Small traces of the world’s most widely used insecticides have been detected in tap water for the first time. Of the many pesticides that American farmers have embraced in their war on bugs, neonicotinoids are among the most popular. One of them, called imidacloprid, is among the world’s best-selling insecticides, boasting sales of over $1 billion a year. But with their widespread use comes a notorious reputation — that neonics, as they are nicknamed, are a bee killer. A 2016 study suggested a link between neonicotinoid use and local pollinator extinctions, though other agricultural researchers contested the pesticides’ bad rap.
Every water sample contained three types of neonicotinoids: clothianidin, imidacloprid and thiamethoxam.
The University of Iowa scientists tracked neonicotinoid concentrations in the local drinking supply from May to July, the seven-week span after the region’s farmers planted maize and soy crops. Every sample contained three types of neonicotinoids: clothianidin, imidacloprid and thiamethoxam.
“Everything in the watershed is connected,” LeFevre said. “This is one of many types of trace pollutants that might be present in rivers.” (The USGS released an interactive map of the nation’s water quality on Tuesday, where those inclined can track trends in common pollutants.)
Most water filtration systems target clay, dirt or other particles, as well as pathogenic contaminants like bacteria. They’re not designed to eliminate chemical pesticides — and the properties of neonicotinoids make these compounds unusually challenging to remove. Other types of pesticides stick to soil particles, which are then filtered out. But neonicotinoids can slip past sand filters because they are polar chemicals. “They dissolve very readily in water,” LeFevre said. He invoked a chemistry aphorism: “Like dissolves like.”
Now researchers report that in some areas, drinking water also contains the substances — but they also have found that one treatment method can remove most of the pesticides. The study, conducted in Iowa, appears in ACS’ journal Environmental Science & Technology Letters.
Neonicotinoids are potent insecticides that are used widely around the world, often applied to seed coatings of crops. But some research has associated the compounds in certain cases with harm to bees. Other studies have suggested that chronic exposure to the compounds can cause developmental or neurological problems in other animals, too. The pesticides are so commonly used in agriculture that surveys of streams in farming-intensive regions in the U.S. have found that neonicotinoids are widespread in surface waters. Gregory H. LeFevre, David M. Cwiertny and colleagues wanted to investigate the fate of these compounds as water from the Iowa River and an aquifer supplied by the river is treated and ends up at the tap.
The researchers tested water as it went through two different water treatment systems. They found that a system serving Iowa City, which uses granular activated carbon filtration, removed 100 percent, 94 percent and 85 percent of the neonicotinoids clothianidin, imidacloprid and thiamethoxam, respectively. The rapid sand filtration system serving the University of Iowa reduced the same substances only by about 1 percent, 8 percent and 44 percent, respectively. Drinking water samples from this treatment plant contained between 0.24 and 57.3 nanograms of individual neonicotinoids per liter. Regulatory limits for these substances are not currently in place as researchers are still working to understand if and how neonicotinoids impact human health, the researchers note. They add that more studies are needed to figure out whether chronic, low-level exposure to neonicotinoids might be harmful.
Melissa Perry, a public health researcher at George Washington University who was involved in that review, said via email that the new study “provides further evidence that neonicotinoid pesticides are present in our daily environments. From a public health standpoint, this issue clearly needs better attention.” “There is currently no national effort to measure to what extent neonicotinoids are making it into our bodies, be it through water or food,” she noted.