Pesticide Residues on Fruit and Vegetables

Yesterday, while working on the Growing Healthy Kids curriculum, I was asked to comment on one of the recipes we're planning to include in the revision.  This recipe is intended to support the 'Water for People and Plants' lesson and to encourage kids and their families to choose water over sugar-laden beverages.  The recipe is simply water flavored with things such as lavender, mint, cucumber, or citrus.

My concern with the recipe was that fruit and vegetables may contain pesticide residues, and that we needed to place STRONG cautions on the recipe card.

Here's my line of thinking:

1. The limits for pesticide residues on fruit and vegetables are set by the EPA.  However, although pesticide residues are limited, it is unlikely that fruit and vegetables purchased at the store have zero pesticide residues. 
2. Some of these pesticides are organophosphates.  Organophosphates inhibit cholinesterase, which is an enzyme that insects have - but that humans and other mammals also possess.  Thus, the same pesticides which act against insects also impact humans.  It's no surprise then, that organophosphates are often implicated in cases of pesticide poisoning.
3. Their higher metabolic activity and lower body mass make infants and children more prone to pesticide poisoning, compared to adults.
4. Water is the universal solvent, and is often used to dissolve the active ingredient of many pesticides.

However, this line of reasoning was more of a 'thought experiment'.  Ever curious, I wanted to make sure that my recommendations weren't too severe.  Thus, I decided to work through this issue, using citrus as a model.  I chose citrus, because it tends to have a bumpy rind, which can better 'hold' onto dirt, debris and pesticide residues.  Yes - you could simply peel the citrus rind off of the fruit prior to making citrus water.  However, in restaurants and in homes, it seems to be 'en vogue' to keep the peel.

I searched the USDA Maximum Residue Database for the maximum allowable residue limits (MRL) for malathion (a common organophosphate) on lemon, lime and sweet orange in the United States.  All had a MRL of 8 parts per million (ppm).  It was interesting to note that the MRL of 8 ppm in the USA is orders of magnitude higher than the default MRL for citrus set by the European Union (0.01 ppm), Canada (0.1 ppm), Japan (0.01 ppm), Malaysia (0.01 ppm), New Zealand (0.1 ppm) or South Africa (0.01 ppm).

Although the MRL for malathion on citrus is 8 ppm, in practice, citrus water likely contains far less than 8 ppm.  First, the 8 ppm is a maximum residue level, and not the actual residue level.  Second, not all of the residues are likely to dissolve back into the water.  But, in my line of thinking, it is probably that **some** of the residue will dissolve. And, although I couldn't find many examples of published research on what would be termed 'sub-chronic exposure' (i.e., very low levels of exposure, over an extended period of time), one study performed on mice found no discernible impact of low level exposure to malathion.

So, in one sense, I'm probably being over-reactive.  But, I still maintain that it's better to be safe than sorry - particularly when working with children.  And, with a few easy tweaks, we can easily reduce potential sub-chronic exposures to pesticides.  Thus, there's no real need to bother with a recipe that could potentially expose kids to low levels of pesticide.

What tweaks would I recommend, if you're preparing your own flavored waters at home?

1. Peel cucumbers or citrus prior to placing them in the water.  This will greatly reduce pesticide residues, as the vast majority of residue resides on the outer peel.  Maybe people leave the rinds and peels on because it provides a beautiful shot of color.  However, it's not worth it (in my opinion) to needlessly introduce potential pesticide residue into your water.
2. Follow the National Pesticide Information Center's tips for reducing pesticide residues on fruit and vegetables.  Briefly,  wash produce under running water.  Don't dunk or soak.  Don't use soap, bleach or veggie washing products, as these have been shown to be no more effective than running water, and may even 'trap' residues in pores of the produce.
3. Choose organic over conventionally produced fruit and vegetables.  Organic pesticides aren't necessarily less toxic than synthetic pesticides.  After all, organic pesticides are still pesticides - and pesticides are generally formulated to *kill* something.  However, the major advantage of organic over synthetic pesticides is that organics tend to degrade quicker.  In fact, studies show that organically grown produce has about 1/3 the pesticide residue of conventionally grown produce.
4. For flower-flavored waters or for pastries or other drinks those that use flowers as a garnish, use ones that you've grown in your own garden, so that you can know how they have been grown.  The MRL database doesn't list residue limits for flowers - probably because flowers aren't considered edible crops.  So, when you garnish your cake with pansies, or add lavender as a garnish on ice cream - the pesticide residues may be higher than what you would find in edible crops.  Once again, better safe than sorry - and the best way to be safe is to know 100%, without a doubt how those flowers were grown.

