by Pamela Coleman, PhD
Consumers often choose organic food because of the perceived health benefits—particularly the reduced exposure to pesticides—but is that a valid reason? In a recent scientific article, Charles Benbrook and Brian Baker examined the evidence; they concluded that organic food does, indeed, have lower levels of pesticides than conventional food.
In fact, the authors say: “Organic food offers consumers a choice that dramatically reduces dietary exposure to pesticide and thus potential pesticide-related health risk.”
Benbrook and Baker examined data on pesticide residues in organic fruits and vegetables collected by the USDA’s Pesticide Data Program from 2002 to 2011. In that time period, more than 1,000 of the samples tested had some level of pesticide residue. Detection of pesticide residue is not necessarily cause for alarm. Some pesticides of low toxicity may be used in organic crop production. Conventional pesticides, although they are not approved for organic crops, may be present at low levels due to environmental contamination. Recent advances in analytical chemistry have lowered the limits of detection, increasing the likelihood that very low levels of residues will be detected during sampling.
In addition to the testing done by the USDA, the National Organic Program (NOP) requires each certifier to test a small percent of organic farms each year and, if any pesticide residues are detected, to investigate the reasons.
If organically produced food does have unacceptable levels of pesticide residues, the certifier investigates the cause, as it may indicate intentional fraud. In addition, the food may not be sold as organic. Unacceptable levels are defined as “greater than 5% of the EPA action level” or “above FDA action levels”.
Benbrook and Baker divided the types of pesticide residues into four groups: (1) 15% were legacy contaminants, (2) 28.9% were post-harvest pesticides, (3) 21.9% were allowed organic pesticides, and (4) 34.2 % were other conventional pesticides.
Legacy pesticides are those that were used in the past, such as DDT. Although they are no longer used, they still persist in the environment. These were found mostly in root crops such as carrots and potatoes.
Post-harvest pesticides are often applied to conventional crops to preserve them in storage. Examples include anti-sprouting compounds on potatoes, or fungicides on apples, bananas, and oranges. These post-harvest pesticides can contaminate organic crops if there is insufficient separation from conventional crops during the storage and handling, but this contamination may be avoidable with careful management by the packinghouse.
The synthetic pesticides allowed for organic crop production have been determined to pose minimal harm to people or the environment (and even then, they are only used as a last resort after other cultural practices and natural materials have failed).
The conventional pesticides represent the vast majority of synthetic pesticides, and include some highly toxic compounds. The residue levels give some indication of the possible cause of the contamination, because direct application of a pesticide will typically result in a higher level of residue than inadvertent contamination. High residues of conventional pesticides in organic produce could indicate fraud—the intentional application of a prohibited pesticide. Low residues might be the unavoidable result of spray drift from neighboring farms, irrigation water, or contaminated compost.
Although 34% contamination with conventional pesticides may sound high, current methods of analysis can detect extremely low levels of pesticides. The authors put the data into perspective by using a “Dietary Risk Index” that takes into account both the level of residue and the toxicity of the pesticide. Most of the residues were incidental and low risk, such as the allowed residues of organic pesticides, and the inadvertent residues of legacy pesticides. The samples with a high Dietary Risk Index were combined with samples where direct contamination was suspected, for a total of 15.2% of the samples. These were classified as high priority for action by the NOP and organic certifiers. Focusing on the highest risk cases would be an effective way to protect organic integrity.
Organic crop production emphasizes the process of building fertile soil, along with using cultural and biological practices to manage diseases and pests. This analysis of pesticide residues over the past decade indicates that organic crops have significantly lower pesticide residues than conventional.