Pesticide testing: What's the best way?

Are the new methods for pesticide testing as good as manufacturers claim?

February 1, 1995

15 Min Read
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In recent years, new relatively inexpensive analytical test kits have been developed for the rapid testing of pesticides in foods and water. Many manufacturers of these kits boast that users can get results faster and at less cost than ever before, and that the kits can detect pesticide levels as low as or lower than the conventional solvent extraction/gas chromatography based multi-residue methods.

Are these new methods as good as kit manufacturers claim? What are their best applications? What are their limitations, if any? Have the new kits made expensive instrumental tests obsolete? For that matter, do food companies really even have to worry much about performing routine pesticide testing?

While there are no simple answers to these questions, consideration of General Mills Inc.'s recent pesticide fiasco can give some useful insights into the need for pesticide testing and how to do it.

The General gets burned

This summer, General Mills learned that some 21 million bushels of oats were tainted with an unauthorized pesticide. As a result, GM destroyed approximately 50 million boxes of Cheerios and Lucky Charms and 15 million bushels of raw oats. The pesticide, chlorpyrifos-ethyl, is approved for use with some grains, but not oats.

Y. George Roggy, a Minnesota contractor hired by GM, reportedly intentionally sprayed the unauthorized pesticide on the oats during a 14-month storage period. Roggy even charged GM for the more expensive pesticide that should have been used. While Roggy was found guilty of 13 counts, including 11 counts of mail fraud, the unrecouped losses to GM were astonishing- reportedly as much as $140 million.

Considering only the dollars lost due to oats and cereals that had to be destroyed doesn't reveal just how devastating the whole episode really was to GM. A few months before the pesticide debacle, the company decided to try a bold new marketing strategy: to build value into its products by reducing price. To accomplish this, GM significantly cut its consumer promotion budget. Evaluating the effectiveness of its revolutionary new strategy is a problem for GM because it is practically impossible to factor in the negative impact on sales attributed to consumers' concern over buying tainted cereal. Making a major shift in marketing strategy and then not being able to evaluate results in a timely manner has put the company at a distinct disadvantage in the highly competitive cereal market.

Also of concern: How badly has the company's image been tarnished in the minds of consumers? How long will consumers remember? Because of the chlorpyrifos-ethyl contamination problem, GM has taken steps to improve its pesticide monitoring program. It has invested considerable money in purchasing state-of-the-art analytical instrumentation to upgrade the pesticide-testing capabilities of Medallion Labs, a subsidiary of GM. Beginning in early 1995, the lab will have sophisticated instrumentation to screen food samples for over 400 different pesticides. In addition, GM now requires ingredient suppliers to test for pesticides.

The GM pesticide ordeal clearly suggests that food companies should pay more attention to potential pesticide contamination problems, and it shows how expensive such problems can be.

Multi-residue screening

A Minnesota state regulatory lab reportedly detected the unauthorized pesticide in General Mills' cereal during a routine check using a gas chromatography, multi-residue screening test. If GM had used a similar multi-residue screening check, it could have averted the entire disaster.

How do you set up such a program?

"That gets involved," says Don Gibbons, president of Corbett, OR-based Columbia Laboratories Inc. "First you look at a specific crop and then consider all the possible pesticides that are normally used on that particular type of fruit, vegetable or grain. Next is to consider how familiar your field people are with the contract farmer."

Gibbons says he often finds that field people think they know exactly what's going on in the fields, but sometimes they don't. For example, a farmer may be having a problem with a crop, and when the field man isn't there the farmer will apply a pesticide he shouldn't be using to correct the problem. Or he may substitute a less expensive but unapproved pesticide for the one he should be using.

"The danger," says Gibbons, "is that a pesticide is used that's not registered for a specific crop." This is similar to what happened with General Mills' tainted oats.

