Indexed on: 23 Apr '13Published on: 23 Apr '13Published in: Environmental Toxicology and Chemistry
Soil leaching has been proposed as a way to reduce soil-spiking artifacts (i.e., increased acidity, metal solubility) that occur in soils amended with trace metal salts. Leaching metal-spiked samples prior to ecotoxicity testing is therefore expected to reduce toxicity; however, leaching not only removes excess amounts of the trace metal being tested, but also reduces the concentrations of cations that could decrease the toxic effects of the metal of interest. To clarify these conflicting processes, the effects of leaching on toxicity and bioaccumulation of Cu, Ca, and Al were investigated using 14-d plant assays conducted on leached and nonleached, Cu-spiked soils. The median effective concentration (EC50) to root elongation ranged from 78 µg/g to 589 µg/g. Leaching was found to reduce toxicity by 1.2-fold to 2.1-fold. The Cu(2+) activity predicted toxicity better than root or shoot Cu concentrations, which were generally not affected by leaching. