PFAS, Part 3: To what extent are PFAS taken up by plants?
We know that PFAS (Per- and Polyfluorinated Substances) are nearly ubiquitous in our water and soils (see PFAS Article #2). But how much of these chemicals actually get into the plants we eat and make remedies with?
After digging through academic journal articles this month, I’ll share my beginner’s understanding of PFAS + plant interactions. This article builds on the Soil article, so I recommend taking a gander at the piece linked above before reading this one.
Image description: Ripe tomatoes, peaches, and blueberries on display at the Dunkirk Farmers Market, NY.
A Little Review: Short-Chain vs. Long-Chain PFAS
In Article #2, we learned that short-chain PFAS are readily taken up by plants and can move relatively easily within the plant. Short-chain PFAS move freely in above-ground plant parts partly because they don’t “sorb,” or bind, readily in soils (Costello & Lee). Short-chain PFAS are generally more water soluble, and since our environment and plants are so watery (plants are around 90% water), short-chain PFAS mingle and move about.
Since long-chain PFAS (like PFOA and PFOS) are known for bioaccumulating in animals and in the environment, short-chain PFAS are being subbed in to replace them. Though their lower tendency to bioaccumulate sounds like a good thing, short-chain PFAS are still toxic and have the potential to cause ill health effects (see PFAS Article #1). The fact that short-chain PFAS are more readily pulled into a plant’s above-ground parts seems to make them a notable concern for plant-eaters.
This short-chain vs. long-chain pattern holds true across many plant species (Costello and Lee). That said, whether PFAS sorb in the soil vs. remain available for plant uptake can vary due to a number of factors, such as soil carbon, soil mineral content, specific structure and polarity of PFAS molecule, plant protein and lipid content, pH, and more (plus the interaction between these variables). This journal article goes into further detail than I do if you’d like to learn more.
PFAS presence in different plant species & parts
Uptake of PFAS can also vary by plant species, and depending on which plant part we’re looking at. Do PFAS tend to accumulate in some parts more than others?
In general, fruits and seeds tend to have lower concentrations of PFAS than leaves and stems (University of Maine). “Fruits” also includes “vegetables” that have seeds inside, such as summer and winter squash, cukes, tomatoes, peppers, eggplant, okra, peas, beans, soybeans, and more. Rhubarb is an example of an edible stem.
This sounds like good news for the grains (seeds) we eat—whether directly or by consuming grain-fed animal products. However, the grass family was found to have a relatively high tendency toward bioaccumulation of PFAS compared to other plants in a 2021 review. Oats, wheat, corn, rice, sugarcane, and barley (a popular beer ingredient) are all in the grass family, Poaceae.
In a study of Minnesota home gardens where PFAS contamination was detected in the water, floret vegetables had higher concentrations of PFAS than other plant parts (Scher et al.). Floret veggies include broccoli and cauliflower. Both short- and long-chain PFAS were present in the water used to water the gardens tested, but long-chain PFAS didn’t readily move into the veggie plants (Scher et al.).
According to the University of Maine Extension, “[L]eafy greens are often the most likely to accumulate soil contaminants and this appears to hold true for PFAS as well” (2022).
Given this news, am I going to swear off of kale and broccoli and start living off of potato chips? Nope, as fun as that sounds. My hope is that the benefits of eating naturally-grown green veggies outweighs these contamination concerns. And—taking action to reduce the presence of PFAS and other contaminants in our environment feels imperative for a veggie-lover like me.
Higher levels of plant protein have been correlated with increased movement of carbon-based compounds like PFAS within a plant. In two studies of seven veggie plants by Wen et al., higher root protein content was correlated with a greater ability of roots to accumulate contaminants (2018). Higher protein content in the above-ground plant parts was linked to greater ability of PFAS to move into the leaves and shoots (2016). Which plants tend to have higher protein content? Wen et al. reported the following protein levels in plants they tested:
3.35% protein in rye root
10.4% protein in mung bean root
6.37% protein in corn above-ground parts
29.1% protein in mung bean above-ground parts (2016, 2018).
It’s no surprise that protein-rich beans are relatively high in protein throughout the plant.
Image description: My brother Matt holds our oatstraw harvest for the day. Oatstraw makes a mild-flavored, mineral-rich tea.
