ISOTOPIC ANALYSES – RESOLVING INTRACTABLE ISSUES IN ENVIRONMENTAL FORENSICS

Tracking the passage and age of contamination is a complex task in most environmental systems with multiple known and unknown sources of natural and anthropogenic origins. The classical chemical, physical and geological measurements, as sophisticated as they are today, may leave many forensic questions unanswered. Only unique characteristics or signatures not subjected to random changes could lead to a reliable contamination history. Isotopes may provide just such signatures as they have usually a noticeable natural variability within different sources of organic and inorganic matter that may be tractable regardless of any system change. In other words, isotopes may be the key to many intractable environmental forensic issues. The stable isotopes are normally used to determine the source of contamination, while the radioisotopes are used for the age of contamination.

Most elements have identified isotopes and their proportions vary (within ranges) depending on the natural source of provenience. The difference in isotopic composition of the same compounds from different sources could be used to track the provenience and passage of contamination. In an environmental investigation of groundwater, the stable and radioactive isotopes of H and O as well as of other compounds present in water could be used to age-date the water, to evaluate the source and flow path, to estimate the recharge area and season, as well as the residence time, and sources of contamination.

This presentation will give an overview of isotopic analysis, principles of utilization, and forensic applicability, concluding with different case studies as examples for successful applications. The case studies will include contaminants such as chlorinated solvents and MTBE. The potential for perchlorate source tracking (including natural vs. anthropogenic) will also be discussed. And so will be their potential application in vapor intrusion issues.