Chlorothalonil and Dacthal in Great Lakes air and precipitation samples

Two chlorinated pesticides, chlorothalonil and Dacthal, have been found at relatively high concentrations in air and precipitation samples taken from around the Great Lakes. Chlorothalonil is a fungicide used mainly on peanut s and potatoes; Dacthal is a pre-emergence herbicide used primarily on onio ns and broccoli. These compounds were identified using electron capture, ne gative ionization gas chromatographic mass spectrometry, and they were quan titated by electron capture gas chromatography. The concentrations of these compounds in Great Lakes air and precipitation were as high as or higher t han those of other organochlorine pesticides now being measured by the Inte grated Atmospheric Deposition Network. Long-term measurements of the atmosp heric and precipitation concentrations of these two compounds is recommende d.