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Asparagus – This Seasonal Vegetable Rarely
Has Pesticide Residues

Report from a day in the lab

                                Fans of this „royal vegetable“ can hardly wait for
                                the beginning of asparagus season in mid-April.
                                Whether the classic variant with potatoes and
                                hollandaise sauce or as a gourmet concoction,
                                the average German eats about two kilos per
                                year of this ivory-colored seasonal vegetable
                                delicacy.             As our analyses show, the enjoyment
                                of this underground cultivated vegetable is rarely
                                marred by pesticide residues.

In the years 2010 to 2013, 116 samples of asparagus (106 white and 14
green) were analyzed for the presence of over 650 pesticides. None of
the analyses revealed exceedances of the maximum residue limits (MRL).
However, 56 of the samples (48.3 %) were found to contain residues of
various substances, among which 11 (9.5%) had multiple residues. The
measured values were found overwhelmingly at trace levels under 0.01
mg/kg. In addition, 22 of the samples were analyzed for very polar sub-
stances and their metabolites. Fortunately, only one sample was found
with an excess of the MRL (fosetyl). Additionally, 10 asparagus samples
were tested in 2013 for perchlorate, whereby no suspicious values were to
be found.

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Everything You Wanted to Know About Asparagus

Description of the plant
Asparagus is a monocotyledonous, herbaceous perennial that belongs to
the asparagus family (Asparagaceae). At our latitude the genus Aspara-
gus officinalis L is cultivated. Over the winter only the root stock (rhizome)
survives in the soil, about 35 cm below the soil’s surface. In the spring
several sprouts shoot up from the rhizomes, which grow in a raised, sandy
mound where they stay pale and tender. As soon as the heads of the
sprouts reach the surface the soil
is pushed to the side and the
white stalks are cut off with a
hooked asparagus knife. In the
sunlight        the    white asparagus
stalks     turn       violet   and   finally
green. The asparagus season
officially ends on 24 June (the
birthday of John the Baptist,
closely connected to the onset of
summer). After this, the remain-
ing sprouts grow into up to two-
meter high bushes that provide
the rhizomes with the necessary
nutrients for the following spring.
Despite the adherence to a rest- Asparagus field in autumn.
ing phase in summer and au-
tumn, an asparagus field will be depleted after 10 to 12 years and can no
longer be planted, even with new, cultivated rhizomes. Green asparagus
differs mainly by the cultivation method.      If no mound is formed, the
sprouts grow on the flat soil and can then be harvested as green aspara-
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left: an asparagus sprout pushes into the light; middle: harvesting; right: flat aspar-
agus mound

Origin and History
Asparagus, a domestic European plant, was cultivated much earlier by the
ancient Greeks. They used the dried roots as a diuretic. For the Romans
asparagus was part of every feast. In the 17th century Ludwig XIV of
France made asparagus into a popular culinary trend. But the break-
through for this vegetable came only as it became possible to preserve
asparagus in cans. And it was only in the 19 th century that asparagus
changed its color. It was only by coincidence that the so-called “pale as-
paragus” was discovered to be more tender to the taste. Since then, as-
paragus in Germany has almost solely been grown “under the earth”.

The production of asparagus is lengthy and labor intensive. Asparagus
thrives in light, sandy, water-permeable soil which, ideally, warms up
quickly in the spring. The rhizomes, cultivated out of the red colored ber-
ries, are planted in soil that has been deep-treated with fertilizer in the
previous year. It takes three years before the asparagus can be harvest-
ed for the first time. For pale asparagus a mound of earth will be built up
over the rhizomes planted in rows. The mound must be well-flattened on
top so the asparagus farmer knows in time when the asparagus must be
harvested. A fine tear in the soil indicates the breakthrough of an aspara-
                                   gus sprout. The farmer must then carefully
                                   remove the soil from the sprout up to 35 cm
                                   deep, and then cut the sprout away with an
                                   asparagus knife. The surface of the mound
                                   must then be smoothed over again, so that
Green asparagus.
                                   the next growing sprout is discovered be-
fore it comes into the light.
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Asparagus grown on very large farms is harvested with special machines
that, with help from lasers, find the ripe stalks and cut them completely
automatically.   Today asparagus is often cultivated under plastic. With
clear plastic the starting point of the harvest can be controlled and, in gen-
eral, ensue earlier. With black plastic the coloring of the asparagus can be
prevented and the growth of weeds minimized. Green asparagus is less
laborious – it grows up out of the flat ground and is harvested with a sharp
knife when it has reached its correct height.

Nutrients in Asparagus
Asparagus contains a high amount of water (about 94%) and has a very
low calorie count (13 kcal (52 kJ) per 100 gr asparagus). The heads are
the most tender part and contain more vitamin C than the lower part of the
stalk. The relatively high amount of free aspartic acid accounts for the typ-
ical asparagus aroma.

