Beyond the Peel: The Deeper Issue of Pesticide Contamination

Pesticide is a catch-all term used to describe the chemicals (natural or synthetic) used to control insects, fungi, rodents, weeds, or plant diseases—and they are a massive part of modern farming. It is estimated that 2 million tons (and growing) of pesticides are used globally each year, with the top contributors being China, the United States, and Argentina, respectfully.¹ But opponents warn of adverse health effects associated with long-term pesticide exposure—both for the workers who apply pesticides and spend ample time in treated fields^2,3 and for the consumers who eat the produce. With this in mind, many of us may choose to grow organically without chemicals in our own home gardens and allotments, but when you consider that 45% of annual food production is lost to pest infestations, this route isn’t practical on an agricultural scale.^1,4 On top of this, it has been estimated that we will need to produce more food in the next 35 years than ever before in human history⁵—and with no additional land available, this is driving novel technologies to sustainably increase production of safe foods. The World Health Organization, while recognizing that pesticides play a significant role in food production and global food security, aims to protect public health by setting maximum limits for residues in food and water.⁶

As part of these efforts, there remains a need for sensitive analytical methods that can identify the smallest trace levels of potentially harmful substances in our food without needing to destroy the produce. Just in time for apple picking season, a new study published in Nano Letters reports on a novel imaging method that uses the help of Surface-Enhanced Raman Spectroscopy (SERS) to detect low levels of pesticide contamination on fruits and other foods.⁷ SERS traditionally uses metal nanoparticles or nanosheets to amplify the signals created by molecules when they are exposed to a Raman laser beam. The subsequent patterns created act like molecular signatures and can identify tiny amounts of specific compounds.

Dongdong Ye, Ke Zheng, Shaobo Han and colleagues set out to improve SERS sensitivity specifically for pesticide detection, using a silver-coated cellulose hydrogel film that could be placed on farm-grown produce. Using apples as the test subject of choice, they sprayed them directly with pesticides, left them to air dry, and then washed them in a similar way that the average consumer might after bringing fruit home from the store. The SERS-enhancing silver membrane helped to detect pesticides on the washed apples, with clearly resolved scattered-light signatures for each pesticide type. Additionally, this method detected contamination below the fruit’s peel, in the outer layer of flesh. The authors conclude that pesticide ingestion cannot be avoided by simple washing alone, and that it may be wise to peel fruits and vegetables first to remove those first layers of flesh. In addition to apples, the authors also tested the SERS membrane system on cucumbers, shrimp, chili powder and rice.

Related hydrogel research from Ye and other colleagues includes anisotropic cellulose hydrogels made from nanoscale aligned nanofibers, which they achieved by dissolving cotton liner pulp in an alkali solution.⁸ But rather than testing apples, they used them to grow and develop cardiomyocytes, unveiling a promising strategy for heart cell regeneration. Other work has also looked into nanostructured cellulose films for applications in biodegradable packaging, device screens, and optoelectronic materials.⁹

References

1. Sharma, A. et al. Worldwide pesticide usage and its impacts on ecosystem. SN Applied Sciences 2019, 1, 1446.
2. Bonner, M.R. et al. Occupational Exposure to Pesticides and the Incidence of Lung Cancer in the Agricultural Health Study. Environ. Health Perspect. 2017, 125 (4), 544– 551.
3. Duporté, G. et al. Dislodgeable Foliar Residue Measurements and Assessment of Dermal Exposure to Captan for Workers in Apple Orchards. Environ. Sci. Technol. 2024, 58, 31, 13605–13612.
4. Abhilash, P.C. and Singh, N. Pesticide use and application: an Indian scenario. J Hazard Mater. 2009, 165, 1–3, 1–12.
5. The challenge. Global Food Security 2024.
6. Pesticide residues in food. World Health Organization 2022.
7. Lin, Z. et al. Cellulose Surface Nanoengineering for Visualizing Food Safety. Nano Lett. 2024, 24, 33, 10016–10023.
8. Ye, D. et al. Robust Anisotropic Cellulose Hydrogels Fabricated via Strong Self-aggregation Forces for Cardiomyocytes Unidirectional Growth. Chem. Mater. 2018, 30, 15, 5175–5183.
9. Ye, D. et al. Ultrahigh Tough, Super Clear, and Highly Anisotropic Nanofiber-Structured Regenerated Cellulose Films. ACS Nano 2019, 13, 4, 4843–4853.