Comparing soil chemistries of leached and nonleached copper-amended soils

Leaching metal‐spiked samples has been proposed as a means to reduce the artifacts of the spiking procedure (e.g., salt effect, increased metal solubility) that can artificially increase metal bioaccessibility and toxicity in laboratory ecotoxicity tests. The effects on soil chemistry from leaching Cu‐spiked samples were investigated by comparing chemistries of freshly spiked samples to samples that underwent the spike/leach procedure. Chemical parameters investigated included electrical conductivity (EC), pH, ethylenediaminetetraacetic acid‐ and CaCl2‐extractable Cu, soil‐solution Cu, Cu2+ activity (estimated using Visual MINTEQ), and other solution parameters (dissolved organic carbon [DOC], Ca, Mg, Al). In leached samples, the electrical conductivity values of the spiked samples did not vary significantly from those of the control samples (p > 0.05), confirming that the leaching procedure had sufficiently minimized the salt effect. In the range of soil Cu concentrations where Cu ecotoxicity is expected, the pH in freshly spiked samples was as much as 0.52 units lower than the pH from leached samples at the same total‐soil Cu concentration. The CaCl2‐extractable fraction was up to 2.3‐fold smaller in leached samples and inversely related to the pH of the spiked soil. Despite little to no difference in soil‐solution Cu, up to 100‐fold less Cu2+ activity was observed in leached samples. Reduced Cu2+ activity was related to less Al3+ competition for DOC. Leaching resulted in solution chemistries that were more consistent with those of the control samples and reduced the artifacts of traditional soil‐spiking procedures. Environ. Toxicol. Chem. 2012; 31: 2253–2260. © 2012 SETAC