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Research Article

Choosing Organic Pesticides over Synthetic Pesticides May Not Effectively Mitigate Environmental Risk in Soybeans

  • Christine A. Bahlai,

    Affiliation: School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada

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  • Yingen Xue,

    Affiliation: School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada

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  • Cara M. McCreary,

    Affiliation: School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada

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  • Arthur W. Schaafsma,

    Affiliation: Department of Plant Agriculture, University of Guelph, Ridgetown, Ontario, Canada

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  • Rebecca H. Hallett mail

    rhallett@uoguelph.ca

    Affiliation: School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada

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  • Published: June 22, 2010
  • DOI: 10.1371/journal.pone.0011250

Reader Comments (2)

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Study is useful, but...

Posted by MarkS on 24 Jun 2010 at 18:49 GMT


A study should be considered flawed if it measured environmental impact, risks, and safety of the controls based only upon the mortality rates of two specific non-target insect species. It would even be more flawed if you provided general conclusions based upon such a faulty measure.

Since your study does not deal with other potentially undesirable effects or risks from the use of these substances, you cannot conclude which pesticide actually has the lowest environmental impact (whether allowable in certification programs or otherwise).

To imply in your study that those who provide advice to, and work with organic certification programs in Canada base their recommendations on the ideology that naturally occurring substances are always more environmentally benign than synthetics is untrue. It is also an insult to the biologists, universities, and agricultural extension offices that provide guidance to those making such policy decisions.

In fact, there have been many, many other studies that look at the environmental impact of "natural" controls, and these studies (including your own) are welcome input for those who make scientific recommendations to certification bodies and even by the farmers themselves. Frankly this would be a much better paper if the sweeping assumptions and unfounded conclusions were removed. Luckily for you, I’m not refereeing this one.


No competing interests declared.

RE: Study is useful, but...

RHallett replied to MarkS on 25 Jun 2010 at 02:46 GMT

Thank you for your comments on our paper. However, you have misinterpreted some aspects of our study. To clarify, our conclusions are based upon three distinct measures – contact toxicity to predators in the lab, selectivity in field trials (which incorporated measures of the entire foliar natural enemy community), and the EIQ and EIQ-field use ratings – not simply toxicity to two predators.
Assessment of overall environmental impact was based on the EIQ field use ratings. The EIQ measure incorporates multiple aspects of a chemical that contribute to its overall environmental impact – e.g. toxicity measures, residual life, leachability, and farm worker exposure. Thus, “assessment of other potentially undesirable effects or risks from the use of these substances” are included in the EIQ measures.
Our comments about policy makers were not directed at organic certification bodies, but are based on the decisions and policies of several government agencies, as cited in the paper. For example, when the Pesticide Risk Reduction program, an Agriculture and Agri-Food Canada initiative, was implemented in 2003, a specific emphasis was placed on replacing older pesticide chemistries with reduced risk, natural products, and biopesticides. The guiding tenants of the program have since been re-written slightly, but more information on this program is available at: http://www4.agr.gc.ca/AAF... and http://www.hc-sc.gc.ca/cp... The second link, in particular, specifically states one of the goals of the program as “Help increase grower awareness and adoption of biopesticides” which implies the assumption that biopesticides, such as Beauvaria bassiana, would offer improved environmental profiles over synthetic pesticides, which was shown empirically not to be the case in the soybean system. There are similar examples available in Ontario, the US and UK policies.
Our statements on perception of the safety of natural vs synthetic comments were directed at an opinion prevailing among the public, and are supported by the surprised reaction expressed by many representatives of the public since this paper was published.

Rebecca Hallett and Christie Bahlai

Competing interests declared: Authors of the study under discussion.

About EIQ ratings ...

MarkS replied to RHallett on 25 Jun 2010 at 16:04 GMT

EIQ limitations aside when used in this context, I do not understand the relevancy of using EIQ field use ratings in your analysis.

While mineral oil does indeed appear on the permitted substances list you provided a reference to (#17), you fail to mention in your paper that the substance is only listed under the Livestock heading in the Health Care Products category for topical use or as a lubricant. Why does your paper leave out such critical and relevant information? And the application of mineral oil where allowed is restricted to use on woody plants during periods of dormancy only (see Ecocert Canada). Therefore I find relating its EIQ field use rating at application rates meeting the efficacy of standard aphid controls for soybeans to the conclusions made in your paper difficult. This use has nothing to do with “organic practice”, contrary to that stated in your paper.

Copper sulfate is also a substance allowed under organic certification standards for specific applications. Attempting to apply enough to control Aphis glycines would likely result in an EIQ use rating that exceeds even that of using mineral oil and would be less selective as well (not to mention kill the host plants). I’m surprised you didn’t select this compound instead, since the title of your paper and conclusions could be even more sensational and newsworthy.

