Bees can't detect toxic metal pollutants in flowers until they've already gotten their feet wet—by which time it's likely too late to avoid negative health effects.
A recent study found that bees can detect the metal nickel in flower nectar, but only once they've landed on the flower and tasted its contaminated juices. The study suggests metal pollution could possibly play a small role in the nationwide decline of bees, said study author George Meindl, a doctoral student and researcher at the University of Pittsburg.
The study, published recently in the journal Environmental Pollution, also found that bees cannot detect aluminum, even when it's present in potentially harmful concentrations.
Pollution from nickel, aluminum and other metals is a problem in many areas with contaminated soils. Plants growing in these places can concentrate metals in their leaves and flowers. These metals can also become airborne from the burning of coal and petroleum, such as that used to power tractors and machinery, after which the chemicals can end up on top of flowers. Both cases could be a buzz-kill for bees foraging on affected plants; these metals affect many aspects of bee biology, including memory, ability to navigate and taste perception, and can be fatal at certain doses, Meindl said.
The metals could build up in bees' bodies over time, he added.
The nation's bees are in serious trouble—about 40 to 50 percent of U.S. hives were wiped out in the last year, according to The New York Times. The reason for the ailment, called colony collapse disorder, remains unknown. A prime suspect is the expanded use of a powerful new class of neonicotinoid pesticides. Diseases, habitat destruction and pests like mites may also play a role. But this study suggests metal pollution could be hurting bees, at least in certain areas.
The study used nectars that had these metal pollutants artificially added to them to mimic quantities found in certain plants that accumulate nickel and aluminum. Sunflowers are one common plant that can accumulate potentially harmful levels of metals in polluted soils, Meindl said.
The researchers found that bees that visited flowers with nickel spent less time on the flower than on uncontaminated blooms. Afterward the insects also flew to a more distant flower, likely to avoid the metal. It's unclear why the bees can sense nickel and not aluminum, although it suggests that the bees may be more tolerant to aluminum, according to the study.
Plants called metal hyperaccumulators can be used to help clean up contaminated sites, in a method called phytoremediation. However, due to the potential negative affects on bees and other insects, it's better to use plants that don't require pollination by these animals, he said. Certain grasses, which are fertilized by the wind, would be preferable, he said.
Usually pollutants concentrated in plants are then moved to another area and more safely disposed. But some people have raised the possibility of using the process to actually "mine" polluted soils, recovering metal ores from the soil, Meindl said.
Bees can taste nectar with specialized sensory hairs on their front feet, and with their antenna and mouthparts. They can distinguish between various chemicals and prefer certain amino acids, the building block of proteins, but not much work has been done to understand how they may be able to sense different pollutants.