A closer look at the pesticide residue question

One man's poison is another man's opportunity: Why food safety will continue driving growth in demand for organic food

By Charles M. Benbrook
Posted April 29, 2004 A version of this paper was originally delivered Jan. 24, 2003, at the Eco-Farm Conference in Monterey, Calif. Reprinted by permission.

Over the last two decades, the organic community has had a love-hate relationship with food safety issues in general, and pesticide risks in particular. For the most part, the community has chosen not to prominently feature food safety as a reason to “buy organic,” and instead has focused messages targeting consumers on freshness and taste, and the environmental and soil quality benefits of organic farming systems.

Anti-pesticide activists, however, have shown less restraint. They have embraced organic farming as the surest way to reduce pesticide use and risks. And the message is getting through. A majority of consumers in virtually all surveys voice significant concerns over pesticides in food. In “The Packer’s” 2003 Fresh Trends survey, 63 percent of shoppers buying organic food stated a preference for “fewer chemicals in food” and 51 percent said organic food is “Better for me/my family.” The next most frequently cited reason—“Better for the environment”—was identified by 37 percent of those surveyed.

For reasons beyond the control of the organic community, there is now a raging food safety/food quality debate underway around the world. It is focusing on the impacts of different farming systems and technologies—conventional farming vs. biotech vs. IPM vs. organic. John Stossel's 20/20 episode of February 2000 ("How Good is Organic Food?") and recent NOP rule-related PR from conventional ag interests shows how low those threatened by the success of organic farming will go in trying to shake consumer confidence in organic food. Hopefully the organic community now realizes that the industry’s critics must not be allowed to set the tone and direction of this very important debate.

Activists opposing genetic engineering (GE) around the world have been criticized in the media as paranoid and anti-progress. Some have stumbled when asked, "Well, if GE is not the answer, how would you solve today’s food production and food security challenges?” With increasing frequency, activists point to organic farming as the more desirable technological path. Proponents of biotech have not been bashful in responding.

This debate is long over due and ultimately should be constructive. There are profound differences between the principles driving today’s GE applications in agriculture vs. the principles underlying organic farming. The sooner the public understands these differences and decides which set of principles should shape their food future, the sooner the country can progress toward more coherent national food, farm, and technology policies. Today’s muddling serves no one well.

New science supports a positive food safety message

There is new information on both the exposure and toxicity side of the pesticide risk assessment equation. Much new data on pesticide residues in food has emerged as a result of the passage of the Food Quality Protection Act (FQPA) in 1996. This historic bill directed the U.S. EPA to conduct a reassessment of all food uses of pesticides, taking into account the heightened susceptibility of infants and children, the elderly, and other vulnerable population groups.

Why the focus on risks to infants and children? Because kids consume more food per kilogram of bodyweight than adults do and eat a much less varied diet. As a result, exposure to a pesticide from consumption of a given food is greater per kilogram of infant/child bodyweight compared to adults (National Research Council, 1993). Moreover, exposure to some pesticides during infancy, even at very low levels, can lead to serious life-long consequences if the pesticides disrupt hormone-driven developmental processes.

"The foods most likely to contain residues of high-risk pesticides are apples, pears, peaches, grapes, green beans, tomatoes, peas, strawberries, spinach, peppers, melons, lettuce, and various juices."
In the early 1990s, surprisingly little was known about the frequency or levels of pesticides in food as actually eaten. Then-existing government data on residues had been collected as part of tolerance enforcement programs and represented residues at the farm gate, prior to washing, shipping, storage, marketing, and preparation. Relatively insensitive analytical methods were used.

To improve the accuracy of FQPA-driven pesticide dietary risk assessments, Congress funded a new USDA program in 1991, the “Pesticide Data Program” (PDP). By design, the PDP focuses on the foods consumed most heavily by children, and food is tested, to the extent possible, “as eaten” (Agricultural Marketing Service, 2002). (A banana or orange samples are tested without the peel; processed foods are tested as they come out of a can, jar or freezer bag.)

