Hello All!
As some of you know, during a recent ongoing thread concerning risk of cancer to home dwellers that are exposed to radon, Mr. Newman referenced three studies which he believed supported his contention that the risk was real and significant.
I promised Mr. Newman that if he provided me with the studies, I would review them, and post a critical review here on this board. Since such reviews take a big portion of my time, I cannot review them all at once – so here is the first review, and I will get to the next two in the next couple of weeks as time permits.
Here it is:
**I have reviewed the paper tiled “LUNG CANCER RISK AMONG FORMER URANIUM MINERS OF THE WISMUT COMPANY IN GERMANY” by **Brüske-Hohlfeld, I; Rosario, AS; Wölke, G; et al. and which appeared in the Health Physics March 2006, Volume 90, Number 3.
Overall, the study appears to have been carefully thought out, properly vetted and used appropriate methodologies and for the task at hand. In my subjective opinion, the authors did an excellent job and the work carries considerable credibility and is a valuable reference.
The authors carefully reviewed their study plan prior to conducting the study, and placed considerable effort into attempting to identify gross potential confounders. The authors explain the identified confounders and how they dealt with those confounders. The authors also explain their concerns with several aspects of the “selectional bias” (a standard epidemiological concept that is associated with virtually all such studies) associated with their study. Although the authors identified and discussed several biases associated with their study, I have only addressed the more pertinent ones here.
The conclusions by the authors appeared to be well supported by their observations, and well within the limits of their observations, errors, biases, and confounders as identified by the authors themselves and spelled out in the paper. Overall, the methods and practices employed by the authors were within acceptable scientific parameters and acceptable epidemiological practices.
The conclusions of the authors are consistent with known science, consistent with my own opinions, and consistent with what I have posted on this board, (actually, beaten to death, to be honest). The authors essentially state what I have been saying for quite a number of years.
(OK… On to the meat of the review)…
The authors tested the following hypothesis: “Uranium miners (especially those who worked in horrific underground mine conditions) do not have an higher lung cancer rate than other members of the mining company who did not work underground in those conditions.”
The authors were unable to find the evidence needed to support the hypothesis, and therefore, they were forced to accept the null hypothesis, namely: “Uranium miners (especially those who worked in horrific underground mine conditions) do have an higher lung cancer rate than other members of the mining company who did not work underground in those conditions.”
The study in no way whatsoever addressed the general risks of lung cancer associated with exposure to radon at concentrations normally seen in houses. The study in no way whatsoever addressed the risks of lung cancer for occupants of houses who may be exposed to radon. The study cannot in any way be used as a reference when discussing exposures to radon at concentrations normally found in homes or indeed, even if those concentrations were as high as those found in underground uranium mines, since the parameters of the study and the selectional bias observed by the authors (as honestly described by the authors themselves) were geared to addressing only the stated hypothesis, and no other question.
The study looked at two groups; the cases (the exposed group) and the controls (the un-exposed group). The cases consisted exclusively of males who had been pressed into slave-labor at an underground uranium mine and many of those miners continued on at the mine, under Soviet control, as employees after the slave labor had ended.
The study was a type of epidemiological investigation known as a “retrospective case-control study.” The study also fit into an epidemiological classification known as an “ecological study” which traditionally has a lower intrinsic confidence than other kinds of epidemiological investigations. The reason for this is multi-faceted, but certainly not least of all, the authors themselves expressed low confidence in their exposure data (as described later).
At the heart of all such studies is what is known as a dose-response evaluation. We attempt to look at what is the biological endpoint (the response) to any given dose. This can be very, very difficult if one doesn’t know what the dose was in the first place. Due to the fact that much of the mining work was performed under forced labor, and then later, under the notoriously harsh conditions of industrializing Soviet power, no exposure data was available to the authors for their early “employees” and very little actual exposure data was available to the authors after that. The authors state:
“The early period of mining at WISMUT during 1946–1955 was characterized by dry drilling underground and no artificial ventilation, which probably led to a very high exposure to dust and alpha radiation (Autorenkollektiv 1999), but no measurements of radon concentrations exist for this period. The[e exposures] were assessed retrospectively based on the earliest available radon gas measurements from 1955 and taking into account uranium deposit and delivery, ventilation, and mine architecture over time.”
The authors then go on to document that it was not until 1966 that regular measurements of radon decay products were introduced. Therefore, the authors were forced to guess what those exposures may have been and then use those guesses in their model. However, all comparative data upon which those guesses were to be made are from monitoring performed under conditions of modern mining techniques as opposed to forced labor with no ventilation systems in place.
Guesswork like this is not unusual, and the authors have made do with what they had to work this. However, the guesswork obviously reduces the confidence in the dose-response evaluation. Here the authors reference the study on the Colorado Plateau mining cohort and state:
“An increased risk of lung cancer associated with radon and its progeny among underground miners is well established. This evidence, however, is nearly completely based on cohort studies, which often suffer from lack of information on potential confounding factors such as smoking or information on occupational exposures outside the employment at the uranium mine.”
