New methods to extend pesticide lifetime

Pesticides have been used in agriculture for decades to protect crops from pests and weeds with consequent increase for production yield. Additionally, they decrease the frequency of plant diseases which is usually the major cause of low crop yields or make harvest unsuitable for sale. With the growth of the global population, more agricultural production is in demand. In fact, it is expected that, within the next decade, the food industry should increase its production by 15% to meet the nutritional needs of the increasing population. [1] Therefore, the use of pesticides to keep up with this demand seems a necessity.

Despite the benefits of pesticides from a farming point of view, their uses and applications pose health problems to living organisms. [2, 3, 4] For example, pyraclostrobin, one of the most widely used fungicides (compounds which kill mushrooms and mould) globally, is highly toxic to marine organisms such as the zebrafish. [2] The intensive use of pesticides has been linked to the loss of some variety of insects [3]. Plus, residues of pesticides in food were linked with some effects such as headache, skin irritation, itching, dizziness, restlessness, neurotoxicity, breathing difficulties, unconsciousness, chronic poisoning-related diseases such as cancer and death incidences. [4]

The opinion of experts in the field is also divided and some experts in the field of crop protections argued that pesticides are valuable tools for farmers and they are essential for producing enough food to feed a fast-growing population. Additionally, pesticides are heavily regulated and their risks are well understood. On the other hand, scientists argued that even low-level exposure to pesticides can have negative effects on human health, and we need more evidence to understand the long-term effects of exposure.

Current trends [5] and lines of research in the field of sustainable agriculture [6, 7] are emerging to find solutions to the problem of pesticides pollutions. In terms of sustainable agriculture, the authors of both pieces of research made interesting observations. They argue that traditional pesticides are formulations either made of water, emulsions or granules and those products are applied by spraying, like in the featured image. However, since the droplets tend to evaporate, bounce, roll off etc, only 10% of the actual pesticides land on leaves. The rest 90% is lost in the environment and pollutes soil and water, eventually threatening human health and the survival of other animal species.

Starting from this observation, in one research study [6], the authors focused on developing better pesticides formulations to improve absorption on the leaves of rice. The surface of leaves is a mixture of wax and silicon, which is a typical super-hydrophobic surface. The wax on the surface of plants is a combination of alkanes, fatty alcohols, free fatty acids, flavonoids, and other substance. Based on the composition of leaves, they created four different pesticide formulations: two oil-in-water solutions and two water-in-oil ones. They were all made of methyl oleate and solvent oil No. 200 in different ratios. An emulsifier was used and the active pesticide was isoprothiolane in all cases.

A series of studies were conducted on the properties of these formulations and their interactions with rice leaves. They identified the water-in-oil mixture, with solvent oil No. 200, to be the best as the droplets of this mixture flattened within minutes since their application on leaves (see figure below). This was the key feature to improve adsorption of pesticides on leaves instead of them being washed away.

In another research study [7], to tag the problem of low deposition of pesticides on leaves, the author used a different approach. They proposed the use of cellulose nanocrystals to deliver the pesticides. Specifically, the cellulose nanocrystals were modified with cyclodextrins first, then the pesticide was loaded and covered with a mixture of copper and tannic acids. The addition of cyclodextrins improved the adsorption of the carrier on the surface of the super-hydrophobic leaves. The addition of the tannic acids and copper created a sort of encapsulation for the pesticide which could be released only when the carrier was anchored to the leaves. In fact, the parasites generally produce acidic substances which break down the copper-tannic acid complex and the pesticides is released only where the infection is located. These carefully designed nanocarriers did kill mould and insects well and demonstrated excellent biosafety.

It’s always cool to see new research and how science can solve everyday problems. Understanding the route cause of pesticide pollution and studies on the droplet-leaf interactions were key to create better formulations and products that can stick to plant leaves better. However, this is a complex problems and pesticides should also be used sensibly. Regulatory bodies do have a list of recommended pesticides and monitor their use. And, ultimately pesticides should be handled and stored according to labels, safety instructions and used following international guidelines.

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[1] OECD-FAO, 2019. Agricultural Outlook 2019–2028. OECD Publishing, Paris/Food and Agriculture Organization of the United Nations, Rome

[2] Chemical Engineering Journal 2022, 439, 135805

[3] Biological Conservation, 2019, 232 Pages 8-27

[4] Cogent Food & Agriculture, 2019, 5, 1601544.

[5] Adv. Mater., 2022, 34, 2105009

[6] Pest Manag. Sci., 2021, 77, 3198–3207

[7] Green Chem., 2023, 25, 2690–2698

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