In any case, from the knowledge that I have gathered over the years about farming and processing grains, I must say that with most grains there is little likelihood of contamination due to the mixing of two different whole grains (i.e., the rotational crop hypothesis). This is due to the different sizes and shapes of different grains, and the machines which sort them after a harvest. If any grains do get mixed together the amount of actual contamination would likely be extremely low.
In Trevor Pizzeys (Vice President of Operations for Can-Oat Milling) October 30, 1998 letter he expresses his belief that celiacs should avoid oats because he finds between 2.1 and 4.1 kernels of barley or wheat in every 4,000 (0.0525% and 0.1025% respectively). He says that this level can legally go up to a maximum level of 10 kernels per 4,000 (0.25%). In either of these scenarios we are talking about very low amounts. Even at these amounts the likelihood that a celiac eating these grains would eat 1 or 2 kernels of wheat or barley on a given day would be very, very low. Also, since most people who eat oatmeal tend to eat the whole oatmeal as a hot cereal, which means they can take very simple additional precautions to make their chances of eating any kernels of wheat or barley practically zero. The obvious way to do this is to look at the oats before you eat them or mill them and pull out any kernels that are of non-oat type.
Now we turn to the other part of the argument to scare people away from grains that, taken by themselves, do not cause harm to people with celiac disease. This is the wheat dust in the mill (or during transport, or somewhere else) argument. There are many reasons, both health and safety, why mills take steps to keep dust levels down. Dust contamination is still possible, but I think we are also talking about even lower amounts that we were with the occasional kernel of wheat that pops up in oats, although there is no data that I know of to back this up. I think with whole oats (i.e., oatmeal) people can reduce any possible risk of wheat-dust contamination to almost zero by rinsing off their oats well with water before cooking or milling them.
The famous oat study that was done in Finland and published in the NEJM used a source of non-contaminated oats to eliminate any possible factors that could ruin the results of their long and expensive study. It is possible that they could have used regular, uncontrolled Quaker oats for their study and gotten the same results, but again, the reasons for not doing so were to eliminate any possible factors that might affect the results of their study. This is the scientific process, and it is important with any study to eliminate any possible factors which could affect the outcome of the study.
Last, there is a danger of contamination which comes from unclean equipment at mills, and at processing plants. This danger is present with any gluten-free grain, bean, etc., that is milled using the same equipment as is used to mill a gluten-containing grain. In other words we cannot speak of only oats with regard to this issue, as rice flour, soy flour, etc., could be contaminated equally in this way. Aside from legislation to require cleaning between milling runs, those who are worried about this need to buy flours from mills which they have researched and found to be gluten-free, or ones that adequately clean their equipment between runs.
I think contamination issues are real, but need to be put in perspective with regard to other, perhaps more important issues, like labeling laws and getting agreement between the major celiac organizations in this country with regard to which grains are safe.
Journal of the American Dietetic Association, Dec. 1997 v97n12p1413(4). Do oats belong in a gluten-free diet? by Tricia Thompson.