No competing interests declared.

RE: About EIQ ratings ...

cbahlai replied to MarkS on 26 Jun 2010 at 14:05 GMT

Hi Mark,

Rebecca Hallett has responded to several of your specific comments below, but I did want to give you a bit more detail on your query about why we classified our mineral oil product as an organic pesticide.

The Canadian General Standards Board Permitted substances list for Organic Production systems (http://www.tpsgc-pwgsc.gc... ) specifically permits “summer oils.” They are listed as products which are “allowed for use in organic production as suffocating or stylet oils on foliage” in the category of “Crop production aids and materials.” A summer oil is a mineral oil product containing the lighter-molecular-weight compounds than those typically used in dormant oils. These lighter molecular weight oils are often referred to as superior oils, and Superior 70 Oil, the mineral oil formulation used in this study, is one such product.

Superior 70 Oil is permitted for use in Canada on the vegetative stages of rutabaga at the rate we tested in this study. See:
http://www.uap.ca/product...

This product was selected because, as outlined in the paper, there was both government and industry interest in reviewing this product, and because this product had demonstrated activity against aphids in other crops in the literature.

EIQ-FUR is a function of a rating of overall environmental impact (EIQ), multiplied by the rate at which the chemical is applied. It is based on the fundamental principle of toxicology, that is, the overall risk posed by a chemical is a function of the toxicity of the substance multiplied by one's exposure to it. More information about how EIQ is calculated and the rationale behind it can be found here: http://www.nysipm.cornell...

-Christie Bahlai

Competing interests declared: Author of the study under discussion

RE: RE: About EIQ ratings ...

MarkS replied to cbahlai on 29 Jun 2010 at 19:08 GMT

Conclusions about actual environmental impact cannot be based on EIQ, as it is simply a rough measure of potential impact. There is a difference. This is why I still maintain that your paper makes broad conclusions about environmental impact based only upon the mortality of two non-targeted species.

The EIQ calculation breaks down completely when more benign substances are considered. The field use EIQ for 100kg of corn starch dusted over an acre would probably exceed the EIQ for 70kg of pure carbaryl distributed over a single acre. The reason for this is because the EIQ rating assumes that the “1” level score of one substance is the same as another, even though the applicability of an entire category might be questionable. Soap and carbaryl have base EIQs almost the same as a result. “Oil” (the database makes no distinction on the type of oil) is has a base EIQ nearly 50% higher than carbaryl. As an experiment, attempt to come up with a base EIQ for pure water following the guidelines and then compare the calculated field use EIQ to that of half the amount of any organophosphate or carbamate. You can’t assume that a gentle spring rain has nearly the environmental impact of large carbaryl dosing because of field use EIQ. I’m afraid real life is just more complicated than this.

I hope that help clarifies my original concerns with this paper.

No competing interests declared.

And about the Pesticide Risk Reduction Program

MarkS replied to RHallett on 25 Jun 2010 at 16:51 GMT

To assume that the ones responsible for this program believe that all biopesticides (and other "natural" controls) have less impact on predator species than all synthetic pesticides simply because part of their mission is to promote biopesticides is a stretch, especially in what is supposed to be an empirically based scientific study. After all, the program also promotes IPM and is included in the same link you provided!

Instead of making the assumptions that government policy makers have a belief that anything "natural" is better than anything "synthetic", why didn't you contact them and ask the program director directly?

Wasn't Art Schaafsma the one originally responsible for the sustainable management of the soybean aphid study at your institution under this program? Where did this taxpayer funded work go? Why isn't it cited in your paper?

No competing interests declared.

RE: And about the Pesticide Risk Reduction Program

RHallett replied to MarkS on 26 Jun 2010 at 11:52 GMT

Mark-

It appears that you have taken personal and/or professional offense to this paper where none was intended.

Public policy is influenced by the public. There is an opinion prevailing among the public that natural is better than synthetic and this is reflected in the policies of a number of governmental bodies.

This study is one part of the sustainable management of aphids project led by myself and Art Schaafsma with AAFC Pesticide Risk Reduction Program funding. All of this is clearly laid out in the paper along with a complete description under the associated materials tab of how and why the pesticides were selected.

Several papers on the impacts of natural enemies and other factors on soybean aphid population dynamics from this program have already been published and several others are in progress.

The next one will report that healthy natural enemy populations can eliminate the need for pesticide use in soybeans for soybean aphid.

As for why we used the EIQ-FUR, the amount of a chemical that is put into an area has a direct relationship to the impact that it will cause (or it's potential for impact). This is a fundamental principle of risk assessment.

Rebecca Hallett

Competing interests declared: An author of the paper under discussion.