The Environmental Working Group (EWG, an activist organization) and the California Department of Pesticide Regulation (a state agency) each have radically different views of the safety of eating celery. EWG recently put celery on the top of their annual “dirty dozen” list – a ranking of fruits and vegetables by the “number” of pesticides that are used by the farmers that grow them. They claim that celery is sprayed with the most pesticides and that they are “difficult to wash off.” Is that sort of analysis meaningful?
The EWG’s list is the equivalent of ranking countries for risk by the number of spider or snake species which live there without saying anything about how many are poisonous or how common they are. Advice like this is unhelpful at best and actually irresponsible.
Celery, like most fruits and vegetables, is a good thing to include in a healthy, diverse diet. So is there really some unacceptable risk associated with the pesticides used to grow a healthy celery crop?
The People Who Actually Do The “Work” To Answer This Question
EWG counts pesticides. The California Department of Pesticide Regulation works much harder. They collect and store all the pesticide use data from farmers in California, and maintain an excellent and user-friendly site where this data can be accessed (which I did for four major celery growing counties). They also conduct annual pesticide residue surveys on the fruits and vegetables that are actually in the market. In 2008 that included 3,483 samples. They looked for residues of 200 different pesticides or breakdown products. 70% of the samples had no detectable residue at all. 29% of samples had residues that were lower than the cautious limits that have been set for each material. 1% (39) of the samples had residues that were from chemicals not registered for the crop, and these were almost all on imports (Mexico, Guatemala, China). 1 sample (0.03%) had a higher than tolerance residue. So, the contamination that EWG is implying does not seem to happen.
Doing The Math
I did a little more of the work that this “working group” failed to do. The California data says that on average, 10.8 pounds of pesticide active ingredients were applied to each acre of celery throughout a growing season (California accounts for 75% of US celery production). Since typical celery yields are 33 tons/acre, that means that there would be 0.07 grams of pesticide on each pound of celery if 100% of it stayed on the celery after application. In fact, pesticides break down in sunlight or by microbial digestion so any residue would be far smaller than that, and the residue of any single chemical only a fraction of that.
All Pesticides are not Created Equal
A little more “work” would have allowed the EWG to show that most of the pesticides used on Celery are far from scary. Only one is listed on the Prop 65 list of potential carcinogens. It represents only 1% of the total use and at low to non-existent residue it represents no real risk. With a little Google searching one can also find out how acutely toxic each of the chemicals is to mammals by looking at the “MSDS” sheets for each chemical. It lists the “Oral ALD50 Rat” – the larger the number the less hazardous it is, the lower the more hazardous. I went ahead and classified all the chemicals in the use data and made graphs showing how much of the chemical use fell into different ranges of toxicity divided using familiar references for relative hazard.
Depending on the county, 26-67% of the pesticide used was less toxic than table salt (ALD >3000 mg/kg). When you add the pesticides that are less toxic than the natural food flavoring, vanillin (1680 mg/kg) you get to around 3/4 of all the use. These are all very low toxicity materials.
EWG’s advice was to buy organic celery. EWG should know (but fails to mention) that there are pesticides that are used on Organic crops as well. One typical example, Copper Sulfate, has an oral ALD50 of 300 mg/kg. Thus an average of 94% of the pesticides used on conventional celery are safer than common pesticides used on Organic.
There are a few more of the pesticides that are still less toxic than the caffeine that so many of us intentionally ingest each day (192 mg/kg). Finally, there are just three pesticides used on celery that are more toxic than caffeine averaging 5% of total use. These are oxamyl, methomyl and rotenone (a rarely used natural product that used to be allowed on Organic by the way). The most toxic of these, oxamyl (9-10 mg/kg), is restricted such that it can’t be used within 28 days of harvest. Any residue left after that time would be insignificant and still spread over the 33 tons of celery.
So, it seems that Celery is just fine and the US EPA and California EPA are doing their work. If the Environmental Working Group wants to be credible, it needs to do a lot more work than counting pesticides. They are promoting Organic, but they do that industry a disservice by unfairly attacking growers who don’t deserve this sort of smear campaign. A lot of organizations, bloggers and journalists that uncritically passed along the “dirty dozen” list could also stand to do a little work of their own.
Celery image from Fir0002, flagstaffotos.com.au
Graph by me based on CALPIP and MSDS data
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