This subject came up in a couple of different forms recently, so I looked it up, how much risk there is from lead exposure in tea. Of course I'm not representing this as developed and conclusive research; I read a half dozen references, and this passes on the most interesting content from that.
Two studies of Chinese tea (one pu'er, one general) and one of tea in Britain, which probably relates more to teas produced in India, Sri Lanka, and Kenya, were all really consistent. Lead exposure in tea might relate to an average of 2+ mg / kg of dry leaf, across all those categories. Is that a lot; is it safe? I'm still not completely sure, but all three said that's fine, just normal limited food exposure.
One study passed on findings related to what that works out to in brewed tea, just not in as complete a form as would be more informative. That said that half the brewed samples were below the threshold range, but didn't offer an average or distribution of the rest.
I'll mention the studies and references, summarize what I took them to mean, and cite a relevant selection that covers that. A more in-depth review would continue on to a closer read of a dozen or so good references; this type of fast review isn't very reliable. I only wanted to get an idea of general level of likely risk, and I think this gets you that, but the confidence of complete results is not there.
Contents of fluoride, lead, copper, chromium, arsenic and cadmium in Chinese Pu-erh tea (2012)
Very interesting; this is basically what I was looking for. I looked up when the Chinese government banned use of lead in gasoline, since that's going to be a factor, and that was in 2000. Another reference, which I'll get to, said that beyond that (generally earlier input) use of coal also amounted to a considerable input factor, and Chinese production of electricity from coal probably increased quite a bit from 2012 to today.
On to considering a relevant citation:
In order to assess safety for consumers and the levels of contamination in Pu-erh tea, the authors studied the contents of fluoride, lead, copper, chromium, arsenic and cadmium in 56 Chinese samples of Pu-erh tea collected from Dali City, Lincang City, Xishuangbanna City, Simao City and Dehong City in Yunnan province.
The ranges obtained for the elements analyzed were 80.2–151.6 mg kg− 1 (fluoride), 0.66–4.66 mg kg− 1 (lead), 14.8–19.3 mg kg− 1 (copper), 1.95–4.98 mg kg− 1 (chromium), 0.07–0.25 mg kg− 1 (arsenic) and 0.023–0.130 mg kg− 1 (cadmium). The mean leached analyte concentrations in tea infusion were 523.86 μg L− 1 for fluoride, 5.70 μg L− 1 for lead, 43.18 μg L− 1 for copper, 13.67 μg L− 1 for chromium, 0.43 μg L− 1 for arsenic and 0.17 μg L− 1 for cadmium after the tea leaves were brewed twice with boil water in a ratio of 1 g/50 ml for 5 min. The mean dissolving rates of fluoride, lead, copper, chromium, arsenic, and cadmium were 45.8%, 24.6%, 26.2%, 35.2%, 30.8% and 27.4%, respectively.
Lots more there to cover than I'll discuss. Note the average finding range I mentioned, 2 mg lead / kg tea, is expressed here as a findings range of .66-4.66 mg / kg, not a complete match. Their conclusion:
Based on a 70 kg individual consuming 15 g of Pu-erh tea daily or 105 g Pu-erh tea weekly, the dietary intake of the studied elements was below the safe limits recommended by various authorities. This suggested that under the current dietary intake, there are no possible health risks to Pu-erh tea drinking consumers.
Since there is no safe level of exposure to lead (per another reference I'll cite later) "no possible health risks" seems a little strong, but I get what they're saying, that limited food exposure happens, so a normal and low range is regarded as conventional and acceptable. Is 5 μg (per liter) a really low amount? I never really do settle that. It's not easy to find an acceptable low limit for lead exposure since the EPA and such say people should avoid any, and then don't want to move on to state acceptable exposure levels, even though it's going to come up.
Note that I've written separately about fluoride here. That's still being added to municipal water in a lot of places; it's only really a contaminant and a health risk within a certain dosage range, which I won't go further into here, beyond saying that scanning that post (really the other earlier one that goes into more detail) 10 mg / day comes up as an earlier recommended adult limit, later dropped to more like half that. I think this 523 μg / liter works out to .5 mg; not much. In that post I state that "the treatment level of fluoride (added to municipal water) is .7 to 1.2 mg / liter," of course citing references, so that brewed tea fluoride level is just below treated water level. On the high side two liters of brewed tea from treated water might contain 3.4 mg then; not above the limit, but high enough, and getting there.
