The nitrate content of drinking water is rising at an alarming rate in several regions of NATO countries and elsewhere in the world. The increase is due to lack of proper sewage treatment, and primarily to excess fertilizer application. Also, eutrophication in several coastal areas is triggered by high nitrate concentrations. The main purpose of this book is to integrate scientific knowledge related to exposure assessment, health consequences and control of nitrate contamination in water. The motivation is related to the magnitude, the possible adverse health effects, and the high cost of control ling nitrate contamination. Future research tasks are defined by an interaction among hydro logists, toxicologists and environmental engineers in an integrated framework for nitrate risk management. The target readership of this book is a mix of university colleagues, practitioners from both the private and public sectors and advanced graduate students working with the hydrological, health science or environmental engineering aspects of nitrate contamination. The main conclusions include: 1. For risk assessment purposes, knowledge and sufficiently accurate models are available to predict nitrate load and its fate in water under changes in land use. 2. Once agricultural exposure controls are implemented, the response times in ground water may be so long as to make controls unrealistic. 3. It is still unknown whether agricultural best management practice is a compromise between nitrate risk reduction and agricultural revenue. 4. The current drinking water guidelines of 10 mg/L NOrN need not be changed.

Groundwater quality monitoring and testing is of paramount importance both in the developed and developing world. This book presents a series of papers illustrating the varied nature of current research into groundwater quality. Urban and rural supplies are covered through a case history approach, and the importance of remedial action to prevent deterioration is emphasized.

Environmental Tracers in Subsurface Hydrology synthesizes the research of specialists into a comprehensive review of the application of environmental tracers to the study of soil water and groundwater flow. The book includes chapters which cover ionic tracers, noble gases, chlorofluorocarbons, tritium, chlorine-36, oxygen-18, deuterium, and isotopes of carbon, strontium, sulphur and nitrogen. Applications of the tracers include the estimation of vertical and horizontal groundwater velocities, groundwater recharge rates, inter-aquifer leakage and mixing processes, chemical processes and palaeohydrology. Practicing hydrologists, soil physicists and hydrology professors and students will find the book to be a valuable support in their work.

This report documents work at the U.S. Geological Sur- vey (USGS) National Water Quality Laboratory (NWQL) to validate enzymatic reduction, colorimetric determinative meth- ods for nitrate + nitrite in filtered water by automated discrete analysis. In these standard- and low-level methods (USGS I-2547-11 and I-2548-11), nitrate is reduced to nitrite with nontoxic, soluble nitrate reductase rather than toxic, granular, copperized cadmium used in the longstanding USGS auto- mated continuous-flow analyzer methods I-2545-90 (NWQL laboratory code 1975) and I-2546-91 (NWQL laboratory code 1979). Colorimetric reagents used to determine resulting nitrite in aforementioned enzymatic- and cadmium-reduction meth- ods are identical. The enzyme used in these discrete analyzer methods, designated AtNaR2 by its manufacturer, is produced by recombinant expression of the nitrate reductase gene from wall cress (Arabidopsis thaliana) in the yeast Pichia pastoris. Unlike other commercially available nitrate reductases we evaluated, AtNaR2 maintains high activity at 37°C and is not inhibited by high-phenolic-content humic acids at reaction temperatures in the range of 20°C to 37°C. These previously unrecognized AtNaR2 characteristics are essential for success- ful performance of discrete analyzer nitrate + nitrite assays (henceforth, DA-AtNaR2) described here.

V.3 ... consists of individual chapters that describe 1) the conceptual background for radionuclides, including tritium, radon, strontium, technetium, uranium, iodine, radium, thorium, cesium, plutonium-americium and 2) data requirements to be met during site characterization.