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Testing for Pesticide Residues: Too Much of a Good Thing?Testing for Pesticide Residues: Too Much of a Good Thing?

June 1, 2000

14 Min Read
Testing for Pesticide Residues:  Too Much of a Good Thing?

Testing for Pesticide Residues:
Too Much of a Good Thing?
June 2000 -- QA/QC

By: Bruce M. Floyd
Contributing Editor

  The United States enjoys one of the cheapest, most abundant food supplies in the world. This is not an accident of nature. Rather, it's due to an agricultural industry that has worked very hard to improve crop yields and farming efficiency. The U.S. farming industry is so efficient that by some estimates, one farmer can feed 79 people, 26 of which live in foreign countries. This efficiency also means we can afford to have an organic-farming sector without the majority of the population going hungry or spending a larger portion of their disposable income on food.

  This efficiency, however, may soon be seriously challenged depending on the outcome of proposed more-stringent testing of pesticide residues. Advances in analytical chemistry have made it possible to detect minuscule quantities of almost anything. The phrase "detectable quantity" has little meaning to the average person, yet is used by experts in press releases almost daily. When it comes to pesticides, this could mean 0.05 ppb. But if it can be detected, does that necessarily make it harmful?

Pesticide politics

  In February 1999, Consumer Reports published an article critical of the U.S. food supply, calling for further regulation of pesticides in this country. This was six months after the EPA's Office of Pesticide Programs (OPP) issued initial regulatory guidelines to control the very pesticides mentioned in the article.

  The article claimed that fruits and vegetables grown in the United States are less safe than imported produce. One source claimed that the FDA is testing only 1 out of every 10,000 lots of imported produce for pesticides, but the state pesticide programs, especially California's, are much more thorough than that. Also, since some of the analytical results referred to in the article relied on chemical-family screens rather than specific analyses, it's surprising that the data's accuracy was not challenged. It could be that the imported products in question were not tested with methods of the same sensitivity as those used to test U.S. product, an issue that was not addressed or disclosed in the piece.

  However, this isn't to say that residue testing isn't an important issue. In response to genuine concerns that certain pesticides and other chemicals could be harmful to infants and children, Congress passed the Food Quality Protection Act (FQPA) in 1996. Among other things, the FQPA assigned to the EPA the job of reevaluating all pesticides that are in use for their potential harm to infants and children. The current tolerances are based on the average population, without specific reference to children, but the FQPA is addressed specifically to this group.

  Additionally, the Federal Food, Drug and Cosmetic Act (FFDCA) provides the OPP with the authority to set tolerances, or maximum residue levels (MRLs), for pesticides in or on foods and animal feed. According to the OPP's 1998-1999 Biennial Report, key elements of FFDCA include:

  • Tolerance Reassessment: All tolerances that were in place as of August 1996 must be reassessed - 33% are due by August 1999, 66% by August 2002, and all must be completed by August 2006.

  • Reasonable Certainty of No Harm Safety Standard: FFDCA now includes a health-based safety standard for pesticide residues in both raw and processed foods. "Reasonable certainty of no harm" is now the general safety standard, both for tolerances under FFDCA and registration of pesticides with food uses under the Federal Insecticide, Fungicide and Rodenticide Act.

  • Special Protection of Children: For explicit determination that tolerances are safe for children, the EPA must apply an additional ten-fold safety factor, unless there is sufficient reliable information to support application of a different safety factor.

  • Aggregate Risk: Pesticide risk assessments must consider all sources of non-occupational exposures (i.e., dietary, drinking water and residential exposures).

  • Cumulative Risk and Common Mechanisms of Toxicity: The EPA must consider the cumulative effects of related pesticides that share common mechanisms of toxicity.

  • Benefit-Based Tolerances: Under very limited conditions, the EPA may retain a tolerance for a pesticide that does not meet the new safety standard if it is deemed to be in the public interest.

  • Right To Know: The agency must develop information to educate the public about the risks and benefits inherent in using pesticides on foods. The EPA must also list any tolerances that are set based on benefits considerations, and explain ways consumers may reduce their exposure to pesticides in or on food.

  • Endocrine Disrupters: Because of concern that human exposure to chemicals that may disrupt the endocrine hormone system, the EPA must develop an endocrine disrupter screening and testing program to evaluate potential adverse effects.

  In essence, the EPA has been given new authority to regulate pesticide use and reexamine all pesticides, new and old. It is to the agency's credit that it has taken a scientific approach to the task and is proceeding at a good pace. Most of its activities are posted on the agency's website at www.epa.gov, along with the regulations for accessing total environmental exposure, evaluation of all data, and rulings as to the effects of a pesticide on animals and humans.