What about maple syrup? Syrup is made by tapping the trunk—the main stem—of the tree, and then simmering the sap to concentrate it. Most of the water evaporates, and 40 gallons of sap makes about 1 gallon of syrup. The NYS Department of Agriculture and Markets tested sap collected from trees in Hoosick Falls and Petersburgh, NY for PFOA. The results ranged “from undetectable to very low trace levels” of PFOA. However, given what we know about long-chain vs. short-chain PFAS and their behavior in plants, the info in this NYS Dept of Health article seemed misleading. I emailed the NYS Dept of Environmental Health and NYS Ag and Markets to share my concerns:
Greetings,
Thanks so much for your resource PFOA in Soils, Water, and Impact on Agriculture. I appreciate you sharing practical information on PFOA levels in milk, eggs, and maple syrup.
I have a concern about how information on PFAS is presented in the article. PFAS research I've seen demonstrates that short-chain PFAS are more water-soluble and mobile in the environment than long-chain PFAS (like PFOA). While PFOA isn't readily taken up into the above-ground parts of plants, short-chain PFAS have been shown to enter plants' stems and leaves readily. So, testing for PFOA doesn't seem like the most appropriate measure of PFAS contamination in a product like maple syrup. Short-chain PFAS would need to be tested for instead.
I wonder: Would some amount of short-chain PFAS evaporate off with the steam during the syrup-making process (since they have been shown to travel by air to some extent)? Or would they be left behind in the syrup, more highly concentrated? I would love to see this data collected.
Your article notes that "Manufacturers began phasing out the use of PFOA in 2006," but there's no mention of the continued widespread use of short-chain PFAS. Unfortunately, short-chain PFAS have been replacing long-chain compounds like PFOA on the market. As noted above, this is a major concern when it comes to agricultural products. I found this 2020 review of PFAS agriculture research very helpful.
PFAS research has focused almost exclusively on PFOA and PFOS until the past few years, and it's understandable that your PFOA article reflects this trend. With newer research emerging that tests for a broader range of PFAS chemicals, I humbly suggest updating this article.
Thanks for your consideration, and for your great work!
A representative from the Bureau of Toxic Substance Assessment (BTSA) at the NYS Dept of Health kindly replied. They agreed that this resource needs to be updated given the new PFAS data available. I was happy to learn that BTSA “has been actively reviewing the literature and developing an update, including an expansion to address additional PFAS.” I’ll share an update when this information is available.
Image description: A deciduous WNY forest looking beautiful in yellow and red autumn color.
Teaser: A Heroic Plant Part
Learning about PFAS has turned up info about an intriguing plant part that can help prevent PFAS and other toxins from being taken up by plants. Stay tuned for a dedicated writeup about this juicy plant structure.
Differences due to growing location: in the ground, potted plants, and hydroponics
Lucky for us, scientists have examined how PFAS uptake varies depending on a plant’s growing medium. How does growing in a pot vs. the soil affect PFAS levels in plants? What about hydroponic systems, where plants grow in nutrient-rich water rather than soil?
Costello and Lee compiled data on 63 different food plants and their PFAS uptake in hydroponic, container, and field settings, and they created this handy table. I find the table overwhelming at first glance, so I’m grateful for their analysis. They report that short-chain PFAS have been found to accumulate around the root zone of potted plants, since the container traps PFAS inside. In a field or garden bed, these compounds are free to leach out of the garden down to the groundwater, and are thus found in lower concentrations. The table linked above shows that PFAS became hundreds or thousands of times more concentrated in potted soil than in field soil when the same concentration of PFAS was applied in both settings (2020).
What about hydroponic systems? Costello and Lee note that “in hydroponic systems, overall PFAS availability is high compared to soil since it is not moderated by sorption” (2020). With no soil to bind them, PFAS are much more free to be taken up by plants. On the other hand, root development is much lower in hydroponic systems than when plants grow in soil. Lower root surface area means less area for PFAS absorption. So—in hydroponic systems, roots are more able to take up PFAS, but there are fewer roots to be exposed. “For example, red chicory root development in hydroponic systems was reduced; thus, uptake surface area decreased compared to chicory grown in soil” (2020). The cited study addresses additional factors I won’t get into here.
Image description: bushel baskets of green beans, apples, potatoes, broccoli, and hot peppers on display at the Dunkirk Farmers Market, NY.
My Takeaways
In the journal articles I looked at, I read over and over that more research is sorely needed—particularly on newer (often shorter-chain) PFAS that are replacing PFOS and PFOA. In the meantime, below are the takeaways I’m bringing with me to my garden:
My purpose in exploring this topic was simply to learn: Can PFAS get taken up into plants, or is this not a concern? Quite simply, the answer is yes. The types of PFAS we’re transitioning to using can be readily taken up by plants. Since PFAS can be detrimental at extremely low levels, and since they travel in the environment via water and air, gardeners and foragers everywhere have good reason to take action.
