Neonicotinoids are on everyone´s lips, but are they also on everyone´s plates?

Residue Situation in Fruits and Vegetables

Report from a day in the lab

Ellen Scherbaum

 

Photo: Fruits and Vegetables.

 

It was already back in 2003 that CVUA Stuttgart developed and published a method for determining the presence of neonicotinoids [1]. At that time there were a large number of violations due to the exceedance of the legal maximum level for this relatively new class of substances in fruits and vegetables. In the meantime, the maximum levels for this substance have been harmonized EU-wide and exceedances are seldom. However, in the last few years this group of substances has attracted attention once again: they are toxic to bees. The EU Commission decided in the summer of 2018, therefore, that three of these substances may only be allowed for cultivation under glass. This gave us reason to evaluate the current residue situation in fruits and vegetables once again.

 

Maria Roth, former head of CVUA Stuttgart, said in a 2004 interview:

It is not difficult to analyze fruits and vegetables for 200 different pesticides and find no residues. The trick is to detect the right substances. In 2003 CVUA made a giant leap forward: the examiners developed a method that was able to detect neonicotinoids, a relatively new pesticide group. Suddenly the rate of violations for solanaceous plants such as tomatoes and eggplants shot up.

 

A Story of Ups and Downs for Neonicotinoids

Neonicotinoids are a group of substances that have excellent insecticidal properties. The first substance to be commercialized was imidacloprid, in 1991. It was extremely successful, and other substances and preparations soon followed (see Illustration 1).
The basis for this worldwide triumph of neonicotinoids (offspring of the natural insecticide nicotine) lies in their extraordinary properties: they have a wide spectrum of efficacy, are well absorbed into plants, and are distributed systemically within the plants. Moreover, even small amounts are effective, they have a low toxicity for warm-blooded animals, and they have an effect mechamism of action that differs from other insecticides. The substances attach themselves to the acetylcholine receptors of the nerve cells in insects and cannot be degraded by the enzyme acetylcholinesterase. This causes a constant irritation and disturbance of the chemical signal transmission. Nicotine has the same effect.   

 

Ill. 1 Structural formulae of the most important neonicotinoids: degradation of chlothianidin, results in the formation of thiamethoxam, a substance which is also used on its own.

Ill. 1 Structural formulae of the most important neonicotinoids: degradation of chlothianidin, results in the formation of thiamethoxam, a substance which is also used on its own.

 

In 2008 massive numbers of bees died in Oberrheingraben (a German region on the river Rhein), where 700 beekeepers with about 12,000 bee colonies were affected. Abraded dust particles resulting from the improper application of chlothianidin on maize ended up on surrounding fields, where it came in contact with the bees [2].
This problem was resolved by taking appropriate technical measures, but the issue of neonicotinoids as a cause of bee mortality continued over the following years. 
In February 2018 the European Food Safety Authority (EFSA) finally determined that most of the applications of neonicotinoid-containing pesticides pose a risk for wild and honey bees [3]. EFSA updated the risk evaluations for three neonicotinoids (clothanidin, imidacloprid, and thiamethoxam). On 19 September, 2018 the EU Commission banned these three substances for use in open fields [4].

 

Neonicotinoids – Residues in conventionally produced fruits and vegetables

The annual analyses of over 2,500 plant-based samples for pesticide residues in Baden-Württemberg are centralized at CVUA Stuttgart. Over 1,000 different substances are covered in this analytical spectrum, some of which are neonicotinoids, of course.

 

This is what we found in 2018:

A total of 1,857 samples of conventionally produced fruits and vegetables were analyzed for this substance group in 2018. Residues of one or more neonicotinoids were detected in 550 samples (30 %). Since the amount of insectide needed is comparatively small, the residue amounts tend to be low as well. If we only consider the residue amounts that were equal to or higher than 0.01 mg/kg (the orientation value for organic foods and the limit value for baby food), only 232 samples (12.5 %) remain.

As seen in Table 1, residues of acetamiprid and imidacloprid were detected in approximately 10–1 % of the samples; with thiacloprid it was 8.5 % of the samples. Dinotefuran and nitenpyram don’t play much of a role, as they were never authorized for use in the EU. One sample of coriander of unknown origin contained nitenpyram in amounts exceeding the legal maximum and was therefore rejected.  

 

Table 1. Neonicotinoids in Conventional Fruits and Vegetables, 2018. Sample size: 1,857
Parameter
w/ Residues (in %)*
Min (mg/kg)
Max (mg/kg)
No. >MRL**
Acetamiprid
210 (11 %)
0,001
1,6
2
Clothianidin
69 (3,7 %)
0,001
0,11
 
Dinotefuran
0
 
 
 
Imidacloprid
183 (9,9 %)
0,001
1
 
Nitenpyram
1
0,11
0,11
1
Thiacloprid
158 (8,5 %)
0,001
1,9
 
Thiamethoxam
94 (5,1 %)
0,001
0,26
1

* No calculation for samples < 5

** MRL=Maximum Residue Level

 

A total of only four samples contained neonicotinoids in amounts over the legal maximum limit (see Table 2). Two samples were formally rejected and were found to be unmarketable; two had amounts over the legal maximum, but in consideration of the analytical variance the exceedance was not verified. In these cases the commercial enterprises were informed of our findings so that they could take appropriate measures into their own hands.

