Methods of Analysis—Determination of Pesticides in Filtered Water and Suspended Sediment using Liquid Chromatography- and Gas Chromatography-Tandem Mass Spectrometry

The widespread application of pesticides in agricultural and urban areas leads to their presence in surface waters.
Presence of these biologically active chemicals in environmental waters potentially has adverse effects on
nontarget organisms. To better understand the environmental fate of these contaminants, a robust method to capture
chemicals with wide-ranging physicochemical properties has been developed. The method was developed by the
U.S. Geological Survey’s Organic Chemistry Research Laboratory to monitor pesticides, pesticide degradates,
and other agrochemicals in environmental surface waters throughout the country. The analysis involves a multiresidue
method to determine 183 pesticides and pesticide degradates in filtered water samples and 178 pesticides and pesticide
degradates in paired suspended sediment samples. After the filtration of whole water, contaminants are individually
measured in the filtered water and the collected suspended sediment. Filtered water is extracted via solid-phase
extraction, whereas suspended sediment is extracted using an ultrasonication, solid-liquid extraction. Samples are analyzed by liquid chromatography-tandem mass spectrometry using an electrospray ionization source in positive and negative modes and analyzed by gas chromatography-tandem mass spectrometry using an advanced electron ionization source in positive mode. Instrument parameters were optimized for the highest sensitivity, and at least two transitions (quantifier and qualifier) were monitored for each analyte.

Recoveries in test filtered water (n=9; 183 analytes) from the American River, California, and suspended sediment
(n=9; 178 analytes) samples fortified at 15 nanograms per liter (ng/L) ranged from 70.1 to 121.0 and 71.1 to 117.0 percent
in water and suspended sediment filter samples, respectively.