Spatial and vertical determination of chosen potentially toxic metals and soil properties on a former sewage farm near Berlin

In the past 150 years, sewage disposal onto agricultural land was a common practice around the world that resulted in accumulation of organic matter, salts, nutrients and heavy metals in the soils and the subsequent percolation into the groundwater. We present a study conducted on a former sewage farm in Germany, state of Brandenburg, were wastewater coming from Berlin was used for more than one century to irrigate the surrounding fields. In the area of a sewage sedimentation basin, 110 soil samples at the depth of 15-20 cm (waste layer) and 4 boreholes (10 samples up to 100 cm depth) were collected in order to determine pH, LOI and concentration of chosen metals. For the elemental analysis, two methods: X-ray fluorescence (XRF) and Atomic Emission Spectroscopy (MP-AES) were used. The analysis confirmed the presence of relatively homogenous sewage waste layer at the 20 cm depth, characterized by slightly acidic to neutral pH (6.3-7.5), high OM accumulation (up to 49%) and elevated concentrations of potentially toxic chosen metals (Cu, Ni, Pb, Cr and Zn). The correlation analysis performed by R software revealed strong between metal distribution and OM content. The XRF elemental analysis performed prior and after LOI, revealed metal concentration increase in mineral samples (up to 50% of the original value). An empirical correlation using a linear regression was found between OM content loss and metal concentration increase. Comparison of the AES and XRF elemental analysis of the mineral samples revealed significantly higher results for the X-ray fluorescence method, except for Cr. A correction factor, based on OM reduction, applied to the values, resulted in better correlation of XRF and AES results, questioning feasibility of this method for samples highly affected by sewage influence.