I was curious if rinsing conventionally grown vegetables, as many people do, reduces or removes pesticides. Upon searching, most of the studies measuring pesticide consumption and accumulation in human tissue date from the late 60s and early 70s when DDT was actively being investigated. While perhaps relevant to societies where DDT is still used (Africa, South America), it is not useful data for Europeans and Americans. The studies I did find showed that casual washing did reduce pesticide residue, but not entirely. Heat treatment further reduced pesticide levels. However, it remains unknown whether those pesticides are transformed into other harmful contaminants by the heat, or simply deteriorate. It also remains to be seen (well I haven't personally looked for studies) whether these trace amounts of pesticides are actually harmful. Also, one has to wonder whether soil fumigants do in fact enter the plant by other means instead of just accumulate on the surface?
My recommendation for the cautious life extensionist is to shop organic only. If you must by conventionally grown foods, buy those items with least pesticide usage. Here is a good list.
Study: Changes in concentration of pesticide residues in potatoes during washing and home preparation
"Monitoring of pesticide residues in potato tubers and their prepared products (“pommes frites” and chips) was undertaken. Experiments were carried out to determine changes in concentration due to the washing, peeling and cooking process (blanching and frying) to assess the stability of pesticides in potatoes and their products. Pesticide residues were quantified by using gas chromatography. Results show that malathion, HCB, lindane and p,p-DDD were predominant in potatoes and their products. The highest mean was detected in potatoes, followed by pommes frites, while the lowest mean was recorded in chips. On the other hand, potato skin samples were found to contain the highest levels of DDT and its derivatives, lindane and HCB. Peeling was necessary to remove the greatest amount of pesticides in the skin. Washing with water and/or other solutions as well as the cooking process (blanching and frying) helped to eliminate most of the pesticide residues from the potato tubers."
Study: Effect of commercial processing on pesticide residues in selected fruits and vegetables.
"Commercial food processing operations such as washing, blanching, and cooking remove major portions of the pesticide residues that are currently permitted on the raw agricultural crop. These unit operations are reviewed for selected products, along with degree of residue removal at each step. For example, washing plus peeling removes 99% of carbaryl and malathion residues from tomatoes. Washing removes 83% of benomyl residue from tomatoes and further processing reduces the residue by 98% in tomato puree and catsup. Even in the most concentrated fraction from tomatoes (tomato paste), residues were below the initial level in the raw product."
Study: Residual behaviour of profenofos on some field-grown vegetables and its removal using various washing solutions and household processing
"Profenofos (Selecron 72% EC), was sprayed on field-grown pepper and eggplant at the recommended rate of 1.28 kg a,i/ha. Fruit samples were collected at 1 h to 14 days after application and analysed to determine the content and dissipation rate of profenofos. The effect of different washing solutions and some household processing on the removal of such residues from treated vegetables were also investigated. Profenofos residues were quantified by using gas chromatography. The results showed that the consumable safety time were found to be 10 days on sweet pepper and 14 days on hot pepper and eggplant fruits. The initial disappearance of profenofos appeared to follow first order kinetics with different rates of reaction of 0.38, 0.40 and 0.35 day−1 for hot pepper, sweet pepper and eggplant, respectively. The corresponding half-lives (t1/2) were 1.84, 1.74 and 1.96 days. Also, the results indicated that tap water, potassium permenganate and acetic acid solution gave high percent removal of profenofos residues from hot and sweet pepper fruits, while no detectable residues was found in eggplant fruit after washing with soap and acetic acid solutions. In general, all tested washing solutions gave higher percent removal of profenofos residues from eggplant fruit than the two other pepper fruits. Blanching and frying of pepper and eggplant fruits resulted in great reduction to almost completely removed (not, vert, similar100%) of the deposited profenofos. In addition, pickling process removed 92.58 and 95.61% from hot pepper fruit after one week and after two weeks, respectively."
Study: Pesticide residues in field-sprayed and processed fruits and vegetables
"This study was initiated to determine what residues of six insecticides (organochlorine, organophosphorus and pyrethroids) and four dithiocarbamate fungicides remained on raw agricultural commodities after harvest and to study the effect of the subsequent commercial processing on the residues. Sprayed crops of tomatoes, red peppers, asparagus, spinach, artichokes and peaches harvested after controlled field trials contained residues well below the maximum residue levels, except for lindane in tomatoes and acephate in artichoke. Commercial processing procedures led to large reductions in residue levels in the finished products. Washing removed all residual lindane, chlorpyrifos and cypermethrin from tomatoes. Chlorpyrifos residues were reduced by 67% during wood-fire roasting of peppers, and subsequent peeling removed all the remains. Peeling and blanching of asparagus reduced chlorpyrifos concentrations to undetectable levels. Processing of artichokes eliminated acephate and chlorpyrifos after blanching. Acephate in peaches survived successive processing steps until the final heat process that destroyed remaining residues. The net results can contribute to assure the consumer of a safe wholesome food supply."
Study: Research Article Effects of washing, trimming, and cooking on levels of DDT and derivatives in green beans (PDF)
Study: A study on residual pesticides in commercial fruits & vegetables
"The 88 kinds of pesticide residues were analyzed in 12 kinds(289 samples) of fruits and vegetables brought at department store & mart in Kwangju from Feburary to September in 1999. The detection rate of pesticide residue in 12 kinds(289 samples) of fruits and vegetables was 21.1 percent, and the rate exceeds standard was 5.2 percent. The order of highly exceed rate in fruits and vegetables were perilla leaf, lettuce, spinach and chickery. The order of pesticide which founded frequently in fruitsand vegetables were procymidone, endosulfan, vinclozoline, chlorpyrifos, cyprermethrin, pirimiphos-M, fenvalerate, fenarimol, and monocrotophos. And that of pesticide which exceed highly standard were procymidone, vinclozolin, endosulfan, pirimiphos-M, fenarimol, monocrotophos, etc. Eight different washing methods were compared for removal efficiencies of residual pesticides(procymidone, vinclozoline) on the perilla leap, the lettuce, the spinach, the strawberry, and the minitomato. Residual pesticides such as procymidone and vinclozoline were removed most efficiently by ultrasonic washing."
Study: Removal of residual pesticides on vegetable using ozonated water
"Degradation of the four pesticides by dissolved ozone was investigated in order to establish the effect of operational parameters: methyl-parathion, parathion, diazinon and cypermethrin. They were commonly used as broad-spectrum insecticides in pest control, and high residual levels had been detected in vegetables. In the present study, the effectiveness in pesticide oxidation in aqueous solution using low level of dissolved ozone was determined using solid-phase micro-extraction (SPME) and GC–MS. Dissolved ozone (1.4 mg/l) was effective to oxidize 60–99% of methyl-parathion, cypermethrin, parathion and diazinon in aqueous solution in 30 min and the degradation was mostly completed in the first 5 min. Trace amounts and unstable paraoxon and diazoxon were tentatively identified as primary ozonation byproducts of parathion and diazinon. The feasibilities of using low level of dissolved ozone (1.4–2.0 mg/l) for removal of the four pesticides residue on vegetable surface (Brassica rapa) were also tested. Ozone was mostly effective in cypermethrin removal (>60%). The removal efficiency of pesticides highly depended on the dissolved ozone levels and temperature. The present study validated that ozonation is a safe and promising process for the removal of the tested pesticides from aqueous solution and vegetable surface under domestic conditions."
