Heavy metal accumulation in honey

A couple of beekeepers have been asking 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 about twenty papers concerning this issue, 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.

Now, the good news

Most of the papers I read were written by researchers who were hoping to find a way to use honey bees—or their hive products—to monitor environmental health. The thought was that hives could be put on various patches of land and then the hive products could be analyzed to give us a picture of the amount of soil contamination in that area.

What they found was that hives on severely contaminated soil 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

1

2011

2

8038

3

18086

4

32154

5

50240

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.

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.

Rusty
HoneyBeeSuite

Comments

Phillip
Reply

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.

Thanks.

Toronto Honeys
Reply

Hi Phillip,

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.

Phillip
Reply

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.

Beth
Reply

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?

Rusty
Reply

Beth,

I have the links somewhere in my notes. I’ll see if I can find them.

Greg
Reply

Hi Rusty

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?

Kind regards,

Greg

Rusty
Reply

Greg,

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.

MJ
Reply

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?

Rusty
Reply

MJ,

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.

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