time, the single strand break will cause an error in the DNA. If this error occurs in the segment of DNA responsible for regulating cell division, whether caused by radiation or chemicals or other cellular processes, it can lead to cancer.
It is important to keep in mind that for low radiation doses, the damage radiation does is called "stochastic" or random. That is to say, if you are exposed to radiation, it is not predetermined that anything in particular will happen. Another way to say this is that a single radioactive particle interacting with your body does not always cause cancer -- in fact, it is a rare occurrence.
What steps would you recommend members of the public take to avoid the radiation?
In our laboratory we all learn the three basic rules of radiation protection: time, distance, and shielding. That is, minimize the amout of time during which you might contact a radioactive material, recognize that distance is very effective in reducing dose, and use shielding if the dose is high. As scientists but not health professionals, our expertise lies in detecting and quantifying trace radioisotopes in our samples. We try to put the dose from these radioisotopes in perspective by using comparisons to radiation doses that the public routinely accepts, such as the small dose one receives on an airplane flight, which is an element of background exposure. All we are showing is that we are observing extra radiation exposures to the public that are far, far smaller than the variations in background exposure that the public routinely accepts.
Therefore, we will not issue statements recommending that people take steps to receive a smaller dose of radiation, such as avoiding milk, drinking filtered water, or taking potassium iodide pills. Recommending such actions would be irresponsible, both because we are not health professionals and because such actions could have unintended health risks such as malnutrition or sickness. These decisions are left for you to make in consultation with your doctor.
Some have asked what the members of the team are doing in response to Fukushima. The answer is that none of us are changing our lifestyles in any way due to the fallout from Fukushima.
How do your measurements compare to regulatory limits from the EPA or other government agencies?
Many people have brought up comparisons to regulatory limits, such as the EPA limits for drinking water. We have decided to report our measurements without reference to regulatory limits for a number of reasons:
First, limits vary widely -- they depend on the country, the agency, and what is regulated (e.g., drinking water, sewage water, air, milk, kind of food). It would be complicated to present our results with respect to many different limits.
Second, the limits are difficult to compare to each other. Often limits make different assumptions for safety factors, and some limits regulate activity (pCi or Bq) instead of equivalent dose (Sv or rem). So our measurements could be above one limit but below another limit, and unfortunately this would have to do more with the definition the agency has used than the actual risk of the radiation exposure.
Third, we are interested in focusing on the raw measurements of the radioactivity. The dose is also important, and to quantify it we use standard estimates of the dose conversion factor from ICRP numbers, and make our calculations explicit on the Dose Calculation page.
Lastly, in many cases the regulatory limits do not apply. For example, many of our rainwater measurements of I-131 are quantitatively above EPA drinking water standards. But the EPA limits do not apply in that case for two reasons. The first is simply that rainwater is never held to drinking water standards. The second is that drinking water limits assume constant year-long exposure, which simply could not be reached by someone drinking rainwater with I-131 in it.
Is there a health risk from low doses of radiation, such as the levels you are measuring?
The short answer: Scientifically speaking, the risk is not zero. However, radiation is not unique in the risk it poses. As discussed above, for other chemicals and radiation sources such as the Sun, any amount of exposure could potentially lead to health effects. However, even if one chooses the most conservative dose conversion, the risk from radiation at the levels we are measuring is still insignificant.
The long answer: At very low levels there is no measurable health impact, but the theory is that radiation can cause single strand breaks in your DNA. See the FAQ on what kind of damage radiation does to your body.
Concerning levels that would actually be dangerous to one's health, the dose we are reporting is already relatively conservative. This means that the real relative risk compared to a plane flight is probably much less. This is due to the fact that our calculation assumes that you have been consuming water contaminated with that level of that isotope for an entire year. For a short exposure like this, the radioactive isotope does not reach an equilibrium concentration in your body so the actual exposure is less.
In our calculation we assume that a round trip plane flight from San Francisco to DC is 5 millirem. To put that in perspective, the radiation background in the United States is on average of 300 millirem from natural sources (e.g., radon gas, cosmic rays, uranium in concrete) plus 300 millirem from medical sources (e.g., medical X-rays). So the total background is 120 times higher than the dose from a plane flight. In addition, if you live above sea level, every year you are exposed to about 2 millirem for every 1000 feet of elevation due to a slight increase in exposure to cosmic rays. For people who work with radiation, the limit is 5 rem per year or 1000 times the dose of a single plane flight.
Which risk model do you assume in your calculations?
The numbers that we use in our calculations implicitly assume the linear-no-threshold (LNT) model for risk. This means that the risk of health effects from radiation is proportional to the radiation dose, even down to a dose of zero.
The use of the LNT model is recommended by the BEIR VII report: "Health Risks from Exposure to Low Levels of Ionizing Radiation", a study performed by the National Research Council of the National Academies:
"At doses of 100 mSv or less, statistical limitations make it difficult to evaluate cancer risk in humans. A comprehensive review of available biological and biophysical data led the committee to conclude that the risk would continue in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans. This assumption is termed the 'linear-no-threshold' (LNT) model. "There are two competing hypotheses to the linear no-threshold model. One is that low doses of radiation are more harmful than a linear, no-threshold model of effects would suggest. BEIR VII finds that the radiation health effects research, taken as a whole, does not support this hypothesis. The other hypothesis suggests that risks are smaller than predicted by the linear-no-threshold model are nonexistent, or that low doses of radiation may even be beneficial. The report concludes that the preponderance of information indicates that there will be some risk, even at low doses, although the risk is small."
This report says that there are other theories about how risk scales with radiation dose. Some claim that the impact from low dose may be larger than the LNT model predicts. However there are also studies that show there may be benefits to chronic low-dose radiation. The reason we use the LNT model is because there simply is not enough evidence to conclude one way or the other -- if anything, the evidence is against the risk being higher than the LNT prediction.
