How much pesticides do we drink together with our tea? To answer this question, Sciensano studied tea leaves contaminated with pesticides to determine their transfer factors. These help us to see how much of the different pesticides transfers into our tea and the difference between different types of tea (black, green, herbal, green perfumed tea).
In Belgium, the maximum residue limit (MRL) for pesticides in tea and herbal tea is often exceeded (> 10% non-compliant). Between 2017 and 2019, more than 90 different residues were detected in samples taken by the FASFC. Even if MRL exceedance is not necessarily a synonym of risk for the consumer’s health, it is important to perform risk analysis. As tea leaves/herbal tea are not consumed as such, it must be considered that tea leaves are infused before consumption. Hence, it is important to use transfer factors to estimate the risk. However, these transfer factors don’t exist for a lot of pesticides found on the Belgian market. The purpose of this project is first to identify in scientific literature or databases these transfer factors. Then, determine experimentally transfer factors for pesticides residues that are still unknown. In the meanwhile, effect of some infusion parameters on the pesticides transfer have been assessed such as tea type, infusion time and temperature and water hardness.
The impact of the type of tea
It was shown for 29 out of 54 pesticides studied that the tea type has an important impact on the transfer rate of the pesticides to the brewed tea. In general, green tea is associated with lower transfer rates compared to black tea, while herbal tea has the highest transfer rates. Lower transfer rates were found for green tea with orange and lemon flavours than for unflavoured green tea. No significant differences were observed for the infusion temperature (80-100°C) nor for the infusion times (2, 3, 5, 10 min) or the water hardness. This is an interesting observation since these parameters are consumer-dependent, but thus have no significant impact on the risk analysis.
Pesticide polarity as most relevant parameter
The obtained experimental data were then used to construct models to predict transfer rates (one model for each type of tea) based on various physicochemical properties of the pesticides:
- log P (polarity)
- solubility (mg/L)
- vapour pressure (mPa).
These models aim at minimizing the deviations between the experimentally observed transfer rates and the predicted transfer rates. When the pesticide is not present in the database, these models can be used to estimate the transfer rate. The model showed that log P is the most relevant parameter for pesticide transfer, followed by solubility. Vapor pressure is only relevant for herbal tea.
Transfer factors database as a tool for the risk assessment
Finally, all transfer factors considered relevant from scientific literature or databases (EFSA and BfR), experimentally determined and predictive models were compiled into an Excel database. This database contains 1206 transfer rates for 108 pesticides for different types of tea (black, green, herbal, green perfumed tea). Oolong tea was also added due to the high availability of these teas in supermarkets and specialty stores.
In conclusion, to perform a risk assessment, it is recommended to proceed as followed:
- Consult the database and take the maximum transfer rate for the pesticide/tea combination in question. This will give you the highest possible amount of pesticides that can transfer to the tea.
- If no information is available on the transfer rate, the developed model can be applied. The different physicochemical parameters should be introduced with respect to the units listed. If necessary, a unit converter has been created and could be used. Next, the transfer rate is automatically calculated. However, it should be noted that the model is only applicable for compounds with Log P < 4. For pesticides with a Log P > 4, the transfer rate can be estimated at maximum 20%.