Personalized Pesticides â A New Paradigm - American Chemical

Chapter 10

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Personalized Pesticides – A New Paradigm Case Study: Volatilization of Individual Components of Botanical Insect Repellents from Human Skin Saber Miresmailli* Sumatics LLC. New York, New York 10022, United States Current address: 2501 Mahon Ave., North Vancouver, BC V7N3S5 Canada *E-mail: [email protected].

The idea of using generic substances for blanket management of arthropod pests has been long pursued by pesticide manufacturers despite various factors that affect efficacy of chemical pesticides. Plant essential oil-based pesticides are generally considered as safer alternatives for conventional pesticides and represent a relatively new class of natural pesticides efficacious against a wide range of pests. Unlike conventional pesticides, botanical pesticides consist of several active and inactive components that can chemically synergize or suppress each other, as well as affect physical properties of botanical pesticides such as rate of volatilization. Results from preliminary human trials that explored volatilization of individual components of a botanical insect repellent from human skin will be presented. In addition, variable patterns of volatilization of individual components of botanical insect repellents over time will be discussed, as well as their possible relation to the subjects’ gender, ethnicity and skin condition.

© 2013 American Chemical Society In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


For more than six decades pest management programs extensively relied on toxic synthetic chemical pesticides. Several classes of pesticides have evolved over this period, from the chlorinated hydrocarbons to the organophosphates, carbamates and pyrethroids and most recently to the neonicotinoids (1). These pesticides have been favored by growers for many years due to their strong efficacy against various pests in large-scale agricultural practices. However, overuse of these products and their resilience not only rendered many of them ineffective – due to target resistance – but also imposed dire long lasting environmental and health risks to non-target organisms (2). Concerns over their negative impacts have lead to increasingly restrictive regulation of synthetic chemical pesticides and a new era of exploration for safer alternatives (3). Natural products, specifically botanical pesticides based on plant essential oils, have been at the center of attention as safer alternatives for synthetic chemical pesticides. Plant essential oils are complex mixtures of monoterpenes, sesquiterpenes, phenols and other compounds. Some constituents of essential oils are low molecular weight volatile compounds that account for the fragrances of the oil. Several studies have demonstrated contact and fumigant toxicity of various terpenoids found in plant essential oils against arthropod pests (4). It has been shown that presence or absence of certain constituents in a mixture could significantly affect the efficacy of essential oil-based botanicals as contact pesticides (5). When rosemary oil was tested as a repellent against two-spotted spider mite (Figure 1), it was discovered that major constituents do not evaporate at the same rate and the composition of volatiles in the air, evolve over time (6). In the case of rosemary oil (Figure 1), some constituents were only present in the headspace after the level of other constituents decreased (i.e., d-limonene and camphene versus 1,8-cineole and camphor).

Volatilization of Botanical Insect Repellents From Human Skin To analyze volatilization of selected essential oils from human skin, a zNose, an ultrafast portable gas chromatograph, was used (7). The zNose system was tuned with an n-alkane solution and calibrated with neat reagents prior to its application in each experiment. The zNose inlet, valve and initial column temperature were set at 200 °C, 165 °C, and 40 °C, respectively. During analyses, the column temperature was increased at 10 °C/sec to 200 °C. The surface acoustic wave (SAW) sensor was kept at 60 °C and the trap was kept at 250 °C. The helium flow during the 10 sec sampling period was set at 3.00 mL/min. The sampling period was set for 10 sec at a sample flow of 20 mL/min, after which the system switched to 20 sec of data acquisition. Thereafter, the sensor was heated to 150 °C for 30 sec, and parameters (see above) were reset. 0.25 mL of rosemary essential oil, as insect repellent, was applied on forearm of two human subjects and volatilizations of constituents were measured for 120 minutes (Figure 2).

146 In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Figure 1. Comparing volatilization pattern of rosemary oil major constituents with position of naïve spider mites in a test arena over 60 minutes. (a) test arena, (b) zNose. Error bars represent mean ± SE.

Results of this pilot study supported previous observations. Major constituents did not evaporate at the same rate and the composition of volatiles in the air changed over time. However, another interesting phenomenon was also observed as a result of this pilot study. There was a significant difference in the overall volatilization pattern of the rosemary oil from the skin of the male subject compare to the female subject used in the pilot study. To better understand this phenomenon, a human trial was conducted with subjects of different gender, ethnic background (Caucasian, Indian, Asian, Middle Eastern), age (25-35) and skin condition (normal, dry, hairy) (n=18). Specific demographic details of 147 In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


subjects are not presented here following the guidelines of UBC ethics board. Experiments were conduced in a laboratory under controlled conditions. Prior to each test, subjects washed their arms with unscented soap and lukewarm water and sat down for 30 minutes to bring down their heart rate to resting level. Each subject then received a single dose (0.25 mL) of a commercial botanical insect repellent (EcoSMART Insect Repellent) on his or her forearm (Figure 3).