We know more about acute high-dose radiation exposure (e.g., Hiroshima) than we do about long-term low-level radiation exposure. There have been many studies trying to correlate cancer rates in regions with different levels of background radiation, but no conclusions have been drawn. The main reason for this is that the normal human cancer rate is so high that the number of additional cancers that may be caused by background radiation exposure is much less than the statistical variation of the overall rate.
Is it valid to compare doses from these radionuclides to a cross-country plane flight?
Yes. See the explanation of total effective dose equivalent (TEDE), which is the the dose quantity that we use in our calculations. TEDE takes into account all variables of the radiation -- energy, type of particle, type of tissue, part of the body, how long the isotope is in your body, internal or external exposure -- and normalizes the dose to a full-body dose for ease of comparison between different doses.
For example, in the case of iodine-131, the TEDE accounts for the energy of the beta particles and gamma rays from radioactive decay, the fact that iodine is taken up preferentially by the thyroid gland, the susceptibility of the thyroid to cancer, and the 8 day half-life of I-131. A weighting factor is used to relate the particularities of the I-131 radiation dose to a full-body dose.
The dose from an X-ray or plane flight is different in that the source is outside the body, the radiation is distributed over all the body, and there are different amounts of different types of radiation compared to the isotopes we see. However, background gamma rays and cosmic rays are not blocked by our skin and still interact inside our body. The TEDE calculations attempt to normalize for all of these differences so that doses can be compared.
For more quantitative information, please see our Dose Calculation page.
What is total effective dose equivalent (TEDE)?
Total effective dose equivalent (TEDE) is a measure of the biological effects due to radiation exposure. TEDE accounts for the amount of energy deposited by the radiation, the type of radiation (alpha, beta, or gamma), the type of tissue exposed, and the part of the body exposed. It also accounts for the manner of exposure (inhaled, ingested, or external), the rate of uptake of the specific isotope, the biological and radiological half-life of the isotope, and the total energy deposition in the body over the entire time it is present.
By accounting for all of these factors that go into radiation dose, TEDE is the most appropriate quantity for comparing the risks of different types of radiation doses. For example, radiation dose to the thyroid due to I-131 ingested through water can be compared on equal footing with the radiation dose from a medical X-ray.
The units of measure for dose equivalent are Sieverts (Sv) or Roentgen equivalent man (rem). These units are related such that 100 rem = 1 Sv, so they are interchangeable. For a sense of scale, the average TEDE that a person receives from natural radioactive background is approximately 300-500 millirem (3-5 milliSieverts) per year. The standard TEDE that we are using in the calculations for this website are 5 millirem (50 microSieverts), which is approximately the TEDE one receives on a round-trip flight from San Francisco to New York.
According to the NRC glossary of terms, TEDE is "the sum of the effective dose equivalent (for external exposures) and the committed effective dose equivalent (for internal exposures)."
The effective dose equivalent (EDE) is used for external exposures such as medical X-rays or airplane flights. It is the absorbed dose (i.e., energy deposited by the radiation per kilogram of tissue), times a quality factor that takes into account the susceptibility of the particular tissue to damage, times "other necessary modifying factors at the location of interest." The "equivalent" in the name of EDE means that an additional weighting factor is applied -- the weighting factor is specific to the organ or area of the body irradiated and is meant to normalize the dose to the entire body.
The committed effective dose equivalent (CEDE) is used for internal exposures such as medical isotopes that are ingested for PET scans. This quantity is similar to the EDE except that the the chemistry of the body and the time over which exposure happens is taken into account -- including how the isotope was taken in (ingestion or inhalation), the rate of uptake of the isotope into tissue, the biological half-life of the isotope, and the radiological half-life of the isotope. These processes are considered for 50 years, and all exposure one would receive during that time is included. This is why it is the committed dose -- since it is in one's body, there is an amount of radiation that winds up "committed" to the body over time. As with the EDE, the "equivalent" in the name of CEDE means that a weighting factor that is specific to the organ or area of the body irradiated is then multiplied to normalize the dose to the entire body.
As seen in the definition, the TEDE is the sum of the EDE (external) and CEDE (internal). Because of the consideration for whether the radiation is external or internal and all the effects that go into each type of exposure, and because of the use of weighting factors to relate different organ and body part exposure to full body exposure, the TEDE is the most appropriate measure of radiation dose for comparing the risks of different types of radiation exposure.
Can you point me to some resources that discuss radiation dose and its effects on health?
We have compiled several sources of useful information on the radiation dose and its effects on health:
- Our FAQ on equivalent dose
- Our method of calculating dose: http://www.nuc.berkeley.edu/UCBAirSampling/DoseCalculation
- This is a chart that shows relative amounts of radiation. The conversion factor is 1 Sv = 100 rem: http://xkcd.com/radiation/
- You can calculate your background radiation dose using the EPA's background dose calculator
- Limits on radiation exposure for workers and how they are calculated: http://www.icrp.org/publication.asp?id=ICRP%20Publication%2030%20(Index)
- Useful information from the Health Physics Society: http://www.hps.org/fukushima/
- The BEIR VII report on health risks from exposure to low levels of radiation: http://dels-old.nas.edu/dels/rpt_briefs/beir_vii_final.pdf
- United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) report on radiation effects from Chernobyl: http://www.unscear.org/unscear/en/chernobyl.html
- UNSCEAR 2006 Report: Effects of Ionizing Radiation: http://www.unscear.org/unscear/en/publications/2006_1.html
- UNSCEAR FAQ about radiation: http://www.unscear.org/unscear/en/faq.html