Monitoring of total and extractable barium concentrations in floodplain soils

Purpose Although barium (Ba) is a non-regulated element in soil in most European countries, some countries, such as Canada, are adopting quality guidelines for Ba in soil because it can be toxic in high concentrations. The aim of the present study was to assess Ba concentrations and availability in foodplain soils. Methods Besides the determination of total concentrations, a rapid screening of Ba availability with single extractions recommended by the Standards, Measurements and testing (SMT) program of the European Commission (with CaCl2 (0.01 mol l −1), acetic acid (0.43 mol l −1) and ammonium-EDTA (0.05 mol l −1) solutions) were performed. Additionally, an extraction with a 0.1 mol l −1 CaCl2 solution was executed, to determine 'soluble Ba' in soil as stipulated by the guidelines established in Canada by Alberta Environment. A comparison was also made with Ba concentrations reported in the literature, and with Ba concentrations in foodplain soils included in the FOREGS (Forum of European Geological Surveys) database. Results Single extractions indicate that in all the soil samples, only a very small proportion of Ba (0.7 to 8.7 mg kg−1, corresponding to 1.5 to 6.6% of the total Ba content) is readily available for uptake by living organisms or for leaching. Elevated total Ba concentrations in soil are not indicative of a higher risk for Ba mobilisation, even when other parameters such as matrix composition and pH are taken into account. Conclusions The use of single extractions should be considered when environmental quality guidelines are set up for Ba, as they can be useful for a fast screening of potential Ba contamination with an acceptable risk.