Pesticide residues are an important and often controversial issue in the food industry. In the U.S., pesticides are defined as a substance or mixture that is intended to prevent, destroy, repel, or mitigate any pest. Pesticides are used throughout conventional and organic agriculture and play a critical role in controlling public health, economic, and nuisance pests in many settings, spanning from pre-harvest use in crops to packinghouses, transportation, retail, and restaurants. Pesticides also range widely in their toxicity, requiring a high degree of regulatory structure for approval in the marketplace. This article covers how residue levels are regulated in the U.S., who regulates them, the global scientific framework for trade, and how residues fit into food safety regimes.

Pesticide applications can leave trace chemical levels, called residues, in raw or processed foods. Typically, residue levels range from non-detectable to parts per million. Since we intentionally apply pesticides to our food supply, a system has been established over decades to determine an acceptable level of residue that does not pose an unreasonable risk to consumers. This acceptable level depends on toxicity, type of food consumed, application method, and several other factors. In some cases, certain pesticides are deemed to be unsuitable for use on human food and animal feed because they pose an unacceptable risk to consumers, farmworkers, animals, or the environment.

To determine acceptable risk levels, we rely on a risk assessment framework to make science-based decisions. From this process, we ultimately develop a maximum residue level (MRL), also called a tolerance in the U.S. According to the Food and Agricultural Organization of the United Nations (FAO), an MRL is the maximum concentration of a pesticide residue to be legally permitted in food commodities and animal feeds. The MRL is not a safety limit; rather, it is a regulatory tool as outlined in the following section.

Regulating Pesticide Residues

In the U.S., several federal agencies and authorized state or tribal agencies have a role in regulating pesticide residues. Initially, pesticides are registered by the Office of Pesticide Programs in the Environmental Protection Agency (EPA) through the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). As part of the registration process, EPA requests data from the registrant covering a wide range of issues from environmental fate to formulation of the product. The Federal Food, Drug, and Cosmetic Act (FFDCA) authorizes EPA to set a tolerance on how much pesticide will remain on food or feed. This information is often based on field trials that test pre-harvest intervals, application rates, varying environmental factors, and other relevant parameters. EPA then evaluates several consumer, environmental, and occupational risks, including the use of dietary consumption models to estimate exposure. If food tolerances are developed for a pesticide use on a specific food, then EPA will publish notices for comment in the Federal Register. EPA can also make the determination that a pesticide or use is exempt from the requirement for a tolerance.

While EPA develops the tolerance, the U.S. Food and Drug Administration (FDA) is responsible for enforcing the tolerances for interstate commerce, as well as the import for all fruits and vegetables, most seafood, dairy, most processed foods, and most egg products. Through the FFDCA, FDA can deem a food or feed to be adulterated if a pesticide residue is found at greater levels than the tolerance, or if pesticide residue is detected for which there is no established tolerance or tolerance exemption. These products are subject to seizure by the government. FDA applies these rules equally to domestically produced and imported food and feed. Therefore, it is important that countries that wish to export to the U.S. understand the country's regulations and framework. Similarly, it is paramount that U.S.-based companies understand the tolerances, or MRLs, that exist in other countries when exporting raw and processed products.

Monitoring programs are implemented to obtain data to determine if pesticides residues are in compliance with MRLs. Monitoring results help determine if modifications to pesticide registrations are needed, possibly requiring additional research. The data also serves to plan future monitoring activities for both domestic and imported food. Ideally, the selection of commodities, frequency and number of samples should be based on risk and informed by prior studies. FDA has been publishing residue monitoring reports since 1987. In 2020, FDA found that 96.8 percent of domestic and 88.4 percent of imported foods were compliant with federal standards. Furthermore, they detected no pesticide residues in 40.8 percent and 48.4 percent of domestic and imported samples, respectively.

The U.S. Department of Agriculture (USDA) is responsible for monitoring residue levels in meat, poultry, catfish, and certain egg products. In addition, it oversees the Pesticide Data Program (PDP). The PDP is published annually and assesses a wide range of products, including fruits and vegetables, fish, grains, meat, dairy, and infant formula.¹ In the 2020 PDP report, over 99 percent of tested samples had residues below tolerances (MRLs) established by the EPA, and 30 percent had no detectable pesticide residue.

Developing a Maximum Residue Level or Tolerance

When EPA sets a tolerance (or MRL), it must determine that the residue level is "safe," which is defined as "a reasonable certainty that no harm will result from aggregate exposure to the pesticide residue." The setting of an MRL is a relatively long process that includes defining the residue, conducting supervised crop field trials, and performing consumer risk assessment and safety testing. The objective of the consumer risk assessment is to determine whether the pesticide residue in a raw agricultural product poses an unacceptable risk to consumers as a result of authorized application under local conditions of use (that is, as recommended on the pesticide label and adhering to pre-harvest intervals).

To assess whether the expected residue level does not lead to unacceptable consumer risk, residue data are combined with dietary information to estimate the potential residue intake by consumers, which is compared to toxicological reference values. It is important to recall that an MRL is not a redline that signifies whether a health effect is likely when it is exceeded. Rather, a residue detection above an MRL is a violation of the authorized limit in the country where the crop was grown and the pesticide was registered.