After considering all possible pesticides that are normally used and determining that your field man has good control over what's being applied in the fields, the next thing to consider is what type of pesticide applications are occurring in adjacent fields. Say, for example, you've contracted carrots for your canning operation, and the farmer in the next field is spraying beans with a pesticide that's not registered for carrots. If significant drift occurs, you can end up with canned carrots tainted with an illegal pesticide. Also, according to Gibbons, there are an amazing number of instances where state highway departments have sprayed for any one of a number of pests and inadvertently contaminated farm crops.

Since the carrots you are canning may have a long shelf life, the fact that they're contaminated with an illegal pesticide might not be discovered for two to three years. By then it's usually too late to sue the people responsible, and it is unlikely that you'll be able to recover your losses. The best way to avoid contamination by drift is to screen crops and soil routinely for pesticides.

"When you consider the damage not only to your pocketbook but also to your reputation if consumers find an illegal pesticide in your food product, it gets really expensive," points out Gibbons.

Once you've considered all reasonable possibilities of what pesticides are being used and which ones are most likely to contaminate fields accidentally, then you must consult with a reputable laboratory to decide how many of those candidates will fit in a screen. Your goal is to determine the most judicious way to spend money on multi-residue screening - i.e., exactly which multi-residue test or combination of tests will be required to ensure a reasonable degree of safety.

Columbia Labs has several multi residue screening tests it can use. Each involves a slightly different extraction procedure, followed by either gas chromatography or HPLC using different detectors. For example, the lab's Basic Pesticide Profile (the Luke screening test) can detect approximately 58 compounds, and its Extended Pesticide Profile can detect another 48 pesticides. The lab has 11 screening tests that it can use to detect over 250 commonly used pesticides.

"It's exactly like buying insurance," says Gibbons, "but it gives you an additional advantage because if you've done this testing ahead of time and then something slips by you, the regulatory people are going to be far more tolerant with your good faith effort than if you blatantly disregard possible pesticide contamination in your quality assurance program."

The major advantage of the multi-residue screening tests is that they can accurately detect with great sensitivity several hundred possible pesticide contaminants. Of course, even with broad-spectrum multi residue tests there is no guarantee that all pesticide residues present in a food material will be detected; after all, there are approximately 11,000 different registered pesticides listed in the "Farm Chemicals Handbook." Still, you have a much better chance at detecting a possible contaminant than if you only used the less-expensive, quicker ELISA-type test kits which detect only specific classes of pesticides.

The downside of multi-residue testing is that it's expensive and time consuming. But, using GM's recent problem as an example, multi residue screening likely would have caught the problem early and saved the company millions of dollars.

Columbia Laboratories has an international reputation for its pesticide-testing capabilities. It has been certified by Japan's Ministry of Agriculture, Forestry and Fisheries, and its Ministry of Health and Welfare. The laboratory accreditation awarded to Columbia by the Ministry of Agriculture also includes the JAS (Japanese Agricultural Standards) program. Columbia is the first and only private testing laboratory in the world to receive the prestigious JAS laboratory accreditation.

"There is increased concern in almost all foreign markets about pesticides," says Gibbons. "Any U.S. company exporting foods should be aware of this." Besides product for export to Japan, Columbia Labs tests a variety of products for export to many Pacific Rim countries and Europe. Japan, Germany, Russia and Korea are especially interested in upgrading pesticide screening for food they purchase from the United States.

Rapid test kits fill a need

When properly applied, rapid test kits for pesticide analysis are an invaluable tool for food companies. For example, Newtown, PA-based Ohmicron has developed a panel of immunoassay kits for residues that are very difficult and costly to detect by traditional techniques. These include 1,4-D, benomyl, paraquat and captan. The company has several magnetic separation immunoassay kits available for analyzing herbicides, insecticides, fungicides and environmental contaminants in food. For most kits, detection limits are in the 10 to 50 ppb range and analysis time is less than 60 minutes.

