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A diet rich in whole plant foods has numerous health benefits, but the application of pesticides to these foods is a growing concern. Pesticide exposure is associated with respiratory problems, neurological disorders, reproductive issues, endocrine disorders, and cancer. Moreover, many pesticides are persistent, meaning they remain in soil, water, and air, causing long-term and downstream impacts on the environment. While pesticides are a problem for human health and the environment, their application is intended to improve crop quantity and quality. Without them, crop losses are estimated to be 78% for fruits, 54% for vegetables, and 32% for cereals/grains. However, because the route of exposure for most people is through foods eaten, finding solutions to minimize pesticide residues on foods is a first step solution for preventing long-term health consequences related to pesticides.

What are pesticides & why are they a problem?

Pesticides are chemical substances used to prevent pests, fungi, diseases, and weeds in crops. They are also used to increase crop yield, improve crop quality, and prevent the normal growth of plants. While their application has an economic benefit, ingesting pesticide residues on plants is considered hazardous to health, with both acute and chronic exposure outcomes. For example, acute exposure may contribute to nausea, headaches, diarrhea, convulsions, eye irritation, breathing discomfort, or even death. Long-term exposures at low doses are linked with chronic diseases and disorders due to the biomagnification effects of pesticides in the body. The impact of the pesticide depends on the type of chemicals used, dose, duration, and type of exposure. While maximum residue limits (MRLs) have been set to prevent negative health outcomes, the safe application of pesticides is not always practiced, and it is estimated that 99.9% of the pesticides applied are released into the environment.

Another factor in the persistence, accumulation, degradation, and behavior of pesticides is the chemical structure, molecular weight, polarizability, ionizability, and volatility of the pesticides used. Environmental conditions, such as temperature, light, and relative humidity, may also affect how pesticides behave. For example, organochlorine pesticides (i.e., DDT) are steady and can withstand changes in the environment over long periods. Because they are fat-soluble, they require an organic solvent to dissolve them. Nearly 40% of pesticides used in modern agriculture belong to this class of pesticides, though their use is banned or restricted in most advanced countries. Over time, pesticides may accumulate in fatty tissues and contribute to disease.

Pesticide residues remain on plants and may be higher on leafy vegetables with large surface areas and non-peelable produce. Because pesticides accumulate in the food chain, they may remain in or on other foods, including meats, fish, nuts, and oils. Although it may be impossible to completely avoid these persistent chemicals, it is possible to limit their ingestion without adding more toxins.

Washing agents to reduce pesticide residues on produce: Do they work?

Various methods are used to remove pesticides from plant foods. For some pesticides and certain foods, simple running water will remove residues, while fat-soluble chemicals will require emulsifiers or solvents. Other methods include physical peeling, trimming, heating, or soaking. Because leafy vegetables cannot be peeled and have a large surface area, pesticide residues are more likely to remain on the surface of these plants after harvesting than peelable fruits and vegetables if not properly treated.

One comparative study on contaminated leafy vegetables (lettuce, perilla leaves, spinach, crown daisy, and ssamchoo) tested different pesticide removal methods. Removal methods included blanching, boiling, baking soda washing, detergent washing, running tap water washing, stagnant tap water washing, ultrasonic cleaning, vinegar water washing, and alkaline electrolyzed water washing. Running water and boiling water had the greatest effects on residue reduction (77% ± 18% and 59.5% ± 31.2%, respectively). However, boiling and blanching leafy vegetables reduced chlorfenapyr, diniconazole, indoxacarb, fludioxonil, pyraclostrobin, and lufenuron the least compared to other methods (p < 0.05). Detergent washing was the least effective method for residue removal (43.7% ± 14.5%). The removal of contaminants was greatest from lettuce (67.5% ± 7.3%), whereas the removal from ssamchoo was lowest (40.6% ± 12.9%). No significant reductions in contaminants were found for spinach and crown daisy. Removal rates appear to vary between vegetable types. Based on these results, heat treatments may improve the reduction of some pesticides, while running tap water may effectively remove others.

Another study evaluated how cooking processes affect pesticide residues on Chinese kale and yard long beans. Cooking methods used include boiling, blanching, and stir-frying. Vegetables were tested for 88 pesticides before and after cooking. For Chinese kale, residues were reduced by 18-71% from boiling, 36-100% from blanching, and 25-60% from stir-frying. For yard long beans, residues were reduced by 38-100% from boiling, 27-28% for blanching, and 35-63% from stir-frying. Based on these results, thermal heating may be a strategy for preventing pesticide ingestion.

However, despite the effectiveness of thermal processing to remove some residues, there are some problems with this method, especially if processes do not include moisture. Thermal processing, such as drying, blanching, baking, and roasting, can cause pesticides to concentrate or produce toxic metabolites. Additionally, heat reduces ascorbic acid content and some antioxidants in foods (e.g., phenolics and carotenoids). What’s more, thermal processing is not an ideal solution for foods meant to be consumed raw, such as lettuce. Non-thermal processing techniques effectively remove pesticide residues while maintaining the nutritional qualities of foods. For example, ultrasound, cold plasma, pulsed electric fields, and high-pressure processing have been identified as effective strategies for promoting residue degradation without altering produce quality or producing additional contaminants.

