What foods have pyrrolizidine alkaloids? Understanding PA Contamination

November 1, 2025 •

4 min read

According to the Food Standards Agency, pyrrolizidine alkaloids (PAs) have been detected in over 6,000 plant species worldwide, and their presence can lead to food contamination. Understanding what foods have pyrrolizidine alkaloids is crucial for minimizing dietary exposure to these naturally occurring toxins, which can pose a health risk, especially to the liver, upon regular consumption. This guide explores common food sources and explains how contamination occurs.

Quick Summary

A review of dietary sources reveals that pyrrolizidine alkaloids are most commonly found in certain herbal teas, honey, spices, and dietary supplements. These toxins can also appear in grains, salads, milk, and eggs due to contaminated animal feed or accidental co-harvesting with PA-producing weeds. Understanding these sources is key to mitigating health risks.

Key Points

Herbal Tea Contamination: Many herbal infusions, including chamomile and rooibos, have been found to contain PAs due to cross-contamination with PA-producing weeds.
Honey as a Vector: Bees foraging on PA-containing plants, such as Paterson's Curse, can transfer the toxins to honey, leading to variable levels of contamination based on geographic origin.
Spices and Herbs Risk: Certain dried spices like oregano, marjoram, and cumin can be contaminated with PAs when weeds are accidentally co-harvested and processed.
Supplements High Risk: Herbal dietary supplements, particularly those containing borage or comfrey, can contain concentrated PA levels, posing a greater risk from regular, long-term use.
Agricultural Products: Grains like wheat and animal products such as milk and eggs can contain low levels of PAs due to feed contamination, though the risk is typically lower than with direct plant-based sources.
Variable Levels: The concentration of PAs in food is highly variable and depends on factors such as plant species, growth conditions, and harvesting practices.
Minimizing Exposure: Consumers can reduce their risk by choosing transparent brands, opting for a varied diet, and avoiding herbal supplements known to contain PA-producing plants.

Understanding Pyrrolizidine Alkaloids

Pyrrolizidine alkaloids (PAs) are a large family of natural toxins produced by certain plants as a defense mechanism against herbivores. While many plants contain them, only a subclass, known as 1,2-unsaturated PAs, poses a genotoxic and potentially carcinogenic risk to humans. The primary health concern related to long-term PA exposure is liver damage, which can lead to liver cirrhosis or, in severe cases, liver failure.

Contamination typically happens in two main ways: direct consumption of PA-containing plants, such as certain herbal remedies, or indirect ingestion via agricultural products contaminated with weeds that produce PAs. For instance, bees may forage on PA-containing weeds and transfer the toxins to honey. Similarly, weeds can be accidentally co-harvested with crops like grains or leafy vegetables.

Primary Food Sources of Pyrrolizidine Alkaloids

Certain food categories are more susceptible to containing PAs, either because they are derived from PA-producing plants or are frequently contaminated by them during harvest.

Herbal Teas and Infusions

Herbal teas are a well-documented source of PA exposure. Some plants commonly used in herbal infusions belong to families known to produce PAs, particularly the Boraginaceae family. Contamination can also happen when PA-producing weeds are mistakenly harvested alongside the desired herbs. Studies have detected PAs in various herbal teas, including:

Chamomile: Known to sometimes have elevated levels of PAs.
Rooibos: Research has found PAs in some rooibos tea infusions.
Peppermint: Studies have identified low levels of PAs in some peppermint tea samples.
Lemon balm: Some samples have been found to contain PAs.

It is important to note that PA levels can vary significantly between brands and batches, often depending on the sourcing and quality control during production.

Honey

Bees that forage on PA-producing flowers can transfer these toxins to their honey. Honey is a notable source of dietary PA exposure, and contamination levels vary widely depending on the region and local flora. For example, honey derived from plants like Paterson's Curse (Echium plantagineum) is more likely to contain PAs. Frequent consumption of certain types of honey is considered a risk factor, especially for vulnerable populations like children.

Spices and Dried Herbs

Dried herbs and spices can be contaminated with PAs if weeds are accidentally harvested and processed alongside them. Examples of affected dried products include:

Oregano
Marjoram
Lovage
Cumin

High levels of PAs have been detected in some herb and spice mixtures, presumably due to co-processing.