Enzyme-linked immunosorbent assays (ELISAs) combine selective antibodies with sensitive enzyme reactions to produce analytical systems capable of detecting very low concentrations of chemicals. Ohmicron's technical concept is based on the use of novel magnetic particles as the solid support and means of separation in an ELISA system. Food companies are using Ohmicron pesticide test kits for HACCP analysis, import/export testing requirements, and crisis management.

If a company has a potential pesticide crisis and it has identified the pesticide contaminant, then the screening tests are extremely useful. For example, once General Mills had learned that its oat supply was potentially contaminated with chlorpyrifos-ethyl, it could have used an Ohmicron test kit to screen oats and cereal samples to decide which ones had to be destroyed.

In crisis-management situations, companies are often forced to test hundreds of samples and make decisions rapidly, and it could be impossible to keep up with analytical testing demands with traditional solvent extraction/gas chromatography methods. The test kits provide the benefits of reduced testing time, reduced solvent consumption (and disposal), and reduced cost per test.

One limitation of the ELISA based kits is what analytical chemists call specificity, or the ability of a test to measure only the analyte of interest and not similar or interfering compounds. The specificity of the ELISA tests is described in terms of its antibody cross-reactivity to other related compounds. For example, Ohmicron's Alachlor RaPID Assay(tm) kit measures not only alachlor but other chloroacetanilide analogues as well, including butachlor, metolachlor and propachlor. Each of these chemicals responds differently to kit reagents. The test, for instance, is approximately 1,000 times less sensitive for propachlor than for metolachlor.

What all this means is that it is difficult to get accurate quantitative results for specific pesticides. Nevertheless, the kits are an excellent screening tool. Frequently, companies use the ELISA screening test to find potentially contaminated samples and then test the "hot" samples with traditional solvent extraction gas chromatography tests for confirmation. Compared to ELISA tests, gas chromatography-based tests offer greater specificity.

Another limitation of ELISA tests is that there may not be a test kit developed for your particular contaminant. There is, for example, no kit for testing alar, the pesticide used on apples that caused such an uproar a few years ago.

Ohmicron manufactures and markets the only captan kit available in the world. The kit is used extensively by the Florida strawberry industry to ensure that strawberries for import and export contain acceptably low levels of captan.

In addition to food companies, users of Ohmicron RaPID Assay pesticide test kits include the FDA and various branches of the USDA, including the Agricultural Research Service, the Agricultural Marketing Service, and the Department of Interior (the United States Geological Service). Also, the Bureau of Alcohol, Tobacco and Firearms uses the kits for screening wine samples.

The company has developed dozens of extraction procedures for fruits, vegetables, fish, meats, etc., for alachlor, aldicarb, atrazine, benomyl/carbendazim, captan, carbaryl, carbofuran, chlorothalonil, chlorpyrifos,2,4D, cyanazine, metolachlor, paraquat, pentachlorophenol, PCB, and procymidone.

Another company that markets a pesticide test kit is Lansing, MI-based Neogen. Its AgricScreen Ticket is an enzyme-based test method that rapidly detects the presence of approximately 50 different carbamate, thiophosphate and organophosphate pesticides. The test is less specific than ELISA/immunoassay tests and is not quantitative. It has been used for measuring pesticide levels in air, water, soil, crops, spills, solvents, surfaces and produce.

"The Ticket is a general screening test for choline esterase inhibitors," explains Greg Weihl, a Neogen product manager. "The test is based on the reaction between the pesticide and an enzyme impregnated on a filter disc... It is very sensitive to choline esterase inhibitors like carbamates."

Since other chemicals besides the 50 pesticides will inhibit choline esterase, testing may provide false positives. If you're unfamiliar with the samples you are testing, there is a chance of getting erroneous results.

"If a farm laborer is working in one field and the farmer in the next field is spraying a pesticide, the laborer can clip one of the discs to his shirt pocket and then test the disc for the presence of pesticides at the end of the day," says Weihl. "That's one application."

