Honey is a sweet natural food produced by bees (Apis mellifera, Family: Apidae). Briefly, the bees collect nectar from flowers that is ripened in the honeycomb by diastase and invertase enzymes from their midgut. The nectar is then matured by evaporating water content by the bees fanning with their wings, until the stored nectar reaches ~ 18% water content. Harvested honey is typically a mixture of matured nectar collected from a wide variety of flora and contains over 200 substances that reflect the botanical and geographical origin. Sugar content is predominantly fructose (45 ± 5%) and glucose (35 ± 3%), while other components include organic acids (e.g. succinic, acetic, formic), minerals (e.g. calcium, potassium, zinc, copper, iron, manganese, phosphorus), vitamins (e.g. ascorbic acid, pantothenic acid, niacin, riboflavin), polyphenols (e.g. gallic acid, apigenin, chrysin, kaempherol), and flavonoids (e.g. pinocembrin, quercetin, galangin, tocopherols) [1, 2]. Honey is the only food produced by an insect that humans consume.

Honey is a natural food and medicine that humans have harvested and prized for time immemorial. The earliest archaeological evidence of humans harvesting honey dates to the Mesolithic period (around 9600–4000 BCE) and the earliest evidence of apiculture was found in the sun temple of Neuserre, Abu Ghorab (around 2400 BCE). References to the health-giving properties of honey are prominent in medical and religious texts spanning global written history and continue to advance and expand in modern texts and practices [3–6]. Much of the health benefits from honey are attributed to the polyphenols and flavonoids as active ingredients serving anti-inflammatory, antioxidative, anti-fungal, and wound-healing effects [1, 2, 7]. Today, beekeeping is a multi-billion dollar industry worldwide, and much of our agriculture depends on bee pollination services expanding the value of the beekeeping industry beyond bee products. Global honey production was approximately 1.72 million metric tons and is currently a $50 billion market expected to grow significantly each year [8, 9]. The character and quality of honeys are strictly defined and lawfully enforced by federal governments across the globe, to combat the prevalence of honey adulterated with other sweeteners. However, the chemical quality of honey is often overlooked and may be a critical oversight in protecting human health against other honey contaminants, such as pesticides, PCBs, PFAS, or metals [10–13]. Metals are the most commonly reported contaminant in honey [14].

Metal contamination continues to be a hot topic in food security and public health, as evidenced by recent recalls with baby foods, packaged apple sauces, and many other similar instances [15–17]. Common metals of concern include lead (Pb), arsenic (As), cadmium (Cd), and mercury (Hg) due to these contributing to a wide range of health issues including risk of cancer, neurological issues, kidney or liver toxicity, and cardiovascular disease [18–20]. Currently there are no maximum contaminant levels (MCLs) for metals in honey defined by the World Health Organization (WHO) or the U.S. Environmental Protection Agency (EPA), though there are two Commission Regulations from the European Union (EU) that define a maximum residue level (MRL) in honey of 0.01 and 0.10 mg/kg for mercury and lead, respectively [21, 22]. Over 100 studies from at least 38 countries have described metal contamination in honey, with the majority from Turkey, Iran, Poland, and Iran [11, 12, 23, 24]. The highest reported level for Pb was 79.815 mg/kg from Ghana; for Cd was 3.810 mg/kg from Romania; for Hg was 0.852 mg/kg from Turkey; and for As was 5.146 mg/kg from Kosovo [25–28]. One study published from the U.S. reported lead levels in honey from central Kentucky as high as 5.65 mg/kg, with 56% of tested honeys higher than 0.05 mg/kg [29].

Metals can also threaten the health of bees and their colony, and are a significant concern for honeybee populations [30, 31]. Bees can be exposed to metals through the food and water they harvest, from dust particles in the air, or from pesticides applied near or directly onto the hive. Many metals (e.g., As, Cu, Pb) are present in licensed pesticides used worldwide and a recent study found most glyphosate-based herbicides contain harmful levels of As, Cr, Co, Ni, and Pb [32]. Given the ubiquity of honeybees and environmental metal pollution, bees are an ideal model species for One Environmental Health [33]. The core principle of the One Environmental Health perspective is recognizing the health of humans, wildlife, and ecosystems are all interconnected and are collectively threatened by environmental pollution. Honeybees are essential pollinators for 80% of flowering plants globally and produce a highly profitable food source for humans, hence they are a critical species to consider within the One Environmental Health framework [34].

