Pesticides in Tea: Strange Brew Indeed

Early in 2014, CBC’s Marketplace decided to investigate pesticide residues in dry tea leaves. After using an accredited lab with a testing method employed by the Canadian Food Inspection Agency (CFIA), here’s what they concluded:

Half of the teas tested contained pesticide residues above the allowable limits in Canada. And eight of the 10 brands tested contained multiple substances, with one brand (Uncle Lee’s Legends of China Green Tea) containing residues of 22 different pesticides.

Following the publication of this kind comes the inevitable comment from the manufacturer, ” Pesticide residues in food are a modern reality but pose no danger at low concentrations”. Health and Welfare Canada then echoed the sentiment. So is this really just journalistic sensationalism?

Far from it. Upon a closer look at the data, here is what I found interesting:

(1)  One of the compounds found in 2/3 of the teas tested was acetamiprid, an insecticide of the neonicotinoid class, which is often used to kill aphids.  A recognised irritant in mammals, it is highly toxic to birds and earthworms and moderately toxic to most aquatic organisms.

ADI – Acceptable Daily Intake (mg kg-1bw day-1) means mg per day per kg of body weight from  University of Hertfortshire’s data base on pesticides. 0.07

0.07 mg kg-1bw day-1 is equivalent to  4.55 mg/day for a 65 kg person.  Superficially, it seems that one would have to drink a liter of Uncle Lee’s Legends of China green tea (1 mg?L= 1 ppm) tea to ingest about a quarter of the “acceptable” limit, but tea is not the only source of acetamiprid.greentea

The same data base I consulted reveals the following concentrations(in ppm) of the same pesticide measured in European fruit:

Citrus: 1.0; Cherries: 0.2; Curcubits with edible peel: 0.3; Pomes, apricots, peaches, tea and hops: 0.1; Plums and cotton seed: 0.02; Cereals, berries, soft fruit, other fruit, vegetables and treenuts: 0.01

(2) As Marketplace reported and contrary to what “Uncle Lee” stated, pesticide residue in tea is not inevitable. Red Rose tea had no detectable pesticide residue because it comes from Kenya, Ceylon, India and Indonesia where presently no pesticides are used in the cultivation of tea and probably not in the surrounding areas either. Bear in mind that pesticides are common in China, Europe and North America. In China:

almost a fifth of China’s soil is contaminated, an official study released by the government has shown. Conducted between 2005-2013, it found that 16.1% of China’s soil and 19.4% of its arable land showed contamination.The report, by the Chinese Environmental Protection Ministry, named cadmium, nickel and arsenic as top pollutants.

They did not release pesticide results but it’s obvious from the tea concentrations that the problem for such compounds is equally severe.

(3) Some teas contained chlorphenapyr, which I found startling. In 2000, the United States Environmental Protection Agency initially denied registration of chlorphenapyr (0.66 ppm in Legends of China green tea) for use on cotton primarily because of concerns that the insecticide was toxic to birds and because effective alternatives were available. However, it was registered by EPA in January, 2001 for use on non-food crops in greenhouses.

In fact the PA stated, “The use on ornamental crops grown in greenhouses is a non-food use so there will be no dietary exposure. Since there are no residential uses of chlorfenapyr, no chronic residential exposure is anticipated.”

Glad they thought so.

The maximum limit for chlorphenapyr in food residue ranges from 0.01 to 0.5 ppm, and the Legends of China green tea surpasses the threshold. Tetley green tea contains 0.14 ppm of the same pesticide.

(4)  Still another insecticide found in Legends of China green tea is imidacloprid, also a neonicotinoid. The concentration found was 0.55 ppm, more than ten times the concentration that kills honeybees.

(For a honey bee, the amount of imidacloprid that must be ingested to kill 50% of the test subjects is an extremely small amount of 0.0037 micrograms.  The mass of an average honeybee is  0.1 g, so we’re talking about an LD 50 of 0.0037 X10-6 g /0.1 g = 0.0037 X10-3  mg/0.1 X 10-3 kg = 0.037 ppm ) (


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