One of the most common misconceptions about the term “organic” is the idea that organic is always good for you. In this article, we’ll take tea as an example of a plant product whose organic variety is often preferred because of concerns about safety, specifically related to heavy metal and aluminum toxicity. We’ll look into research-backed data and compare how standard versus organic teas fare.
Chronic Heavy Metal Poisoning
In the most mundane ways, we’re exposed to small amounts of heavy metals everyday through food, water, air, and commercial products. Certain plastic toys, herbal medicines, tap water sources, and produce have all been found at some point to be tainted with heavy metals.
We know from a substantial body of research that absorbing heavy metals and other metalloid elements can be damaging. Health effects of chronic, low-level exposure run the gamut from feeling tired to immune dysregulation to neurodegeneration to cancer. Heavy metals can also accumulate in our bodies over time, causing symptoms to appear slowly and leading to illness much later on in life, even possibly affecting our genes via “epigenetic changes” so that damage is transferrable to following generations.
The proven relationship between certain metal exposures and illness is why governing bodies have established limits for safe daily exposure levels:
In this article, we’ll focus on lead and aluminum since they’ve been studied most in teas. Chronic exposure to lead poses problems like brain damage, neurological impairment, kidney failure, and anemia in adults. Pregnant mothers are subject to additional concerns as lead accumulates in the fetus’s brain and dampens cognitive development. Aluminum, another potential neurotoxin, has been linked to Alzheimer’s disease.
Lead and Aluminum Accumulation in Tea Plants
Plants get their heavy metals from contaminated soil, and contaminated soil is a product of industrialization. Mining, automobile activity, gas-powered manufacturing, and the use of synthetic chemicals (e.g. pesticides, paints, batteries, industrial waste) all contribute to urban and agricultural soil contamination. Lead is highly immobile as it stays put in the upper 8 inches of the soil, which in turn lends to its accumulation. Aluminum is the most abundant metal in the earth’s crust, and while it generally occurs in a form that can’t be absorbed by plants, acidity makes aluminum soluble.
All plants that grow in contaminated environments will pick up some of the soil’s contaminants and the tea plant, Camellia sinensis, is no exception. Because tea is cultivated on acidic soil and aluminum and lead are made more biochemically available as acidity rises, instead of dying off, as many plants do in harsh environments, C. sinensis has adapted a mechanism to thrive in spite of that fact. Research has found that C. sinensis is a special type of plant called a “hyperaccumulator”, a plant that has built-in molecular mechanisms to extract metals from the soil, move them up through its shoots, and then accumulate the metals in its leaves without harming its other metabolic functions. Water evaporation from its leaves may also help volatilize some of these contaminants into the atmosphere at very low concentrations.
Tea plants in fact accumulate lead and aluminum, but we mustn't forget that the manufacturing process plays a significant role in metal levels of teas too. While most commercial teas are made with young leaves, teas with a higher percentage of old leaves can have higher metal loads because those older leaves by nature will have had more time to gather heavy metals. One study found that aluminum concentrations in old leaves were 20 times higher than in young leaves. Another study also hypothesized that the mere twisting and water-removal stages in normal tea production caused an increase in lead content of the tea product being studied. The charts below depict the relevant data assuming average tea drinkers drink about 3 cups (or ~600mL) of tea per day.
To be fair to the study that produced the data used for the charts above, we must be clear about the limitations of data. Namely, we’re looking at one study and a very limited sample of teas, so the conclusions we draw may not be universal. In addition, calculations were not performed as to whether or not the differences we see between groups were statistically significant. Still, some glaring observations are apparent:
1) Teas can have dangerously high levels of metals.
It’s clear from the data that there are tea products that exceed the reproductive safety limits for lead and some that come very near to exceeding restrictions for aluminum. In the study, 83% of the teas exceed safe lead limits during pregnancy. Black teas seemed to perform best in lead safety while oolong teas were worst. Green and white teas were somewhere in between. The data in this study also confirms findings from other research that high aluminum levels can be concerning in tea products. As a whole, research predicts that for many people, tea can be the most important single source of dietary aluminum (even though there is still debate over whether the aluminum is absorbed by our bodies). A daily diet of 3 cups of tea coupled with other sources of heavy metals like water, other beverages, herbal supplements, prenatal vitamins, and produce can easily exceed safe heavy metal limits for the average adult.
2) Steeping teas for longer than 3 minutes should be avoided.
