Poisonous Weeds Among Salad Leaves? Ragwort Found in Arugula

Ein Bericht aus unserem Laboralltag

Silvia Zechmann and Thomas Kapp

 

Much that nature provides us with must be enjoyed with caution. Ragwort (Senecio jacobaea), a poisonous weed, has yet again been found in a package of arugula (rocket salad); this weed can be confused with arugula because it looks similar. The problem is that ragwort contains high concentrations of the poisonous pyrrolizidine alkaloids (PAs). These can cause serious liver damage, and have proven to be carcinogenic and genetically harmful to some types of animals. The contamination of arugula with ragwort has already made headlines in the past.

 

Arugula.

Photo: Silvia Zechmann

 

What is ragwort and how can it be distinguished from arugula?

The term “ragwort“ encompasses the various types of plants of the botanical species Senecio. All Senecio species belong to the family of composite plants (Asteraceae). Most important, however, are the widespread “common ragwort“ (Senecio vulgaris, L. and Senecio jacobaea, L.).

 

The buds and blossoms of composite plants, including ragwort, differ significantly from the flowers of arugula plants. As a typical cruciferous plant (Brassicaceae), depending on the type, arugula forms bright yellow to cream-colored blossoms with exactly four leaves shaped in the form of a cross. In addition, the closed buds of the arugula plant are drop-shaped. In contrast, the undesirable ragwort has basket-shaped inflorences (see Illustration 1), which are filled with several yellow single flowers (so-called tubular florets).

 

Common ragwort with flower buds.

Illustration 1: Common ragwort (Senecio vulgaris) with its characteristic basket-shaped flower buds.
Source: Pixabay.de, Image: senecio-vulgaris-844623, CC0 Public Domain.

 

It is more difficult to recognize the difference when there are no flowers to be seen. Thus, when in doubt, one should generally remove any unusual-looking leaves. This is especially so, when the leaves in question are hairy or have unusual, serrated edges. Another distinction would be the absence of arugula‘s characteristic smell.

 

Examples of arugula leaves.

Illustration 2: Examples of arugula leaves, differing by age and type. In very young leaves the typical lobed leaf forms are not always fully pronounced. Photo: Silvia Zechmann.

Leaf forms of common ragwort.

Illustration 3: Leaf forms of common ragwort (Senecio vulgaris). If the serration of the leaves is not very pronounced there is a higher likelihood of confusion with arugula. Photo: Silvia Zechmann.

 

What are pyrrolizidine alkaloids and what effect do they have on humans?

Pyrrolizidine alkaloids (PA) are a group of several hundred structurally related single compounds. They protect the plants from predators and exist in their natural form in over 6,000 types of plants, most of whom belong to three major families:

  • the composite plants (daisy family) (Asteraceae),
  • the leguminous plants (Fabaceae or Leguminosae), and
  • the rough-leaved or borage plants (Boraginaceae).

 

As a rule, the toxic effect of the PAs is gradual – the damage appears after constant but low-level exposure to PA over a long period of time. Acute adverse effects or even poisoning from food are improbable, because one would have to consume extremely high amounts of the substance within a short period of time. The most prominent effect of PA in the body is severe liver damage. The 1,2-unsaturated, two-fold esterified representatives are considered to be especially poisonous, and are suspected of being capable of causing genetic damage, as well as cancer. For this reason, even small amounts of PA could pose a risk to consumers’ health. The available toxicological data is incomplete, however.

 

Structural forms of various pyrrolizidine alkaloids.

Illustration 4: Structural forms of various pyrrolizidine alkaloids (PAs). All PAs contain a similar basic structure (here: retronecine), which can be esterified with various carbonic acids. In addition to free alkaloids, the N-oxides in plants are observed in particular. Graphic: Thomas Kapp.

 

The Federal Institute for Risk Assessment (BfR) recommends not exceeding a daily dose of 0.007 µg unsaturated PA/kg body weight. This would amount to the extraordinarily small quantity of 0.42 µg PA per day for an adult weighing 60 kg, and even less for children.

 

For comparison, the current samples of arugula found to have been contaminated with ragwort contained a total of approximately 260 µg PA. If the ragwort/arugula mixture had been consumed, the recommended daily dose of PA for adults would have been exceeded by a factor of 500. The sample was therefore not suitable for consumption and was ruled as unsafe.

 

What has been investigated thus far?

That PAs can occur in foods has been known, at least theoretically, for decades. However, analytical techniques capable of detecting PAs in trace amounts have only been available for a few years. It was only in the summer of 2009 after the finding of ragwort in a package of arugula lettuce that this issue landed in the public’s eye. In the meantime, PA investigations have become a fixed component of food control. The analytics needed for detecting these poisonous substances have forged ahead in the last few years; today CVUA Stuttgart can identify 30 of the most important PAs. Among these are also the alkaloids formed from ragwort, including senecionine, senecivernine, seneciphylline, and integerrimine, as well as their N-oxides.

 

Shortly after the first findings of ragwort in arugula were made it was discovered that honey can also be contaminated with PA, in amounts that are not negligible (see the investigatory results (in German) from CVUA Freiburg and Stuttgart). Since 2013 further findings of PA have been made in teas, especially herbal teas. In fact, teas contaminated with PA have attracted the attention of food controllers and made newspaper headlines several times (see the investigatory results (in German) from CVUA Karlsruhe and Stuttgart ).

 

Given the current findings of ragwort in arugula, two comparative samples from the same manufacturer, as well as 11 other arugula samples, were also examined for the presence of ragwort. The samples (each consisted of up to 8 individual packages of arugula) were given a leaf-by-leaf morphological, visual inspection. All of the samples were also analyzed for any traces of PAs. No visually recognizable parts of poisonous ragwort were detected in any of the 13 samples. Nevertheless, there were occasional findings of other, non-poisonous, weeds in very small amounts. These could be easily recognized as weeds, even without any special botanical expertise; the consumer can simply remove them when washing the salad leaves. The chemical analysis yielded the same results – no PAs were detected in any of the 13 arugula samples. This is good news for arugula fans. These results suggest that ragwort is only found in arugula in comparatively rare, individual cases. Moreover, there were no indications of PA contamination in Arugula that could have been caused by, e.g. small, easily over-looked parts of other plants.

 

The issue of ragwort in arugula known among food controllers is not off the table, however, and the manufacturers should also keep an eye on the problem. The consumer, on the other hand, can enjoy his arugula salad without much concern. Nevertheless, it is recommended that arugula be thoroughly washed and sorted through, and that any unusual or different looking leaves be removed. In the great majority of cases these will only be harmless weeds.

 

Artikel erstmals erschienen am 07.11.2016