By the way, I love learning new things.  This week, a paper I submitted with my amazing graduate student, Abha Gupta, was accepted for publication in HortTechnology.  Briefly, we re-analyzed published data from the literature, and found that nutrition education programs that have gardening component increased vegetable consumption in kids.  However, nutrition education programs without a gardening component had no such effect.  As part of the revision process prior to publication, I need to make sure that our format is correct, as well as fix minor errors in grammar.  I never knew that the plural of fruit is fruit.  I always thought that fruit was singular and fruits was plural.  Who knew??

Land Planarians in Portland? Who Knew!?

Oregon State University, like many land grant Universities, has an Ask an Expert service.  Through this service, anyone can submit a question on just about any topic: gardening, nutrition, agriculture, livestock, landscaping, pesticides, hens, food safety . . . . you get the picture.  Your question is then answered by an Oregon State University faculty member, or in some cases, expert Master Gardener volunteers.

Many people submit photos of insects, arthropods or other invertebrates that they would like us to identify.  I have quite a bit of training in entomology (M.S. and Ph.D. from the University of Maryland and post-doctoral research at UC Davis).  I'm not usually stumped.  But this week, a question referred to me by one of our most prolific Ask an Expert volunteers left me perplexed.

What is this?

I had no idea!

The picture is in 2 frames.  The one on the left shows the beginning of a 'nob'.  The one of the right shows the same critter, a few moments later.  The photo was taken in Multnomah County (photo posted with permission of the person who submitted the question).

Luckily, I'm not the only person at Oregon State University who can field such questions.  The esteemed Dr. George Poinar, a courtesy professor of Entomology at Oregon State University, provided the answer.

"I think it is a land planarium of the family Geoplanidae.  Very little is known about them, but they suddenly appear and then are gone.  The structure sticking down on the ventral (bottom) side would be the pharynx.  They are predaceous, eating earthworms and snails. The systematics (biological classification) is complicated, and photos are difficult to find on the web."

Poinar then added further details.

"The Geoplanidae is a large, diverse family with several subfamilies.  Check the images of the members and the 6 tribes of the Rynchodeminae. Some of these are round in cross-section.  It would be nice if someone did a synopsis of this group along the Western coast."

Since so little is known about this group, and so few photos are posted on the web, I wanted to get this information posted.  It's a real treat to glimpse something so rare and fleeting in our own backyard.  

By the way, Dr. Poinar's extraction of 130 million old DNA from insects preserved in amber was the inspiration for Micheal Crichton's novel turned movie, Jurassic Park!

Your Questions Answered, Intrepid Web Searchers

A few of the notable searches, that have lead folks to my blog, are questions that are relatively easy to answer. So, here it goes.

Q: Can flea beetles come from dogs?
A: No. Flea beetles are herbivores, that have to feed on plants to grow and reproduce. Fleas are parasites, that need a blood meal in order to grow and reproduce.

Q: How do you kill cabbage worm eggs?
A: The best thing to do is to first make sure you know what cabbage worm eggs look like. Next, use your fingernail to 'pop' them or squeeze them. If you don't want to pop them, you can simply knock them off the plant. Once the egg hatches, the caterpillar won't have anything to eat. Since it will be too small to burn all the energy needed to find a cabbage or kale plant on which to feed, it will likely die before it reaches a meal. For a least toxic pesticide, you can use horticultural oils to smother the eggs.


Cabbage worm eggs (two of them) on kale.

Q:  Can you grow potatoes without soil?
A:  Yes, you can grow potatoes hydroponically, or without soil.  The University of Florida has a nice set of instructions on the topic.