Thursday, April 30, 2015

More on Gypsy Moth Spraying: Bioaerosols and Medical Symptomatology

I had really hoped that after my first and then second posts on gypsy moth spraying that I could get off the topic and move on to more interesting discussions, but the topic is like the bad guy in a horror movie: you think you have dealt it a death blow only to have it re-emerge for another fight. Like my last post, this one is going to be a bit shambolic as I will attempt to cover several topics that have been raised since the last blog posting. 

On being a paid “shill”
As my regular readers know, I have previously discussed the “shill gambit” in my post “On “Bullies”, “shills” and using labels to shut down legitimate debate”. In that post I was talking about other scientists being called shills, but I wasn’t fooling myself. I knew full well that as I continued to blog about evidence-based decision making, it was only time before I was labelled a “shill”. Now admittedly, I have been called it a couple times on the topic of pipelines, but if pipelines get people excited then spraying for gypsy moths turns it up to an eleven. In the last week I have been called any number of names from “shill” to “unethical” with a few people pointing out that my work as a government scientist, and the owner of a money-making blog, puts me in position of a conflict of interest. I’m afraid to say that both my employer and my wife would be a bit surprised by that line of reasoning. My employer because they didn’t realize that I had left my job to go work for the government and my wife because she knows nothing about the slew of slush money apparently coming my way from unknown “corporate interests”. To put this all to rest, let’s start with the obvious. I do not work for the government. I work in the private sector. I do not get paid to blog, and since my blog site has no ads I derive no income from my blog. I blog on my own time, and never on the company dime, as I enjoy my real job far too much to put myself in any conflict of interest on that front. It goes without saying that since I blog on my own time, the opinions expressed here are entirely my own. For those of you wondering, some friends at work read my blog but my wife does not.

On Bioaerosols and Inhalation Risk
A number of people have directed me to a Facebook page: StopGypsyMothSpraying. At the site is a prominent link to an undated New Zealand TV article on Btk spraying (ref) which I believe refers to spraying conducted in New Zealand in May 1999. The story features a very likable epidemiologist Dr Simon Hales from the University of Otago in Wellington, New Zealand. Dr. Hales brings up some very important points about spraying programmes. Specifically he points out that at the time of the spraying, in May 1999, very little was known about the science of bioaerosol dispersion of this particular compound. For those of you not familiar with the term a bioaerosol is simply a suspension of airborne particles that contain living organisms. The Foray 48B spray is a bioaerosol made up of Btk (a biological organism) in a liquid suspension. Most of the “inert” compounds discussed in my previous posts relate to the liquid suspension. To explain, you can’t simply spray raw bacteria into the air. The sprayed material consists of an active agent (the Btk) in a liquid. If designed correctly, the suspension will not clump and when sprayed correctly will produce uniform droplet sizes which will disperse in a manner that effectively covers the area being sprayed. The chemistry of these suspensions is very tricky and most of the suspensions are the result of years of study (and are thus patented and not shared with competitors). As I discuss in my previous post, the components are known to regulators but are not shared openly to protect all the work invested in producing the recipes. You need the right particle size to get effective coverage and to ensure that the compound hits and stays on the target. For the keeners out there I include a reference that details particle sizes and how they relate to the effectiveness of sprays (ref). 

In the clip from the television programme, Dr. Hales points out that not a lot was known about this topic at the time. That being said, a lot of research has been carried out and many of Dr. Hales’ concerns have been addressed. An example of this is a report titled: “Bioaerosol Health Effects and Exposure Assessment: Progress and Prospects” (2003). It indicated that in some cases, under the wrong wind/humidity conditions, droplet sizes can vary from designated parameters and respirable particles can result in both allergic and non-allergic responses in sensitive populations. The Annals of Occupational Hygiene did a major issue on the topic in 2014. I have attached a copy of the feature editorial which discusses the state of the art in the field (Advancing the Science of Bioaerosols’ Exposure Assessment 2014 ref). The literature indicates that for endpoints like cancer there exists no identified mechanism to elicit the response and thus the likelihood of cancer as a result of the spraying is extremely low (below the de minimis risk level). Moreover, the research indicates, when sprayed under the correct environmental conditions, only a very, very small percentage of the spray actually reaches respirable size. Specifically, Foray 48B spray droplet size is calibrated for ~120 μm. This is far larger than the maximum respirable size of <10μm. In the testing, approximately 0.17% of the volume of spray was determined to be <14 μm in size in bench tests (ref). So while it is clear that the possibility exists that respirable particles will be produced by the spraying, the recent literature dismisses the likelihood that it serves as a significant health risk for the typical community. The language used was pretty certain:
  • Some people may experience minor eye, nose, throat and respiratory irritation. The HRAs [health risk assessments] raised the possibility of asthma aggravation of asthma [sic], which was considered biologically plausible, although epidemiological research and surveillance from the WSTM [white spotted tussock moth] operation did not support this.
  •  Some people would find the odour of F48B unpleasant. Some people may experience nausea, headache or other symptoms if exposed to unpleasant smells.
  • Available evidence does not support any effects during pregnancy on either mother or fetus, or effects on prematurity, miscarriage rates, birth weights, congenital abnormalities.
On Hospitalization and Asthmatics:
In keeping with the sensationalization of the topic, nothing beats the headline from The Province Newspaper on Tuesday: “Two hospitalized as spraying continues in Surrey and Delta against the gypsy moths”. Reading that headline, I thought it might be time to set up the barricades to protect us from the hoards of people rushing to escape Cloverdale for the kinder, gentler world of Langley. Upon reading the article I discovered that The Province was being a bit liberal with the use of the term “hospitalized”. The story describes two individuals who went to the Surrey Memorial Hospital Emergency Room after encountering the spray. Based on my reading of the story, neither “patient” was admitted but rather as a representative of the Health Service noted: “they were fine and they were released”. Now my understanding is that the definition of “hospitalize” includes the requirement for “treatment”. The simple act of walking into an ER and asking to see a doctor really doesn’t count as being “hospitalized” in my books...unless you are trying to drive readers to your online article....

