Pesticides in Honey

Research on Pesticide Residues in Honey Samples

Where humans work with plants, there are pesticides. In the case of honey bees, who forage up to 10 kilometres from their hive, it is these foraging bees who will encounter pesticide residues on flowers and return contaminated nectar to hive (unless their hives are located away from human activities).

Research into pesticide residues in wax and honey samples aims to determine the impacts of these potentially toxic compounds and how they they impact human health. We have previous examined the impacts of pesticides on honey bees, and how exposure to low doses while foraging can harm bees through sublethal effects. Now, we move to investigate the impact of turning contaminated nectar into contaminated honey and the worldwide regulations to safeguard human health from pesticides in honey.

This article further examines the natural properties of honey, and provides some speculation as to how pesticide residues can impact its structure. It ends by describing honey’s antimicrobial properties, and succinctly summarises the current research on pesticides in honey (hint: it doesn’t tell us much more than “oh look, this honey is contaminated!”).

What Types of Pesticide Residues have been Found in Honey?

Pesticide residues find their way into honey as a result of contaminated forage, and sometimes via beekeeper application (i.e. chemical treatments for Varroa mites). This can be either from systemic applications, as in the case of neonicotinoids seed coating (commonly seen in agricultural use) or as direct application to the foliage of plants during bloom, as in orchards and many residential settings.

To protect crops used in food production, multiple pesticides are often applied on the same land in the form of tank mixes or specific, timed administrations. The highest levels of pesticide residues are from chemicals used in Varroa mite control, which accumulate in the wax comb, pollen and bee bread (Al-Waili et al., 2012). Of those pesticide residues found honey samples, they are split into four major categories:

• Insecticides, such as neonicotinoids, organophosphates and pyrethroids,
  • The class of insecticides tend to include acaricides, used in the management of Varroa mites. Essential oils, like thymol, are also found here.
• Fungicides, such as ergosterol biosynthesis inhibitors, dicarboximides and demethylation inhibitors,
• Herbicides, such as glyphosate, DDT (still used in many developing countries) and translocated herbicides like amitrole,
• Antibiotics & antimicrobials, such as oxytetracycline, chloramphenicol and erythromycin.
  • Antibiotics make their way into honey as beekeepers use them for treating bacterial diseases like American Foulbrood & European foulbrood diseases.

Can Pesticides in Honey Harm Bees?

The short answer is yes. For the honey to contain pesticide residues, it must have been made from contaminated nectar. Bringing this nectar back to the hive exposes the bees to the pesticides, which spread throughout the colony as the bees share the food via trophallaxis, or bee-to-bee feeding. The toxicological effects of pesticide pollution vary between compounds, with herbicides and fungicides exhibiting different properties compared to neonicotinoids on bees.

If the pesticides do not harm the individual organism, then they can exhibit their effects by harming the gut microflora of the insect, which manifest in sublethal effects. Sublethal effects accumulate and lead to chronic health effects as a result of prolonged pesticide exposure leading, to honey bee population declines directly and indirectly.

Examples of sublethal effects include memory loss, movement impairments and altered foraging behaviour. Bees from social species like Apis mellifera and the bumble bee, Bombus terrestris, will spread contaminated nectar and pollen to other bees inside their hive, rapidly increasing pesticide concentrations within the colony (Banks et al., 2020).

Multiple Pesticide Exposure and the Risk of Synergy

Extracted from “pesticides on honey bees“.

Synergy is when the combined effects of two pesticides are greater than the sum of their individual effects. Assessing such risks is complex and depends on factors like pesticide application methods, timing and concentrations. While any two pesticides may be marked safe for solo use, it is the combination that could lead to unknown, harmful effects. Such scenarios occur when bees forage on crops treated with different pesticides, irrespective of the application method.

The effects of a pesticide depends on the lifestyle of exposed bee species. Individual bees in social species like A. mellifera and B. terrestris are not as vulnerable to chemical exposure as they buffer their effects at the colony level, termed “superorganism resilience”. An analysis of bees foraging on neonicotinoid-coated canola, showed negative effects on wild bee nesting and B. terrestris colony growth, but no significant effects on the development of A. mellifera colonies (Rundlöf et al., 2015).

Pesticides in Honey and Human Health Concerns

Regional environmental protection agencies have issued guidelines in the form of “maximum residue limits”. One example is from the European Union’s Good Agricultural Practice, who defines it as “the highest level of a pesticide residue that is legally tolerated in or on food when pesticides are applied correctly”. These limitations and tolerances vary around the world, and the underlying concept behind maximum residue limits sets out the concentration of pesticides in food that will be safe for human health.

Just because there are detectable pesticide residues in honey, it does not automatically mean a health hazard, as the product’s safety is assessed against regulatory limits and a “daily intake risk assessments”. For example, after smoking a pack a day, Habib likes to unwind with a spoonful honey that contains pesticides within the acceptable limit. Which activity causes him more harm?