 

Table 2. Exceedances of MRL: Neonicotinoids in Conventional Fruits and Vegetables, 2018. Sample size: 1,857
Food Country of Origin Substance Amount (mg/kg) Assessment
MRL (mg/kg)
Pomegranate Turkey Acetamiprid
0,13
> MRL*
0,01
Eggplant Spain Acetamiprid
0,24
>MRL, statistically not verified
0,2
Coriander Unknown Nitenpyram
0,11
> MRL
0,01
Ginger Unknown Thiamethoxam
0,015
>MRL, statistically not verified
0,01

*MRL=Maximum Residue Level

 

Due to the low level of toxicity for warm-blooded beings, none of the amounts found in any of the samples presented any health risk.

 

Info Box

Maximum Residue Levels (MRL)

Maximum levels for residues are no toxicological endpoint or limit value. They are derived from residue experiments that are conducted under realistic conditions. A comparison of the expected residues is then made with the toxicological limit values, to ensure there is no health risk associated with life-long or even a one-time intake of the substance.

Maximum residue levels regulate trade, and may not be exceeded. Foods with residue amounts over the MRL are not marketable; they may not be sold. Not every exceedance of the MRL is associated with a health risk, however. A differentiated consideration is therefore necessary [5].

 

Among the neonicotinoids that will no longer be authorized for use in open fields is imidacloprid, the most commonly detected substance in fruits and vegetables. The distribution of imidacloprid residues found in individual fruit and vegetable groups is presented in Table 3. At this time the most affected food groups are fruiting vegetables (e.g. beans, cucumbers, bell peppers and tomatoes), sprouting vegetables (e.g. broccoli, cauliflower, kohlrabe, asparagus and fennel), stone fruits (e.g. plums, peaches, nectarines and apricots), and citrus fruits.

Illustration 2 shows that most of the residue amounts are low.

 

Table 3. Imidacloprid in Conventional Fruits and Vegetables, 2018. Sample size: 1,857
Food Category
No. Samples
w/ Residues (%)
Ave. amount* (mg/kg)
Max (mg/kg)
Min (mg/kg)
Leafy Vegetables
413
35 (8,5 %)
0,041
1,0
0,001
Fruiting Vegetables
427
65 (15,2 %)
0,021
0,20
0,001
Sprouting Vegetables
139
17 (12,2 %)
0,005
0,018
0,001
Root Vegetables
91
6 (6,6 %)
0,003
0,006
0,001
Exotic Vegetables
3
0
-
-
-
Berries
219
8 (3,7 %)
0,149
0,97
0,002
Pome Fruit
106
1 (0,9 %)
0,004
0,004
-
Stone Fruit
193
24 (12,4 %)
0,007
0,030
0,001
Citrus Fruit
109
20 (18,3 %)
0,006
0,025
0,001
Exotic Fruit
157
7 (4,5 %)
0,026
0,075
0,002

*Ave. amount of the positive samples

 

Ill. 2 Frequency Distribution of the Detected Imidacloprid Residues.

Ill. 2 Frequency Distribution of the Detected Imidacloprid Residues.

 

We’ll have to wait and see whether the change in application possibilities also reduces the amount of detected residues. What is known, at least, is that fruiting vegetables are mostly grown under glass or sheets, so not much change is to be expected for this food group.
One difficulty for the laboratory is that the method of cultivation is not subject to labeling. Revealing whether a food sample came from a greenhouse or an open field is optional. That means we can’t differentiate samples that came from a market; only those coming directly from the producer.
In any case, the situation regarding neonicotinoids in fruits and vegetables has quieted down in comparison to 2003. At that time we reported that this substance group accounted for 43 % of the MRL exceedances in solanaceous plants and the pumpkin family (cucurbits) [6]. Our conclusion today: about 30 % of the fruit and vegetable samples contain residues of neonicotinoids, but most of the amounts are very low and exceedances are seldom.

 

Outlook: we’re staying vigilant and will continue our investigations.

 

Photo Credit

Andrea Karst, CVUA Stuttgart

 

References

[1] Simultaneous Determination of Neonicotinoid Insecticides in Fruits and Vegetables by LC-MS and LC-MS-MS – Methodology and Residue Data, Diane Zywitz, Michelangelo Anastassiades, Ellen Scherbaum, Deutsche Lebensmittel-Rundschau 99 (2003) 188–196

[2] Minister Hauk legt Ergebnisse von Untersuchungsprogramm zu den Ursachen des Bienensterbens am Oberrhein vor (viewed on 16.01.2019)

[3] EFSA, Neonicotinoide: Risiken für Bienen bestätigt, (viewed on 16.01.2019)

[4] BVL, Widerruf der Zulassung von Pflanzenschutzmitteln mit den neonikotinoiden Wirkstoffen Clothianidin, Imidacloprid und Thiamethoxam zum 18. September 2018 (viewed on 16.01.2019)

[5] BVL-Broschüre, Pflanzenschutzmittel – sorgfältig geprüft, verantwortungsvoll zugelassen, November 2009

[6] Rückstände von Pflanzenschutzmitteln in Nachtschatten- und Kürbisgewächsen 2002–2004 (viewed on 18.01.2019)

 

History of Updates

22.07.2019: Flonicamid findings were removed from the report to correct an error in its classification.

 

Translated by: Catherine Leiblein

 

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Report published on 07.02.2019 10:19:31