Which Pesticides Are on NZ Food, and Does Washing Get Them Off?

When New Zealand Food Safety explained why silverbeet carrying 360 times the legal limit of an insecticide wasn't a risk, washing was part of the answer. Its deputy director-general, Vincent Arbuckle, told RNZ that washing silverbeet can cut residues by about a quarter.

Whether washing helps depends entirely on what's on the food. So I went through MPI's newest results.

The 2024 Total Diet Study bought 47 everyday foods in Auckland, Palmerston North, Christchurch and Dunedin, in winter 2024 and summer 2025. Of the 352 samples in MPI's results spreadsheets, 154 carried at least one pesticide residue. That's nearly half.

Here's the detail that matters for washing. MPI tests food prepared the way people normally eat it. So these residues are what was still there after preparation.

MPI says none of it was a food safety concern.

Three places a pesticide can be

Washing only works on one of them.

On the skin. Some pesticides sit on the surface. These are the ones washing is for. Researchers at the Connecticut Agricultural Experiment Station found a short rinse under the tap significantly cut nine of the twelve pesticides they tested. Commercial produce washes did no better than plain tap water.

Inside the plant. Others are systemic. The plant takes them up through its roots and leaves and carries them inside. A rinse can't reach that. In one apple study, a baking soda soak cleared the surface completely, but a systemic fungicide had already gone four times deeper into the peel than a surface one, and no wash got it out. In spinach, a one-minute rinse took only 8% off one systemic pesticide.

In the food itself. Some go on after harvest, into stored grain. They end up in the flour. You can't rinse a loaf.

What was on what

Strawberries and stone fruit were only tested in summer, so there are four samples of each.

A few of these are worth knowing more about. Captan, on every apple, is a fungicide flagged for possible cancer and hormone effects. It sits on the skin, so washing and peeling both help. Imazalil, in the citrus, is a systemic fungicide used against storage rots. It gets into the peel. Sulfoxaflor, on the glasshouse vegetables, is a systemic insecticide. Pirimiphos-methyl, in the bread, is an organophosphate used on stored grain.

Those hazard flags come from the University of Hertfordshire's pesticide database. They describe what a chemical can do at some dose, not what it does at the levels found here.

A few were over the legal limit

I checked each of these against MPI's current residue limits. Most were within them. Some weren't, assuming the food was grown here. MPI's data doesn't say.

• Kale, chlorothalonil at 13 mg/kg. MPI classes kale as a leafy vegetable, which has no set limit for this fungicide, so the default of 0.1 mg/kg applies. That's 130 times over. MPI's own 2022-23 survey treated 3.5 mg/kg on kale as a breach on the same basis.
• Kale, carbendazim at 3.8 mg/kg. Same default, so 38 times over. Europe no longer approves it.
• Spinach or silverbeet, chlorpyrifos at 1.4 mg/kg. That's 14 times the default. Chlorpyrifos is the organophosphate the EPA is phasing out by 2027.
• Strawberries, acephate at 0.29 mg/kg. Acephate isn't permitted on strawberries at all, so the limit is 0.01 mg/kg. That makes it about 30 times over. The same punnet carried methamidophos, the chemical on that silverbeet. MPI says methamidophos now comes from acephate breaking down. It hasn't gone away. It's arriving by another route.

What to do in your kitchen

Wash everything under running water, and rub it. It's free, and it gets what's on the skin. Rubbing seems to do most of the work.

Take leafy greens apart. Wash kale, spinach, silverbeet and lettuce leaf by leaf rather than dunking the bunch. These carried the most residues.

Dry it afterwards. New Zealand Food Safety says it's good practice to wash and dry fresh produce, especially anything eaten raw.

Skip the produce wash and the dish soap. The tap did just as well in testing. Hong Kong's food safety agency also warns they can leave residues of their own. If you soak, keep it to 5 to 20 minutes, because longer adds little and you lose nutrients into the water.

Baking soda is worth it for apples. A soak in about half a teaspoon per cup of water for 12 to 15 minutes did better than tap water on the apple skin. It's not much use on soft fruit; in later testing it softened and faded strawberries.

Peel what you'd peel anyway. Peeling was the most effective step in a 2024 review, taking 67% of one insecticide off cucumbers. The catch is that a lot of the good stuff is in the skin.

Don't zest conventional citrus. Imazalil sits in the peel. Peel the fruit and eat it, but buy organic lemons and oranges for zest and marmalade.

Leave the dishwasher out of it. Washing vegetables in one has done the rounds on TikTok. A Massey food safety professor called it totally unnecessary.

Where buying organic counts most

Washing can't help with what's inside the plant or baked into the flour. So on this data, those are where organic makes the biggest difference:

• Bread and flour. The grain insecticides are in the food itself.
• Kale and other leafy greens. The most residues, the most chemicals, and the worst of the over-limit results.
• Strawberries. Every sample had residues, with twelve chemicals between four samples.
• Capsicums, tomatoes and cucumbers. Sulfoxaflor was in most of them, and it's inside the plant.
• Mushrooms. Carbendazim was in every one.
• Citrus, if you use the peel.

And where conventional did fine: nothing was detected on kiwifruit, pumpkin or cabbage, and onions, avocados and carrots had one or two traces in eight samples. Those are the safest places to save money.

Why organic takes most of this off the table

MPI's own explainer says organic production doesn't use most human-made pesticides. BioGro requires its growers to exclude synthetic pesticides. Every chemical in that table is synthetic.

From 31 March 2028, that's law. Under the Organic Standards Regulations, any input not on an approved list is prohibited. Even an approved input is a last resort: used only when the grower can't get the result from what's on the farm, in the minimum amount, with records kept.

It isn't a guarantee of zero. Spray drifts, and in MPI's latest residue survey one watercress sample picked up a residue that way.

But the difference shows up fast. When researchers switched families onto organic food, the pesticide markers in their urine dropped within days.

Washing gets some of it off. Organic means most of it was never put on.

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