Back to the next reference and considering lead instead.
Tea (Camellia sinensis) is a popular beverage that is consumed globally. However, a better understanding of potentially toxic elements (PTEs) content in tea leaves and infusion is necessary to minimize risk on human health. Therefore, 249 tea samples (grown in different areas) covering six types of tea were collected in China to investigate the PTEs contents, identify their potential source and assess the health risk associated with drinking tea.
PTE contents in tea leaves across six tea types were ND–0.900 (Cd), 0.005–2.133 (As), ND–5.679 (Pb), ND–13.86 (Cr), 1.601–22.93 (Ni), ND–2.048 (Se), 0.109–622.4 (F), 13.02–269.9 (Rb), 1.845–50.88 (Sr), and 2.796–53.23 (Ba) mg/kg. The result of tea infusion showed that 14.3 %–44.1 % (green tea), 14.5 %–46.7 % (black tea), 10.5 %–25.3 % (dark tea), 13.6 %–34.2 % (oolong tea), 16.9 %–40.7 % (yellow tea), and 19.9 %–35.1 % (white tea) of F were released. All tea types, except green tea, exhibited comparatively low leachability of Cd, As, Pb and Cr in tea infusion.
The source apportionment revealed that PTEs in tea leaves mainly originated from soil parental materials, while industrial activities, fertilizer application, and manufacturing processes may contribute to exogenous Se, Cd, As, and Cr accumulation. Health risk assessment indicated that F in tea infusion dominated the health risk.
It's interesting that a relatively similar finding for fluoride level, as in the earlier study, was identified as a potential health risk, while it wasn't earlier. That earlier study identified an average of 80 to 150 mg / kg Fluoride and this a range of .1 to 644 (so four times higher on the high end, but negligible on the low side).
Here the lead range is not detectable to 5.7 mg / kg of dry leaf; a little higher top range, but similar (the other was 0.66–4.66 mg / kg (lead). Extraction rate was 24.6% in the last study for lead (just mentioned as low here), but we're still back to considering if the earlier exposure level was ok or not (5.70 μg / liter for lead). It sounds low, but really a second review of food exposure levels would really help place that, and I didn't get to that here.
Google does offer this, as a starting point:
What are the maximum levels for lead in certain food categories?
Heavy metals
The maximum allowed lead content ranges from 0.01 mg/kg in some baby foods to 3 mg/kg in food supplements. Most meat products, fats, and oils should not contain more than 0.1 mg/kg of lead, while the limits for fruit, vegetables, and fungi vary between 0.1 mg/kg and 0.8 mg/kg.Jun 4, 2566 BE
.1 mg would be 100 micrograms; that's a good bit in comparison to what's turning up here. It's necessary to note that I'm switching around between dosage level per liter and amount per kg; it takes awhile to brew up a kg of tea, and that 24% extraction rate is positive (versus that being higher). If you eat a kg of lettuce presumably that .1 to .8 mg--100 to 800 μg--goes right into you. That's a lot of lettuce, but nothing like brewing 1000 grams of tea 5 to 8 grams at a time.
Analyses of lead levels in tea (seemingly from a 2014 review)
This study was carried out to address the urgent need to gather more data on levels of lead (Pb) in tea, to inform current EU discussions on a proposed maximum limit of 1 mg/kg Pb in tea (‘dried leaves and stalks, fermented or otherwise of Camellia sinensis’).
Levels of Pb were quantified in 51 samples of black and green tea leaves.These samples were also analysed as tea liquid (drink), after steeping the tea leaves for both a shorter and a longer brew time, following an agreed protocol. 11 different varieties of dried tea (including a white tea) from different tea growing regions were also purchased and analysed to ensure there was good geographic and tea-type coverage.
Note that the tested range went way beyond that considered 1 mg / kg limit in those other studies, up to 4.6 and 5.7 mg / kg.
The study findings showed that the levels of lead in the 51 samples of dried tea varied significantly and ranged from 0.125 to 2.56 mg/kg.
The levels of lead found in the brewed teas were very low with half the results being less than the limit of detection 0.2µg/L (1 µg/L=0.001mg/kg).
Teas brewed for a longer period of time resulted in only a slightly higher level of lead.
The levels of lead found in the additional 11 dry teas ranged from 0.177 to 1.96 mg/kg.