According to Weihl, if you're concerned a neighbor is overspraying, the discs can be stapled to fence posts and trees on your property. Then when the neighboring farmer finishes spraying, the discs can be tested to provide an idea of how much drift has occurred. Water from drainage ditches, soils and vegetables also can be monitored.

Wanting to ensure a safe potable water supply during warfare, the U.S. Army developed the application to test for pesticides in water. The kit was designed as a field test for infantry personnel.

Because the test is nonspecific, quantitation and even determination of sensitivity is a problem. Weihl estimates that the test can detect pesticide contamination in the range of 6 ppm to low ppb levels, depending on the sample matrix, extraction efficiencies and the type of pesticides present. Detection can be enhanced by using longer exposure times, longer development times and various concentration techniques. If positive tests are found, the samples should be retested by traditional methods for confirmation.

A food company that supplies McDonald's with its side salads and garden salads checks the lettuce and vegetables it uses for pesticides with Neogen's test kit. Another user monitors malathion in corn. By spiking corn with known levels of malathion before testing, the user has been able to estimate a detection level for malathion in corn for the test.

Another application is spill identification - that is, to test soil samples in the area of a pesticide spill.

Growing applications for AgricScreen Ticket are in areas where it was never practical to do a cursory check. In the past, before development of the rapid test procedures, it would not have been possible for a snack food producer to check each shipment or even one in 10 shipments of corn or wheat that it used because testing was cost-prohibitive and required too much time to complete. With kits from Neogen and Ohmicron, it is now possible to screen more ingredients for possible pesticide contamination.

Today two approaches are available for pesticide analysis: traditional multi-residue screening using solvent extraction and gas or liquid chromatography with various types of detectors; or the rapid immunoassay/enzyme test kits. The traditional approach is more expensive and time consuming, but can detect a broader range of possible contaminants. The test-kit approach is quicker and less expensive, but it offers less specificity, is subject to more interferences, and is only semi-quantitative.

While both approaches have their place, you should realize when to use traditional methods and when to use the kits, and you should know the advantages and disadvantages of both. The analytical strategy of most food companies is to use the kits for screening many samples and then use traditional testing for confirmation of the few samples that test positive by the screening test.

Will consumers eat higher prices for pesicide reduction?

In 1992, the University of Kentucky conducted a national survey of consumers' major food safety concerns. The phone survey interviewed 3,228 primary food shoppers and was followed up by a mail questionnaire.

Attitudes regarding pesticides varied considerably. Some 30% of respondents believed that current levels of pesticides were safe, while 31% thought the government should ban all pesticides. Sixty-two percent said they occasionally refused to buy certain fresh fruit and vegetables because of information provided in the media about harmful pesticide residues. An overwhelming number (90%) wanted all produce to be clearly labeled with pesticide-use information. (Presently, hardly any produce is labeled with pesticide information.)

Respondents ranked the importance of factors they consider when deciding which fresh fruit and vegetables to purchase. Freshness/quality was ranked most frequently as being very important (by 27.2% of respondents). Other factors ranking high in the "very important" category were nutritional value, product appearance and certified PRF (pesticide residue-free).

Consumers surveyed said they would pay more for foods to reduce their risk from pesticide residues. For example, respondents said they would pay an average of between 15 and 69 cents above the normal 50-cent price for a grapefruit if that grapefruit was certified PRF. Five percent said they would pay 100% more for a PRF grapefruit than one containing pesticide residues.

Pesticide contamination of food is an important issue for consumers and will likely remain so, thanks to the activities of consumer groups. After the recent General Mills ordeal with pesticide-tainted oats and cereals, the Chevy Chase, MD-based Rachael Carson Council Inc. made the following statement on the incident:

"What are the implications of this episode? Even a non-expert may perceive that the situation is more complex and more troubling than the present method of pesticide evaluation would suggest. Are dietitians to be forced to consider food for not only its nutritional value, palatability and freshness, but also its level of pesticide contamination, in order to keep vulnerable individuals from being in the minority that is poisoned by too many similar residues?"

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