Why washing fruit and vegetables can aid a clean bill of health

The benefits of consuming your five a day are clear, but pesticide residue can pose a health risk

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One health message we all hear is that we should eat plenty of fruit and vegetables.

The World Health Organisation recommends a daily intake of at least five portions of different fruit and vegetables, although some research indicates that we should consume 10 a day.

Potential benefits include a reduced risk of strokes, heart attacks and some cancers.

Yet when we follow such advice, we may consume pesticide residues alongside the vitamins, minerals, antioxidants and fibre.

How common are pesticide residues in fruits and vegetables?

A paper published in the journal Food Control in January last year analysed previous studies and found that 61 per cent of fruit and vegetable samples from the Middle East “contained insecticides above the authorised limits”.

As well as insecticides, herbicides used to control weeds may find their way into food.

Another study, by researchers at Dubai Municipality and the University of Sharjah and released in Food Control in November, looked at fresh vegetables imported into Dubai in 2018 and 2019. It found that 30.5 per cent of samples had pesticide residues above the maximum residue limit.

“The majority of the samples with pesticides above the MRLs were imported from developing countries,” the researchers wrote. They said broad beans were among the most heavily contaminated foodstuffs.

A US organisation, the Environmental Working Group, publishes a list of the “dirty dozen” fruits and vegetables most heavily contaminated with pesticides.

Tomatoes are on the dirty dozen list of fruit and vegetables most likely to have traces of pesticide. AFP

The 2022 group includes strawberries, spinach, kale, collard and mustard greens, nectarines, apples, grapes, bell and hot peppers, cherries, peaches, pears, celery, and tomatoes.

With some fruits and vegetables, including apples and strawberries, more than 90 per cent of samples contained residues of at least two pesticides.

The organisation also publishes a “clean 15” list of fruits and vegetables with low contamination rates: avocados, sweetcorn, pineapples, onions, papaya, frozen sweet peas, asparagus, honeydew melons, kiwis, cabbages, mushrooms, cantaloupes, mangoes, watermelons and sweet potatoes.

What health effects can consuming pesticide residues have?

The University of Washington reports that limited research has been carried out on the health effects of consuming pesticide residues in food, with studies focusing instead on people, such as farmworkers, exposed to the substances at work.

Links with conditions such as respiratory problems, miscarriage, birth defects, cancer and Parkinson’s disease, among others, have been detected.

One study that did look at the effects of consuming pesticide residues found that Attention Deficit Hyperactivity Disorder was more common in children thought to have eaten larger amounts.

These children had higher levels of the breakdown products of pesticides in their urine, indicating that they had consumed more in the first place.

As well as pesticide residues, fruit and vegetables — like other foods — may be contaminated with potentially harmful bacteria and viruses.

How can washing and cooking remove pesticide residues?

DUBAI, UNITED ARAB EMIRATES, MAY 18, 2016. Washed apples at Fruitful Day's sorting facility.

Fruitful Day, founded by a group of friends, delivers fresh fruit directly to people's homes and workplaces.

Photo: Reem Mohammed/ The National (Reporter: Michael Fahy / Section: NA) Job ID 50541 *** Local Caption ***  RM_20160518_FRUITFUL_04.JPG

Prof Parvez Haris, professor of biomedical science at De Montfort University in the UK, says that washing fruits and vegetables “is likely to reduce your exposure to pesticides”.

“Some of the pesticides located on the outer surface of fruits and vegetables are likely to be removed by washing, but not those that are located within the fruits or vegetables,” he says.

The effectiveness of washing increases with time, says Charles Ssemugabo, who researches pesticide residues in food at the School of Public Health of Makerere University in Uganda.

“If you’re going to wash, wash for a minute and not just 10 seconds,” he says. “If you’re using warm water, that could be more effective than just cold water.”

Washing is best undertaken shortly before fruits and vegetables are eaten or cooked, because otherwise moisture may allow bacteria to grow and cause the food to go off.

Sodium bicarbonate is sometimes used to improve the effectiveness of washing, with fruits or vegetables soaked for between 12 and 15 minutes in a solution of one teaspoon in two cups of cold water.

Where possible, fruit and vegetables should be peeled, says Prof Haris. He says that removing the outer leaves of leafy vegetables may be useful, since they are likely to have higher levels of pesticides.

The ideal, says Mr Ssemugabo, is to combine washing and peeling, as this can maximise pesticide removal. Cooking, such as boiling or blanching, also reduces pesticide residues.

“Applying these methods in combination does make them more effective, so by the time you get to actually eat the fruit and vegetables, the levels that you’re now getting exposed to, if at all, are below the toxicological standards,” says Mr Ssemugabo.

How does choosing what you eat help?

Melons, Oranges, and Sweetcorn at Farmers Market (iStockphoto.com)

Another recommendation is to eat a diverse array of fruits and vegetables to limit exposure to particular pesticides common in certain fruits or vegetables.

“Do not consume very high quantities of any one type of fruit or vegetable, especially if they are likely to be categories of fruits and vegetables that are widely known to be most often contaminated with pesticides,” says Prof Haris.

“Whenever possible eating organic fruits and vegetables, where pesticides have not been used, is advisable. If you have access to a garden or even a rooftop, you could consider growing your own organic fruits and vegetables.”

Both Prof Haris and Mr Ssemugabo are clear that people should not cut their overall fruit and vegetable intake to limit their exposure to pesticides, as the benefits of consuming these natural and healthy foods outweigh the drawbacks.

“I would encourage people to eat them in large quantities,” said Mr Ssemugabo. “Consume them, but be cautious, especially in environments where they do not have a good monitoring system.”

Updated: April 09, 2022, 6:28 AM