In practically all cases, steeping tea for longer periods of time increased levels of lead and aluminum. The researchers estimate that metal load could increase 10 – 50% compared to at 3 minutes alone. For aluminum specifically, all teas already had significant levels of aluminum at 3 minutes, but after 15 minutes, 20% of the teas exceeded the total daily limit for safe aluminum intake.
3) Organic tea might be better, but only some of the time.
In terms of lead safety, organic black and oolong teas performed better than non-organic black and oolong teas. Organic oolong teas, for example, had on average, 40% lower lead concentrations than standard oolong teas brewed for 3-4 minutes.
Interestingly though, and going back to our question about whether organic is better, green teas paint a different story. Organic green teas in the study had more than 30% higher lead concentrations than regular green teas. With a 3-4 minute steeping time, the highest level of lead found in an organic green tea product was 1.54 ug/600mL. The highest lead level in a standard green tea product was only 1.13 ug/600mL. Unfortunately, that's where the story ends in the research. We have a surprising finding, but no documented mechanism yet to explain it. Various theories could account for it though, ranging from more powerful plant mechanisms to sequester contaminants due to a lack of pesticides to a lack of oversight in organic tea quality control.
To move forward in lowering the risk of toxic element contamination, governing bodies agree that considering “cumulative burden” is paramount. This means being aware of all sources of heavy metals in our daily activities. For tea, not only can metal toxicity be a concern in tea leaves themselves, but tap water is worse than distilled water for brewing teas because tap water contains more metals, and some fine chinas can add toxicants to the drink while the tea is steeping. For now, we can limit some of the risk factors for heavy metal poisoning like type of water we use, the tea containers we choose, steeping time, and especially with more research, perhaps type of tea.
- Image Designs: Sherzod Max
- Agency for Toxic Substances & Disease Registry. (2007). Lead Toxicity – What are the Physiologic Effects of Lead Exposure?. Environmental Health and Medicine Education.
- Andersson M. (1988). Toxicity and tolerance of aluminum in vascular plants. Water Air Soil Pollut. 39:439-462.
- Carr HP, et al. (2003). Accumulation and distribution of aluminium and other elements in tea (Camellia sinensis) leaves. Agronomie. 23:705-710.
- Centers for Disease Control and Prevention. (2013). Sources of Lead.
- Chen Y, et al. (2010). Lead contamination in different varieties of tea plant (Camellia sinensis L.) and factors affecting lead bioavailability. J Sci Food Agric. 90(9):1501-1507. DOI: 10.1002/jsfa.3974.
- Flaten TP. (2002). Aluminium in tea – concentrations, speciation and bioavailability. Coordin. Chem. Rev. 228:385-395.
- Jin CW, et al. (2005). Lead contamination in tea garden soils and factors affecting its bioavailability. Chemosphere. 59(8):1151-1159.
- Jin CW, et al. (2005). Lead contamination in tea leaves and non-edaphic factors affecting it. Chemosphere. 61(5):726-732.
- Khokar S & Magnusdottir SGM. (2002). Total Phenol, Catechin, and Caffeine Contents of Teas Commonly Consumed in the United Kingdom. J. Agric. Food Chem. 50(3):565-570. DOI: 10.1021/jf010153l.
- Leitenmaier B & Kupper H. (2013). Compartmentation and complexation of metals in hyperaccumulator plants. Front Plant Sci. 4:374. DOI: 10.3389/fpls.2013.00374.
- Oregon Public Health Division. (2011). Heavy metals and your health: Frequently asked questions about testing, treatment and prevention. Office of Environmental Public Health.
- Ruan JY & Wong MH. (2001). Accumulation of fluoride and aluminium related to different varieties of tea plant. Environ. Geochem. Health. 53-63.
- Schwalfenberg G, et al. (2013). The Benefits and Risks of Consuming Brewed Tea: Beware of Toxic Element Contamination. Journal of Toxicology. DOI: 10.1155/2013/370460.
- Tangahu BV, et al. (2011). A Review on Heavy Metals (As, Pb, and Hg) Uptake by Plants through Phytoremediation. International Journal of Chemical Engineering. DOI: 10.1155/2011/939161.
- Wong MH, et al. (2003). Aluminium and fluoride contents of tea, with emphasis on brick tea and their health implications. Toxicol. Lett. 137:111-120.
- World Health Organization. (2007). Exposure of children to chemical hazards in food. Fact Sheet No. 4.4. European Environment and Health Information System.
- United States Department of Agriculture. (2000). Heavy Metal Soil Contamination. Soil Quality – Urban Technical Note No.3.