Pesticides in Asparagus Cultivation
In Germany there are currently 13 fungicidal substances in various pesti-
cides that are authorized for the treatment of the most significant aspara-
gus foliage and root illnesses. Five insecticidal substances are permitted
for use against the asparagus fly and other sucking and biting insects; 11
herbicides are authorized for use in the control of weeds and grasses dur-
ing the various phases of asparagus cultivation.

Table 1: Pesticides Authorized in Asparagus Cultivation in Germany,
Fungicide               Acaricide/Insecticide Herbicide
Azoxystrobin             Dimethoate                Flufenacet
Chlorthalonil            Thiacloprid               Metribuzin
Boscalid                 Alpha-Cypermethrin        Pendimethalin
Epoxiconazole            Lambda-Cyhalothrin        Clomazone
Copper hydroxide         Pyrethrin                 Glyphosate
Dithianon                                          Dimethenamid-P
Kresoxim-methyl                                    Tepraloxydim
Metiram                                            Clethodim
Iprodione                                          Glufosinate
Difenoconazole                                     Bromoxynil
Pyraclostrobin                                     Pyridate
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Detailed Investigatory Results
From 2010 to 2013, using the QuEChERS multi-method, 116 asparagus
samples were analyzed for residues of over 650 pesticides. The largest
portion of these samples (88%) consisted of white, so-called pale aspara-
gus. Only 14 samples (7.1%) were green. Most of the samples came from
Germany (67%), followed by Peru with 19%. Peruvian asparagus mainly
comes onto our supermarket shelves when there is no fresh asparagus
here (e.g. at Christmas). The good news up front: the investigations re-
vealed no exceedances of the MRL. All of the findings were under the EU-
wide established maximum limits (see Table 2).

Table 2: Analyses of over 650 Pesticides with the QuEChERS Multi-
          Matrix               No. Samples                  Samples w/        Samples >        Samples w/
                                                             Residues       Maximum Limit        Multiple
Asparagus,                              14                   5 (35.7%)              0            1 (7.1%)
Asparagus,                              102                  51 (50.0%)             0           10 (9.8%)
TOTAL                                   116                  56 (48.3%)             0           11 (9.5%)

Residues under the ML were detected in 39.5 % of the German and in 75
% of the Peruvian asparagus samples, whereas 6.6% of the German and
20% of the Peruvian samples were contaminated with multiple residues
(see Tables 3 und 4).

Table 3: White Asparagus, by Country of Origin
     Country of             No. Samples                 Samples w/         Samples >      Samples w/ Multiple
        Origin                                              Residues      Maximum Limit        Residues
Germany                            76                   30 (39.5%)              0              5 (6.6%)
Peru                               20                       15 (75%)            0              4 (20%)
Spain                               2                          2                0                 11
Greece                              1                          1                0                 0
Italy                               1                          1                0                 0
Morocco                             1                          1                0                 0
Unknown                             1                          1                0                 0
TOTAL                             102                   51 (50.0%)              0             10 (9.8%)

    No percentage is given for sample quantities under 5.
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Table 4: Green Asparagus, by Country of Origin
   Country of       No. Samples            Samples w/           Samples >      Samples w/
        Origin                             Residues         Maximum Limit        Multiple
Spain                     9                2 (22.2%)               0                  0
Germany                   2                    2                   0                  1
Peru                      2                    0                   0                  0
Thailand                  1                    1                   0                  0
TOTAL                    14                5 (35.7%)               0             1 (7.1%)

Boscalid, a fungicide that is permitted for use in Germany on asparagus
fields, accounted for the largest proportion of the findings. The fungicide
was detected in 25 % of the samples, although mostly at trace levels un-
der 0.01 mg/kg. Chlorpyrifos und imidacloprid, insecticides that are not
approved in Germany for any plant protectors used in asparagus cultiva-
tion, were detected in 12 % and 7 % of the samples respectively: none
were from Germany, mostly from Peru. But also here the amount was
mainly at trace levels of under 0.01 mg/kg, as with the other substances
(see Table 5 and Illustration 1).

