Dissolved Inorganic Contaminants in a Floodplain Soil: Comparison of In Situ Soil Solutions and Laboratory Methods

Abstract

The applicability of laboratory tests for the prediction of soil solution composition and concentrations of inorganic contaminants is still under debate. Therefore, we carried out two batch-leaching tests differing in their liquid/solid ratios and column experiments (saturated flow, two flow velocities, four flow interruptions ranging from 4 h to 21 days) with a contaminated humic horizon (total contents: As, 196 mg kg−1; Cd, 4 mg kg−1; Cr, 202 mg kg−1; Cu, 227 mg kg−1; Ni, 64 mg kg−1; Pb, 308 mg kg−1; Zn, 1,176 mg kg−1) from a Mollic Fluvisol near the rivers Elbe and Saale (Germany) and compared the aqueous contaminant concentrations with those of soil solutions obtained in situ with ceramic suction cups on a monthly basis between 2002 and 2006. Contaminant release in the field slightly depended on the water regime, pH, and redox potential and was characterized by partially high concentrations (e.g., As, 47 µg l−1; Cd, 136 µg l−1; Ni, 328 µg l−1; Zn, 8.68 mg l−1), which exceeded the German inspection values. Metal concentrations obtained in batch-leaching tests partially fitted to those determined in the soil solution and to those from the column experiments even irrespective of the varying liquid/solid ratios. The column experiments yielded realistic concentrations of Cr, Cu, Ni, and Pb and their ranges. Furthermore, they provided an insight into release kinetics and release processes as well as into potential contaminant release due to enforced reducing conditions. As column experiments allow a larger temporal sampling resolution and enable quickly to manipulate experimental conditions, they are a useful complement of soil solution monitoring.