Pesticide residues in food: risks of multiple residues and how to avoid them
What are pesticides?
Before listing the things you need to know in order to avoid pesticide residues in food, a clarification is necessary: we say pesticides, but we mean generically “all phytosanitary products“; that is those used in conventional (but also in organic) agriculture, to protect crops from weeds, or from parasites or diseases, with the intent to safeguard food production. These substances are considered among the regulated risks, just like additives and GMOs.
Each year worldwide we consume about 2 million tons of pesticides1, which can be divided into 47.5% herbicides, 29.5% insecticides, 17.5% fungicides and 5.5% other pesticides2.
In every civilized country, human health is protected by law against risks related to pesticide residues in food. The Italian Ministry of Health defines the point as follows: “Products of plant origin must not contain, at the time they are put into circulation, residues of active substances contained in plant protection products (in other words, pesticide residues) that exceed the maximum residue limits (MRLs) established by law”. These levels (MRLs) are the legally authorized upper limits for the concentration of pesticide residues in or on the surface of food or feed, and are used to calculate the acceptable daily intake, ADI3.
To approve a pesticide and thus identify its threshold of toxicity, it is necessary to first determine the value of no-observed adverse-effect level (NOAEL): that is, the level of concentration for which it does not generate any effect, even on the subjects most at risk.
In the United States, the allowable level of pesticide intake (the amount a normal person would consume in a day) on any food is set at 1% of the NOAEL. This means that you would have to eat 100 times the normal amount just to get to the level that could begin to affect a highly sensitive individual.
So can we consider ourselves out of danger? Despite all these compelling premises, apparently not.
Why should we be concerned about pesticide residues in food?
No one is excluded from the risk of low-level poisoning due to pesticide residues in food; and with it the risk of chronic disease and adverse health effects, including: cancer, reduced fertility, various levels of cognitive and neurological disorders such as Parkinson’s, Alzheimer’s, or other; autoimmune diseases, hormonal disorders, particularly thyroid problems, and many others4, 5, 6, 7.
How we are protected?
EFSA, the European Food Safety Authority, in its 2018 periodic report, showed that in a total of 91,015 samples analyzed among fruits and vegetables grown and put up for sale on European soil, 95.5% contained traces of pesticides within permitted levels8. The percentage of samples containing quantifiable residues within the legal limits was 53.5%.
If the risk is so low, why consumers associations are not satisfied?
Multiple residues: what does it mean?
EFSA or other monitoring bodies in their reports mainly take into account the single active ingredients, but in reality the use of mixes of pesticides is anything but rare. The EFSA report shows that in about one out of three food products (29% of samples) residues of two or more pesticides have been detected.
To define the term “more residues”, I could talk about the Made in Italy results: in the “Stop Pesticides” report published by Legambiente in 2019, in Italy 18% of samples contained multiple residues – approximately one out of five – with some striking examples: strawberry samples up to 9 pesticides; or peppers with as many as 25 of different formulations9.
And here’s the pitfall!
Paracelsus said “it is the dose that makes the poison“, a statement that was accepted by all scientists; but in spite of the possible cumulative risks of single residues, we must also analyze how these possible 8 or more chemicals interact with each other: something that nobody knows exactly!
When it comes to multiple residues, two potential effects are generally feared: one is the synergistic effect (one substance increases the toxic effect of the other), not taken into much consideration because of the doses involved, insufficient to create damage; the second is the cumulative effect, which requires more in-depth analysis.
And the problem does not concern only a few specimens, since the multiple residue seems to be more frequent than the single residue: from the report of Legambiente, 18% vs 15%.
In April 2020, EFSA proudly announced that it had developed a model of analysis ‘Euro Mix‘, for the Assessment of Cumulative Risks caused by mixtures of toxic substances in food. While we all hoped to have finally arrived at the application of the famous precautionary principle (consisting in prohibiting the use of a substance until it is verified that it has no dangerous consequences), we have experienced yet another disappointment.
The study (even if defined as pilot) shows that pesticide mixtures have no effect on human health, including for the most vulnerable groups such as young children or individuals with serious health problems: this is based at the moment only on acute toxic effects on the nervous system and chronic toxic effects on the functioning of the thyroid gland.
I am not a doctor but I certainly know enough to understand that looking for acute effects on the nervous system, for which the mode of intake of such poisons occurs normally in low doses especially if we are talking about infants or fetuses, it does not seem to me the best choice.
I have studied a great number of studies on this subject and, frankly, I think that the method adopted, i.e. the completely hypothetical approach (in other words, probabilistic, thanks to computer-aided models in silico rather than in vivo) is rather inadequate, given the high stakes involved10.
Of course, I am happy that animal testing has been avoided, but even with cruelty-free methods, I would expect a better study. The evaluations mentioned above cannot offer us certainties on such a delicate issue, as unexplored or perhaps better to say currently “unexplorable”: today on the market there are more than 500 active ingredients registered as pesticides 11, for which the variants and variables to be tested in various concentrations and / or formulations, would require an endless work of analysis, but not for this indispensable.