High standards

  To ensure the safety of the food supply, the OPP has decided to use a 10X factor when considering maximum residue allowances. This is on top of the EPA's initial safety factor used at the time of pesticide registration, as determined by acute and chronic animal studies. FQPA added other test criteria to the registration process, including cumulative analyses based on a weighted average of all registered uses for a product. If a food is tested for a common pesticide used on that food and no residues are found, it will be assumed that the pesticide is in the food at one-half the lowest level of detection, or LOD (see "Level-Detection Policies" sidebar).

  The total of all pesticides in a class of biological activity - such as cholinesterase inhibition - will be held to one maximum residual level. Let's say, for instance, that a product is tested for all pesticides in a category that are allowed to be used on the product in question. We'll assume there are eight pesticides in this category and that the new FQPA 10X safety factor is 0.01 ppm. After testing, none of the eight pesticides in question are detected. However, the LOD of the method is 0.005 ppm for each. The product would technically be in violation of the new standards (0.005 ppm/2X8 = 0.02 ppm).

  Think about this. If you look at the Pesticide Tolerance Commodity/Chemical Index (40 CFR Chapter One, pages 580 to 680), it's easy to imagine such a tolerance for some of the organophosphates in the near future. Take chlorpyrifos, or Dursban®, for instance. At present, the MRL on most fruits and vegetables is 1.0 ppm. The OPP announced on August 8, 1998 that Dursban would fall under the 10X FQPA safety factor. That brings the maximum allowable MRL to 0.1 ppm combined for food, drinking water and environmental exposures. This insecticide continues to receive much attention in the press. It's likely the MRL will be reduced to 0.1 ppm in the near future, and it may be reduced even further once all other environmental factors are included, such as allowed uses in the home and on pets. What if the ultimate MRL is 0.01 ppm? What will farmers and pesticide companies do then?

  The United States isn't the only country dealing with the pesticide dilemma. On July 1, 1999 Taiwan changed its pesticide tolerances on fresh produce grown within that country, and will begin enforcing these standards on imported produce July 1, 2000. This will affect 60 chemicals used on 300 crops for which Taiwan has much more stringent standards than does the United States at this time.

  Taiwan is already screening imports at this time, checking one out of every 40 containers, which is a much higher rate than that tested by the FDA. According to sources, inspectors have already found detectable residues on recent imports at levels not detected by U.S. labs prior to shipment. It's not certain that these levels, though detectable, were in violation, but it does point out a hole in the present testing system.

Lab standards

  At present, many analytical screening procedures for pesticides are not accurate to the levels needed by the new standards. Many procedures are not specific for individual pesticides, or do not reach the detection levels necessary to determine the new, reduced MRLs. It's not uncommon for today's procedures to be accurate to 0.1 ppm ±0.05, which is adequate when looking for levels of 1 to 5 ppm, but which will not be adequate in the future.

  Although very little research is being done in the area of food analysis to develop sophisticated procedures to extract and analyze specific pesticides at very low levels, one laboratory is conducting research on analytical procedure development at the new, very low levels of detection. According to Mike Ray, a chemist with the Agricultural and Priority Pollutants Laboratory, Inc., Fresno, CA, this laboratory is regularly conducting analysis down to 0.05 ppb. It has received research grants from the EPA and other organizations to work in this critical area, and has found, perhaps not surprisingly, that the lower the level of detection, the greater the chance for finding a given chemical.

  What problems may be encountered when moving from 1 ppm to 1 ppb? According to Ray, one problem is the source of standards for calibrating the instruments. It can make a big difference whether these are primary or secondary standards. Primary standards come from government-registered manufacturing laboratories, of which there are currently three in operation. Secondary standards are prepared by chemical supply houses and large-company labs by comparing results from primary standards to the batch in question. This can yield standards that aren't as reliable as primary results. Even labs that regularly run two primary standards have found a variation of 2% to 5% between the two - the difference between secondary standards could be even greater. And, even in the best-case scenarios, how many labs are actually shooting one fresh standard each day to verify the calibration of their equipment?

  The March 27, 2000 Wall Street Journal reported that the EPA's Central Regional Laboratory in Chicago was not shooting fresh standards every day, but at times "allegedly skipped the calibration phase and manipulated the data by augmenting or diminishing the peaks to produce the standard linear result." Whether or not this claim is true, it illustrates how important it is that every lab maintains its own record of calibration standards and calibrations as a regular part of its in-house QC program.

