Use of Compound-Specific Nitrogen (d15N), Oxygen (d18O), and Bulk Boron (d11B) Isotope Ratios to Identify Sources of Nitrate-Contaminated Waters: A Guideline to Identify Polluters

The use of various isotopes (d(15)N, d(18)O & d(11)B) to identify the sources of nitrate (NO3-) present in natural waters is described. Then a new guideline of how to apply the multi-isotope approach is presented. This guideline is written for policy makers and scientists who are involved in the different steps and processes related to nitrate contaminated waters including monitoring and data interpretation. NO3- is a common pollutant in water (both surface and groundwater). In several water bodies over Europe, point measurements identify that the level of this pollutant is higher than the reference value of 50 mgL(-1), defined by the European Union (EU) Water Framework Directive 2000/60/EC (European Parliament, 2000). This directive also states that all waters have to reach a "good status" (i.e., good quality) by 2015. This statement implies that EU member states have to take actions to achieve this goal. One of the major obstacles with NO3- contamination in water is the identification of the corresponding source(s) of pollution, a prerequisite for properly designing appropriate actions and remediation. Recent studies have proven the added value of analyzing compound specific isotopic signature (CSIA) of nitrate (both nitrogen (d(15)N), oxygen (d(18)O) and bulk boron (d(11)B) isotopic composition) to define the origin/source of NO3- in waters. This definition is possible because different sources of nitrate have distinct isotopic signatures. The recent EU-LIFE ISONITRATE project demonstrated the benefit of the multi-isotope approach, while the presented guideline to implement this method is one of the outcomes of this project. More details on the scientific results of ISONITRATE are available at http://isonitrate.brgm.fr/.