Tuesday, June 28, 2011

BPA Followup (1/2)

An anonymous reader tipped me off to a couple of articles related to BPA absorption through the skin. Fortunately both articles are open access, so you can read along with me. I'll cover one article in this post and the other article in another post.

C & E News (Stephen K. Ritter, Transdermal BPA Exposure Confirmed, Chemical & Engineering News, ISSN 0009-2347) issued the following statement about the articles:
"Daniel Zalko of the French National Institute for Agricultural Research, in Paris, led a team that measured the diffusion of 14C-labeled BPA through samples of pig skin and human skin. A significant amount of BPA diffused through both types of tissue and was metabolized to glucuronide and sulfate derivatives (Chemosphere, DOI: 10.1016/j.chemosphere.2010.09.058). Separately, Harvard University’s Joe M. Braun and coworkers monitored the diets and analyzed BPA in urine samples of 389 pregnant women. Cashiers had the highest BPA concentrations in their urine; teachers and industrial workers had significantly lower concentrations (Environ. Health Perspect., DOI: 10.1289/ehp.1002366)."
Being a publication of the American Chemical Society, you would expect C & E News to provide good coverage of technical research, but as you will see that is not the case.

Looking at the second article first, it looks like Mr. Ritter only read as far as the abstract of the article, which states:"By occupation, cashiers had the highest BPA concentrations". That seems pretty clear cut, but looking into the article, the researchers themselves question the result:"These results should be interpreted cautiously because estimates from cashiers were based on 17 women and were attenuated with adjustment for socioeconomic factors." That's pretty clear cut to me.

I was pleasantly surprised to so that the authors don't stop there, but continue to criticize their own efforts in the following paragraphs:
"There are several limitations to this study. First, our results and others demonstrate that a single spot urine measurement has the potential to misclassify BPA exposure (Mahalingaiah et al. 2008). Second, many of our predictor variables were measured imperfectly, and we were missing some potentially important sources of exposure. We did not have women’s occupations classified by an industrial hygienist, which likely resulted in misclassification of this variable. Furthermore, the dietary variables used in this study were not originally designed to assess BPA exposure, but rather pesticide and mercury exposure. In addition, urinary BPA concentrations likely reflect exposure over the last day, whereas dietary questionnaire data reflected consumption over a longer time (weeks). Third, we did not collect information regarding other potential sources of BPA exposure including plastic or paper/cardboard use, packaged food consumption, medical devices, medications, dental treatment, or amount and type (tap, bottled, or well) of water consumed during pregnancy (Carwile et al. 2009; Gehring et al. 2004).

An additional limitation is the imperfect correction for urine dilution using urinary creatinine concentrations. Pregnancy-induced changes in creatinine metabolism and excretion may occur independently of BPA metabolism and excretion, so the degree of correction of urine dilution may change throughout pregnancy. Our results suggest that creatinine concentrations become progressively lower and more variable throughout pregnancy. Other measures of urine dilution, such as specific gravity, have been used and should be compared with creatinine patterns in pregnancy in future studies (Mahalingaiah et al. 2008)."
(Note: Urine concentration can fluctuate greatly with water consumption, so the researchers attempted to compensate for it by considering the ratio of BPA to creatinine in the urine.)

I have several comments on this situation, both good and bad. Given all of thoughts of the authors, I think we can safely treat the "cashiers have higher BPA levels" as unproven. Further research might show it to be true, but this research doesn't.

But what's with that strong statement in the abstract? I'm assuming the authors put it there, but then how did the reviewers let that pass? Or did some editor add it? And how come C & E News only read the report that far?

At the same time, I highly praise the researchers for discussing the shortcomings of their research, a very rare example of quality scientific reporting. Sadly, when that level of integrity was shown in this research, C & E News didn't even catch it. That would make better copy than what was actually written.

1 comment:

Andrew Sun said...

Although 2/2 hasn't come out I know what you want to talk about. The bottom line of 'news and communication' professional is quite vague. The author of this piece of news, for example, might argue that, due to the high concerned status of the BPA effect among the public, any clues even merely suggested without proof may be suitably reported. News (impact) defeats itself (truth).

Thanks for sharing this good example, though. I will blog about this in Chinese in my blog.