Fertilizer characterization: Isotopic data (N, S, O, C, and Sr)

Abstract

A detailed isotopic characterization (δ15N Ntotal, δ15NNO3, δ 18ONO3, δ34SSO4, δ18OSO4, δ13CCtotal, and 87Sr/86Sr) of 27 commercial fertilizers used in Spain is presented in this paper. Results together with a compilation of fertilizer isotopic published data are used for two purposes: (i) to identify the origin of the primary constituents and raw materials used in fertilizer manufacture and relate these data with their heavy metals and rare earth elements (REE) contents; (ii) to compare the fertilizer isotopic signatures with natural values and other anthropogenic pollutants and evaluate the usefulness of multi-isotopic analyses to trace fertilizer contaminations in future study cases. Isotope data permit us to know, in most cases, the origin of the primary constituents of fertilizers, and the 87Sr/86Sr ratio distinguishes the origin of the phosphate content-phosphorites or carbonatites-which in turn implies a qualitatively defined and potentially contaminant presence of REE and heavy metals in fertilizers. δ15N, δ34S, and 87Sr/ 86Sr have already been used to trace fertilizer contaminations. Their utility can be improved by the coupled use of δ15N NO3-δ18ONO3 and δ 34SSO4-δ18OSO4 to evaluate the fractionation processes that can affect contaminants. Moreover, multi-isotopic analyses, using heavy isotopes, allow us to see beyond the fractionation effects to the fertilizer stable isotope signatures and a better distinction from other anthropogenic contaminants.