Maximum Residue Limits Examples from Around the World

In general, the European Union tends to be stricter on these values than the rest of the world, as demonstrated below:

• For the neonicotinoid clothianidin, in the United States, the maximum residue limits for this compound in food and feed commodities is 0.01 parts per million, or 0.01 mg/kg.
  • In the European union, it was 0.05 parts per million or 0.05mg/kg. However as of 7th March 2026, the new MRL of both clothianidin and thiamethoxam will be reduced to zero¹.
• For the organophosphate pesticide chlorpyrifos, the EU banned* the presence of this pesticide in any food product.
  • In Australia and New Zealand, the Food Standards code sets the accepted concentrations at 0.01 parts per million.
  • In 2022, the U.S. also listed a ban on chlorpyrifos residues in food, to the address human health concern.

These are general guidelines regarding the maximum residue limits set by regulatory bodies and not specific to honey. In the field, one or more neonicotinoid insecticides tend to be used, and since extracted honey is the product of (generally multiple) floral sources, there would be various pesticide residues present in the final product (the exceptions tend to apply for honey bees used in monofloral, commercial pollination operations).

Outside of developed countries, the regulations are not as strict, whether due to necessity or a lack of solid legislation surrounding pesticide use on crops and in food production. Due to this author’s lack of linguistic diversity, data on non-English speaking with high agricultural produce (such as in South America) could not be included, for the primary material is written in the local language.

Can Pesticide Residues Affect Honey’s Natural Properties?

Yes. The physical quality of the honey declines, and this depends on the concentrations of pesticides in the particular finished product. Honey reflects the environmental exposure of foraging bees and serves as a bio-indicator of pesticide presence in the landscape. If consumers are concerned, then they should solely purchase (the more-expensive) certified organic honey.

Firstly, there is the health risk associated with sublethal exposure to pesticides: chronic health effects can ramp up or slowly start to accrue due to the extended exposure to the chemicals in the form of ingested honey (Panseri et al., 2020). The maximum residue limits are one way to mitigate these risks, and consumers should ensure food is sourced from countries that adhere to these limits.

Honey’s Antimicrobial Properties: Facts & Fictions

In more speculative terms, investigating the impacts of pesticides in honey begins with an investigation into the properties of honey from a chemical and consumption perspective. Pesticides can impact the quality and flavour of honey, and this is most evident in monofloral honey samples, where different tastes can be discerned based on the presence or absence of these chemicals. Whether pesticides also affect the nutritional content of honey, that is also unclear. The antimicrobial nature of honey is dependent on various factors working either singularly or synergistically, such as:

• Hydrogen peroxide, a byproduct of glucose oxidase activity after the honey is diluted. This causes oxidative damage to the cells of microorganisms, inhibiting the growth of bacteria and other pathogens,
• Phenloic compounds, such as flavonoids and other polyphenols that function as antioxidants,
  • Proteins like like Bee Defensin-1 and methylglyoxal (MGO, associated with Manuka honey) and nitric oxide compounds are other components that contribute to the honey’s antimicrobial properties.
• The acidic, low pH of the honey, which inhibits microorganism growth;
• Osmotic pressure², which dehydrates and kills microorganisms.

Honey is Acidic in Nature

The acidic nature of honey is one contributor to its antimicrobial properties. The acidity varies between floral sources, and is generally between pH 3.2-4.5: low enough to inhibit the growth of several common pathogenic bacteria such as E. coli Salmonella spp., P. aeruginosa and S. pyogenes, whose minimum growth values are pH 4.0 and higher (Koochak et al., 2010). This acidity further stabilises the honey against breakdown and spoilage by the majority of microorganisms.

Honey Has a Higher Sugar Content Than Moisture

The high sugar content of honey, along with its low water content generate a strong osmotic pressure, whereby honey draws water out of cells (Mandal & Mandal 2011). As the concentration of solutes inside the honey are greater than those inside the microorganism, this forms a concentration gradient for the movement of water out of the cells. Unfortunately for the microorganism, this pressure is so high that the cells become dehydrated, which eventually leads to cellular death.

Enzymes Produced by Honey Bees for Suppressing Bacterial Growth

During the ripening of honey from nectar, bees produce enzymes that contribute to its natural antimicrobial properties. The two primary enzymes are Glucose Oxidase and Bee Defensin-1. The former is added by bees during the processing and regurgitation of nectar between bees, and is responsible for generating hydrogen peroxide (Bucekova et al., 2014). Specifically, this Hydrogen peroxide is produced as a byproduct in the conversion of glucose to gluconic acid in the presence of water and oxygen (which also contributes to honey’s acidic nature; a twofold blow to microorganisms).

