Heavy metal accumulation in honey

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
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.

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.

Rusty
HoneyBeeSuite