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Is chemical residue on fruit and vegetables worth worrying about?

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The chemical residues on fruit and vegetables are not dangerous, but rinsing is still advisable.

QUESTIONBefore eating or cooking fruit and vegetables, I soak them in salty water for an hour or two, then rinse them, in the belief this will remove unwanted chemicals. Does this actually work?

ANSWER: Fungicides, insecticides and herbicides are credited with improving crop yields and consequently lowering the price of fresh fruit, vegetables, cereals and nuts. But, in high doses, some of these chemicals can cause serious health problems, such as damage to the nervous system, lungs, reproductive system, endocrine and immune systems and possibly cancer.

That’s why there are strict regulations about the amount of chemical residues allowed in our food. Compliance is routinely monitored through the New Zealand Total Diet Study, done on average every five years. The study assesses our level of exposure to chemical residues, contaminants and certain nutrients in our most popular foods.

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The last study was in 2016 and tested three types of commonly used agricultural chemicals: insecticides, fungicides and herbicides. For the first time, it included two chemicals commonly found in disinfectants used in the food industry and in homes. In total, 1056 food samples were analysed and 406 were found to contain residues.

“We tested more agricultural chemicals than ever before,” says Andrew Pearson, the Ministry for Primary Industry’s specialist adviser on environmental chemistry and toxicology. “And although about 40% of the samples had a detected level of agricultural chemical residue, all of the exposures in the diet were very low, and far below the levels that would be a food-safety risk.”

Still, if you want to remove any lingering residues, what is the best method?

A 2018 review, published in the Journal of the Science of Food and Agriculture, assessed how effective common household preparations were in removing pesticide residues from fruit and vegetables. Although not specifically looking at fungicides and herbicides, it provides some helpful guidance.

For instance, many factors, such as the properties of the chemical, the type of vegetable, the processing procedure and the application of the chemical, can affect the ease of residue removal. We know, for example, that the longer a pesticide has been on a crop, the more difficult it is to remove residues, and that systemic pesticides – those that are absorbed by the plant – cannot simply be washed off.

The review noted that the simplest and most effective way to reduce exposure to chemical residues is to peel fruit before eating, or trim outer layers of bulb vegetables, such as onions, before cooking.

On the downside, this can lead to significant nutrient loss of food value, as nutrients are stored close to the skin surface, potentially outweighing the benefits of removing the residues. Hence, peeling and trimming should be done carefully.

Alternatively, a simple wash under tap water works, to a reasonable extent, without a loss of nutrients. Soaking in water is only marginally better compared with rinsing under running water.

Soaking in a chemical bath is an even more effective method, but thought needs to be given to the chemicals used, given the potential for environmental pollution.

Using baking soda has been touted as a way of removing chemical residues. A 2017 study, published in the Journal of Agricultural and Food Chemistry, noted that a baking-soda solution of two teaspoons per litre of water was more effective than bleach, taking 12 to 15 minutes to remove most of the recently applied non-systemic pesticide residues.

Blanching vegetables in boiling water for a minute is another very good method, if followed by plunging them into iced water or rinsing under cold running water to remove any degraded products or metabolites that are formed. Blanching vegetables before cooking or eating is the best alternative to peeling.

This article was first published in the May 4, 2019 issue of the New Zealand Listener.