Plants take up soil water that was ultimately sourced from precipitation and they hydrogen atoms of this water are incorporated into organic matter initially during photosynthesis, but also during other biosynthetic reactions. Strontium isotope ratios vary geographically based principally on bedrock/parent material composition and age, and Sr deposition patterns. Although there is no fractionation with uptake, other processes such as erosion and Sr cycling can also affect the Sr isotopic composition of plant-available Sr. Our results show that Sr isotope ratios also yield geographic information for marijuana and we are continuing to explore these tools for geo-sourcing marijuana. (Sr map predictions based on: Beard BL, Johnson CM J Foresnic Sci 45: ).

The carbon and nitrogen isotope compositions of various types of diets are known and can be compared to the compositions of your fingernails. Hence, the graphs of your fingernail d 15 N and d 13 C values can help to identify your diet. In general, if you eat more fruits, vegetables, grains, and meat fed with these foods (like beef), your fingernail will plot farther to the left. In contrast, eating more corn, sugar, and corn-fed meat will result in fingernails that plot farther to the right. People who eat more animal protein, and especially marine fish, will plot higher up on the graph, whereas those who eat less meat will plot lower down. Keep in mind that, on average, your isotope values are 1 unit higher in C isotopes and 3 units higher in N isotopes than your average dietvarious types of dietsfingernails