Dietary Supplements

Herbal dietary supplements can be a significant source of PA exposure, especially those containing extracts from PA-producing plants like borage or comfrey. Due to their concentrated nature, these supplements can contain high PA levels and are of particular concern. Health authorities recommend avoiding supplements with known PA-producing plants.

Grains and Animal Products

PA contamination can also enter the food supply indirectly. Grains such as wheat and cereals can become contaminated with PA-producing weed seeds during harvest. Additionally, PAs can transfer from animal feed to animal products such as milk, eggs, meat, and offal. However, the concentrations in animal products are generally very low and considered less of a risk compared to direct plant-based sources.

Comparison of Food Contamination Sources


Food Category	Primary Contamination Route	Examples	PA Level Variability	Health Risk Factors
Herbal Teas & Infusions	Derived from or contaminated with PA-producing plants during harvest.	Chamomile, Rooibos, Peppermint, Lemon balm	High variability; depends heavily on sourcing and processing.	Regular consumption, especially for sensitive groups.
Honey	Bees foraging on PA-containing flowers.	Honey from Paterson's Curse or other PA-rich flora.	High variability; depends on the geographical location of the hives.	High consumption, particularly in children.
Spices & Dried Herbs	Accidental co-harvesting and processing of weeds.	Oregano, Marjoram, Cumin.	High variability; depends on harvesting and sorting practices.	Accumulation from small but consistent intake.
Dietary Supplements	Use of PA-producing herbs or concentrated extracts.	Supplements containing borage or comfrey.	High, with some potentially containing very high levels.	High concentration and dose, often for long periods.
Grains & Animal Products	Accidental contamination during harvesting (grains) or transfer from contaminated feed (animals).	Wheat, milk, eggs.	Generally low levels, but widespread.	Overall dietary exposure from multiple sources.

Conclusion

While pyrrolizidine alkaloids are naturally present in many plant species, they can enter the food chain primarily through the contamination of herbal teas, honey, spices, and dietary supplements. Less common but still possible sources include grains and animal products. Public health bodies have recognized the potential long-term risks, particularly liver damage, associated with chronic exposure to PAs. To minimize risk, consumers should be mindful of the sources of their food and herbal products, consider product transparency, and opt for a varied diet to avoid over-exposure from any single food source. Good agricultural and manufacturing practices, such as effective weed control and rigorous sorting, are essential to reducing overall PA contamination in the food supply.

Frequently Asked Questions

The primary health risk associated with long-term exposure to 1,2-unsaturated pyrrolizidine alkaloids (PAs) is liver damage, which can lead to hepatic veno-occlusive disease, cirrhosis, and, in severe cases, liver failure.

Pyrrolizidine alkaloids contaminate food primarily through two routes: the accidental co-harvesting of PA-producing weeds with crops like grains, herbs, and leafy vegetables, and the transfer of PAs into honey when bees collect nectar and pollen from PA-containing plants.

No, not all herbal teas are dangerous. The presence of PAs varies greatly and depends on the sourcing and manufacturing practices. However, some teas like chamomile and rooibos have shown higher levels of contamination in some studies. Choosing brands with good quality control can reduce risk.

Yes, it is possible for PAs to transfer into animal products like milk and eggs if the livestock consumes contaminated feed. However, the levels detected in these products are generally much lower than in direct plant-based sources.

Herbal dietary supplements that are made from known PA-producing plants, such as borage and comfrey, can contain significant concentrations of PAs. It is recommended to avoid these particular supplements to minimize exposure.

To reduce exposure, you can vary your diet to avoid consistent intake from a single source, choose trusted brands for herbal teas, honey, and spices, and be cautious with herbal supplements containing known PA-producing plants. Good agricultural practices by suppliers are also key.

Key plant families and genera known to produce PAs include Asteraceae (like Ragwort), Boraginaceae (including borage, comfrey, and echium), and Fabaceae (genus Crotalaria). Weeds from these families can contaminate agricultural fields and forage.