Figure 2. Volatilization of rosemary oil major constituents from human skin.

Subjects’ arms were then placed on a clean laboratory desk. The zNose was positioned to collect volatiles at 10 cm above the skin of the subject every 3 minutes for one hour with the same parameters used in the pilot study. Subjects’ skin surface temperature and pH were measured by a thermal scanner and pH meter. Changes in the patterns of volatilization were analyzed by generalized 148 In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


estimated equations (GEE) regression using R statistical analysis software (www.r-project.org). Various volatilization patterns were observed in relation to the subjects’ gender, ethnicity and skin color and condition (Figure 4).

Figure 3. Volatilization of a commercial insect repellent from human skin. (a) insect repellent, (b) thermal scanner, (c) zNose, (d) chromatogram.

The results of this preliminary human trial indicated differences existed in the volatilization patterns of an individual product used on subjects of different genders, ethnic backgrounds, and skin conditions. However, because of the small sample size and great variation that existed among subjects, the results of this initial trial are not statistically powerful enough to make a strong correlation between either of those factors and different volatilization patterns. Larger standardized clinical trials (minimum of 1,000 subjects as it is customary in trials of this nature) with greater control over variables such as diet and exercise regime, sleep, drug intake, age group, etc. are necessary to fulfill experimental requirements for more definitive results. Despite the statistical shortcomings of this trial, the observed differences can perhaps encourage a different approach towards production of complex botanical pesticides. The results also suggest that a “one size fits all” approach is no longer a viable option and that generic formulations cannot provide the blanket management of all target pests under all conditions – particularly in the case of insect repellents. What these results imply in practical terms is that a new 149 In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


method of botanical pesticide manufacturing is needed to cater the needs of end users with specific biological features, hence the introduction of “personalized pesticides” as a new paradigm (Figure 5).

Figure 4. Various volatilization patterns of major constituents of insect repellent relative to the subjects’ gender (a), skin condition (b), and ethnic background (c). Error bars represent mean ± SE (n=18). 150 In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.


Our understanding of how end users’ biological features could affect volatilization of botanical insect repellents is limited at the moment. In the case of botanical pesticides, it is entirely possible that few features play a major role in efficacy of the botanical pesticides and thus enable manufacturers to develop specific types of pesticides that best match the needs of specific users. Such modifications and customizations have long been performed for cosmetics and hygiene products. In the era of cloud-based computation, it should be possible for end users to order and customize their specific personalized insect repellent via their smartphone by entering few key biological features that help the manufacturers to formulate them the best possible formulation that match their unique biological attributes.

Figure 5. Proposed model of “personalized pesticide” production.

Acknowledgments Based on a symposium paper presented at the 244th ACS Annual Meeting in Philadelphia PA, August 19, 2012. I thank Dr. Murray Isman for his guidance, supervision and academic support, Nancy Brard for technical assistance, and all volunteers who participated in the human trials. Supported by grants from MITACS, Ecosafe Natural Products Inc. and EcoSMART Technologies Inc. 151 In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.

References 1. 2. 3. 4. 5.


6.

7.

Thacker, J. R. M. An Introduction to Arthropod Pest Control; Cambridge University Press: Cambridge, U.K., 2002. Benbrook, C. M. Pest Management at the Crossroads; Consumer Union: Yonkers, NY, 1996. Isman, M. B. Annu. Rev. Entomol. 2006, 51, 45–66. Isman, M. B. Crop Protect. 2000, 19, 603–608. Miresmailli, S.; Bradbury, R.; Isman, M. B. Pest Manage. Sci. 2006, 62, 366–371. Isman, M. B.; Miresmailli, S. In Recent Developments in Invertebrate Repellents; Paluch, G. E., Coats, J. R., Eds.; ACS Symposium Series 1090; American Chemical Society: Washington, DC, 2012; pp 67−77. Miresmailli, S.; Bradbury, R.; Isman, M. B. Arthropod Plant Interact. 2010, 4, 175–180.

152 In Pest Management with Natural Products; Beck, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2013.

Personalized Pesticides â A New Paradigm - American Chemical

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Personalized Pesticides â A New Paradigm - American Chemical