A study conducted by researchers from the University of Iowa and the U.S. Geological Survey has found traces of pesticides known as neonicotinoids, for the first time, in US' drinking water.

According to the report, three kinds of the neonicotinoids-containing insecticide -- clothianidin, imidacloprid, and thiamethoxam -- were found despite purifying and treating the water.

United Press International notes that neonicotinoid contamination has previously been traced in rivers and streams. However, this is the first time it has been traced in drinking water.

Samples of water drawn from three of Iowa's major water source show it has maximal concentrations of 260, 43, and 190 ng/L for clothianidin, imidacloprid and thiamethoxam, respectively. The samples were garthered from May to June 2016, following the maize/soy plantation season.

"These are very low levels, these are nanograms per liter which means parts per trillion, a very low concentration," Gregory LeFevre, one of the authors from the University of Iowa, told BBC.

"But at the same time there are concerns about what those low levels might do from an exposure standpoint," he added.

Neonicotinoids persist in the environment, as such, it is likely to end up as runoff chemicals from agricultural fields that use them.

In the market, neonicotinoids is branded as one of the newest and safest insecticides to use. As such, they are the most used pesticide in America. According to Washington Post, imidacloprid is among the world's best-selling insecticides, boasting sales of over $1 billion a year.

However, it was found by other studies recently that it actually causes harm even on other organisms. Beyond Pesticides said exposure to imidacloprid at environmentally relevant levels decreases not just bug population, but mosquitos, bees and beetles as well. In turn, this hurts the population of bigger animals that feed on them, such as birds.

At present, the Environmental Protection Agency has not yet defined safe levels of neonicotinoids in drinking water because as mentioned, it is a newcomer in the market. They are currently working on numerous studies to set safety guidelines.