Does Washing Produce Remove Pesticides?

“Don’t eat that! It’s not washed,” I remember being told as I munched on unwashed fruit as a kid.

From a very early age, I was taught to wash any produce before eating. You’ve probably heard the same, whether from the media or from family members.

We tend to think washing produce will somehow make it safer to eat, but does it really?

If you’ve ever had a garden, you’ll know that some vegetables absolutely require some washing simply to remove dirt (unwashed potatoes, anyone?). But most of the produce we encounter at the grocery store has already been washed.

So why are we re-washing it?

Some experts will argue that washing produce will remove pesticide residues, but I’ve always been a bit skeptical that a quick rinse under the faucet would have any meaningful effect on pesticide residues.

Some even suggest that the choice between organic or conventional produce based solely on the argument against pesticide residues is misguided because you can simply “wash off” pesticide residues.

That’s why I decided to look into the research and find my answers.

Here’s what I found.

Short answer: It depends.

Long answer: See below.

I’ve always had an interest in the effect of growing conditions on the nutrition of our food – everything from the soil quality, plant variety, choice of fertilizer (such as compost vs. synthetic), use of pesticides (including type of pesticide), and more.

I even took an elective class in college called “Pesticides, Public Policy, and the Environment” for fun (yes, you can call me a nerrrrrrrd!).

And after reviewing the science, I still can’t give a super simple answer to the “pesticides & produce” question.

That’s because there are thousands (yes, thousands) of different pesticides used commercially and not all of them behave the same.

The effects of food processing on pesticide residue levels may be influenced by the physical location of the pesticide residue as well as the physico-chemical properties of the pesticide such as solubility, volatility, hydrolytic rate constants, water–octanol partition coefficient and thermal degradation.” (Food Research International, 2009)

In addition, not all pesticide residues can simply be washed off. Some pesticides, called systemic pesticides, are absorbed into the plant.

For produce treated with systemic pesticides, no amount of washing will significantly reduce residues. It’s IN the food, not ON it.

For non-systemic pesticides (of which there are many sub-classes), washing is effective at reducing pesticide residues. Peeling may further reduce pesticide residues that have been absorbed by the fruit or vegetable.

Washing has been found to reduce pesticides that are loosely attached to the surface while peeling removes even those that have penetrated the cuticles of the fruits or vegetables.” (Food Chemistry, 1999).

The challenge is that it’s hard to predict which pesticides can simply be washed off (or even know what pesticides – or what combinations of pesticides – were used on your produce).

In one study, twelve pesticides were measured on washed and un-washed produce (the fungicides captan, chlorothalonil, iprodione, and vinclozolin; and the insecticides endosulfan, permethrin, methoxychlor, malathion, diazinon, chlorpyrifos, bifenthrin, and DDE (a soil metabolite of DDT). Washing produce reduced residues of nine out of the twelve pesticides. (Journal of Agricultural and Food Chemistry, 2000)

But what I found most surprising:

The rinsability of a pesticide is not correlated with its water solubility.” (Journal of Agricultural and Food Chemistry, 2000)

Adding to the confusion, the type of vegetable may also play a role in whether or not washing will make much of a difference.

A study out of India looked at pesticide residues left on eggplant, cauliflower, and okra after washing. Residues of organophosphates (a type of insecticide) were reduced by 77% for eggplant, 74% for cauliflower, and 50% for okra when washed. (Journal of Agricultural and Biological Science, 2008)

And finally, a meta-analysis (read: legit review) of 33 studies that quantified the effects of food processing techniques on pesticide residues in produce echoed the above findings. Washing, among other food processing (such as cooking and peeling), reduced pesticide residues anywhere from 10-82%. (Food and Chemical Toxicology, 2010)