Monday, December 23, 2013

True or False: "Washing Your Fruit and Veggies is Useless - You Can't Wash Away the Pesticides, Anyway!"

It's a good idea to wash your veggies, but this is not the most effective method. Bath them in warm water, don't wash them under the faucet.
Despite the fact that I had my reasons to end the SuppVersity "True or False" Series back in the day. The popularity of the corresponding articles that appear from time to time as SuppVersity Classics on Facebook does yet tell me that you won't be mad at me, if I revive it and try to tackle a statement I've overheard in one of those infamous gym conversations between two ladies on the cross-trainer: "I always wash those pepper extra thoroughly, you know... tomatoes are among the veggies with the highest amounts of pesticides on them." Answer lady two: "Ha, you don't really believe the pesticides are on the outside of the tomatoes only, do you? They are in the tomato. Washing them will at best remove some of the dirt on their skin!"

True or False: "It's useless to wash your peppers."

False - I was surprised, when I realized that the answer to this True or False item was much easier to find than I had thought. It took me a while, though, before I found a study that analyzed data from more than just one vegetable variety, but the basic answer,  i.e. "No, it's not useless to wash your peppers - quite the contrary!" popped up right in my first cursory database search.
Figure 1: Amount of ethylenebisdithiocarbamates and chlorpyrifos on selected vegetable (µg/kg) before and after washing; the figure above the bars indicate %-change from pre to post washing (Chavarri. 2004; Randhawa. 2007)
If you look at the data of two studies I selected more or less randomly (see Figure 1) you will yet see that the effectiveness of the "wash away the pesticide approach" depends on both, the type of vegetable and the type of pesticide. With a mean total endusulfan reduction of >20% it should however be absolutely obvious that not washing your veggies would be wreckless.
Table 1: Current European Union Maximum Residue Levels in mg/kg (Council Directives 76/895/EEC and 90/642/EEC, last revised in June 2004)
Artificially contamination ➫ standardization: The baseline pesticide level of the vegetables in the Chavarri study was achieved by spraying fresh produce from controlled plots with no previous pesticide applications with those pesticides farmers usually use in the EU. The reason should be obvious: standardization. Thus, the pesticide levels were within the contemporary EU limits (s. Table 1) - something you cannot necessarily expect from every product you buy in the supermarket.
I mean, I shouldn't have to tell you to that it's unquestionably healthy not to be exposed to the full load of 24µ/kg chlorpyrifos and 1,626µg/kg ethylenebisdithiocarbamates (both have carcinogenic effects in humans; cf. Houeto. 1995, Josephson. 2005), from the tomatoes - specifically in view of the fact that 5.% of the tomatoes that are sold in the EU exceed the contemporary pesticide limits (Nasreddine. 2002) and would thus contain way more of these hazardous substances to begin with.

Aprospos washing! How do you do that?

You don't know how to wash veggies? Well, I obviously can't tell you what the absolute optimal way is, but what I can tell you is how scientists washed the specimen that were used in the studies the data in Figure 1 is based on: They placed the veggies in a dish or a clean lavatory with warm tap water and cleaned them with "gentle rotations of the hand" (Randhawa. 2007), before they grapped a conventional paper towel and blotted them dry.
Figure 2:  Illustration of the processing steps in Chavarri et al. (2007).
That's similar to what you do? Great, and you know what, I would bet that's not the only similarity between yourself and the average scientist. Just like you, scientists don't eat all their veggies raw. Consequently, both Chavarri et al. as well as Randhawa et al. conducted additional analyses of the pesticide content of their veggies after the produce had been blanched (the peppers were roasted, not blanched), peeled, pureed (Chavarri. 2004; see Figure 1) and cooked or peeled and cooked (Randhawa. 2007), respectively.
Figure 3: Relative ethylenebisdithiocarbamates and total endosulfan levels (in % of baseline) after washing, peeling, blanching / cooking & co. (Chavarri. 2004; Randhawa. 2007)
As you can see in Figure 3, each of these processing steps lead to a further reduction of pesticides. For the initially highly intoxicated asparagus, for example, even the last traces of pesticides ended up in the cooking water. If you would now decide to recycle the water for a soup or whatever, all your efforts to rid yourself of the pesticide would have been in vein.

"Conventional vs. Organic is not about getting more, but about getting  less for your money" | more
Bottom line: Wash your damn veggies you lazy *****! If you still don't believe that it's well worth spending this inconvenient extra-minute it takes to prepare warm water (28-32 °C), put your foods in, scrub a little with your hand and then continue processing them, I'd suggest you take a look at a recent meta-analysis from Ghent University in which the authors dealt with the exact same question and conclude:

"Reduction of residue levels was indicated by blanching, boiling, canning, frying, juicing, peeling and washing of fruits and vegetables with an average response ratio ranging from 0.10 to 0.82." (Keikotlhaile. 2010)

References:
  • Chavarri, M. J., Herrera, A., & Arino, A. (2005). The decrease in pesticides in fruit and vegetables during commercial processing. International journal of food science & technology, 40(2), 205-211. 
  • Houeto, P., Bindoula, G., & Hoffman, J. R. (1995). Ethylenebisdithiocarbamates and ethylenethiourea: possible human health hazards. Environmental health perspectives, 103(6), 568.
  • Keikotlhaile, B. M., Spanoghe, P., & Steurbaut, W. (2010). Effects of food processing on pesticide residues in fruits and vegetables: a meta-analysis approach. Food and Chemical Toxicology, 48(1), 1-6.
  • Nasreddine, L., & Parent-Massin, D. (2002). Food contamination by metals and pesticides in the European Union. Should we worry?. Toxicology letters, 127(1), 29-41.
  • Randhawa, M. A., Anjum, F. M., Asi, M. R., Butt, M. S., Ahmed, A., & Randhawa, M. S. (2007). Removal of endosulfan residues from vegetables by household processing. Journal of Scientific and Industrial Research, 66(10), 849.