Given the lack of data on metal contaminants in U.S. honeys and no reports on essential metals, we sought to investigate metal levels in honeys across the continental U.S. to establish metal levels for 28 honeys from 14 different states collected between 2022–23 (Table 1). We first report metal levels from all honeys for 20 metals (Fig. 1), then report levels for Pb, Cd, Hg, and As by state (Fig. 2) and consider these toxic metal data with a geographic map of the U.S. Critically, we found the vast majority of U.S. honeys greatly exceed MRLs set by EU, indicating a significant concern for metal contamination in U.S. honeys. Finally, we calculated an estimate for daily metal exposure assuming daily consumption of 300 mg honey/kg body mass per day and compared these data against the provisional tolerable weekly intake (PTWI) (Table 2).

We assessed levels of 20 metals in U.S. honeys from 15 different states, which is the most thorough report on contaminants in U.S. honeys reported thus far. Sodium (406.8 ± 8.3 μg/g) and calcium (234.8 ± 11.35 μg/g) were the highest metals we measured, with relatively similar levels regardless of U.S. state of origin; while vanadium (0.021 ± 0.004 μg/g) and titanium (0.056 ± 0.039 μg/g) were the lowest metals measured. We then focused our analyses on four toxic metals (Pb, Hg, As, Cd) and regional differences by state, and found honey samples from Massachusetts and Tennessee exhibited the highest of these metals. Notably, the majority of samples assessed were well above levels considered safe by the EU, implying a potential metal contamination concern for U.S. honeys. We then considered the U.S. mean levels of these metals in the context of JECFA PTWI values, assuming daily consumption of 300 mg/kg (15–20 mL). For each toxic metal, the estimated weekly metal intake greatly exceeded the recommended PTWI values set by JECFA.

Honey is a useful indicator of local environmental contamination. Honeybees forage their local environment within an ~ 7 km radius, effectively sampling the local flora, air, and water. Hence, contaminants measured in honey can give us a view of local environmental contamination and provide valuable monitoring data and insight into areas in needing remediation. In many cases, honey contamination can be isolated to a single point source (e.g., major highway, factory, agriculture), as may be the case for our honey sample from Boxboro, MA which is within 5 km of U.S. Interstate-495. In other cases, further investigation may be required to determine sources based on the land history or geogenic sources, such as our honey sample from Tennessee, which was from a very rural area with no major roadways or industry that could contribute to the high metal levels we observed.

Metal contamination in honey can also challenge the health of bees and the success of their hive [30, 31]. Certain metals honeybees can detect in nectar with their antennae or proboscis and avoid or reject that nectar source, such as Cu, As, Pb, or Zn [50–52]. Exposure to As, Cd, Pb, or a combination can impair honeybee’s short- and long-term memory for odor discrimination, resulting in impaired cognitive flexibility [53–56]. Honeybee exposure to Ni, Pb or Mn resulted in shorter and less frequent flights to visiting flowers [57–60].

Critically, honey has been used in medicine for thousands of years to treat a variety of diseases and recent reports suggest it can improve health for liver, cardiovascular, reproductive, metabolic, and neurological health [5, 47, 49]. Further, a recent review summarized 19 reports describing honey’s ability to alleviate metal toxicity for Pb, Cd, and As across many organs including the liver, kidney, brain, and testes [46]. However, none of these studies reported metal levels in the honeys used for such therapeutic effects. Critically, our results and similar reports from other groups suggest there is a significant potential for metal toxicity from honey consumption [61, 62]. Further research is needed to determine if these levels of these toxic metals outweigh the health benefits of daily honey consumption.

In conclusion, our study is the most extensive to date for metal contamination in U.S. honeys and our results suggest there is a critical concern for metal contamination. Similar or worse metal contamination has been reported in 38 other countries, most often from Italy, Iran, and Turkey. Metal contamination is an important consideration, as honey is a significant commercial industry in the U.S. with about $296 million in annual revenue and with over 565 million pounds consumed in 2022 [63]. Metals may threaten the health of honeybees and the fitness of their hive. Additionally, honey is a bioactive food that can improve health outcomes for multiple organ systems and many disease states which may be exacerbated by metal exposures. Results from our study indicate the levels of many toxic metals in U.S. honeys may result in metal exposures that exceed the recommended PTWI from JECFA when assuming ~ 15 mL (1 U.S. tablespoon) of honey consumption per day. Hence, further investigation is necessary to understand the extent and the threat of metal toxicity from honey consumption and if metal contamination outweighs the health benefits from honey.