Herbicide safeners and associated stream flow for water samples collected across Iowa and Illinois (2016-2017).

Four dichloroacetamide herbicide safeners (AD-67, benoxacor, dichlormid, and furilazole) and two co-applied herbicides (acetochlor and metolachlor) were measured in water samples from 7 streams across Iowa and Illinois. Iowa water samples were collected from March 2016 to June 2017, and Illinois water samples were collected from September 2016 to June 2017. The compounds studied are applied to corn, and Iowa and Illinois are the two largest corn producing states in the U.S. The seven stream sites are all adjacent to agricultural fields in corn production. Water samples (1-L) were collected in amber glass bottles using a grab or depth weighted approach. With the exception of one site, Iowa River at Wapello (USGS Site ID 05465500), all water samples were collected using a hydrologic based sampling approach. This means that samples were collected near peak flow during storm events and periodically during base flow conditions. Water samples were filtered (0.7 micrometers), extracted via solid phase extraction (Oasis MAX cartridge), and analyzed for each herbicide and safener by gas chromatography with mass-spectrometry.