Lab Chapter 7.5.4

7.5.4 An Extraction Procedure for the Investigation of Pesticide Residues on Strawberries by Kyle Byrd-Fisher

Agriculture is as vital to the health of the United States and the world as ever. Over the course of the 20th century, the scale of food production in the United States increased dramatically to cope with the increased demand of the larger population. An increase in the scale of food production is more cost effective for farmers, but it does have some very significant draw-backs. Most notably, large-scale production carries with it the cost of crop vulnerability. If a pest is mobile or transferable, such as an insect or fungi, it has the potential to damage a much larger quantity of food. For this reason, the ability to contain pests or eliminate them is of vital importance to the modern farmer. This is how pesticides have found a home in modern agriculture, especially within the United States.

To better give an indication of the pervasive use of pesticides, in 2006, of the states surveyed by the United States Department of Agriculture Pesticide Data Program (USDA PDP), 98 percent of all head lettuce producing acreage received applications of insecticide, 63 percent of head lettuce acreage received applications of herbicide, and 87 percent of head lettuce acreage received applications of fungicide (United States, 2010). One of the issues with the broad use of pesticides is that the health effects of human consumption have often not been sufficiently studied by the time a pesticide is approved by the Environmental Protection Agency (EPA). In the case of azinphos methyl, which was approved as a coddling moth insecticide in 1959, it was not until 2006 that the EPA decided to phase it out due to its consumption and application toxicity (United States EPA). Pesticides are currently regulated by three separate branches of the Federal Government: the EPA is responsible for approving pesticides for use and setting tolerance levels on their presence in or on food, the USDA is responsible for monitoring the pesticide residue levels in food with the PDP, and the Food and Drug Administration (FDA) is responsible for enforcing standards with the Total Diet Study. This paper is concerned with the monitoring aspects of pesticide regulation, specifically extraction and identification methods for determining the presence of pesticide residues on the surfaces of fruit. The focus is on strawberries, which, like head lettuce, have significant quantities of pesticides applied on them every year.

Pesticides on Strawberries

In 2008, 2.5 billion pounds of strawberries were produced domestically, the vast majority coming from California (United States, DoA, 2008). Strawberry monitoring by the PDP in 2008 came in the form of 741 samples analyzed with a total of 113,071 analyses performed. Of these analyses, 3.3 percent detected pesticide residues, with 46 different pesticide detections reported1. Of these detections, 16 pesticides were detected on more than 5 percent of the samples, with the top three pesticide detections being boscalid, captan, and myclobutanil in that order (Anastassiades, 2003).

Extraction Standard Operating Procedure:

Strawberry samples were obtained from Safeway, which purchased them from Boskovich Farms of Oxnard, CA. A sample size of seven strawberries was obtained by washing the surface of each strawberry twice with methylene chloride. No prior wash with water was conducted. The methylene chloride wash was evaporated overnight and reconstituted in 10 mL of methylene chloride. The reconstituted methylene chloride organic wash was then put into a separatory funnel and washed twice with a concentrated aqueous sodium chloride solution. The remaining organic layer was then filtered through a syringe filter into a GC vial, totaling 0.5 – 1.0 mL. A methylene chloride blank was created and run on an Agilent 6890N GC-MS (quadrupole) alongside the sample. The temperature program was set to run at 90°C for 2 minutes before ramping by 2°C per minute to 270°C.

Results:

This extraction procedure produced a chromatogram showing evidence of three sharp peaks. The first peak had a retention time of 52.716 minutes, a percent area of 19.58%, and an approximate number of counts of 300,000. The library search report conclusively identified this compound (quality of 96) as cis-1,2,3,6-tetrahydropthalimide also known as cis-4-Cyclohexene-1,2-dicarboximide. This is a breakdown product of captan, which was identified as the third peak. The second peak had a retention time of 74.38 minutes, a percent area of 4.81%, and an approximate number of counts of 80,000. The library search report conclusively identified this compound (quality of 98) as cyprodinil or 4-cycloproplyl-6-methyl-N-phenyl-pyrimidinamine. This compound is an insecticide commonly applied to the foliage of grapes, almond trees, and stone fruit targeting scab and brown rot blossom. The third peak had a retention time of 81.401 minutes, a percent area of 75.61%, and an approximate number of counts of 1,200,000. The library search report conclusively identified this compound (quality of 99) as captan. Captan was listed above as the second most common pesticide found on strawberries and is also listed as a Pesticide Action Network (PAN) bad actor and a probable carcinogen (EXTOXNET, 2011). Captan is a broad-spectrum fungicide applied on many fruits and vegetables, and is also applied to the surfaces of fruit after harvesting to improve the fruit’s appearance (PAN Pesticide Database, 2011).

Figure 7-34. Total Ion Chromatogram of Strawberry Extract.

Conclusion

This investigation was not meant as a quantitative study as in the PDP analyses, but rather as a proof of extraction/concept and analyte identification without an external standard. Finding that pesticides residues can be readily identified with an easy extraction procedure is a strong starting point for a more extensive quantitative project.

References

United States. Department of Agriculture. National Agricultural Statistics Service. Agricultural Statistics 2010. Ed. Rich Holcomb. Print.

United States. Environmental Protection Agency. California. Azinphos-Methyl Risk Characterization Document. By Carolyn M. Lewis. Print.

United States. Department of Agriculture. Agricultural Marketing Service. Pesticide Data Program Annual Summary 2008. Pesticide Data Program. Web. <http://ams.usda.gov/pdp>.

United States. Department of Agriculture. Agricultural Marketing Service. USDA Pesticide Data Program Analytical Methods. Agricultural Marketing Service. Web. <http://www.ams.usda.gov/AMSv1.0/getfile?dDocName=STELPRDC5049940>.

Anastassiades, M.; Lehotay, S. J.; Stajnbaher, D.; Schenck, F. J. Journal of AOAC International. 2003, 86, 412-31.

"Captan Pesticide Information Program." EXTOXNET - The EXtension TOXicology NETwork. Cornell University. Web. <http://extoxnet.orst.edu/pips/captan.htm>. Accessed 2011.

"Captan - Toxicity, Ecological Toxicity and Regulatory Information." PAN Pesticide Database. Pesticide Action Network. Web. http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id= PC34569, Accessed 2011.

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