It’s time to change the course!
More specific and consumer-friendly laws are needed, as well as tangible supports to farmers in economic but also educational terms: for an ecological and sustainable agriculture, it is not enough to enact laws and ask operators to reduce pesticide use, if they are not provided with widespread know-how or valid alternatives to plant protection chemicals dangerous to humans and the environment.
Especially if governments have allowed the global use of pesticides to increase as much as 46% from 1996 to 201612, they will have to find a way to halve their quantity; but without inventing projects, which are “green” on paper and useful only to distribute subsidies always to those who practice intensive agriculture.
Of course, I am referring to “the New Green Deal“, developed by EFSA in order to improve the food production sector by 2030.
4 goals/key points were set (13):
– more sustainable agriculture in terms of energy and greenhouse gas emissions;
– 25% increase in the area used for organic farming;
– reduction, i.e. halving of plant protection products (PPPs) and 20% of fertilizers;
– and last but not least the halving of the consumption of antibiotics for livestock and aquaculture (if you want to learn more you can read the mini book).
However, last October, the Council and the European Parliament changed the rules of the game, leaving all those who were yearning for a finally positive change, strongly disappointed; as stated by the national president of Legambiente Stefano Ciafani “We were expecting an ambitious CAP (Common Agricultural Policy) aimed at reducing emissions and impacts, undertaking a radical change of the agricultural and food system. Nearly 60 billion euros of EU contributions are spent every year on CAP subsidies, mostly to finance a model of intensive agriculture”.
How can we avoid pesticide residues in food?
That’s the picture we have ahead, unfortunately, and I know that we can’t wait until 2030 to be sure that we are bringing nothing toxic to our tables; so we should consider our options.
According to the 2019 Mintel Global New Products Database, over the past 10 years the total number of new organic food products introduced in Europe, has increased from 9% to 17%14. There is much more awareness, interest in wellness, health but also ethics; of course wealth compared to the rest of the world contributes to this tendency.
On the other hand, we all would buy food that does not harm us or the environment, such as most of the organic labeled products, only if they were cheaper.
For several years in the United States, a group of independent activists under the non-profit organization Environmental Working Group (EWG) have been drawing up two lists of foods each year: the “Clean 15” and the “Dirty Dozen“, thus telling consumers which foods can be purchased from conventional agriculture and which can only be purchased from organic agriculture15.
In the list of 15 clean we find (from cleanest to least): avocado, sweet corn, pineapple, onion, papaya, frozen sweet peas, eggplant, asparagus, cauliflower, cantaloupe, broccoli, mushrooms, kale, green melon, kiwi.
Among the dirty instead we have (from the most to the least dirty): strawberries, spinach, kale, nectarines, apples, grapes, peaches, cherries, pears, tomatoes, celery, potatoes (the thirteenth place was assigned to red peppers).
Many contest the methodology in determining the foods defined as “toxic” for health, as they also use probabilistic methods (!). Some rightly ask why they do not do the same analysis for pesticide residues on organic food. I write “rightly”, because organic farming does not mean zero pesticides; on the contrary they use a lot of them, even if not synthetic ones (conventional agriculture uses on average 3.2 different pesticides, while organic 0.8).
But if you are a EU resident, you would like to know which unprocessed food products contain the highest frequency (above 65%) of multiple residues according to EFSA8: was found in currants (black, red and white) (75.6% of the total unprocessed samples analyzed), chilli peppers (70.2%), lemons (68.1%), table grapes (68.1%), strawberries (67.7%), grapefruit (67.4%), Roman rocket/rucola (65.8) and sweet cherries (65.1). Celeries, lamb’s lettuce/corn salads, limes, parsley, pears, mandarins, peaches, basil and edible flowers, wine grapes, yard long beans, raspberries (red and yellow), oranges, passion fruit/maracujas and bananas were found to contain multiple residues in more than 50% of the samples analyzed. The highest frequency of multiple residues (above 40%) was found for processed dried hops (76%), castor beans (63%), grapefruit (59%), goji berries (55%), grape leaves and similar species (53%), poppy seeds (50%), table grapes (44%) and teas (41%). And no MRL exceedances were reported for wine grapes, chestnuts, coffee beans, rhubarb, soybeans, walnuts, kidney (from sheep), milk (cattle and goat) and muscle (poultry and swine). But the highest MRL exceedance rates (greater than 15%) were identified for watercress, coriander leaves, grape leaves, chilli peppers, fruits and tree nuts, basil and edible flowers, horseradish, passion fruit, pomegranates, yard long beans, peas with pods, cassava roots, teas, pithaya and rice.
Is there anything we can do to reduce the concentration of pesticide residues in food?
Consider that just simply washing with running water, removes about 75-80% of it.
The Italian CSE – Center for Science and Environment, recommends using lightly salted water to remove most of the pesticide residues on fresh food surfaces. Exactly the same thing is suggested by the Center for Science and Environment in New Delhi, India: washing fruits and vegetables in a 2% solution of salt water will remove most of the residues present on the skins.
