A couple of beekeepers have asked me to write about the possibility that heavy metals—particularly lead—are getting into their honey from contaminated soil. In the past year I’ve read several research papers concerning metal accumulation in honey, but instead of writing a literature review, I’ve decided to write like a blogger—in other words quick and easy.
One thing I learned is that “heavy metals” is an ambiguous term and the list differs depending on who you talk to. For my purposes here, I’m referring to the toxic-to-human metals such as arsenic, cadmium, chromium, copper, lead, manganese, mercury, and nickel.
First, the bad news
The bad news is that heavy metals do indeed enter plants from contaminated soils. The metals are picked up by the roots and distributed throughout the entire plant including the nectar and pollen. The amount of metal in the plant increases with the amount of metal in the soil. Also, in regions where there is a significant amount of lead in the air, it may land on the plant and adhere to the sticky surfaces of pollen.
Bees collect both the contaminated pollen and nectar and transport it back to the hive. In controlled experiments these heavy metals have shown up in pollen pellets, honey, beeswax, royal jelly, and in the bodies of the honey bees themselves.
A large foraging area restricts metal accumulation in honey
did not show significantly different levels of heavy metal accumulation from those hives on clean soil. The researchers concluded that these findings were due to the way honey bees forage. Honey bees will easily forage within a three-mile radius and, in times of nectar dearth, may extend that to five miles. The bees also sample the flowers of many different plant species, each of which have different rates of heavy metal assimilation.
Consider this little chart. If we take a circle with a one-mile radius, square the radius (1 x 1 = 1) and multiply it by 3.14 (pi) we get the area in square miles (3.14). Now we take that number and multiply it 640 (the number of acres in a square mile) and you get 2011 acres. So a chart of acres covered by foraging bees looks like this:
Foraging Distance from Hive in Miles
Acres within that Range
This means that even if your bees are sitting on a contamination hot spot, your honey is probably not going to have significantly more heavy metal contamination than most other honey. Only a very small proportion of the total harvest will come from the area immediately adjacent to the hives.
Of course the numbers will vary—the larger the contaminated area, the higher the chance of accumulation. But, as you can see, even if the contamination site is 100 acres, that is only about 5% of a one-mile foraging radius and 1.25% of a two-mile radius.
Now, the good news
Of the papers I read, none of them found honey samples with dangerous levels of toxic metals. A few had fairly high levels of iron, but not at a level considered harmful to human health, especially in view of how much honey we actually eat.
Now whether there is enough heavy metal accumulation in individual bees to affect their health is an entirely different question. Some of the papers suggest that the metals accumulate in various parts of the bee body and may adversely affect things like organ function, but I’ll take up that topic on another day.
Thanks for the info, Rusty. It’s a mixed bag, isn’t it?
I’m wondering now if cities known for high leaded soil (e.g. St. John’s, Newfoundland) have lead in the flowers everywhere, not just in 5% or so of the bees forage radius — but in all of it. Flowers from trees may be a different story. I don’t know.
I’ve made contact with a local government official in charge of agricultural services (and about 10 other departments). She’s looking into it for me.
In the meantime, I’ve already found a few studies on lead in pollen and nectar. I haven’t had time to read them yet, but I got them. I plan to have my honey tested regardless. I’m not too worried (yet). But leaded soil –> leaded pollen & nectar –> raw leaded honey. It seems like a obvious area of concern, at least for urban beekeepers.
I’m curious what came up in the results of your testing?
We’ve been testing our urban honey in Toronto for a few years and the results keep coming back clear.
I contacted someone who works for the government, but she’s couldn’t do anything for me. So I called an entomologist at a local university. He didn’t have exact figures but he said lead transference from soil to flowers to bees has never been detected in any of his studies over the past 30 years.
I live in West Oakland, CA and have backyard bees. Our house was near a highway that came down in an earthquake. We have lead-contamination in our soil, and I suspect most of Oakland does.
A neighbor and I had our honey tested through the Center For Environmental Health (ceh.org) for lead and the results 75-85 ppb.
I’d like to drum up more interest in this topic as it is really important for urban beekeepers. Rusty and Phillip, Do you have links to the papers you’ve both mentioned?
I have the links somewhere in my notes. I’ll see if I can find them.
This is a really interesting article, as I am currently basing my MSc in Pollution and Monitoring dissertation upon heavy metal pollution in honey, so far testing over a dozen sites from rural and urban areas in and around London. With so far, supporting results which show the high level of purity of honey which has come clean in terms of heavy metals, am following this up with examining organic compounds testing.
However I am curious to know what were the journal articles you read?
I had a professor of agronomy from Virginia Tech help me with that post, and at the time he sent me the several journal articles that I mentioned. It’s been a few years, so I will have to do some serious digging in my files. I will be happy to share if I can find them.
I’m currently doing some studies on heavy metal pollution and whether bumble bees would recognise and avoid heavy metal polluted nectar and pollen. Do you know anything about this subject? What would you suggest would be the best way to test this in the lab or outdoors?
I’ve read a few studies on this but I am no expert, and I certainly do not know if bumble bees can recognize it or not. Lead used to be found frequently on flower stigmas when there was still lead in gasoline, but that has declined over the years.
Thank you very much for your kind message. Do you have any papers that I could read about this topic?
I do somewhere, but I will have to hunt around for them. I put it on my to-do list, but you may be better off searching on Google Scholar.
Dear Rusty, thank you for your kind message. if you have it by hand i would much appreciate your articles for my research but don’t worry if they are really hard to digg out. 😉
earth greetings! 😉
Is there a way I can have the honey that I use regularly (4-5 tsp/day) tested for heavy metals? Who does this kind of testing?
If you Google somethings like “testing for heavy metals in food” you will find many places that do it. Most likely, you will have to send a sample to a private lab and I suspect it can be expensive.
Hello, do you have any links to the papers that talk about the heavy metal concentration please?
Google it. There are many.