When I have the opportunity to grow plants in the ground rather than in pots, that’s an easy way to drastically reduce roots’ exposure to toxins like PFAS. When I do grow plants in containers, I’ll be sure to use organic potting soil that doesn’t contain biosolids (a known source of PFAS contamination).
If my water supply was known to have above-average PFAS contamination, or if I lived near an airport, military base, or firefighter training center that has used PFAS, I might consider using an alternate watering source or purchasing organic produce grown in other communities. However, knowing that most US soils and water supplies now contain PFAS (as well as globally), I don’t have reason to believe that produce I buy at a store or farmers market is any less contaminated than what I can grow in my garden. When in doubt, I’ll be sticking to homegrown or locally-grown food for all the nutritional, environmental, and economic benefits of doing so.
This is a personal bias, but: I love soil. Hydroponic systems can be an innovative approach for folks who don’t have the space or clean enough soil to cultivate in the ground, and it’s great that hydroponic systems may incorporate healthy soil microbes and fungi into the growing solution. (I hope plants benefit from these organisms in this medium as much as they do in soils.) And—the more I learn about the ability of soil organic matter to bind certain toxins and render them less available to plants, the more my old-fashioned preference for soil-based agriculture is reinforced.
A lesson learned from maple syrup: When I encounter a somewhat conclusive statement about PFAS not being present in something, I’ll ask myself, “Which PFAS did they test for? Did they test for any short-chain PFAS? Or are they really only talking about PFOA and PFOS?” The latter is often the case. There are thousands of PFAS chemicals floating around our environment, but studies generally test for only a few, at most. When I see conclusive statements made about PFAS’ absence in a water supply, soil, or plant, I’ll request a more accurate representation of what’s actually known.
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Sources
Costello, M. Christina Schilling and Linda S. Lee. “Sources, Fate, and Plant Uptake in Agricultural Systems of Per- and Polyfluoroalkyl Substances.” Current Pollution Report (2020). Webpage.
Ghisi, Rossella et al. “Accumulation of perfluorinated alkyl substances (PFAS) in agricultural plants: A review.” Environmental Research, vol 169 (pp. 326-341). Feb 2019. Webpage.
Gredelj, Andrea et al. “Uptake and translocation of perfluoroalkyl acids (PFAAs) in hydroponically grown red chicory (Cichorium intybus L.): Growth and developmental toxicity, comparison with growth in soil and bioavailability implications.” Science of The Total Environment, vol 720. June 2020. Webpage.
Lesmeister, Lukas et al. “Extending the knowledge about PFAS bioaccumulation factors for agricultural plants - A review.” Science of the Total Environment, Apr 2021. Webpage.
Mei, Weiping; Hao Sun; et al. ”Per- and polyfluoroalkyl substances (PFASs) in the soil–plant system: Sorption, root uptake, and translocation.” Vol 156, Nov 2021. Webpage.
Minnesota Department of Health. “PFAS and Homegrown Garden Produce.” Jan 27, 2022. Webpage.
Scher D.P., J.E. Kelly et al. “Occurrence of perfluoroalkyl substances (PFAS) in garden produce at homes with a history of PFAS-contaminated drinking water.” Chemosphere. vol 196 (pp. 548–55). 2018. Webpage.
University of Maine Extension. “Steps to Understanding PFAS, Step 8: Should I Eat Produce Grown in my Garden?” Website. Viewed Nov 22, 2022.
Wang, Wenfeng, Geoff Rhodes et al. “Uptake and accumulation of per- and polyfluoroalkyl substances in plants.” Chemosphere, vol 261. Dec 2020. Webpage.
Wen B, Y. Pan et al. “Behavior of N-ethyl perfluorooctane sulfonamido acetic acid (N-EtFOSAA) in biosolids amended soil-plant microcosms of seven plant species: accumulation and degradation.” Science of the Total Environment, vol 642 (pp. 366–73). 2018. Webpage.
Wen B, Y. Wu et al. “The roles of protein and lipid in the accumulation and distribution of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) in plants grown in biosolids-amended soils.” Environmental Pollution, vol 216 (pp. 682–8). 2016. Webpage.
Zhao, S., T. Zhou et al. “Uptake, translocation and biotransformation of N-ethyl perfluorooctanesulfonamide (N-EtFOSA) by hydroponically grown plants.” Environmental Pollution, vol 235 (404–10). 2018. webpage.
