It would seem illogical that organic compounds are all more sustainable than synthetics, or vice versa. The term “organic” has a health halo, biasing many people toward believing organic growing techniques are best for the environment. I’ve already covered analyses suggesting that there isn’t enough evidence that suggests organic foods are better for your health, so is the higher cost justified by a lessened environmental impact? Bahlai et al. published a paper suggesting that the dichotomous classification of organic and conventional is not optimal for sustainability, we must evaluate pesticides individually.
According to the authors, sustainable agriculture programs put an emphasis on the development of organic and natural insecticides to control pests, with the assumption that they are safer on the environment compared to synthetics. Public opinion also leans toward this assumption as well. The various practices (organic, conventional, or integrated) have been studied producing different results on sustainability. Differences in methodologies, practice classifications, and a number of other variables make it difficult to draw conclusions at this point. Importantly, they note:
…each system is characterized by a suite of practices which are ideologically, rather than empirically defined, these systems are not mutually exclusive from each other, and vary from region to region depending on regulations. Because of these variations, generalizations about the overall sustainability of one system over another are never universal.
Organic farms do indeed (generally) use pesticides, they just aren’t synthetically made, while conventional farms can use both natural and synthetics.
This study focuses on soybean aphid, which is a major pest in North America. The investigators chose 4 new “potential reduced risk” insecticides with the Agriculture and Agri-Food Canada, 2 synthetic and 2 natural (certified for organic crops in Canada). 2 synthetic controls (currently used) were also included (click to see a full size table):
First, lab tests studied toxicity of the pesticides against 2 species that help control aphid populations: Harmonia axyridis and Orius insidiosus, and found that the currently used synthetic pesticides were most toxic to the beneficial species compared to the 4 new ones. Of these, the 2 organics were more toxic than than the synthetics.
Then, a 2 year, 5 site study examined efficacy and selectivity of target pests. The organic pesticides had a lower efficacy than the synthetics at 1 and 2 weeks post-treatment. Selectivity was greatest with both synthetics. Here are the graphs; the mineral oil and beauveria bassiana are the organic pesticides, compared to the new synthetic spirotetramat and flonicamid.
Going back to the first table, the net environmental impact was estimated as an Environmental Impact Quotient (EIQ), which is a ranking that incorporates MSDS data and application rate. According to the EIQ-FUR (field use), the organic pesticides had a higher (in the case of the mineral oil, much higher) environmental impact compared to synthetics. The authors mention some controversy about using EIQ compared to other ranking methods, but point out the inverse relationship they found between selectivity and EIQ in this study, supporting its use.
The synthetic pesticides studied here tend to be more sustainable compared to the organics. The authors clearly favor integrated pest management systems over completely organic techniques:
Carefully designed integrated pest management systems are likely the best strategy for minimizing environmental impact of agriculture: where certified organic systems may reject the technology with the smallest environmental impact based on ideology, IPM maintains the flexibility to incorporate any strategy empirically determined to have the smallest impact.
This sounds most sensible to me: we should study each pesticide using methods like this rather than making misguided generalizations about sustainability. Indeed, the authors sum it up nicely:
… we reject the organic-conventional dichotomy and emphasize that, in order to optimize environmental sustainability, individual tactics must be evaluated for their environmental impact in the context of an integrated approach, and that policy decisions must be based on empirical data and objective risk-benefit analysis, not arbitrary classifications.
I do have to question whether measuring only efficacy and selectivity and making conclusions about sustainability is appropriate. Hopefully future studies will measure other impacts.
Bahlai CA, Xue Y, McCreary CM, Schaafsma AW, & Hallett RH (2010). Choosing organic pesticides over synthetic pesticides may not effectively mitigate environmental risk in soybeans. PloS one, 5 (6) PMID: 20582315