Bee Defesin-1 is a positively-charged [cationic] antimicrobial peptide found in both honey and royal jelly. It exerts antimicrobial activity by interacting with membranes of pathogen (recall that cellular membranes are negatively charged) and disrupting their structure, leading to cell death (Bucekova et al., 2017).

Other phytochemicals and antimicrobial enzymes produced in honey do not directly suppress microorganism growth, rather serve secondary functions in preserving its stability:

• Invertase, which breaks down sucrose into glucose and fructose, making it easier for humans to digest, and contributes to its stability; few organisms can grow in a high-sugar environment (Sanchez et al., 2001),
• Amylase, which functions similarly to invertase by breaking down starches and dextrins present in honey into their component simple sugars (Babacan & Rand, 2007),
• Catalase, used to break down residual hydrogen peroxide in the honey, converting into water and oxygen (Majtan et al., 2014).
  • The very same hydrogen peroxide used in antimicrobial defenses can degrade other components in the honey, so this natural removal helps prevent honey spoilage.

Natural Contamination: Does Honey Get Bad?

Honey itself does not go bad in the terms of “unsafe to eat”, rather it undergoes chemical reactions that alter its physical characteristics. Over time, crystallization, fermentation and the Milliard reaction (which darkens the honey) lead to changes in its texture, colour, and flavour (Alaerjani et al., 2022), and proper storage in an airtight container away from light can prevent this.

In crystallization, the high sugar content of honey (specifically the glucose to fructose ratio) leads to the formation of small crystals that separate from the water, turning it semi-solid. Honeys with a higher glucose to fructose concentration tend to crystallise faster as glucose is far less soluble in water (Weber et al., 2022). If honey has crystallised, it can be reverted to its liquid state by placing the jar in a pot of warmed water (~40-50°C).

Fermentation, the process by which honey is turned into an alcohol by yeasts and microorganisms, is a great outcome when deliberate, and a nuisance when not. Yeasts breakdown the sugars in honey and turn them into ethanol. Fermentation of stored honey occurs in high-moisture environments that promote the yeast activity. imparting an off-taste and smell to the product. Proper storage in a dry location and tightly sealed containers prevents this.

In the Milliard reaction, the amino acids react with the glucose and fructose to cause a change in colour, flavour, and aroma. The honey darkens, and the resulting flavours may become more complex or caramel-like. Even under ideal storage conditions and in low temperatures, the Milliard reaction can occur in honey, leading to gradual darkening and flavour changes (Alaerjani et al., 2022).

Adulterated Honey

While not always laced with pesticides, honey can be adulterated by humans for commercial and financial reasons, the most obvious of which being the mislabelling of honey origins to fetch a higher price . As with any venture, purchasing honey from reputable beekeepers and companies is the best way to avoid impure honey.

Adulterated honey arises due to the high demand of honey in comparison to its relatively low supply. The most common way to adulterate honey is to blend it with cheaper sugars or syrups, like corn syrup, cane or beet sugar. Chemically, they are similar to honey and be difficult to discern by taste (Fakhlaei et al., 2020). A beekeeper can further argue that bees fed on a diet exclusively of sugar syrup will lead to honey devoid from the natural complexity profiles of foraged nectar, and the resulting extracted product is of a lower, even impure, quality.

Ultrafiltration, the same process that preserves honey for sale in supermarkets, will also be listed as a way to lace honey. Despite being an “accepted” practice that prolongs shelf-life, much of the pollen grains and beneficial compounds are left behind in the finished product, leaving consumers with something a little better than sugar syrup.

Can Pesticides Affect Honey? Yes, Yes They Can

As you read above, the complex product that is honey is robust to change; naturally protecting itself from degradation and contamination. Honey has developed over many millions of years alongside their insect creators. When novel chemicals like pesticides are added into the mix, it can have untold, and perhaps yet-to-be understood effects on structure, antimicrobial activity, longevity, or health risks from consumption.

This article served as an overview and a major “what if” on the impacts of pesticides on bees and honey samples. Most of the published research around the world state some variation of “we found XYZ residues in honey in ABC region. We should be careful when selling as it could cause health issues.” For the cautious consumer, purchasing organic honey may be the way to go in terms of minimising, but not eliminating pesticide exposure to the human body. After all, when using organic pesticides on bees, the resulting product can still be deemed organic if it meets the other criteria.

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Footnotes

1. The banning of any pesticide residues in foods does not imply a zero value must be present, rather it it is set to to the lowest level that can be measured by analytical laboratories, usually 0.01 parts per million. As analytical technology advances, it lowers the detectable and hence acceptable concentration of a pesticide. ↩︎
2. “Osmotic pressure” is a measure of the movement of water across a semipermeable membrane (such as a cell membrane) from an area of lower solute concentration to an area of higher solute concentration. ↩︎