Pesticide residues in food: myths and reality

By Juan Eduardo Ortúzar

May 9, 2018

Due to my relationship with the world of food, I constantly hear inaccurate comments about GMOs and agricultural pesticides.  While these conversations indicate that people are increasingly concerned about what they eat, they also reveal a disturbing level of misinformation.

In my opinion, this is due primarily to activists and institutions who achieve their political and ideological ends largely by disseminating partial, biased, erroneous or false information. The scientific community also has been ineffective in transmitting to society, in simple terms, the enormous advances that we live with every day.

In a time when scientific evidence is easily conquered by feelings, political correctness and ideologies, it is important to generate spaces where ideas can be discussed, and a fluid diffusion of facts and truths occurs. To that end, I’m seeking here to explain the reality of pesticide residues in foods and the highly conservative assessment process used to ensure that they have no harmful effects on human health.

As we explore step by step the process of establishing legally allowable pesticide residues in food, it will become clear that there is an exhaustive scientific method that strongly protects human health and delivers clear production rules to farmers.

MRLs in food

During the production of whole foods, such as fruits, vegetables, milk, eggs and meat, chemical products are used to prevent or reduce the presence of insects, fungi, microorganisms or pests that can destroy crops or make livestock sick. Due to the regular use of these compounds, it is possible that traces — very small amounts — can persist in food. We call these trace amounts “residues.”

It’s essential to use these chemicals prudently to ensure that either no residues occur, or that they are under legal limits. We call this limit the Maximum Residue Limit (MRL).

There is great debate today on how and when MRLs should be established, and great confusion in the public sphere about what an MRL really is, how limits are set and the implications of MRLs in terms of human health and food trade.

In agricultural production, MRLs are established for pesticides and veterinary drugs. To simplify the discussion and explanation, we will use pesticide residues as an example, though the same principles apply for residues of veterinary drugs.

What is an MRL?

The Codex Alimentarius defines an MRL as: “A maximum residue limit (MRL) is the highest level of a pesticide residue that is legally tolerated in or on food or feed when pesticides are applied correctly in accordance with Good Agricultural Practice (GAP).”

Although the definition is clear in indicating that the MRL is strictly linked to good agricultural practices (GAP), the method of establishing an MRL also considers strict human health elements. This makes it possible to generalize that although MRLs are legal limits that reflect the correct use of pesticides from the GAP perspective, these in turn constitute a limit that exceeds the safety criteria for human health by several orders of magnitude. This phrase will be clearer when we explain the elements of an MRL.

How is an MRL established?

To fully understand what an MRL is, it is best to review in detail how they are established. The process described below is what developed nations generally use. Depending on the legislation, the procedures may be different, but they all have the following common elements:

  1. Dossier of information: A collection of documents that contain all the necessary information to support the establishment of the MRL, such as toxicological data, waste, analytical methods and metabolism in plants and food.
  2. Toxicological evaluation: The chemical composition of the molecule is studied to ensure that it is not carcinogenic, teratogenic or mutagenic, among others.
  3. Risk assessment: It is not enough to have a proposed MRL (MRLp). It is necessary to evaluate if this amount of residue present in the food could have an effect on human health. For this, an assessment of acute and chronic risk is made, studying the effects of exposure to the pesticide in the short and long term. In order to simplify the explanation of this stage, we will use an example of chronic risk assessment.

There are two elements that must be considered in order to estimate the risk to human health of the MRLp: 1) amount of food consumed in the population and 2) Concentration of the pesticide in the food (in this case, the proposed MRL).

The internationally accepted methodology for relating these two data points is through the Admissible Daily Intake (ADI). The ADI is defined by the Codex Alimentarius as “an estimate of the amount of a food additive in food or beverages expressed on a body weight (bw) basis that can be ingested daily over a lifetime without appreciable health risk to the consumer”1.  Therefore, the calculation of the amount of residues to which people are exposed (product of the proposed MRL) must be less than the ADI.  

Figure 1: Conceptual map of the risk assessment of a hypothetical pesticide in apples whose MRLp is 1mg/kg and its ADI is 0.01 mg/kg. I used the consumption data for Chile, since I am from there.

It is important to highlight that this risk assessment contains highly conservative assumptions, which provide several layers of security in terms of ensuring human health. For example, the MRLp are usually  much higher than the residues detected in the field trials. Additionally, the risk assessment is carried out with the assumption that all the crops that you eat for your whole life have this high level, which in reality very seldom happens. Finally, it is essential to mention that a much more complex and restrictive evaluation is still carried out for acute risks.

What happens if the MRL is exceeded?

Let’s remember that the MRLs are legal limits, which are set by each country and reflect an attachment to GAP. In addition, these do not represent measures of protection of human health; however, they indirectly provide assurance that the food is safe. Figure 2 perfectly illustrates this using extreme case scenarios. Having gone through the process of establishing MRLs, we realize that behind it there is an exhaustive scientific procedure that protects human health with a wide range of safety.

Figure 2. Explanation of how varying concentrations of pesticide residues can be safe even if several times above the MRL.

Takeaways

By explaining the process of establishing an MRL, I hope to demystify how agriculture is actively developing in harmony with the health of the human beings. Significant efforts from scientists, industry and regulators are put together to provide healthy foods for everyone. It is very important that the scientific community engage more actively with the general public in order to effectively transmit the contents and advances that science generates every day for us.

Juan Ortúzar is a biologist with an MSc in food sciences who has been working in the Chilean Food Safety Agency since 2012. He has collaborated in the development of several food safety projects, and is currently working in trade facilitation studies and risk assessment projects, the latter with the objective of establishing a strong scientific organizational and professional structure to provide evidence-based information to the Chilean food safety control system. He is interested in communicating food safety related concepts to the public to advance the dissemination of science and create a food safety culture.

References

  1. GUIDELINES FOR THE SIMPLE EVALUATION OF DIETARY EXPOSURE TO FOOD ADDITIVES, CAC/GL 3-1989. Revision 2014