In the United States, farmers treat most crops with pesticides to increase yields and the foods' eye appeal. Inevitably, studies have shown, traces of these pesticides remain on the food after harvest and are in the food we eat. However, switching to organically grown produce for as little as 2 weeks eliminated urine residues of potentially toxic organophosphate pesticides in children, a recent study reported (SN: 9/24/05, p. 197: Available to subscribers at http://www.sciencenews.org/articles/20050924/fob6.asp).
People might be tempted to read that study's findings as suggesting that organically grown fruits and veggies are free of potentially toxic pesticides. In fact, the researchers tested only for a few pesticides—those currently approved for use on foods in the United States.
In contrast, an undergraduate chemistry student, in a separate small-scale study, recently screened veggies for a number of banned pesticides and made an interesting discovery: The chemicals showed up on both conventionally grown and organic veggies—in roughly comparable amounts. In fact, organic carrots had higher amounts of some chemicals than the conventional vegetables did.
Beth Wolensky, a senior at Chatham College in Pittsburgh, purchased 20 batches of carrots from local groceries and natural-foods stores. Half were labeled as organic, and half weren't, presumably meaning that the latter had been treated with pesticides. To carry the organic label under federal law, crops must be grown without the use of synthetic-chemical pesticides, chemical fertilizers, or sewage sludge. In fact, such agricultural amendments must not have been used on a field for at least 3 years prior to an organic crop’s planting.
That pesticide-free period is supposed to permit rain to wash the soil of chemical residues. However, many long-used toxic—and now-banned—organochlorine pesticides can take decades to break down, Wolensky says. Moreover, many linger in soils for far longer than 3 years. Because root crops, such as carrots, make direct contact with soil, they have plenty of opportunity to contact lingering residues of formerly used pesticides.
To student Wolensky, that scenario offers the best explanation for her new findings.
Every carrot she tested harbored traces of p,p'-DDE, a breakdown product of the insecticide DDT. The leftover chemical is not only toxic itself but also functions inside the body as a weak hormone (SN: 7/15/95, p. 10). Many carrots carried residues of chlordane, a chemical widely used in treating homes threatened by termites. Some samples also contained small amounts of heptachlor, another once-popular termiticide. Wolensky presented her findings last week at the Society of Environmental Toxicology and Chemistry annual meeting in Baltimore.
In all the carrot samples, concentrations of these chemicals tended to be small, in the low–parts-per-trillion (ppt) range. Not surprisingly, the skin of the vegetables had accumulated higher concentrations of these chemicals than fleshy interiors had. For instance, in whole carrots, the mean concentration of p,p'-DDE was 40 ppt in the conventional vegetables, and 340 ppt in the organic ones. However, skin concentrations were 588 ppt for the conventional carrots and 3,050 ppt for the organic ones.
Last year, Chatham senior Tanieka Motley reported similar data for potatoes. The same range of pesticides showed up in both conventionally and organically grown spuds, with the highest concentrations in the skins. For instance, among organic potatoes, mean p,p'-DDE concentrations were 40 ppb in skin but only 1.6 ppb in the flesh. Those values were roughly double the p,p'-DDE concentrations in conventionally labeled potatoes.
The variety of DDT breakdown products, termiticides, and other banned pesticides detected in both studies is consistent with that detected several years ago by the Chatham students' advisor, analytical chemist Renee Falconer. Residues of chemicals inappropriate for crops turned up in 38 farm fields and two gardens sampled across four states.
At the concentrations detected, none of the chemicals in the carrots or spuds is dangerous alone, notes Falconer. The veggies’ lingering residues wouldn't deter her from buying organic produce, because overall, she notes, organically grown crops should harbor far lower concentrations of pesticides and other agricultural chemicals currently applied to conventional crops. Still, she notes, the findings are a concern in that they add to the amount of pesticides entering our bodies from a host of sources—the air, water, household chemicals, and foods.
The residues that Wolensky found in her small study were what remained after she had washed each carrot, much as any cook might. She recommends that cooks further cut pesticides in their families' diets by peeling all carrots, spuds, and other root vegetables before cooking or serving.
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Renee L. Falconer and Beth Wolensky
Department of Chemistry
Pittsburgh, PA 15232