  Another problem is extraction techniques, which will need to be improved. This becomes even more difficult in prepared foods, which may have a variety of secondary compounds that interfere or inhibit the separation of organic pesticides. Produce has its own set of problems, but after being made into a fruit-filled granola bar, the extraction becomes much more complex.

  Basic maintenance of gas chromatography equipment is another issue. Maintenance of analytical equipment must become more frequent and time-consuming, and the level of cleanliness will have to improve dramatically at most laboratories. One source says it will be like going from good technique to excellent technique all of the time, which will most likely lead to an increase in cost for each analysis - and a possible short-term reduction in the number of laboratories willing or able to do pesticide analyses.

Industry impact

  The greatest impact of new regulations will likely be a reduction in the number of allowed uses for what had been very effective pesticides. In order to keep a pesticide on the market, the manufacturer will have to consider withdrawing certain applications from the approval list. Remember - all exposures will be considered. In order to maintain the larger market segment for a pesticide, the manufacturer will drop secondary-use markets.

  Fruit crops, for example, are considered minor uses because the total acreage is small when compared to other crops. One industry insider poses the rhetorical question: Will the American consumer be willing to pay $4 for an apple that is blemished and has worms? Many of the chemicals that will have their MRLs reduced are in fact used on fruit crops, and residues on fresh fruits have been a major area of attack by pesticide opponents.

  According to industry sources, the chemical industry is doing a study as to which applications to suspend from product registrations before deciding if the higher cost of more stringent testing has a financial benefit. Even if a crop has a history of very low or non-detectable residues, a farmer may not have access to this product in the United States. The stringent domestic oversight of pesticides will eliminate the chance that non-approved uses will occur in this country, while these same pesticides, along with others that have long been banned in the United States, are still in use in other producer countries. If a shipment is sampled at the port of entry and no residues are found, the product will be allowed to enter regardless of aggregate risk assessment. The upshot? Our farmers will have been made less competitive on the world market - without an increase in safety for the consumer.

  The EPA has the ability to allow special-use permits for pesticides, which is where political pressure may come into play. There will be many calls on the part of concerned groups to ban or severely reduce certain classes of pesticides based on detectable levels in the food supply. A good question to ask is this: What is the detectable level anyway? With advances in analytical chemistry, it might be a number that is unimaginably small.

Level-Detection Policies

  Following are summaries of the key points in three draft science policy papers announced in the Federal Register for public comment in November 1998. The final ruling is expected shortly; check www.epa.gov for updates.

  Threshold of Regulation Policy:

  • Concerns food uses for which data at the farm gate show no detected (ND) residues with a limit of quantitation (LOQ) at 0.01 ppm or less.

  • If NDs for a use are shown to be less than 1/10 the LOQ, residues are deemed to be "essentially zero" and no tolerance would be required.

  • If NDs for a use are shown to have "essentially zero" risk (i.e., risk is 1/1000 of an acceptable level of risk), then no tolerance would be required. The values of the NDs are determined as described below.

  • If neither criterion is met, then a finite tolerance would be established at the LOQ, assuming the use meets Food Quality Protection Act safety standards.

Assigning Values to Nondetected/Nonquantified Pesticide Residues in Dietary Exposure Assessments:

When conducting exposure and risk assessments, the EPA would assign a value to NDs for each treated crop as follows:

1. If an LOD exists, NDs = 1/2 LOD
2. If an LOQ exists, NDs = 1/2 LOQ
3. If only an LLMV exists, NDs = LOQ
4. If nonquantifiable residues are found, NDs = 1/2 LOQ

Statistical Method for Using Nondetected Residues in Dietary Exposure Assessments:

  As an alternative to using 1/2 LOD for NDs, statistical methods (e.g., "Cohen's Method") could be used to estimate the distribution of ND values for treated food. The criteria for using Cohen's method are: First, that the NDs comprise less than half of the data set, and secondly that the values for the detected residues are normally or log normally distributed.

LOD = Limit of Detection
LOQ = Limit of Quantitation
LLMV = Lower Limit of Method Validation
ND = No Detected (residues)

  Bruce Floyd established Process Systems Consulting, Iowa City, IA, after working more than 30 years in the food processing industry. He has had extensive experience in sanitation, quality control, regulatory relations, and product and process development (both domestic and international), and specializes in integrating ingredient and manufacturing specifications into total process systems. A graduate of Georgia State University, he has successfully completed all areas of the Better Process Control School at the University of Minnesota, and has been qualified by the International HACCP Alliance as an instructor. He can be reached via e-mail at [email protected].

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