Selenium Present in Plants Harmful to Honeybees

Man made forms of the element selenium, a common byproduct of copper production, have been shown to cause mortality and developmental delays in honeybees.

Four forms of selenium -- selenate, selenite, methylselenocysteine and selenocystine -- found in plants have been shown to have adverse affects on bee colonies, according to research published in the journal Environmental Toxicology and Chemistry.

"Metal pollutants like selenium contaminate soil, water, can be accumulated in plants, and can even be atmospherically deposited on the hive itself," said University of California, Riverside's Kristen Hladun, entomologist and lead author of the study. "Our study examined the toxic effects of selenium at multiple life stages of the honeybee in order to mimic the chronic exposure this insect may face when foraging in a contaminated area."

The honeybee is an important agricultural pollinator in the United States and throughout the world, the UC Riverside researchers said, adding that honeybees in areas of selenium contamination "may be at risk because of the biotransfer of the metal" from selenium-accumulating plants.

Other than as a byproduct of mining operations, selenium makes its way in to the environment from a variety of other anthropogenic operations, including oil refining and coal-power production. Agricultural runoff can lead to selenium concentrations in soils.

"Selenium occurs naturally in many places around the world, but it also is a byproduct of many industrial activities, and finding ways of recovering and recycling it is key to minimizing the damage to the environment," Hladun said. "Currently, researchers are exploring its use in solar energy technologies."

Selenium's effect on animals is fickle. In low amounts it can be a beneficial antioxidant enzyme. In large doses, however, it can be toxic. Several insect species suffer from toxic effects from feeding on selenium-contaminated food, the researchers said.

Honeybees, which lack the detoxification enzymes that many other insects have, ingest selenium via contaminated pollen and nectar. Organic forms of selenium can cause development problems; inorganic forms can cause oxidative stress.

"It is not clear how selenium damages the insect's internal organs, or if the bee has the ability to detoxify these compounds at all," Hladun said. "Further research is necessary to examine the cellular and physiological effects of selenium."

Hladun said if beekeepers can determine which plants in their area have high selenium concentrations, they can take measures to prevents bees from foraging on those plants.

"Also, better management of weedy plant species that are known to be selenium-accumulators can prevent them from becoming a route of exposure."