The isotope composition of dissolved strontium as a tracer of pollution in the Llobregat River, northeast Spain

The Llobregat River is the main source of water in the study area. Determining the sources of pollutants is essential to the environmental agencies for pollution control, prediction and remediation. Previous work by Soler et al. (1998a,b) demonstrated that the strontium and sulphur isotope composition of the river water could not be related exclusively to the host rocks. This study tests the validity of the ⁸⁷Sr/⁸⁶Sr ratio as a tracer for pollution. Samples from industrial, urban and agricultural wastes were analysed together with river water collected close to the potential pollution sources. Rainfall distribution is markedly seasonal, therefore ⁸⁷Sr/⁸⁶Sr ratios for additional river samples were determined in order to assess any seasonal variation. This study demonstrates (a) that anthropogenic sources dominate the Sr budget in the Llobregat basin; (b) that ⁸⁷Sr/⁸⁶Sr ratios can be used as tracers for specific pollutants; and (c) that Sr isotope ratios are similar for summer and winter samples.