Table 5: Pesticide Residues
        Pesticide       Type           w/          <0.01   <0.02   <0.05     Maxi-    Samples
                                    Residues       mg/kg   mg/kg   mg/kg     mum         >
                                                                            (mg/kg)   Maximum
 Boscalid            Fungicide        29            27      2          0    0.016       0
 Chlorpyrifos        Insecticide      14            12      2          0    0.019       0
 Imidacloprid        Insecticide       8            8       0          0    0.008       0
 Pendimethalin       Herbicide         4            4       0          0    0.002       0
 Cyprodinil          Fungicide         3            2       0          1    0.03        0
 Metribuzin          Herbicide         2            2       0          0    0.004       0
 Isoproturon         Herbicide         1            1       0          0    0.001       0
 Haloxyfop           Herbicide         1            1       0          0    0.002       0
 Fludioxonil         Fungicide         1            0       0          1    0.028       0
 Fenhexamid          Fungicide         1            1       0          0    0.009       0
 Dodine              Fungicide         1            1       0          0    0.004       0
 Diuron              Herbicide         1            1       0          0    0.001       0
 DDT                 Insecticide       1            1       0          0    0.002       0
 Cypermethrin        Insecticide       1            0       0          1    0.03        0
 Bifenthrin          Insecticide       1            0       0          1    0.024       0
 2,6-                Metabolite
 Dichlorbenzamide                      1            1       0          0    0.001         0
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                        Frequency of Detected
                           Substances (>1)
      Metribuzin          2

       Cyprodinil             3

  Pendimethalin                   4

    Imidacloprid                      8

     Chlorpyrifos                                14

         Boscalid                                                             29

                    0             5   10        15        20        25        30       35

Illustration 1:Frequency of Detected Substances (> 1) Among 116 Analyzed Samples

Investigations with QuPPe
            Info Box

            Pesticides with high polarity escape detection with use of the QuEChERS multi-

            method. For these strongly polar substances we developed the QuPPe Method
            (Quick Polar Pesticides Method). The polar substances are extracted from
            homogenized plant-based foods with acidified methanol (w/ the addition of
            stable isotope-labeled standards, when nec.). After centrifugation the extract is
            filtered and the substances are identified by means of LC-MS/MS. Individual
            groups of polar pesticides are quantifiable with various LC-MS/MS methods
            (see also Table 6). The methods are continually updated and developed and
            applied to new substances.

            You can find more information on QuPPe on the Internet, at .

Due to the difficulty of finding highly polar pesticides using the normal mul-
ti-methods, 22 asparagus samples were also analyzed for highly polar
pesticides (see Table 5). Fortunately, only one sample contained a sub-
stance in excess of the ML. This asparagus sample from Germany con-
tained 3.4 mg/kg phosphorous acid. Phosphorous acid exists as a me-
tabolite of fosetyl. The sum of fosetyl and phosphorous acid was over the
EU-wide valid maximum limit of 2 mg/kg for these residues. These anal-
yses of polar pesticides should be continued in 2014.
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Table 6: QuPPe Substances and their Mode of Action

Pesticide                 Type
                          Insecticide from cartap, bensultap,
Nereistoxin               thiocyclam or thiosultap
Difenzoquat               Fungicide/Herbicide
Cyromazine                Insecticide
Chlormequat               Plant growth regulator
Mepiquat                  Plant growth regulator
Chlormequat               Plant growth regulator
Glyphosate                Herbicide
Fosetyl                   Fungicide
Ethephon                  Plant growth regulator
HEPA                      Ethephon-Metabolite
Maleic acid hydrazide     Plant growth regulator
Glufosinate ammonium      Glufosinate-Metabolite
Daminozide                Plant growth regulator
Phosphorous acid          Fosetyl-Metabolite
AMPA                      Glyphosate-Metabolite
N-Acetyl-AMPA             Glyphosate-Metabolite
Glufosinate               Herbicide
MPPA                      Glufosinate-Metabolite
N-Acetyl-Glufosinate      Glufosinate-Metabolite
Trimethylsulfonium-Cation Glyphosate-Counterion
Diquat                    Herbicide
Paraquat                  Herbicide

In 2013 perchlorate und chlorate were integrated into the QuPPe method.
Ten samples of asparagus were also tested for these substances; the
measures values for all the samples were unremarkable.

          Franke, Wolfgang (1997) Nutzpflanzenkunde, Thieme Verlag
          Wyk, van Ben-Erik (2005) Handbuch der Nahrungspflanzen, Wis-
          senschaftliche Verlags GmbH Stuttgart
          Bickel-Sandkötter (2003) Nutzpflanzen und ihre Inhaltsstoffe, Quel-
          le & Meyer Verlag Wiebelsheim
          Pflanzenproduktion 2013, Pflanzenschutz im Erwerbsgemüsebau,
          LTZ Augustenberg,
          Pflanzenschutzmittel-Verzeichnis    2013,   61.   Auflage,    BVL,

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Photo Credits:
Asparagus, val th,, Image-ID=268570.
Dem Licht entgegen, Silke Bogorinski,, Image-ID 651128.
Spargelfeld im Herbst, moorhrmr,, Image-ID 193516.
Spargelzeit: Spargelernte 06, Thommy Weiss,, Image-ID
Spargelstecher, Jürgen Sörensen,, Image-ID 261472.
Grüner Spargel, Hubert Zipper, CVUA Stuttgart.

Authors: Dr. Ingrid Kaufmann-Horlacher, Ellen Scherbaum,
Carmen Wauschkuhn

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