Fruit and vegetable farmers are doing an “impressive” job of complying with the laws and regulations related to pesticide use in production, according to the USDA’s annual Pesticide Data Program (PDP) report. Based on data from 2016, the report found that more than 99% of samples had pesticide residues that were “well below” the EPA’s established tolerances, and more than 23% had no detectable residues. Less than half-a-percent of samples (0.46%) had residues that exceeded the EPA established tolerance.
To compile the PDP report, surveys were conducted in 2016 on several foods, including eggs, milk, and fresh and processed fruit and vegetables. The report contains data from more than 10,000 samples collected throughout the United States.
A release from the Alliance for Food and Farming states that the U.S. food supply is one of the safest in the world, yet: “Activists groups often manipulate the findings from the USDA PDP report taking the very positive results and somehow turning them into something negative. This tactic has been used routinely for 20-plus years to create a so-called ‘dirty dozen’ list, which has been repeatedly discredited by scientists.”
Robust, reproducible quantitation of pesticide residues in food is the most important step in ensuring food safety, and hence, forms one of the most important responsibilities of every food safety laboratories. The analytical process involves characterization and identification followed by quantitation of pesticides across different food matrices. Considering the growing list of pesticides and their adverse effects even for very low concentrations, quantitation with confidence for every sample can pose some significant challenges to the analytical scientist.
Typical practices of using pesticides to control pests and improve yields can often pose a serious risk to human health if and when used inappropriately. Improper use of pesticides in breach of approved procedures, or those that are applied to crops for which their use has not been authorized, unacceptable amounts of these potentially dangerous compounds can find their way onto the plates of consumers.
In order to ensure food is safe for consumption, laboratories require robust, reliable and cost-effective workflows, incorporating highly effective sample preparation steps, separation methods and detection techniques. Owing to its selectivity, specificity, sensitivity, robustness and universal approach, liquid chromatography coupled to triple quadrupole mass spectrometers (LC-MS/MS) are widely used for quantitation of pesticides in food.
Food standards are growing increasingly stringent, so leading laboratories must ensure they consistently meet the requirements of regulators. Thankfully, the latest comprehensive pesticide workflow solutions are helping laboratories deliver the very highest quality of pesticide quantitation, on time and on budget.
Optimizing Sample Preparation
Regardless of the food product that is being tested, pesticide residue workflows typically start with sample preparation, following homogenization and residue extraction steps. This stage is one of the most important parts of the workflow, however, very often they are not highlighted.
The heterogeneity of the sample matrix, as well as the wide variety of pesticide compounds that must be extracted, can significantly add to the complexity of this task. For example, pesticide residues can be lost during sample grinding, compromising the accuracy of quantitative analysis. Loss of critical pesticides can also occur through hydrolysis by water or enzymatic degradation as enzymes are released from cells, or by the formation of insoluble complexes due to interaction of the analyte with matrix components. Each of these factors can impact the quantitation of pesticide residues in food.
Homogenization is followed by solvent extraction and cleanup. Extraction could traditionally be a time-consuming process, often requiring relatively large amounts of sample, and involving use of multiple solvents and work-up steps. In addition, results from this step can vary based on matrix type and pesticides that are being monitored. Time-consuming sample cleanup steps, based on separation techniques such as gel permeation chromatography, could also be necessary, thereby adding another layer of complexity.
The widespread adoption of sample preparation strategies based on QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) methods has significantly simplified the process of residue extraction for a wide range of food types, especially for high-moisture content samples. These generic extraction approaches, coupled with “quick and easy” cleanup techniques such as dispersive solid phase extraction, are able to comprehensively extract residues with a range of different chemical properties, resulting in more consistent and reliable quantitation.
The universal and easy-to-implement nature of QuEChERS methods has also allowed laboratories to reduce the complexity of their workflows. Their simplicity is such that many suppliers are now offering all-in-one kits containing all of the necessary pre-weighted reagents and supplies, which laboratories can use straight from the box. And as they require very little sample material, solvent or equipment, and eliminate the need for time-intensive homogenization steps, they are also helping to reduce laboratory waste and cut operational costs.
The Need for LC-MS/MS Technology
Once analytes are extracted from the matrix, food safety laboratories require reliable, sensitive and precise separation, detection and quantitation technologies to determine their concentration.