The risk-based process to determine an MRL can be summarized as follows:

1. The residue is defined. Toxicological studies are conducted to determine the amount of exposure to the active ingredient before having an adverse health effect. This amount is called the "no observable adverse effect level," or NOAEL. The NOAEL is then multiplied by a safety margin, often set at 100.
2. Before an MRL can be granted for a commodity, the impact of residues from the use of the pesticide on that particular crop is evaluated from the standpoint of consumer safety relative to dietary exposure. MRLs can be granted only if the resulting total dietary exposures to consumers are below the regulatory human reference values. These toxicological values include the acute reference dose (ARfD), which is the estimated amount of a substance in food or drinking water that can be ingested in a 24-hour period (or less) without appreciable health risk to the consumer, as well as the acceptable daily intake (ADI), which is the estimated amount of a substance in food or drinking water that can be ingested over a lifetime without appreciable health risks to the consumer.
3. The dietary intake of the pesticide is estimated by combining national or regional food consumption statistics with the estimated residues in food and/or drinking water.
4. The registrant carries out a number of crop field trials to determine the magnitude of pesticide residues in or on raw agricultural commodities at the time of harvest. MRLs reflect critical Good Agricultural Practices (GAPs), wherein the pesticide is applied to the crop for the maximum number of allowed applications, at the maximum allowed application rate and with the minimum pre-harvest interval according to the directions on the product label.
5. Finally, the MRL is set based on statistical analysis of the range of pesticide residues found on the crop from the field trials, after all applicable harvest and processing activities.

Beyond the steps above, registrants of conventional pesticides must provide detailed information prior to approval of the product in the marketplace. This includes information on fate and transport of the active ingredient and degradation byproducts, animal and plant metabolism studies, physical and chemical properties, and analytical methods of detection. Some pesticide types, such as biopesticides, are exempt from many of these data requirements.

Pesticide Residues and Global Trade

As mentioned above, FDA monitors imported foods for pesticide residues and enforces the MRL. At times, imported foods violate the U.S. tolerance limits due to exceeding allowable levels or detection of a residue where no U.S. tolerance has been established. In an ideal scenario, all countries would determine a single set of MRLs for crop type and active ingredient combinations. However, there are numerous reasons why this has proven to be extremely difficult, resulting in different MRLs between countries. This reality leads to trade barriers and conflicts. A key factor contributing to non-harmonized MRLs is that countries have different climates and agroecosystems. Thus, they may have very different pests, pest pressures, crops, rainfall patterns, and agricultural practices, which can result in the establishment of a pesticide application regimen with high variations between countries, and consequently, different MRLs. What is common among MRLs, however, is that they all meet the safe toxicological requirements for the population of the country.

To facilitate the establishment and harmonization of MRLs between countries, the Codex Alimentarius Commission, an international standard setting body jointly overseen by FAO and the World Health Organization (WHO), has established thousands of voluntary MRLs for global use. Codex MRLs are based on rigorous, science-based risk assessment conducted by an international committee of assessors, called the Joint Meeting on Pesticide Residues. Governments may choose to adopt these Codex MRLs or establish their own, using scientific risk assessments. USDA's Foreign Agricultural Service plays a key role in technical consultation, capacity building, and harmonization, particularly for developing countries.

Other Pesticide Residue Considerations in Food Safety

So, how do residues fit into a food safety plan or within corporate food safety culture? Under the Food Safety Modernization Act (FSMA), many businesses must develop a food safety plan when selling human food or animal feed. Within that plan, they conduct a hazard analysis to determine the potential for microbial, physical, radiological, or chemical risks in their products. The hazard analysis process informs what preventive controls may be needed to ensure safe food, and can bolster prerequisite programs, such as GAPs and Sanitary Standard Operating Procedures (SSOPs).

Most acute pesticide poisonings from food consumption involve an adulterated or illegal application, malicious act, or misuse of a pesticide container that was reused or mistaken for food or beverage. Even so, pesticide residues should be considered when evaluating the chemical hazards potentially present in a food product, particularly if they are a known or foreseeable risk. This may be more relevant for some ready-to-eat (RTE) products without a downstream processing step or certain raw ingredients imported from countries with a history of MRL violations. Supply chain control programs can be helpful in this process.

A secondary consideration is to assess what sanitizers or disinfectants are being used in a supply chain. This is particularly relevant for any food contact surfaces, such as conveyor belts and tabletops. While these areas must be properly cleaned and sanitized, it is critical to follow label instructions to ensure that efficacious levels of residue are present to reduce microbial loads to acceptable levels, and also to limit residue uptake into finished products. For products certified as organic, it is important that only allowed sanitizers are used on food contact surfaces. Finally, food safety personnel should also assess the type and locations of pest control products, such as fly strips and rodenticides, throughout the supply chain to prevent cross-contamination and potential residues in products.

To summarize, pesticide residues are highly regulated through a multi-agency approach using a risk-based framework. The lack of harmonization between countries in setting MRLs presents significant barriers to trade. While residues are typically found below MRLs in most domestic and imported foods in the U.S., it is important to assess their potential hazard to each specific scenario. Fortunately, many tools and databases exist to evaluate residue levels, embedded within a robust scientific structure to deliver safe and high-quality foods.

References

1. U.S. Department of Agriculture, Agricultural Marketing Service. "Pesticide Data Program (PDP)." https://www.ams.usda.gov/datasets/pdp.

Dave Stone, Ph.D., is a Professor of Food Science and Technology at Oregon State University in Corvallis, Oregon.

Jason Sandahl, Ph.D., is the Founder of consulting business Ag Aligned Global.