I came across a post on Facebook recently that stopped me in my tracks. Someone shared photos of mullein leaves they harvested from plants growing around a town lagoon and asked if it was safe to use them for tincture.
Here’s why I had to weigh in.
For anyone unfamiliar, a town lagoon is not a picturesque pond or natural wetland. It’s a wastewater treatment site. It’s a man-made pond designed to hold and treat sewage and runoff. Even if it looks clean on the surface and the plants around it haven’t been sprayed with chemicals, the soil can hold pollution for decades.
That’s where mullein comes in. Mullein is known as a “bioaccumulator,” meaning it readily pulls substances out of the soil and stores them in its tissues. This trait can be useful in phytoremediation projects, where plants are intentionally used to help clean contaminated sites. But it also makes mullein risky to harvest in questionable locations.
When asked on Facebook whether mullein could carry metals into a tea, my answer was yes, along with other toxins. Some heavy metals get trapped in the roots, but others make their way into the leaves and flowers. Other soil contaminants, not just metals, can also move easily into the plant. If you make tea, tinctures, or decoctions from a mullein plant grown in polluted soil, you’re likely ingesting those same contaminants.
And remember, “natural” doesn’t always mean safe. Arsenic, mercury, and lead are all naturally occurring metals, but they’re toxic to humans. If a plant absorbs them, they don’t magically become harmless.
So, while mullein is a wonderful plant with many uses, it’s essential to be mindful of where it grows. Avoid harvesting from areas with potential contamination, such as lagoons, industrial sites, or roadsides. Clean soil matters just as much as the plant itself.
Read more about mullein.
References:
- Ali, H., Khan, E., & Sajad, M. A. (2013). Phytoremediation of heavy metals—Concepts and applications. Chemosphere, 91(7), 869–881. https://doi.org/10.1016/j.chemosphere.2013.01.075
- Prasad, M. N. V., & Freitas, H. (2003). Metal hyperaccumulation in plants—Biodiversity prospecting for phytoremediation technology. Electronic Journal of Biotechnology, 6(3), 285–321. https://doi.org/10.2225/vol6-issue3-fulltext-6
- U.S. Environmental Protection Agency (EPA). (2022). Phytoremediation. Retrieved from https://clu-in.org/techfocus/default.focus/sec/Phytoremediation/
- Rai, P. K., Lee, S. S., Zhang, M., Tsang, Y. F., & Kim, K. H. (2019). Heavy metals in food crops: Health risks, fate, mechanisms, and management. Environment International, 125, 365–385. https://doi.org/10.1016/j.envint.2019.01.067
- Čudić, V., Stojiljković, D., & Jovović, A. (2016). Phytoremediation potential of wild plants growing on soil contaminated with heavy metals. Archives of Industrial Hygiene and Toxicology, 67(3), 229–239. DOI:10.1515/aiht-2016-67-2829
- Glavač, N. K., Djogo, S., Ražić, S., Kreft, S., & Veber, M. (2017). Accumulation of heavy metals from soil in medicinal plants. Archives of Industrial Hygiene and Toxicology, 68(3), 236–244. DOI:10.1515/aiht-2017-68-2990
- Moss, N., Kyzy, N., Kaled, C. F., Karki, B., Gerwitz, E., & Spudich, T. (2025). Exploring heavy metal accumulation in Verbascum thapsus across the St. Louis region (ACS Fall 2024 National Meeting poster). DOI:10.13140/RG.2.2.34757.77286
- Kenny, C. R. (2022). Novel metallomic profiling and non-carcinogenic risk assessment of botanical extracts. Environmental Monitoring and Assessment.
- Lewandowski, M., et al. (2025). The impact of continuous heavy metal emissions on vegetation, with a focus on Verbascum thapsus. Applied Sciences.
About the Author:
Sabrina Halvorson is a journalist and author by profession, herbalist and forager by passion. In addition to her journalism education, she is a University of Minnesota Extension Master Naturalist, the North Dakota chapter coordinator for Herbalists Without Borders, and a graduate of the Chestnut School of Herbal Medicine. Sabrina is the appointed U.S. Country Director for the World Agriculture Forum, an international council of agriculture experts, and the 2024 Farm Broadcaster of the Year from the National Association of Farm Broadcasters. Learn more about her journalism and agriculture experience at sabrinahalvorson.com.
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