Ten years of PDP testing has greatly enhanced understanding of pesticide residues in the US food supply. About a dozen foods are tested annually. Some 600 to 650 samples are tested of each fresh or processed food, reflecting domestic production and imports roughly proportional to their respective share of overall consumption. Plus, market claims associated with a given food item, such as “organic,” “IPM-grown,” “No Detectable Residues” or “pesticide free,” are recorded roughly in proportion to their occurrence in retail market channels (Baker et. al., 2002). As a result, PDP results make possible comparison of the distribution and frequency of pesticide residues in domestic vs. imported foods, across food groups, and by market claim (Groth, et al., 2000).

The first-ever analysis of pesticides in organic vs. conventional foods was published in the peer-reviewed journal Food Additives and Contaminants in early 2002 (Baker et al., 2002). I was among the authors. The full team included Brian Baker, the Organic Materials Review Institute’s director of research, Ned Groth of Consumers Union, and Karen Lutz Benbrook. The paper analyzed six years of PDP data, 10 years of California Department of Pesticide Regulation (DPR) data, and results of Consumers Union testing of four crops. The PDP data covered program years 1994-1999, and the DPR data, 1989 through 1998.

An overview of pesticide residues in conventional and organic foods

Some major food groups—most oils, dairy, meat, and poultry products—contain few detectable pesticides and contribute very modestly at the national level to dietary exposure and risk. About a dozen pesticides are present routinely in fresh produce and juices at levels that pose significant risks. Despite much new data and more refined risk assessment methods, several key children’s foods still contain worrisome pesticide residues six years after passage of the FQPA (Consumers Union, 2001). The foods most likely to contain residues of high-risk pesticides are apples, pears, peaches, grapes, green beans, tomatoes, peas, strawberries, spinach, peppers, melons, lettuce, and various juices.

Nearly three-quarters of the fresh fruits and vegetables (F&V) consumed most frequently by children in the United States contain residues and almost half the F&V samples tested from 1994-1999 in the PDP contain two or more residues (Baker et al., 2002). In general, soft-skinned fruit and vegetables tend to contain residues more frequently than foods with thicker skins, shells, or peels.

The pattern of residues found in organic foods tested by the PDP differs markedly from the pattern in conventional samples. Conventional fruits are 3.6 times more likely to contain residues than organic fruit samples and conventional vegetables are 6.8 times more likely to have one or more detectable residue.

Compared to organic produce, conventional samples also tend to contain multiple residues much more often. Imported foods consistently contain more residues than domestic samples, regardless of market claim.

"A few pro-pesticide activists have gone to great lengths to convince consumers that pesticide residues in organic foods are as risky as those in conventional foods. Fortunately, these claims do not pass the laugh test."
Averaged across the PDP and DPR data sets, just under 7 percent of positive organic samples and 54 percent of positive conventional samples contained multiple residues. The average positive conventional apple sample contained 3.2 pesticides, peaches contained 3.1 residues, and celery and cucumber contained 2.7 (Baker et al., 2002).

Data from DPR testing in 1999 and 2000 shows that conventional food is more than five times more likely to contain residues than organic samples. It is worth noting that organic farmers, processors, and retailers are doing a better job in preventing fraud, pesticide drift and other inadvertent residues, given the downward trend in the frequency of residues in organic foods. In 1996-1998 testing by DPR, just over 12 percent of organic samples tested positive on average, while 7.1 percent contained detectable residues in 1999-2000. There was little change in the frequency of residues in conventional foods, which averaged 38.3 percent annually from 1996-1998 and 40 percent in 1999-2000.

There is growing interest in Europe in comparing the residues in food produced by conventional vs. organic farmers. The British government reported residue findings in organic food samples for the first time in 2001.

The analytical methods used by the British Pesticide Residue Committee are not as broad or sensitive as those used in the PDP, and hence the percent of samples testing positive are lower in both conventional and organic foods. But the differences between conventional and organic foods remain. Over 250 samples of organic foods have been tested by the PRC since 2001—more samples than tested by the PDP over 10 years. Just under 27 percent of all samples tested positive, while 3.6 percent of organic samples contained a detectable pesticide residue. Hence, based on British testing, conventional foods are 7.5 times more likely to contain detectable residues than organic foods.

Pesticide toxicity

Implementation of the FQPA triggered an explosion in toxicological and risk assessment research on the developmental effects of pesticides. During fetal development and the first years of life, infants are much less able to detoxify most pesticides and are uniquely vulnerable to developmental toxins, especially neurotoxins, given that the brain and nervous system continue developing through about age 12 (National Research Council, 1993; Eskenazi et al., 1999).

