Tuesday, February 15, 2011

PBO in the news

A recent study in the March issue of the journal Pediatrics [vol. 127(3): e693-e700] reports on a correlation between pre-natal exposure to the common synergist piperonyl butoxide (PBO) and delayed mental development among 3 year-old children.  In a review of the article, e! Science News reported the author as saying that the drop in IQ points [among children whose mothers had higher PBO exposure] is similar to that observed in response to lead exposure.  Megan Horton, of the Mailman School of Public Health and lead researcher, said the drop, while not severe enough to affect a child's overall function "...is  educationally meaningful..."  Going a little further out on a limb, she added that it "...could shift the distribution of children in the society who would be in need of early intervention services".

The results of this study should be considered preliminary, and certainly indicate the need for more research.  Similar to the study on ADHD that I reported on last year, the data shows a correlation, but does not indicate a cause and effect relationship.  Further studies may or may not substantiate the correlation.  Furthermore, the authors note that this is the first study to ever look at the health effects of PBO on humans (previous studies, presumably having been done only on laboratory animals).

The paper brings up an interesting issue with regard to the pest control industry.  What criteria should we use to make decisions about the kinds of pesticides we use in our business?  Should a new study impact the way we use chemicals?  Or should we always just follow the lead of the EPA when it permits or restricts use of a pesticide? 

Ultimately, and from a legal point of view, the EPA is our guide.  The EPA has hundreds of toxicologists trained to look at studies such as these and determine whether there is enough data to justify a change in label requirements.  However, the process of revoking a use, or a pesticide, can take years. 

The biggest question I had about this study concerned the mothers' exposure to PBO.  Piperonyl butoxide in itself is not toxic to insects.  Rather, it is added to a few insecticides--most notably pyrethrins--to prevent insects from detoxifying the actual insecticide.  It turns out that pyrethrins, by themselves, are great at quickly knocking down, but not killing, most insects.  Adding PBO to pyrethrins merely keeps insects down for the count. 

Most pyrethrins formulations, including a number of over the counter (OTC) consumer products, contain PBO in low concentrations--usually less than 5%.  In recent years, however, some professional products have included higher percentages of PBO (e.g., 60%).  I've never fully understood the reason for the popularity of this mixture, given that PBO is non-insecticidal and that only small amounts of it are needed to synergize pyrethrins.  From what I can gather informally, PBO mixtures are being used increasingly by frustrated PMPs for bed bugs.  But I've always been under the impression that only a small percentage of residential pesticide applications by professionals used PBO.  It was surprising to me therefore to read that PBO was detected in 75% of personal air samples collected in the study. 

The study assumes PBO was used as a synergist with permethrin; however, permethrin is not normally sold with PBO.  Unless a lot of New York PMPs are using this combination (perhaps in bed bug applications?) I am skeptical that this use pattern is common throughout the country.  It's also possible that the PBO is coming from use of OTC products by the householders themselves.  Or there might be some non-pest control source of PBO.  In any case, it seems like one of the first regulatory steps would be to find out where PBO exposure is coming from. [Any insights in this regard from readers would be welcome!]

In the meantime, in my opinion it would be prudent to consider limiting use of products with high percentages of PBO in accounts with pregnant women or infants.  I'm not convinced yet that PBO is posing a health risk to the unborn or very young; but in most cases there are good alternatives. Our industry should be placing highest value on customer safety, so why don't we take a proactive lead on this one?

1 comment:

Mike Merchant, PhD said...

My colleague Doug Van Gundy, with Central Life Sciences, shared with me some additional information about PBO toxicity evaluations done by the World Health Organization. If you are interested, you can read at http://www.inchem.org/documents/jmpr/jmpmono/v072pr27.htm