E. M. THURMAN is an organic geochemist at the U.S. Geological Survey with twenty years of research experience in the environmental chemistry of water and soil, as well as extensive experience in sorption chromatography and XAD and SPE resin technology. Dr. Thurman has published research papers on the theory of XAD resins, applications of SPE in environmental chemistry, drug applications of SPE, and isolation of natural products by SPE and ion exchange. He is the coauthor of Immunochemical Technology for Environmental Applications, the coeditor of Herbicide Metabolites in Surface Water and Groundwater, and has written over 80 journal articles on environmental analytical chemistry.

M. S. MILLS is a research envi-ronmental chemist with Zeneca Agrochemicals at the Jealott's Hill Research Station, Bracknell, U.K. Dr. Mills was formerly employed by the U.S. Geological Survey in Lawrence, Kansas, where her research interests included exploring the mechanisms and applications of solid-phase extraction in environmental chemistry, investigating the organic geochemistry of naturally occurring aquatic foams, and the degradation and transport of xenobiotics in the vadose zone. She has contributed numerous publications and oral presentations on these topics over the past five years, and was cofounder and co-lecturer of the American Chemical Society short course, "Solid-Phase Extraction in Environmental and Clinical Chemistry." Current research project foci include the degradation and transport of xenobiotics in the vadose zone using radiolabeled techniques and the degradation of xenobiotics in the saturated zone.