New toxicological data have forced downward by one to two orders of magnitude the allowable levels of exposure to various pesticides found in food (Office of Pesticide Programs, 2002; Gray et al., 1999). The EPA has had to phase out hundreds of food uses of relatively high-risk pesticides (mostly organophosphate insecticide uses) in order to meet the FQPA’s new “reasonable certainty of no harm” standard (Consumers Union, 2001).

In the last decade much new evidence has emerged on the mechanisms through which pesticides can disrupt development as a result of even very low exposures. Literature through early 1999 is summarized in a special issue of the journal Toxicology and Industrial Health (Colborn et al., 1999). Just a few examples follow focusing on research published since the 1999 review. A review article published in San Francisco Medicine in November 2002 targets lay audiences and provides a useful update on recently published research findings on endocrine disruptors and human health, including several studies on pesticides (Myers, 2002). University of California-Berkeley School of Public Health scientists found that exposures to pesticides during pregnancy significantly heightened risk of children developing leukemia and that the more frequent the exposures and the earlier in life, the greater the increase in risk (Ma et al., 2002). A team in the Department of Preventive Medicine, University of Southern California, found that exposure to pesticides in the home during fetal development increased the risk of Non-Hodgkin’s lymphoma, with odds ratios as high as 9.6 for Burkitt lymphoma (Buckley et al., 2000).

A study in Ontario, Canada, confirmed that exposures to pesticides three months prior to conception and during pregnancy increased the risk of spontaneous abortions (Arbuckle et al., 2001). Research supported by the French Ministry of Environment documented clear linkages between exposures to pesticides commonly used in grape vineyards and long-term adverse cognitive effects (Baldi et al., 2001). Cognitive performance was compared in a group of children living in an upland agricultural region in Mexico where substantial pesticide use occurred, compared to a similar cohort in a nearby village. Children exposed to pesticides had lessened stamina and attention spans, impaired memory and hand-eye coordination, and greater difficulty making simple line drawings (Guillette et al., 1998).

"Conventional fruits are 3.6 times more likely to contain residues than organic fruit samples and conventional vegetables are 6.8 times more likely to have one or more detectable residue."
Recently published work on the developmental neurotoxicity of the most widely used insecticide in the United States, chlorpyrifos, showed that this organophosate (OP) targets neural cell replication and differentiation, as well as the functioning of glial cells (Qiao et al., 2002). The authors conclude that exposures to this OP during the first few years of life are likely a greater risk than during fetal development, although prenatal exposures appear to disrupt the architectural organization of specific regions in the brain and the development of the fetal liver. Antiandrogenic pesticides have been shown to cause demasculinization in several species by blocking the receptor sites needed for male sexual hormones to perform their normal functions during development (Baatrup and Junge, 2001; Gray et al., 1999).

The most compelling new study to appear on pesticide dietary risks in a long time was published online on October 31, 2002, in the highly respected journal Environmental Health Perspectives. A team based at the University of Washington’s School of Public Health and Community Medicine carried out the research. The research assesses the difference in organophosphate (OP) residues and risk faced by two to five year-olds consuming a diet composed of mostly organic foods vs. conventional foods (Curl et al., 2002).

The team found that children consuming mostly organic foods over a three-day period had much lower mean levels of organophosphate (OP) insecticide metabolites in their urine—in fact, children consuming conventional food had 8.5 times higher average levels than children eating a mostly organic diet. The study was carefully designed to avoid other potential confounding variables. The children came from similar socio-economic backgrounds; households with recent use of pesticides in the home were excluded from the study; and rigorous sampling and double-blind testing protocols were used. The research team concluded that, “Consumption of organic produce represents a relatively simple means for parents to reduce their children’s exposure to pesticides” (Curl et al., 2002).

Organic farmers and consumers are not the only ones that should rejoice at these findings. Conventional farmers adopting biointensive Integrated Pest Management systems can also markedly reduce OP insecticide use. Extensive evidence compiled by the EPA over the course of implementing the FQPA suggests that by cutting out all OP sprays within 90 to 120 days of harvest on major kids’ foods, OP residues will largely if not fully disappear from fresh produce. This is also good news for EPA, which can now confidently predict major progress in reducing OP risks following a relatively small number of regulatory actions targeting less than two dozen foods.