What they are referring to was the problems the EPA saw in its own data on the mining cohort when it (the EPA) said:
Exposure in the U.S. cohort is poorly known; cumulative WLM (CWLM) are calculated from measured radon levels for only 10.3 percent of the miners…and guesswork is used for about 53.6 percent of the miners*.*
(Risk Assessment Methodology, Environmental Impact Statement, NESHAPS for Radionuclides, Background Information Document- Volume 1. EPA/520/1-89-005, September, 1989)
So this study experienced similar difficulties as the studies upon which it was built. Additionally, a noted confounder in this study was the lack of exposure information of the cases (as opposed to the controls) which the authors describe thusly:
For most study participants (97.6% of controls and 52.3% of cases), a complete working history could be gathered…
Therefore, for more than half of their cases, the authors acknowledge that the observed lung cancer could have been due to something completely unrelated to radiation. Their uncertainty extended even to their controls wherein, the authors expressed concern about the validity of their own decision to intentionally exclude 14 cases of cancer in the control group (by so doing, they explain that they may have artificially increased the apparent cancer risk due to the radiation). However, they made the exclusion anyway partially because their study already surprised them in that the risks they found among the miners was lower than they expected.
Also unexpected was their observation that their smoking component in their model DECREASED the risk of lung cancer. The authors don’t for a moment believe that is the case, but rather, they are honestly reporting the observation. I too don’t think the observation is something that can be generally drawn into the case group; rather, I suspect that the observation emerged as an “artifact.” Artifacts are observational oddities or anomalies for which one cannot explain within the limits of the model. Frequently, the artifact is a product of the study! (Since all such studies necessarily must contain selectional and other biases). It would be rather like studying the average speed of meteors entering Earth’s atmosphere and finding one meteor whose speed is Zero (i.e., it just hangs in the atmosphere). You know it can’t be right, but you honestly report the observation since that is what the model showed, and you are more interested in credibility than in trying to prove a point (unlike some of my detractors in this forum).
The authors used a type of a model that I have already described at length in other posts on this board called a “linear, no-threshold, dose-response curve.” No serious epidemiological investigator actually believes for a moment that the model represents reality in these kinds of studies, but we use it very often since it greatly reduces the complexity (and the necessary mathematics) to test hypotheses.
In this case, the authors do NOT profess the linear model was appropriate, rather, they honestly state:
**Under the assumption of a linear risk model, there was a significant increase in the relative risk of 0.10 per 100 WLM after adjusting for smoking and asbestos exposure. **
Then, throughout their discussion, the authors honestly and forthrightly point out places where their linear model fell apart and the data argued against the validity of the linear dose-response curve.
Fore example, the authors quite openly and forthrightly sate:
Most cohort studies of miners used a linear risk model for data analysis (NRC 1999; Lubin and Boice 1997), which also provided a good description of the exposure-response relationship in this case-control study. However, one should bear in mind that the categorical risk estimates in our analysis did not show a linear increase below 800 WLM. Whether this relationship is real or artificially induced by errors in exposure quantification (Birkett 1992) or selection bias is hard to tell.
(For those of you who don’t know, 800 WLMs is a HUGE amount of radiation, that is not likely to be seen in but perhaps one or two houses in the entire United States (if indeed it is EVER seen in ANY house ANYWHERE).
Regarding the linearity, the authors also state that they did not see a statistically significant increase in lung cancer until the presumed or demonstrated exposes EXCEEDED 800 WLMs.
Additionally, the authors also explain that in their study:
“Lung cancer risk declined with time since exposure, except for exposures received 45 or more years ago. “
This means that the linear model fell apart since another name for the linear, no-threshold, dose-response curve model is called the “one-hit theory of carcinogenicity.” Which, if valid means that there is essentially no time component, and the risks should be dependent only on the exposure, which, as the authors explain, they saw a time component associated with the risk, wherein risk dropped for equal exposures where the cessation time of exposure increased.
However, the question of linearity really becomes moot when one remembers that the actual exposures in the earlier part of the study were completely unknown anyway, and the fact that the standard deviation (the error) of the known (measured) exposures was also HUGE (the actual statistics are given in the report).
In conclusion:
The authors find an increased risk of lung cancer among uranium miners in harsh conditions when exposures, as defined in their study, exceeded 800 WLMs. The finding is entirely consistent with what I have posted on this board in the past.
The authors conclude that smoking resulted in DECREASED risk of lung cancer in their case cohort. Although the authors did not explicitly call the observation an artifact, I suspect that it is, and I suspect the authors themselves would concur.
The study found that linearity in the dose-response curve did not withstand the rigors of reality. I concur and this is consistent with what I have maintained on this board.
In short, the authors found that if you were a slave, forced to work in a Soviet underground uranium mine with no ventilation, you had an higher probability of contracting lung cancer. I don’t have a problem with that conclusion.
The study did not, in anyway, make any reference whatsoever to any risks that may be observed in homeowners who have radon in their homes. Mr. Newman cannot, within the context of good science or rational thought use this study to support his argument. I respectfully suggest that Mr. Newman either did not read the study, or did not understand the study.
I will get to Mr. Newman’s next reference as time allows. (Probably within a week or so…)
Cheers!
Caoimhín P. Connell
Forensic Industrial Hygienist
www.forensic-applications.com
(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)
AMDG
