Chromatography Tracks Pesticides on Strawberries

Scientists have developed various advanced oxidative processes (AOPs) that use reactive, oxygen-based processes to kill disease-causing germs on fruits and vegetables. However, few studies have looked at whether these cleaning methods also affect pesticide residues that might be left on the produce. A recent study conducted by researchers at the University of Guelph (Ontario, Canada). tested and confirmed laboratory methods, using gas and liquid chromatography paired with mass spectrometry, to measure leftover levels the fungicides azoxystrobin and boscalid and the insecticide chlorpyrifos on strawberries after they had been treated with a vapor-based cleaning process that uses chlorine to generate these germ-killing reactive particles. A paper based on this work was published in the Journal of Environmental Science and Health, Part B.¹

Why Do We Need Ways to Reduce Pesticide Residue on Produce After Harvest, Even Though Farmers Already Try to Control Pesticide Use?

While pesticides play a key role in modern farming by helping to control pests and protect crop yields,² using them comes with a downside: consumers may be exposed to these chemicals through the food they eat, which has been linked to health risks like cancer.^3,4 To help protect public health, regulatory agencies set limits on how much pesticide residue is allowed to remain on a given crop.^5,6 For instance, in Canada, the agency responsible for regulating pesticides (the Pest Management Regulatory Agency, or PMRA) has set a limit on how much of the fungicide azoxystrobin can remain on strawberries: no more than 10 micrograms (millionths of a gram) per gram of dried strawberry weight.^7,8 Farmers reduce the risk of pesticide residue on fruit by carefully controlling how much they spray and when. But sometimes things do not go as planned; for example, a pesticide might not break down naturally the way it is supposed to, or it could end up on crops through contaminated irrigation water, pushing residue levels above what is allowed. When this happens, there is a need for ways to reduce pesticide residue after the crop has already been harvested.^9,10

Does the Advanced Oxidation Treatment Used to Kill Harmful Germs on Strawberries Also Remove Pesticide Residues, and If So, How Effectively?

The researchers chose azoxystrobin, boscalid, and chlorpyrifos for their study because they have previously been found on strawberries grown in North America. Their testing method was sensitive enough to detect even very small amounts of each pesticide—down to fractions of a millionth of a gram per gram of strawberry.¹

The cleaning process used in this study had already been fine-tuned in earlier work to kill harmful germs like E. coli, Listeria, and Salmonella on produce. To see how this process affected pesticide residue, the researchers added a known amount of each pesticide to strawberries, then exposed them to the treatment (a combination of ultraviolet C (UV-C) light, ozone, and chlorine-infused water) for anywhere from 30 seconds to 30 minutes.¹

The treatment did break down the pesticides on the strawberries' surface, but how much varied by pesticide. On average, it removed about 35% of the azoxystrobin and 48% of the chlorpyrifos, but only about 13% of the boscalid. One possible reason boscalid held on more: since the treatment mainly works on the surface of the fruit, any pesticide that had already soaked into the strawberry itself may have been harder to reach and break down.¹

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References

1. Machado, G. B.; Warriner, K.; Prosser, R. S. Degradation of Azoxystrobin, Boscalid, and Chlorpyrifos Residues on Strawberries Using Vapor-Phase Chlorine Radical Advanced Oxidation Process. J Environ Sci Health B 2026, 1-8. DOI: 10.1080/03601234.2026.2714701
2. Popp, J.; Pető, K.; Nagy, J. Pesticide Productivity and Food Security. A Review. Agron. Sustain. Dev. 2013, 33, 243–255. DOI: 10.1007/s13593-012-0105-x
3. Jacobs, N.; Kougias, D. G.; Louie, F. et al. A Screening-Level Human Health Risk Assessment of Dietary Intake of Pesticide Residues in Produce as Compared to Consumer Guide Recommendations. Crit Rev Toxicol. 2024, 54 (4), 215-234. DOI: 10.1080/10408444.2024.2316136
4. Melnyk, L. J.; Xue, J.; Brown, G. G. et al. Dietary Intakes of Pesticides Based on Community Duplicate Diet Samples. Sci Total Environ. 2014, 468-469, 785-790. DOI: 10.1016/j.scitotenv.2013.08.101
5. Ambrus, Á.; Yang, Y. Z. Global Harmonization of Maximum Residue Limits for Pesticides. J Agric Food Chem. 2016, 64 (1), 30-35. DOI: 10.1021/jf505347z
6. MacLachlan, D. J.; Hamilton, D. Estimation Methods for Maximum Residue Limits for Pesticides. Regul Toxicol Pharmacol. 2010, 58 (2), 208-218. DOI: 10.1016/j.yrtph.2010.05.012
7. Maximum Residue Limits, Human Health, and Food Safety. Government of Canada website 2024. https://www.canada.ca/en/health-canada/services/consumer-product-safety/pesticides-pest-management/public/protecting-your-health-environment/pesticides-food/maximum-residue-limits-pesticides.html
8. Maximum Residue Limits Search. Pest Management Regulatory Agency website 2021. https://pest-control.canada.ca/pesticide-registry/en/disclaimer-page.html
9. Krol, W. J.; Arsenault, T. L.; Pylypiw, H. M, Jr et al. Reduction of Pesticide Residues on Produce by Rinsing. J Agric Food Chem. 2000, 48 (10), 4666-4670. DOI: 10.1021/jf0002894
10. Lozowicka, B.; Jankowska, M.; Hrynko, I. et al. Removal of 16 Pesticide Residues from Strawberries by Washing with Tap and Ozone Water, Ultrasonic Cleaning and Boiling. Environ Monit Assess. 2016, 188 (1), 51. DOI: 10.1007/s10661-015-4850-6