Concerns about the declining honeybee population are spreading and scientists are scratching their heads trying to figure out the cause. One suggested culprit is a class of insecticides called neonicotinoids.
Research suggests that the chemical is a potential environmental threat and can collect in pollen, making it a possible danger to pollinators such as bees, birds, butterflies and other species. Its use in the U.S. has increased dramatically over the past 10 years while the European Commission has restricted the use of three neonicotinoid chemicals.
A recent U.S. Geological Survey (USGS) study conducted in the rivers and streams of the Midwest shows that neonicotinoids are commonly found in the water. The study measures the percentage of different types of the insecticide in the water and suggests that the chemicals are runoff from fields where they are applied.
"Neonicotinoid insecticides are receiving increased attention by scientists as we explore the possible links between pesticides, nutrition, infectious disease, and other stress factors in the environment possibly associated with honeybee dieoffs," said Kathryn Kuivila, the leader of the study.
Neonicotinoids are often coated on plant seeds to prevent insects from harming crops, but after rainstorms, the seed treatment flushes into nearby waters. The study found this effect in nine rivers and streams in the Midwest, including the Mississippi and Missouri rivers. These rivers transport water from Iowa, Minnesota, Montana, Nebraska, North Dakota, South Dakota and Wisconsin; these are also the states that have reported the highest use of neonicotinoids.
While the insecticide dissolves in water, researchers found that the chemicals do not break down quickly in the environment. One neonicotinoid chemical, imidacloprid, is toxic at 10-100 nanograms per liter when exposed to aquatic organisms. The researchers found this chemical at 23 percent (32.7 nanograms per liter) in the rivers and streams. The other two neonicotinoids most often studied are clothianidin and thiamethoxam, found at 75 percent (257 nanograms per liter) and 47 percent (185 nanograms per liter), respectively. Previous studies show that they produce toxic effects similar to imidacloprid.
The study, led by scientist Kathryn Kuivila and Michelle Hladick of the USGS, was published in Environmental Pollution. In addition to percentage levels of neonicotinoids, the scientists found that the insecticides applied in the previous year may still be found in the waters, potentially endangering organisms a year later. The U.S. Environmental Protection Agency says it is not likely neonicotinoids are carcinogenic to humans.