Regarding asthmatics, here we have a group that clearly represents an “at-risk” population that was specifically described the earlier risk assessments. That being said this population has not been ignored in the research and the risk to them has been studied. Specifically, during the 1999 spraying in Victoria, a matched-pair cohort study was carried out to establish the risk to this population (The effects of aerial spraying with Bacillus thuringiensis Kurstaki on children with asthma). The result was reassuring. There were no differences in asthma symptom scores between subjects exposed to the spray and control subjects located outside of the spray zone.  Moreover a larger study conducted at the same time (Human Health Surveillance during the aerial spraying for control of North American Gypsy Moth on Vancouver Island, British Columbia) had a similar conclusion: 

Results to date show no apparent relationship between aggravation of asthma in children and aerial spraying of Foray 48B. As well, no short-term health effects were detected in the general adult population nor in hospital emergency room visits.

So when people claim that no studies have been done on this topic, the correct response is “balderdash”. Surrey and Delta are not the first places this spray has been used. It has been in use for almost two decades in a large number of jurisdictions and each and every one did a risk assessment prior to the spraying and all have found the spray to be safe. Of note, I keep reading a comment that Foray 48B was “banned in New Zealand” but I have yet to find any support for this statement and attribute it to an unsubstantiated urban myth.

The Big Conspiracy
The strangest set of comments have dealt with some unspecified conspiracy between government agencies around the world to ignore the few enlightened individuals on this topic. As I mentioned previously, I have been informed that I am either a witting member of the conspiracy or simply an unwitting dupe. I’m not sure which version I prefer, but do not believe either case. As I mentioned in an earlier post: “Public Sector Compensation - You Get What You Pay for” most of the civil servants in the technical end are underpaid with respect to their private sector peers and many work in the public sector out of a sense of public duty. I cannot believe that every one of these people has been bought out by the dark forces. I think it more likely that if such a conspiracy existed we’d have read about it on WikiLeaks or through some other journalistic enterprise. As for the peer-reviewed literature, it is categorical in that researchers have been unable to demonstrate links to any effects beyond minor discomfort associated with ingesting the spray. The particles, when applied according to specifications, are not respirable and thus would not cause effects in non-sensitized populations. Given the number of exposures necessary to sensitize the population, only the most highly susceptible would appear to even have a chance of having issues. For the vast majority of the population symptoms are limited to minor headaches, a minor odor and a bad taste in the mouth. It is possible that the suspension solution may have food additives that may result in minor reactions but given the minute quantities ingested these symptoms would be expected to disappear shortly after exposure ceased. That being said all studies repeat the same warning: most negative reactions in affected communities will be linked to adverse effects promoted by expectation, otherwise known as “the nocebo effect”.


  1. Having slogged my way thru all of the references linked to, (without the help of my chemistry & biology partners of decades long past) I will simply state I am glad the Particle Size and Pathogenicity in the Respiratory Tract reference did not have click-able links. ;-)

  2. Also omitted from the "anti-" camp is just how are we to remove unwanted foreign pests if spraying is not permitted.

    At a certain point the risks of spraying -- thought with good reason to be low -- are outweighed by the known risks of not spraying. Just as I will get into a car to go to work, despite the risk of bodily injury in a car crash, in order to keep an income.

    People opposed to spraying could reasonably be labelled as people who are for imported foreign pests. Because that's what you get without the spraying.