Why organic food sometimes contains residues

Many people wonder why between 10 percent and one-quarter of organic F&V samples contain residues of synthetic pesticides. Like transgenic DNA, pesticides are ubiquitous and mobile across agricultural landscapes. Most positive organic samples contain low levels of pesticides used on nearby conventional fields. They move onto organic food via drift or through use of contaminated irrigation water. Soil-bound residues of persistent pesticides account for a large portion of residues in root crops and squashes. Cross-contamination with post-harvest fungicides applied in storage facilities is a major cause of low-level fungicide residues (Baker et al., 2002). The small percent of samples sold as organic and found to contain relatively high levels of residues likely arise from inadvertent mixing of produce, laboratory error, mislabeling, or fraud.

A few pro-pesticide activists have gone to great lengths to convince consumers that pesticide residues in organic foods are as risky as those in conventional foods. Fortunately, these claims do not pass the laugh test. Expanded residue testing of botanicals and biopesticides would be needed to decisively settle the empirical issues behind such specious claims. Settling this artificial controversy would mean less testing to better understand significant pesticide dietary risks, a tradeoff thus far rejected by government regulatory and research agencies.

By volume, major pesticides used on both organic and conventional farms include sulfur, horticultural/petroleum distillates and oils, and copper-based fungicides. There are some formulations of these pesticides approved for organic production and many others available to conventional growers. These pesticides are used in similar ways for comparable reasons on organic and conventional fruit and vegetable farms. Sulfur is almost certainly the most common pesticide residue present on conventional and organic F&Vs, but it is never tested for because it is exempt from the requirement for a tolerance and poses essentially no risk through the diet. Copper is also not tested for because of tolerance exemptions and the fact that copper is an essential nutrient and harmless at the levels ingested as food residues.

Organic farmers also rely on Bacillus thuringiensis insecticides, pheromones, and products that coat produce with nontoxic, biodegradable materials (e.g., soaps and clays). Residues of these pesticides are rarely tested for because there are no tolerances to enforce and no basis for food safety concerns, given how these products are used in production agriculture.

While there were once several toxic botanical insecticides on the market and approved for organic production, only one remains in relatively common use – pyrethrins. Pesticides containing pyrethrins are indeed toxic but they degrade rapidly after spraying and hence rarely leave detectable residues. They are also applied at very low rates, on the order of one to two one-hundredths of a pound per acre; OP insecticides are applied at rates 50 to 100 times higher. Other botanicals of possible concern include rotenone and sabadilla. The most recent survey of organic farmers carried out by the Organic Farming Research Foundation found that only 9 percent of 1,045 farmers applied botanicals regularly (mostly pyrethrins and neem), and that 52 percent never use them, 21 percent use them rarely, and 18 percent “on occasion” (Walz, 1999).

Two closing thoughts

To the extent consumers become aware of recently published research findings on pesticides in food, it is likely to reinforce already deep-set concerns. It is now clear that purchasing organic food is a reliable way to reduce exposure to pesticides. Less exposure means greater margins of safety. While toxicologists and risk assessment experts can argue until the cows come home over whether 0.05 ppm of pesticide X, Y, or Z is safe or unsafe, many consumers are looking for practical ways to reduce personal risk loads. Consuming organic food is clearly one way to do just that.

Several times in recent years, the USDA has stated publicly that organic food is no safer than any other food. Even more frequently and assertively, the USDA has claimed that GE foods are fully tested and pose no risks. Bush administration and USDA leaders are puzzled why so many people around the world are unwilling to accept these claims. The credibility of the US government and confidence around the world in US food exports rests upon whether food safety conclusions reached by the USDA are grounded in sound science and consistent with the latest research findings. Clearly, the USDA needs to look anew at recent data on pesticide residues in conventional and organic foods and reconsider its message.

For the full text of this article and accompanying data tables, see Additional information about food quality and food safety can be found at Chuck Benbrook can be reached at Benbrook Consulting Services, 5085 Upper Pack River Road, Sandpoint, Idaho 83864; tel. 208-263-5236; email

Walz, E. 1999. Final Results of the Third Biennial National Organic Farmers’ Survey. Organic Farming Research Foundation. Santa Cruz, California.