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 ..