Exposure to lead from the consumption of the brewed teas as tested is not considered to be of concern for consumer health compared to normal levels of exposure to lead from all dietary sources.
They were one stat away from expressing clear findings, identifying the brewed tea lead levels and an average across the samples for that range. It's a lot to go through just to say "it was low" at the end. The paper itself (linked there; that's just a summary) goes further:
Two samples contained Pb levels above 1 µg/L and the highest level, 2 µg/L, was found in a sample of green tea (Chinese Sencha).
Ok then, three samples ranged at or above 1 µg/L, out of 51, which is still low, based on input from the other papers.
Presumably the conclusion here is that a 1 mg / kg dry tea lead level isn't the right threshold limit, and 2 or 2 1/2 is still no problem (relating back to considering 1 mg / kg as an import level limit).
In China, where is the lead contamination coming from?
Initially I was concerned that leaded gasoline might be an issue, but this reviewed identified that was banned in 2000 (so it's surely not being produced or sold in China now, right?). It's an odd starting point but this is how they open that:
It is common to use effluent as a fertiliser in China. This results in accumulation over time, within fields, of heavy metals.- cadmium, chromium, copper, nickel, lead and zinc (Cd, Cr, Cu, Ni, Pb and Zn).
Interesting! A lot of the paper is about lead contamination in water sources, presumably from a number of industrial waste sources, natural sources, or from coal use, as described further:
Lead can be emitted during the mining and smelting of mercury ores, because most such ores also contain lead. Lead is also emitted during the burning of coal. Researchers in Guizhou province, where there are 12 large mercury mining and smelting operations and heavy coal-powered industry, found that rice accounted for 94-96% of the uptake of methyl mercury (Raloff, 2010). They were not testing for lead, but it is likely that the rice was also a source of lead in the diet...
...What the evidence from water catchments in the more industrialised parts of the China shows is that there is a clear link between lead contamination of the environment and industrial activity. Coal use in China is rising steadily and it should be noted that coal naturally contains lead.
Tea gardens would surely never water plants from the Yangtze river, or other polluted sources, but I suppose airborne lead exposure is probably a concern.
WHO guidance to reduce illness due to lead exposure
I never did find much guidance on safe lead exposure limits or relative risk of exposure but this is a start:
The WHO Guideline for Clinical Management of Exposure to Lead recommends a blood lead concentration of 5 micrograms per decilitre (μg/dL) as a trigger for a thorough review of the ways in which a person is being exposed to lead and for action to reduce or end this exposure.
With 1 in 3 children estimated to have blood lead levels in excess of the 5μg/dL threshold[1], according to the United Nations Children’s Fund (UNICEF)...
“There is no known safe level of lead in the human body. The new guideline will help the diagnosis and treatment of lead exposure for individual patients and help health workers tackle mass poisoning incidents,” said Lesley Onyon, Scientist, Chemical Safety and Health Unit.
This covers more on general effects and risk sources:
Lead in the body affects practically all organ systems, travelling to the brain, liver and kidney and accumulating in the teeth and bones, where it can last decades and move from bones back into the blood during pregnancy, exposing the developing foetus.
It is still widespread owing to current and past use of the metal and its salts, most commonly in storage batteries, ammunition, pipes (including those used for water supply) and in alloys such as solder, pigments, paints, glazes, plastics and even some traditional medicines, cosmetics and spices.
Lead was once used extensively in petrol additives, but this has recently been banned in all countries in the world. But in many popular uses, particularly lead in paint, remain although alternatives are known and available.
Framed this way it sounds like more of a "developing world" issue than related to standard risks. I'm still a little concerned about those food exposure levels; surely that's not a complete non-issue, even if lead pipes, paint, glazes, and cosmetics may pose more risk, when that's not carefully controlled.
Another reference says more about lead exposure risk and effects, but I won't go further with that, only mentioning it here for those still interested in going further:
Tea seems to only pose a very limited lead exposure risk, in general, although I guess there could always be exceptions.
I don't love the idea of consuming 5 µg / liter, even if I still don't feel like I can place what that means. At least the teas tested in the British samples study identified 48 out of 51 with levels below 1 µg / liter, two samples around 1 microgram and one at 2, and half below the testing threshold of .2 µg / liter.
So we should probably "use trusted tea sources?" That's always a little problematic, isn't it? At least the worst case doesn't sound so bad. It makes you wonder how bad food risk is, if this is all on the low side compared to that.
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