Pyrrolizidine Alkaloids, Comfrey, and the Boraginaceae Family

I have been catching up on the debate about the limited evidence for 'dynamic accumulation' of key nutrients in plants such as comfrey (calcium: https://earthundaunted.com/which-dynamic-accumulator-plants-are-actually-helpful-for-your-garden-according-to-science/).  

I'd also already decided not to ingest comfrey myself due to the  pyrrolizidine alkaloid content (see below).

But today I learned that pyrrolizidine alkaloids can persist in the soil, both from the breakdown of e.g. comfrey aqueous extract ('tea') and dying plants, but also from root exudates.

Moreover, these persisting pyrrolizidine alkaloids can then be taken up into other plants - including our edible crops - from the soil.

Pyrrolizidine Alkaloids, Comfrey, and the Boraginaceae Family
By the Seed SistAs is a good discussion of the health hazards of pyrrolizidine alkaloids, with a couple of peer-reviewed sources.

https://seedsistas.co.uk/2025/06/30/pyrrolizidine-alkaloids-and-comfrey/

There is some very new peer-reviewed evidence about the conditions under which significant movement of pyrrolizidine alkaloids between soil, ground water and our edible crops can take place:

Fate of Pyrrolizidine Alkaloids in Soil: Insights from Myosotis arvensis L. and Senecio vulgaris L.
Toxins 2025, 17(7), 335; https://doi.org/10.3390/toxins17070335
https://www.mdpi.com/2072-6651/17/7/335

My initial take-aways from this are:
(1) I'm going to stop tolerating ragwort as a volunteer in my crop beds;
(2) As pyrrolizidine alkaloids accumulate in us, too, I'm going to work harder at diversifying my edible green manure options.

I'm hoping to find out significantly more about pyrrolizidine alkaloids in our edible crops in permaculture systems now .. what do we know?

I would still love to know more ..

I didn't see anything in the summaries about crop uptake of the alkaloids - just that it was present in the soil...and more research required.

I think that given a good biodiverse soil biota it wouldn't be something to worry about too much.

More research needed, but PAs have been detected in maize crops (mostly the leaves) for example, according to Nakurte et al. & references therein.  They consider groundwater contamination to be the bigger risk, I think.

"These findings underscore that soil properties—such as pH, organic carbon content, and cation exchange capacity (CEC)—are key determinants of PA fate, and the reversibility of sorption amplifies environmental risks by facilitating plant uptake and groundwater contamination."

Returning to this now the growing season is back in my bioregion ..

PAs in other plants, and foods:

"The levels of PAs found in this survey of 227 samples comprised of teas, herbal infusions, plant-based supplements and honeys are comparable to previously published literature reports (EFSA, 2017)."
https://www.food.gov.uk/sites/default/files/media/document/pyrrolizidine-alkaloids-in-teas-herbal-teas-plant-based-food-supplements-and-honey_0.pdf

This is more encouraging:

'at the time of harvest no PAs were detected in the relevant field products (grains)."

Pyrrolizidine Alkaloids in the Food Chain: Is Horizontal Transfer of Natural Products of Relevance?
Said Chumit et al. 2021, Foods doi: 10.3390/foods10081827
https://pmc.ncbi.nlm.nih.gov/articles/PMC8392022/

this has never been on my radar....interesting that it:s being studyed.

and coincidently I just began some comfrey tea for the garden yesterday🙄

Ac Baker wrote:I'm hoping to find out significantly more about pyrrolizidine alkaloids in our edible crops in permaculture systems now .. what do we know?

I found a useful site that has collected some research together on alkaloid concentration in comfrey here giving references. There seems to be inconsistent results between studies, but most agree that the roots contain more alkaloids than the leaves (possibly by 2 orders of magnitude). I'm suspecting that how the plants are grown may have as much effect as the variety, but there does appear to be some differences in concentration between different comfrey varieties, the Bocking varieties having rather less alkaloids than common comfrey.

I wonder whether it would be worth doing some research on this ourselves?

I have some established honeyberry bushes that have for 10 years been grown in close proximity to comfrey, which has been allowed to die down and mulch the soil. I also have honeyberries that are no where near comfrey. I could easily take samples of both plants (and the comfrey and the soils) for lab analysis. I wonder how much the testing would cost (anyone know a tame chemist?) and whether we could get crowdfunding for a citizen science paper?

How would a good experiment look? What do we want to know?

Nancy Reading wrote:
I found a useful site that has collected some research together on alkaloid concentration in comfrey here giving references. There seems to be inconsistent results between studies, but most agree that the roots contain more alkaloids than the leaves (possibly by 2 orders of magnitude).

Many thanks for these posts!  One of those links has sources for some different ways of measurement:

"The total amount of pyrrolizidine alkaloids given by different authors varies from 0.013% to 1.2% based on the analytical methods used (Tittel et al., 1979; Brauchli et al., 1982; Neidhardt, 1982; Stengl et al., 1982; Gracza et al., 1985; Vollmer et al., 1987; Mütterlein and Arnold, 1993)."

Large businesses can outsource this testing for EU regulatory compliance:

"In 2022, the European Union established [PA] limits for several products, such as teas, infusions, supplements and herbs. It currently covers 21 alkaloids, including 14 compounds that co-elute [overlap in chromatography analysis], which makes individual analytical quantification impossible under current methodologies."
https://www.sgs.com/en/services/pyrrolizidine-alkaloids

Comfrey: A Clinical Overview
Staiger C 2012, Phytotherapy Research
https://doi.org/10.1002/ptr.4612
https://onlinelibrary.wiley.com/doi/10.1002/ptr.4612

The EU has concluded that there is not enough evidence of safety to permit, "‘comfrey steeping’ as a basic substance to be used as an insect repellent and plant elicitor in fruit trees, grass and vegetables." ..

"the available information on the fermented extract from leaves of Symphytum officinale L. did not allow the Authority to finalise a non-dietary exposure risk assessment and the assessment of the risk to consumers.

"Furthermore, there was not sufficient information available regarding environmental exposure and the risks to non-target organisms."

Commission Implementing Regulation (EU) 2021/809 of 20 May 2021 concerning the non-approval of fermented extract from leaves of Symphytum officinale L. (comfrey) as a basic substance in accordance with Regulation (EC) No 1107/2009 of the European Parliament and of the Council concerning the placing of plant protection products on the market (Text with EEA relevance), 2021
https://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:32021R0809

All rather inconclusive ..