G’day, Dr Z! You know, I’ve seen a lot of stories in the media about how radiation has caused so many problems – miscarriages, cancer clusters, birth defects, and so much more. And, while I’m often skeptical, I really don’t know how to evaluate these stories, to try to figure out which ones are likely to reflect accurate reporting on scientific or medical studies versus which are likely to reflect an anti-radiation bias. Can you help me understand what to look for when I’m trying to decide how much credence to give these stories? Thanks!
What a great question! I really wish more people thought this way; there are way too many people who simply accept (or reject) things they read or hear without really thinking about it much – and almost always without knowing which questions to ask or what to look for to help them evaluate what they’re reading or hearing. With radiation there are a lot of picky, specialized questions that can be asked, but only a handful of fundamental or general questions. Let’s see what some of those are.
- Is the claim that’s being made a scientific claim? A scientific claim is one that can be tested and found to be false. For example, if I claim that a ball will fall to the floor when I drop it, I can test that simply by dropping a ball and seeing what it does. With radiation, if I read that exposure to a very small dose of radiation has caused cancer rates in an area to increase by, say, 0.01%…well, that’s not a claim that can be tested because cancer rates fluctuate by enough more than that every year that we can’t “see” such a small increase. So even if that statement is true, we can’t test it, so it’s not a scientific claim – not until we can get better at identifying very small changes in cancer rates.
- Can radiation even cause the effect(s) claimed? There are many health effects that radiation can cause, and many more that it can’t. If I read about a nuclear reactor accident followed by an increased level of thyroid cancers then I need to look more closely because this type of cancer can be caused by exposure to radioactive iodine, which is produced by nuclear reactors. On the other hand, if I read about an increase in prostate cancer following a reactor accident, I’m going to be dubious because that’s not a type of cancer that’s associated with radiation exposure.
- What’s the latency period for the effect(s) claimed? If a person is exposed to radiation, even enough to cause health effects, these effects usually don’t show up for weeks, months…even decades after the exposure. For radiation sickness the latency period is usually days to weeks; for cancers it’s years to decades. So if a research paper reports an increase in, say, liver cancers a few months after a radiological accident then you’re right to question the paper because liver cancers typically take a few to several decades to appear. On the other hand, if there’s a reported increase in leukemia and other blood cancers 5-10 years after a release of large amounts of radioactivity then we need to look a bit more closely because that’s a reasonable latency period for that type of cancer. Note, though, that different cancers have different latency periods! The bottom line is that if something shows up much faster than it’s known to occur (i.e. less than a year for a cancer with a decade-long latency period) its appearance is likely a coincidence and not due to the radiation exposure.
- Was the person exposed to a type of radiation that can cause the effect(s) claimed? Say you read about a person who’s claiming that their child’s birth defects are a result of exposure to beta radiation from tritium contamination in a nearby park in which the mother strolled during her pregnancy. While in utero radiation exposure can cause birth defects, external exposure to tritium can’t expose the baby to radiation because the very low-energy tritium beta can’t penetrate through the skin and abdominal muscles to expose the developing baby. So this type of radiation (beta) can’t even reach the baby, let alone cause any health effects.
- Is there a threshold for the effects that are being claimed? If so, what is it? There are some health effects that simply don’t show up unless a person has received a threshold dose. For example, birth defects don’t occur below a fetal dose of 5 rem, radiation sickness doesn’t appear below a dose of about 100 rem, and skin burns won’t appear at anything less than a few hundred rem to the skin. So if the dose received by a person (or to the fetus or skin or organ that was damaged) is lower than the threshold for a health effect then whatever happened might not be due to radiation exposure.
- What was the dose? And now we get to what’s perhaps the most important question – and sometimes one of the hardest to determine. For health effects that have a threshold, we’ve already seen that a dose less than that threshold simply cannot cause a particular problem. And for health effects such as cancer, a low dose is correlated with a low risk that the radiation can cause the cancer. If the measured or calculated dose is low then the probability of that dose causing a cancer is also low.
- What is the risk from that dose? There’s a general risk coefficient of 5% per 100 rem to develop a fatal cancer. So a person who receives 100 rem whole-body radiation exposure has a 5% chance of dying of cancer from that radiation exposure. For specific cancers there are more precise risk factors – but the bottom line is that if the risk factor multiplied by the dose to the damaged (or cancerous) organ is less than 50% then chances are that the health effects were not caused by the radiation exposure. This can be calculated using a widely accepted program such as IREP.
As I mentioned earlier, these are only a start. You might ask, for example, if a person was exposed to any other agents associated with the cancer(s) they’re suffering from. Or, if a cancer cluster is postulated, ask if the number of cancers of a particular type is proportional to people’s exposure to radiation. But the questions here are a good start, and they’ll help to make you a critical and informed consume of news rather than a person who simply acts on what their gut (or friends or blogs or…whatever) tells them.