I attended a really interesting continuing education session about pesticide residue, titled, “Organic and non-organic foods and pesticide residue: Important information for nutritionists and dietitians”, presented by Amir Golmohamadi, Assistant Professor at the Department of Nutrition at West Chester University of Pennsylvania. I’m sharing some of his slides here.

Each year, a “Dirty Dozen” list of fruits and vegetables is published by the Environmental Working Group. It’s important to understand their methodology and what a “part per million” signifies.

What is a PPM and Inherent Toxicity?

A part per million (PPM) is equivalent to 1 milligram of a chemical substance per liter of water. This would also look like one second in eleven and a half days. Or one single grain of sugar among 273 sugar cubes.

According to Dr. Golmomahadi, the EPA uses risk assessment to characterize the nature and magnitude of health risks pesticides may pose to humans. This includes assessment of how much of a chemical is present in an environmental medium (e.g., soil, water, food), and how much contact (exposure) a person or ecological receptor has with the environmental medium. This helps determine the inherent toxicity (hazard) of the chemical.

Dirty Dozen Tip: You would have to consume 1100 pounds of strawberries per day to potentially pose a risk from pesticide residue! Click To Tweet

Some Background on the History of Farming

In his presentation, Dr Golmohamadi shared some of the history of farming and the Green Revolution. He described agriculture of both past (primitive) and present (modern and industrialized) as an “artificial situation” – man manipulating soil, moving plants, cross breeding and selecting seeds, fertilizing soil, irrigating, etc., in all cases, to increase the yield and quality of food. The output increased significantly with virtually the same inputs from the 1940s to 2016.

In 1990, the Organic Food Production Act was passed in the US. This defined standard organic farming practices and acceptable organic production inputs. This led to the agricultural certification – USDA Organic. This farming method means that the food was produced without genetically modified organisms (GMOs), without synthetic pesticides, and without irradiation. There’s been significant growth in the sale of organics foods over the past 16 years. Interestingly, consumer demand for organic food seems to outweigh the availability of land to produce organic crops

Pesticide and Herbicide Use

Many people who are concerned about GMOs (genetically modified organisms), are also concerned about glyphosate.  Some GM plants involve the use of glyphosate (“Round-up Ready” plants like corn, soybean, cotton and alfalfa), but others do not. Yet public perception about the link between this herbicide and GMOs is strong. Glyphosate is an herbicide that controls broadleaf grasses and weeds. Farmers use Round-up Ready seeds for crops to help them control weeds. Bt-corn is engineered to naturally ward off the pesky corn borer. All of these technologies are tools in a toolbox that help make growing more food safe and productive. While these herbicide resistant crops initially decreased the use of herbicide application, there’s some question whether this affect lasts. Of course as more acreage is grown, more herbicide may be used overall, but in general, these advances have allowed farmers to plant more crops per acre, using less resources, and less pesticide.

Farmers take care to protect themselves and their workers when these chemicals are applied. Pesticides and insecticides need to be handled carefully. There are strict rules to adhere to in terms of amounts used.

As any toxicologist will tell you, “the dose makes the poison”, and this is important to understand when we are discussing pesticide residues on food.

Hazard VS Risk

Hazard is the property of a chemical having the potential to cause adverse effects with exposure. Risk however, is the probability of the adverse effect occurring. So for instance, if you do not work on a farm, your risk is much lower than the worker who applies the pesticide applications each year (yet also takes care to do so safely).

What About Our Food?

Consumer lists, such as the “Dirty Dozen” use flawed methodology to determine residue, and also don’t match the residue to human tolerance levels. Luckily there are science-based risk assessments. In the above slide, the red zone is the absolutely highest tolerable level of a pesticide where no effects have been identified (No Observable Adverse Effect Level). According to Dr. Golmomahadi, crops found to have this level are removed from market. The orange and yellow areas show acceptable daily intakes (ADI – a toxicological safety limit that specifies the amount of a substance can be ingested every day over an entire lifetime without harm – this is usually hundreds times less than the NOAEL). In this case, crops may be assessed on a case by case basis, and prevented from getting to market if necessary.  Finally, the green area is the Maximum Residue Levels (MRL).

Dr. Golmomahadi gave the example below of pesticide residue in strawberries (since they often top the “Dirty Dozen” list).

Facts not Fear

The takeaway here is that some pesticide residue does not equal “toxicity”. Testing is done to determine upper safety levels and the approved tolerance levels (or maximum residue levels, MRL) are hundreds of times lower that the levels determined not to cause issues. Very specific testing is done to determine the upper levels where there is no observable adverse effect (NOAEL), and then the safety levels are set way below them. Ninety nine percent (99%) of the products have lower level of pesticide than the Tolerance Level (TL).

Dr. Golmomahadi stressed that there is no pesticide risk to worry about from food. There is other types of risk in terms of pesticide exposure through direct exposure however (for instance, not following protocol when applying the pesticides, heavy pesticide exposure through the air). He also points out that pesticide residues are found in both organic and non-organic foods. He also feels that over-dependence on pesticides is not sustainable, and farmers and scientists should explore all options. He reassures –

“The US food system is one of the safest in the world. EPA and USDA routinely check the pesticide residue in all foods.”

Should you worry about pesticide residue from your food? No. It’s always good practice to wash your fruits and vegetables (dirt, manure, or other residues can also be present). You are at no more risk eating non-organic fruits and vegetables than you are eating organic fruits and vegetables.



reviewed 3/2023