Another trick is to use washing water at room temperature; in a research done by washing vegetables of the same origin at different temperatures, it was found that compared to 5 and 10 degrees, the best results are obtained with water at 22 degrees; the higher the temperature, the easier it will be to get rid of pesticides.
After everything said so far, you will have understood that buying organic products will not exempt you from washing them: although pesticides are not synthesized in agreement, some of them are naturally toxic.
Also, don’t think that “taking off the peel” exhausts your task: usually research on pesticide residues in food is done on already peeled produce, if it is commonly consumed without the peel.
I should mention that the use of vinegar or baking soda is not recommended in general, because we cannot predict whether vinegar (acid medium) or carbonate (basic medium) can be effective, as the consumer cannot know what kind of pesticide residue is present on food.
Experts from the University of Massachusetts have however demonstrated that by soaking apples in a mixture of water and bicarbonate for about fifteen minutes, it is possible to eliminate pesticide residues by 80-96%: 15 minutes of waiting is a very small organization but with a lifesaving potential for many other vegetables.
When washing vegetables with layered leaves, it is advisable to remove the external parts, i.e. those most exposed to pesticides, before starting the washing process.
Leafy vegetables should be washed leaf by leaf, under running water.
Instead scrub well the skins (if they have a hard skin) of vegetables or fruits such as melon, watermelon, or root vegetables such as carrots, potatoes, etc., with a nail brush.
But perhaps the most useful advice would be to buy only seasonal foods: in a research conducted by Greenpeace Türkiye16, the amount of pesticide residues contained in samples of tomatoes, cucumbers and peppers in August (a total of 56), doubled in October (becoming 96) and tripled (becoming 139) in November. To learn which foods are in season, you can read this article “Seasonal Fruits and Vegetables: the importance of eating seasonally“.
So there is no reason to be alarmed and stop eating fruits and vegetables; the important thing is to know our options and make an aware decision.
Good revolution to all.
1) J. Popp, K. Pető, J. Nagy Pesticide productivity and food security. A review Agronomy for Sustainable Development, 33 (1) (2013), pp. 243-255
2) Mohamed A. Hassaan, Ahmed El Nemr, Pesticides pollution: Classifications, human health impact, extraction and treatment techniques, The Egyptian Journal of Aquatic Research, Volume 46, Issue 3,
2020, Pp 207-220, ISSN 1687-4285
3) Portale del Ministero della Salute visitabile dal seguente link http://www.salute.gov.it/imgs/C_17_pubblicazioni_1981_allegato.pdf
4) Ma K, Wu HY, Zhang B, He X, Li BX. Neurotoxicity effects of atrazine-induced SH-SY5Y human dopaminergic neuroblastoma cells via microglial activation. Mol Biosyst (2015) 11:2915–24.10.1039/c5mb00432b
5) Li Q, Kawada The mechanism of organophosphorus pesticide-induced inhibition of cytolytic activity of killer cells. T. Cell Mol Immunol. 2006 Jun;3(3):171-8.
6) Hoshi N, Hirano T, Omotehara T, Tokumoto J, Umemura Y, Mantani Y. Insight into the mechanism of reproductive dysfunction caused by neonicotinoid pesticides. Biol Pharm Bull (2014) 37:1439–43.10.1248/bpb.b14-00359
7) Colosio C, Alegakis AK, Tsatsakis AM. Emerging health issues from chronic pesticide exposure: innovative methodologies and effects on molecular cell and tissue level. Toxicology (2013) 307:1–2.10.1016/j.tox.2013.04.006
8) Paula Medina‐Pastor Giuseppe Triacchini The 2018 European Union report on pesticide residues in food European Food Safety Authority (EFSA) First published: 02 April 2020 https://doi.org/10.2903/j.efsa.2020.6057
9) il Dossier Stop Pesticidi di Legambiente visibile su www.legambiente.it
10) Maggi, F., Tang, F.H.M., la Cecilia, D. et al. PEST-CHEMGRIDS, global gridded maps of the top 20 crop-specific pesticide application rates from 2015 to 2025. Sci Data 6, 170 (2019). https://doi.org/10.1038/s41597-019-0169-4
11) Peter S Craig et. al Cumulative dietary risk characterisation of pesticides that have chronic effects on the thyroid. European Food Safety Authority (EFSA) 29 April 2020 https://doi.org/10.2903/j.efsa.2020.6088
12) FAO: FAOSTAT Online Database (http://faostat.fao.org/.2019)
14) Mintel Database del 2019 visibile dal seguente link https://www.mintel.com/global-new-products-database
15) for 2020 you can see both twi lists from the official website of EWG https://www.ewg.org/foodnews/dirty-dozen.php
16) Soframızdaki Tehlike – The Danger On Our Table 2020 Greenpeace Türkiye visible on https://www.greenpeace.org/static/planet4-turkey-stateless/2020/01/a314cc16-soframizdaki-tehlike-pestisit-greenpeace-rapor.pdf