News & Media :: Daily Log
May 19, 2010
Celery tops the recently released Environmental Working Group (EWG) "Dirty Dozen" list of foods, ranked by degree of contamination with pesticides. The EWG's methodology is described on their website, and is heavily weighted toward the number of pesticides found on the average sample of food tested by the USDA's "Pesticide Data Program (PDP)."
A quick look at the latest USDA data on pesticide residues in celery makes it pretty obvious why celery ranked high on EWG's list. In 2008 testing, the PDP found 3,819 residues on 727 samples of conventional celery, or 5.3 residues per sample on average.
A California-based consultant has ridiculed the basis of the EWG ranking and methodology, and cites data suggesting that most celery grown in California is nearly clean as a whistle. He chastises EWG for not "digging deeper" and looking beyond the number of residues found.
He also asserts that "...there are pesticides that are used on organic crops as well. One typical example, Copper Sulfate, has an oral LD50 of 300 mg/kg. Thus an average of 94% of the pesticides used on conventional celery are safer than common pesticides used on Organic."
Since this individual encourages "digging deeper" to get at the real facts, let's dig.
Several copper-based fungicides are approved for use by organic farmers, since copper is a natural (non-synthetic) element. There are no tolerances governing copper residues in conventional or organic food because copper is an essential mineral nutrient for all mammals, for which the government recommends a daily intake for adults of 1.5 to 3 milligrams per day.
Copper fundicide residues on food contribute only marginally to this required daily intake, hence the government wisely does not waste money testing for copper residues in food. But this fact does not stop critics of organic farming from raising concerns about the "risky" copper fungicides approved for and used by organic farmers.
Returning to the PDP data on celery for 2008 and why this crop belongs high on any list of high-risk foods.
The Organic Center uses a Dietary Risk Index (DRI) to assess relative dietary risk from pesticides in food. Compared to EWG's method, the DRI is much closer to the risk assessment methods used by the EPA.
The DRI compares risk in one serving of food -- in this case celery -- compared to another serving of the same size. It takes into account the mean residue level found by the PDP in positive samples and the toxicity of the pesticide, based on EPA's review of company-submitted tox data. Mean residue levels and a pesticide's innate toxicity are critical factors that help determine risk levels, and are essential factors to take into account in "digging deeper" to place risks into perspective.
Any DRI score over 0.1 raises dietary risk concerns, since food with residues leading to a score of 0.1 delivers to a child 10% of the maximum amount of the pesticide the child can be exposed to per day without triggering the EPA's "level of concern."
In 2008 the USDA reported mean residue levels of 16 pesticides in celery with DRI scores over 0.1, including six organophosphate (OP) insecticides, a class of pesticides recently shown to contribute to ADHD.
The riskiest chemical found in celery in 2008 -- the OP chlorpyrifos -- had a DRI score of 1.2. The good news is that only 3.2% of the celery samples contained chlorpyrifos, but these 24 samples represent hundreds of thousands of servings of celery, based on the statistical sampling design of the PDP and overall celery consumption in the U.S.
Sometimes digging deeper to get all the facts about the pesticides in some of our most beloved fruit and vegetable crops is not nearly as reassuring as some would lead us to believe. Conventional celery growers have work to do to rid their harvest of OP insecticide residues, and while they are adopting safer, Integrated Pest Management systems, let's hope they also get rid of the high-risk endocrine disruptors in celery. USDA found residues of six endocrine disruptors in celery with DRI scores over 0.1.