Lettuce is eaten raw, but it is susceptible to pests during the growing process, which requires the application of pesticides. Common pesticides used on lettuce include pyraclostrobin, pyrimethanil, sulfoxaflor, deltamethrin, fluopyram, boscalid, and fluopicolide. Because lettuce is not ideal for thermal heating, practical, non-thermal solutions are needed for pesticide removal. One study found that, on average, washing lettuce with rice vinegar or filtered rice water was most effective at removing the pesticides tested. It should be noted that other effective treatments for some of the pesticides tested include grape vinegar, lemon juice, hot and cold tap water, baking soda, and carbonated water.

Tomatoes are also subject to pesticide application to prevent pests. Dichlorvos (DDVP) is still a widely used organophosphate pesticide in the United States. A study comparing washing with tap water, ozonated water, commercial detergent, and ultrasonic cleaner found that longer wash times, higher concentrations of ozone and detergent, and ultrasonic power were more effective at removing DDVP. All methods were effective at removing DDVP but washing with ozonated water and an ultrasonic cleaner were most effective, with a removal of 91.9% and 88.9%, respectively. It is important to note that while ozonated water and ultrasonic cleaning are effective, they may be less practical for at-home cleaning. Additionally, by-products of ozone water and their effect on humans require more research.

While some produce can be peeled to remove residues from skins, some fruit and vegetable skins are eaten with the flesh of the produce. An older study from 2017 tested the effectiveness of different washing agents on the removal of pesticides from the surface of apples. Specifically, researchers assessed whether a sodium bicarbonate (baking soda) solution, Clorox bleach, or tap water could remove the pesticides thiabendazole and/or phosmet from the apple skin surface. Washing apples in Clorox bleach is a standard method post-harvest to remove pesticide residues. Of the three agents, sodium bicarbonate (10 mg/mL solution) was the most effective at dissolving thiabendazole and phosmet when soaked for 12 and 15 minutes, respectively. Each of the pesticides applied penetrated the apple peel, causing pesticide residues in the apple, which could not be washed away by soaking it in the sodium bicarbonate solution. Peeling the apples is a solution offered by researchers to remove the amount of pesticides that penetrated the skins, however, the bioactive compounds in apple skins would be lost.

Peelable fruits and vegetables are considered safer due to the outer protection of the discarded peels before consumption. However, peels may still contain pesticides that should be washed off before peeling the food. A study on various processing methods for oranges (e.g., washing, peeling, processing into another product, freezing, storing) assessed the amount of pesticide residues after each process. Washing orange peels before consumption reduced pesticide residues by 26-84%. Processing oranges into fruit juice and jam reduced pesticide residues by 63-100% and 90-100%, respectively. Some pesticides were absorbed by the wax on the outer coating of the orange peel, which could not be removed by washing with tap water.

Another study on oranges tested the effectiveness of sodium bicarbonate, acetic acid, sodium chloride, apple cider vinegar, and grape vinegar in removing pesticides. Ultimately, sodium bicarbonate (in combination with running tap water) was most effective at removing the pesticide residues tested. However, acidic solutions also removed pesticides. Ultimately, peelable fruits and vegetables may benefit from washing with a sodium bicarbonate solution before peeling.

Practical at-home strategies to reduce pesticide ingestion

It is possible to effectively remove pesticides from fruits and vegetables without adding additional toxins. Additionally, individuals may opt to combine these methods for the removal of multiple types of pesticides or stick with methods that are effective for specific produce.

Fruits and vegetables:

• Wash all fruits and vegetables in running tap water before consuming raw or cooking, even those with peels.
• For foods that will be enjoyed after cooking, boiling and blanching are simple ways to remove some pesticides.
• For foods that will be eaten raw, consider soaking produce in a baking soda solution or vinegar, followed by a tap water rinse.
• Rinse peelable fruits with water before peeling and consuming. For added measure, produce can be soaked in a baking soda solution first.
• For fruits or vegetables with edible skins, consider soaking in a baking soda solution for 15 minutes. Or peel the skins off before eating.
• Choose organic produce when possible to prevent exposure to synthetic chemicals.

Meat and fish:

• Because pesticides can bioaccumulate in fatty tissues, consider minimizing high-fat animal parts/products or larger fish species.

How to prep a baking soda solution:

1. Whisk together 1 liter (~4 ½ cups) of water with 10 grams (~2 teaspoons) of baking soda in a large mixing bowl.
2. Once the baking soda is dissolved, submerge the produce in the solution, soaking for 12-15 minutes.
3. After soaking, rinse produce thoroughly with running water.

How to prep a rice vinegar solution:

1. In a large container, whisk together 500 mL (~2 cups) of rice vinegar with 1.5 L (~6 and ¼ cups) of water. Don’t have rice vinegar? Combine 400 mL (1 and 2/3 cups) of white distilled vinegar with 1.6 L (~6 and ¾ cups) of water.
2. Once combined, submerge the produce in the solution. Leave soaking for 10 minutes.
3. After soaking, rinse the produce thoroughly with running water.

These solutions should be made fresh every time, vs. reused.  

A note on hot versus cold water rinsing: While hot (40 °C) and cold (20 °C) tap water are effective, hot water is better at removing some residues while cold water is more efficient at reducing others. A proactive step may be to rinse produce in both cool and warm water.

Final word

There are several ways individuals can remove pesticide residues from fruits and vegetables at home. The removal method will vary depending on the fruit or vegetable, the type of pesticide used, and the treatment time. While it may be challenging to completely avoid pesticides in the diet and environment, taking the time to wash and process foods will help minimize their ingestion.

As always, talk to a doctor, nutritionist, or dietician before making any diet or lifestyle changes for personal options based on individual circumstances.