Pesticides residues in honey
Josef van der Steen
Pesticides can be detected in honey. There is nothing that a beekeeper can do about it, because pesticides are in the environment and bees collect these pesticide residues along with their food. Based on the recent EFSA report on pesticides in food, the most detected pesticides in honey are the agricultural pesticides thiacloprid, acetamiprid, bimoxystrobin, glyphosate, chlorpyriphos, fosetyl, flonicamid, boscalid, and chlorfluazuron. The varroa control substances amitraz and coumaphos were also detected. In about 4 out of 5 honey samples no pesticides were found in quantifiable amounts, and in 1 out of 5 honeys pesticides could be detected. Only in a few cases did the amount of pesticides exceed the MRL (Maximum Residue Level) threshold, but in all cases, the honey samples analysed met the food safety / trade threshold. How pesticides enter the hive, how the honey bee colony cleans the honey, and how pesticides in honey may relate to honey consumption and toxic effects, is described in this newsletter.
Pesticides in honey
The INSIGNIA results from the 2019, 2020, and 2022 studies demonstrated that pesticide residues were detected in every hive. This is simply a reflection of the environment; pesticide residues are present all over, varying from very low amounts away from the application location because of aerosol drift, soil erosion, dusting, and evaporation, to significant amounts close to the application locations. This raises the question of whether these pesticides also end up in honey. Here a, very interesting mechanism comes into play; it depends on both the physico-chemical properties of the pesticide and the honey extraction- and sieving process. First the physico-chemical features of pesticides. Most pesticides, (active substances + carrying substances) are specifically designed to stick to the natural wax that covers plant leaves, branches, flowers, and fruits. Relevant here, are the lipophilic (fat-loving) pesticides. The vast majority of pesticides are lipophilic. Some other pesticides on the other hand are designed to enter the vascular fluid streams inside the plant. They dissolve in the water in the plants and are therefore hydrophilic (water-loving) pesticides. There are very lipophilic and very hydrophilic pesticides and many intermediates. The better that the pesticide dissolves in water, the more likely it is to end up in honey, and the better it dissolves in fat (and so also in beeswax), the less likely it is to end up in honey. This feature is expressed as “logP”. Apart from the logP, other factors like temperature, concentration, and exposure time will affect the physico-chemical process of the distribution of pesticides over beeswax and honey. Considering the high number of different active substances that are used in agriculture, the range of logP values that can be presented is very wide. In general, the higher the logP value, the more fat-loving, and the lower the logP, the more water-loving the pesticide is. For those interested, I explain the logP in more detail in the attachment to this newsletter, below the references.
Pesticides in the hive
So what happens in the hive? Fat-loving pesticides that enter the hive via nectar, pollen, water, and directly via the forager’s hairs, will be directly incorporated in the beeswax, in beebread and larval- and pupal skins. That is the consequence of the different affinities of the pesticides for these groups of products present in the hive. Most of these pesticides will end up in the wax, as this is the biggest surface in the hive. In case of nectar- and water contamination, they will migrate from the water into the wax. On the other hand, the water-loving pesticides will remain in the honey and water. In practice, the beeswax acts as a cleaner by trapping most pesticides from nectar and after processing, for honey. When honey is extracted and sieved, you can imagine that the more wax particles that are in the honey, the more chance there is that pesticides, attached to these wax particles will be detected in the honey.
What pesticides are in honey?
What pesticides are found in the honey? I took the 2019 European Union report on pesticides in food, made by the European Food Safety Authority (EFSA) to present what has been detected, and thus will be an indication of what will be detected in the INSIGNIA-EU 2023 study. In this EFSA study, 1301 honey and other hive products were analysed. The other food hive product is pollen, but as the majority is honey, I will consider the data in this report here as honey. In these 1301 samples, in approximately 80% of the samples, no pesticide residues were detectable in quantifiable amounts. In the honeys, 27 different pesticide residues were detected; in part of the honey samples, more than one pesticide was detected. The most frequent detected pesticides were thiacloprid*, acetamiprid*, amitraz*, dimoxystrobin, chlorates, azoxystrobin*, glyphosate*, chlorpyriphos, bromide ions, fosetyl, coumaphos, flonicamid, boscalid* and chlorfluazuron*. Seven pesticides, marked with * were detected in amounts above the MRL (see explanation in the next line). In the majority of these cases it concerned only one sample. The MRL is the Maximum Residue Level, which is pesticide-specific. It is the amount of pesticide in food that is considered acceptable for trade and harmless to the consumer. Amitraz and coumaphos are used by the beekeeper to control the varroa mite. The herbicide glyphosate is an interesting substance because it is phytotoxic and kills the majority of plants and by doing this also the food source for bees.
Putting the MRLs and ADIs in honey in perspective
To place pesticides in honey in the perspective of the consumer, I will focus on thiacloprid, a neonicotinoid insecticide. The MRL is explained in the paragraph above – “What pesticides are in honey?”. The ADI is a new concept in this newsletter. It is about human health and stands for the “Acceptable Daily Intake”; the amount which is considered to be safe for human consumption. Based on EFSA publications the MRL = 0.15 to 0.2 mg thiacloprid/kg honey (EFSA 2016.4418) and the ADI = 0.01 mg/kg body weight (bw). The MRL and ADI tell us that a human being of 1 kg must consume 67 grams of honey with 0.15 mg thiacloprid/kg honey to ingest the ADI. “Translated” to a child of 5 kg, this would mean that that the child must consume 5 x 67 grams of that honey = 335 grams per day, to reach toxic thiacloprid levels. An adult beekeeper must consume per day 80 x 67 grams = 5.4 kg to reach the toxic thiacloprid levels. One teaspoon of honey weights about 4 gram, so 335 grams is 84 teaspoons and 5.4 kg is 1350 teaspoons.
Overall, it is obvious that pesticides can be detected in a significant proportion of honey, but it is also obvious that, when we take human health into consideration, a person must consume unrealistic amounts of honey to ingest toxic levels of these pesticides.
The 2019 European Union report on pesticide residues in food European Food Safety Authority (EFSA), Luis Carrasco Cabrera and Paula Medina Pasto: The 2019 European Union report on pesticide residues in food | EFSA (Europa. eu)
Morales, María Murcia, et al. “Distribution of chemical residues in the beehive compartments and their transfer to the honeybee brood.” Science of the Total Environment 710 (2020): 136288.
The log P is the logarithm to base 10 of the quotient of the calculation of the octanol–water partition. In other words, the outcome (P) of the amount of a pesticide that dissolves in octanol (a fatty alcohol), divided by the amount that dissolves in water. For example, if twice the amount of pesticide dissolves in octanol than in water, P = 2 but if twice the amount of pesticide dissolves in water than in octanol, P is 0.5. This quotient can thus be big if a pesticide dissolves only in fat or very small if it only dissolves in water. Therefore the logarithm to base 10 is presented; the logP. The log is the times that one has to divide P by the base 10. For example P = 100 means that 100 times more pesticide dissolves in ethanol than in water. The logo is consequently 2 because the base 10 must be multiplicated 2 times with itself (10 * 10) to come to 100. In case P is 1, meaning that the same amount of a substance dissolves in octanol as it does in water, the logP = 0. It is a logarithm rule that 10log of 1 = 0. Consequently, P numbers below 1 have a negative logP. For example, the aforementioned P =2 gives a logP of 0.3, and the aforementioned P = 0.5 has the logP of -0.3.