Toxic substances hydrology-Surface-and groundwater contamination, by Gail E. Mallard and Stephen E. Ragone 7 3. The state of soil and plant geochemical surveys, by Hansford T. Shacklette 11 4. Geochemical studies-The Missouri experience, by A.T. Miesch 21 5. Written communication on environmental geochemistry in Missouri, to Bruce Doe, by Wallace B. Howe 25 TOPICAL STUDIES Soil and stream-sediment geochemistry 6. Soil studies in the northern Great Plains, by Ronald R. Tidball 27 7. Weathering process research-Pedology and soil geochemistry in drainage basins, by Milan J. Pavich 33 8. The mode of occurrence of extractable elements in soils from the northern Great Plains, by James M. McNeal 37 9. Uranium-series disequilibrium in Quaternary soils-Significance for 222 Rn hazard assessment, by Daniel R. Muhs, Charles A. Bush, and John N. Rosholt 39 Plants 10. Biogeochemical baselines and the importance of species, plant parts, and season-The U.S. Geological Survey's studies of big sagebrush in the West, by James A. Erdman 45 11. Vegetation studies in the northern Great Plains, by Larry P. Gough 47 12. Remote sensing of vegetative responses to the environment, by Nancy Milton 51