As indicated above, LC-MS/MS technology with triple quadrupole mass spectrometers are often the go-to choice for quantitation applications. The high selectivity and sensitivity of these instruments allow analysts to confidently identify pesticides against target lists and accurately quantify even trace levels. Figure 1 shows the distinct separation obtained for a leek sample spiked with more than 250 pesticides at a concentration of 100 µg/kg. The mass range, robustness, specificity, selectivity of the triple quadrupole instrument ensures the ability to handle a wide variety of sample types and deliver reliable results in a cost-effective manner.
To ensure the food on our plates does not contain potentially harmful levels of pesticides, laboratories require robust workflows for their analysis and targeted quantitation. Improvements in the sample preparation methods that are used to extract pesticide residues from food samples, as well as in the sensitivity, accuracy, robustness and reliability of the triple quadrupole instruments used for analyte detection, are helping food safety laboratories confidently quantify these compounds even in trace amounts.
This article is based on research by Katerina Bousova, Michal Godula, Claudia Martins, Charles Yang, Ed Georg, Neloni Wijeratne & Richard J. Fussell, Thermo Fisher Scientific, Dreieich, Germany, Thermo Fisher Scientific, California, USA, Thermo Fisher Scientific, Hemel Hempstead, UK.
Every year the Environmental Working Group (EWG) releases its “Dirty Dozen”, a list of 12 produce items that contain the highest loads of pesticide residues. This year the organization analyzed tests conducted by the USDA, finding that nearly 70% of samples of 48 types of produce were contaminated with one or more pesticide residues, which remained even after the produce were washed (and peeled, in some instances). 178 pesticides and pesticide breakdown products were found on the samples that the USDA researchers analyzed.
“New federal data shows that conventionally grown spinach has more pesticide residues by weight than all other produce tested, with three-fourths of samples tested contaminated with a neurotoxic bug killer that is banned from use on food crops in Europe.” – EWG
For the following items that made this year’s list, EWG recommends always buying organic. Each food tested positive for several different pesticide residues, along with having higher concentrations of pesticides compared to other produce.
Sweet bell peppers
EWG also released a Clean 15 list, produce that was found to have “relatively few” pesticides and a low concentration of residue.
However, there are groups that dispute EWG’s list, because the ranking of produce has been found to have a negative effect on the consumption of produce, whether conventional or organic, especially among low-income consumers. “EWG’s list has been discredited by scientists, it is not based upon risk and has now been shown to potentially discourage consumption of healthy and safe organic and conventional fruits and vegetables,” said Teresa Thorne, Executive Director of the Alliance for Food and Farming (AFF) in a press release. She referred to analysis conducted by a toxicologist with the University of California’s Personal Chemical Exposure Program, which found that a child could eat excessive amounts of produce daily without any negative consequences from the pesticide residues. “For strawberries, a child could eat 181 servings or 1,448 strawberries in a day and still not have any effects from pesticide residues,” Thorne said. AFF also lists some of the regulations regarding pesticide use [http://safefruitsandveggies.com/regulations/organic] on its website.
After publishing data from its 2014 Pesticide Data Program (PDP) earlier this week, the USDA has stated that it is not concerned with the level of pesticide chemical residues in the U.S. food supply. More than 99% of products sampled through the USDA’s Pesticide Data Program had residues below EPA tolerances (residues exceeding the tolerance were detected in 0.36% of samples).
“The PDP plays an essential role in ensuring the safety of the U.S. food supply. Under the Federal Food, Drug, and Cosmetic Act, the FDA has authority to take enforcement action when a food bears or contains unlawful pesticide chemical residues,” said Susan Mayne, Ph.D., director of FDA’s Center for Food Safety and Applied Nutrition in a press release. “By providing an accurate assessment of pesticide levels in the most commonly consumed commodities in America, the PDP generally confirms the U.S. food supply is safe with respect to pesticide chemical residues.”
Among the foods tested were fresh and processed fruits and vegetables, oats, rice, and salmon. The findings from the PDP annual summary can be accessed via the USDA’s website.
The idea of controlling pests dates as far back as 2500 B.C. From using soaps to copper sulfate to DDT, industry has evolved in how it controls pests in agricultural crops. In a video shot at Food Safety Tech’s 2015 Food Labs conference earlier this year, Angela Carlson of SGS discusses the regulations involving maximum residue limits (MRLs) as well as how MRLs are set at a global level.
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