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, [boasts] sales of over $1 billion a year. A 2016 study suggested a link between neonicotinoid use and local pollinator extinctions. As the bee debate raged, scientists studying the country's waterways started to detect neonicotinoid pollutants. In 2015, the U.S. Geological Survey collected water samples from streams throughout the United States and discovered neonicotinoids in more than half of the samples. And on Wednesday, a team of [researchers] at the USGS and University of Iowa reported that they found neonicotinoids in treated drinking water. It marks the first time that anyone has identified this class of pesticide in tap water. The Environmental Protection Agency has not defined safe levels of neonicotinoids in drinking water. The pesticides ... work their way into plant tissue rather than just coating the leaves and stems. Neonicotinoids can slip past sand [water filtration systems] because they ... dissolve very readily in water. The research team looked at how effectively the university's sand filtration system ... blocked the three neonicotinoids studied. The university's sand filter removed 1 percent of the clothianidin, 8 percent of imidacloprid and 44 percent of thiamethoxam.