The samples indicated that the local water plant removed about half the thiamethoxam in the water supply, but none of the other two chemicals. But when the water was treated with activated carbon filters, levels of all three "were substantially lower," and further experiments with such filters removed almost all of them.
The traces of neo-nics were quite small, ranging from 0.24 to 57.3 nanograms per liter—that is, on a scale of parts per trillion, Ben Guarino reports for The Washington Post. Gregory LeFevre, a study author and University of Iowa environmental engineer, told the Post that the discovery was important but not an immediate cause for alarm: “Having these types of compounds present in water does have the potential to be concerning, but we don’t really know, at this point, what these levels might be.”
Guarino writes, "Regulators have not defined safe levels of neo-nicotinoids in drinking water, in part because the chemicals are relative newcomers to the pesticide pantheon. The pesticides, most of which were released in the 1990s, were designed to be more environmentally friendly than other chemicals on the market. The compounds work their way into plant tissue rather than just coating the leaves and stems, requiring fewer sprays. And though the pesticides wreak havoc on insect nervous systems, neo-nicotinoids do not easily cross from a mammal’s bloodstream into a mammalian brain. In 2015, environmental health scientists at George Washington University and the National Institutes of Health published a review of human health risks from neonic pesticide exposure. Acute exposure—to high concentrations over a brief period—resulted in 'low rates of adverse health effects.' Reports of chronic, low-level exposure had 'suggestive but methodologically weak findings,' with a Japanese study associating neo-nicotinoids with memory loss."