New research from the U.S. Geological Survey (USGS) found that insecticides known as neonicotinoids were found commonly in streams throughout the Midwest, reports the Wildlife Management Institute. The group of chemicals has increasingly come under fire in recent years as research begins to show impacts to species outside of the target insects. Recent studies suggest that neonicotinoid residues are found in the pollen and nectar of treated plants resulting in the death or impairment of the pollinators that consume it. In addition, a study from the Netherlands that was published on July 17 in Nature notes the potentially related declines in some insectivorous birds.

"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 USGS scientist Kathryn Kuivila, the research team leader.

The various chemicals that are considered neonicotinoids are chemically related to nicotine and similarly affect the nervous system, primarily in invertebrates. The chemicals are used for agricultural crops as well as for home insecticide use, and the use of neonicotinoids has increased dramatically in recent years. Use of one chemical, clothianidin, on corn in Iowa alone doubled between 2011 and 2013. The chemicals are easily dissolved by water allowing them to be taken up into the plant through the vascular system to kill sap-feeding insects. In commercial applications, seeds are pre-treated with the chemicals, however they are also prevalent in many home garden products and can legally be applied at higher concentrations in gardens than in farms.

While the water solubility benefit allows for more direct application of the product reducing insecticide drift, neonicotinoids do not break down in the environment allowing them to persist in soils or be transported from agricultural fields by runoff. The nine rivers and streams studied by the USGS researchers drain most of Iowa and parts of Minnesota, Montana, Nebraska, North Dakota, South Dakota, and Wisconsin ? the states with the highest use of neonicotinoids. Clothianidin showed up in 75 percent of the studied streams and at the highest concentration. Thiamethoxam was found at 46 percent of sites and imidacloprid was found at 23 percent. Three other neonicotinoids were found in a limited number of locations.

"We noticed higher levels of these insecticides after rain storms during crop planting, which is similar to the spring flushing of herbicides that has been documented in Midwestern U.S. rivers and streams," said USGS scientist Michelle Hladik, the report's lead author. "In fact, the insecticides also were detected prior to their first use during the growing season, which indicates that they can persist from applications in prior years."

Imidacloprid is known to be toxic to aquatic organisms at 10-100 nanograms per liter if exposed for an extended period of time, and the other neonicotinoid chemicals are expected to have similar effects. Maximum concentrations of clothianidin, thiamethoxam and imidacloprid in the Midwestern rivers studied by USGS were 257, 185, and 42.7 nanograms per liter, respectively. The chemicals can also persist in soils for months or years after a single application and untreated plants can absorb chemical residues from the soil. In addition, residues are found in the pollen and nectar of treated plants, sometimes at lethal concentrations.

As a result, the Xerces Society for Invertebrate Conservation and a number of other groups have raised concerns about how neonicotinoids are affecting plant pollinators. A 2012 report released by the Xerces Society reviewed existing research about the impacts of neonicotinoids on pollinating insects such as honey bees and native bees. Imidacloprid and clothianidin are highly toxic to a variety of bee species, and other neonicotinoids have varying degrees of toxicity. Some pollinators will die immediately from toxic levels of the chemicals, however sublethal amounts can impact flying and navigation resulting in reduced foraging ability and activity; bumble bees and solitary bees respond differently to neonicotinoids than honey bees do. While some reports initially linked the chemicals to Colony Collapse Disorder (CCD) in honey bees, recent research suggests there is not a direct link but that neonicotinoids may make honey bees more susceptible to parasites and pathogens that have been implicated as a causative factor in CCD.

Concerns have also been raised about the impacts of neonicotinoids on birds. A 2013 report by the American Bird Conservancy outlines how treated seeds can kill birds if ingested directly, and that the impacts of the chemicals on aquatic systems can affect food sources at the bottom of the food chain. The Dutch study published recently in Nature found that where imidacloprid was found in concentrations of more than 20 nanograms per liter, insectivorous birds declined by 3.5 percent on average annually.

"It is clear that these chemicals have the potential to affect entire food chains. The environmental persistence of the neonicotinoids, their propensity for runoff and for groundwater infiltration, and their cumulative and largely irreversible mode of action in invertebrates raise significant environmental concerns," said Cynthia Palmer, pesticides program manager for ABC and co-author of the report.

In a July memo, Jim Kurth, chief of the national wildlife refuge system for the U.S. Fish and Wildlife Service, told refuge managers to phase out the use of neonicotinoids and genetically modified crops on refuges by January 2016. Some refuges can be exempted including refuges that are mandated for agriculture use like Tule Lake and Upper and Lower Klamath refuges in California and Oregon and Crab Orchard in Illinois.

Kurth wrote: "We have determined that prophylactic use, such as a seed treatment, of the neonicotinoid pesticides that can distribute systemically in a plant and can potentially affect a broad spectrum of non-target species is not consistent with Service policy. We make this decision based on a precautionary approach to our wildlife management practices and not on agricultural practices."

The USGS paper, "Widespread occurrence of neonicotinoid insecticides in streams in a high corn and soybean producing region, USA" and was published in Environmental Pollution. (jas)