After a busy festive period you may be enjoying a relaxing cup of tea and probably not giving a second thought to the ingredients and chemicals you may be consuming. You would think that tea should only be tea, but read on for beverage testing analysis with a difference.
World tea production increased significantly in 2013, by 6% to 5.07 million tonnes, with China as the largest tea producing country in the world, accounting for more than 38% total production. India is the second largest producer. Developing countries like Kenya, Sri Lanka and Vietnam also being major exporters of tea. Increased tea prices resulted in export earnings in 2013 of $5.7 billion, significantly improving rural incomes and household food security. To sustain this trade and to meet forecasts for production of black and green tea to 6.87 million tonnes by 2023, it is essential that food safety standards particularly for pesticides are met by tea exporting countries.
Unauthorized Pesticides Found in 50% of Tea Samples
In the Journal of Agricultural and Food Chemistry, Hayward and co-workers from the US Food & Drug Administration (FDA), found that in 62 black, green, white, and Oolong tea products, 50% had pesticide residues for which no tolerances for tea are established in the USA. Although, a total of 20 pesticides are authorized for use in tea production, with maximum residue levels (MRLs), ranging from 0.002 mg/kg for pyriproxyfen to 50 mg/kg for acetamiprid, in this survey 17 unauthorized pesticides were identified on tea leaves. Particularly surprising was that concentrations of dichlorodiphenyltrichloroethane (DDTs) and hexachlorocyclohexanes (HCHs), in teas ranged from 1 to 136 μg/kg, for DDTs and the sum of the HCHs. Compliance with good agricultural practice (GAP) and only using agrochemicals which are authorized for tea should ensure that safety standards (MRLs) are met. However, this survey demonstrates that the rules are not being followed and it is therefore incumbent on tea exporters to conduct analysis to demonstrate due diligence.
Tea Presents Severe Analytical Challenges
Unfortunately, dried botanical products, such as tea, can present severe analytical challenges, even to experienced laboratories when attempting to measure trace levels of pesticide residues. Acetonitrile extracts using the conventional approach of clean-up with QuEChERS (Quick, easy, cheap, effective, rugged, safe) from botanicals like tea have too much co-extracted matrix to be injected directly into chromatographic systems. Hayward et al., extracted tea samples with acetonitrile/water and then employed dual phase solid phase extraction (SPE) columns containing layers of graphitized carbon black (GCB) and primary secondary amine (PSA) to provide an effective sample clean-up. The extracts were injected using a TriPlus autosampler, onto a Thermo Fisher TRACE™ gas chromatograph coupled with a TSQ™ Quantum triple-quadrupole mass spectrometer (MS), a variety of tea samples were screened for 170 specific pesticide isomers and metabolites in a single tea sample.
Understanding the Source of Residues in Tea
Both DDT and HCHs, which were found in the tea, are listed by the Stockholm Convention as persistent organic pollutants (POPs). The use of DDT is banned and it was suggested that a possible source could be application of dicofol, which is approved for use in tea production. It is likely that technical grade dicofol is contaminated with DDT, although the US EPA and the EU both stipulate that the sum of DDTs must be less than 0.1% in dicofol formulations.
Clearly, efforts should be put into minimizing sources of unauthorized pesticides and authorities should maintain vigilance in surveillance and monitoring programs to ensure consumer safety. Fortunately, excellent methods such as the one described here have been thoroughly validated and by employing the power of GC-MS/MS provides a high degree of confidence in the accuracy and reliability of the results.