The results from the first national-scale investigation looking at the environmental prevalence of a controversial and widely used pesticide are in, and they’re pretty stunning: a little more than half of the streams sampled by the United States Geological Survey contained neonicotinoids, a class of insecticides that has been closely examined for its potential impact on key pollinators like honeybees.
The study tested for six different types of neonicotinoids in 24 states, as well as Puerto Rico, between 2011 and 2014. Samples were collected from both urban streams and agricultural streams.
“In the study, neonicotinoids occurred throughout the year in urban streams while pulses of neonicotinoids were typical in agricultural streams during crop planting season,” USGS research chemist Michelle Hladik, the report’s lead author, said in a press statement.
The prevalence of neonicotinoids varied among types — one type of neonicotinoid was found in 63 percent of samples, while another was not detected in any samples. In all cases, the levels were low — below thresholds mandated by the Environmental Protection Agency’s aquatic life criteria.
Still, researchers said that the results would serve as an important baseline for future research.
“The occurrence of low levels in streams throughout the year supports the need for future research on the potential impacts of neonicotinoids on aquatic life and terrestrial animals that rely on aquatic life,” USGS scientist Kathryn Kuivila, the research team leader, said in a press statement. “These results will serve as an important baseline for that future work.”
Neonicotinoids — derived from nicotine — are a relatively new kind of pesticide that impact an insect’s nervous system, causing paralysis and death. They’ve become especially popular in recent years because they’re generally considered less toxic to humans and mammals than older insecticides — neonicotinoids target a specific pathway in the nervous system that’s a lot more common in insects than in warm-blooded mammals. Neonicotinoids are also water soluble, meaning they can be applied to soil — or to seeds before planting — and readily taken up through roots into plant leaves.
Neonicotinoids were first developed in the 1990s, but became especially prevalent starting in the mid-2000s, driven largely by an increase in neonicotinoid-treated seeds (mostly corn and soy). The rise of neonicotinoids has stoked fears that their prevalence could be contributing to colony collapse disorder (CCD), a syndrome of bee colony collapse that was first noticed in 2006. No studies have found a definitive link between neonicotinoids and colony collapse disorder (though one widely criticized 2014 study did name neonicotinoids as the main cause of CCD).
None of this is to say that neonics, or pesticides in general, have been given a complete pass when it comes to bee deaths. Some studies have suggested that neonicotinoid pesticides can make bees forget the scent of food, hindering their ability to pollinate crops. Others have suggested that pesticides, including neonicotinoids, likely do make bees more susceptible to infection. Another study found persistent levels of neonicotinoids in beehives for most of the year, suggesting that the pesticide is pervasive among bee colonies. Whether neonicotinoids are the leading cause of bee deaths is complicated and still being studied, but a growing body of science seems to suggest that they are at least one factor in the decline of pollinator populations around the world.
Still, the lack of a definitive link between neonicotinoids and CCD hasn’t stopped a wave of opposition to the pesticides from both businesses and government. In October of 2014, 60 members of Congress wrote a letter to the EPA urging them to issue a ban or restriction on the use of neonicotinoids, citing their adverse effect on pollinators and wildlife. In January, a coalition of more than 100 businesses — including many food companies — also penned a letter to the EPA and the White House, calling for a ban on neonicotinoids. In May, the White House announced a national strategy aimed at combating pollinator loss; the strategy calls for more studies aimed at understanding the link between neonicotinoids and pollinator health.
USGS researchers see their study as a useful addition to the White House’s official strategy.
“This research will support the overall goals of the Strategy, by helping to understand whether these water-borne pesticides, particularly at the low levels shown in this study, pose a risk for pollinators,” Mike Focazio, program coordinator for the USGS Toxic Substances Hydrology Program, said in a press statement.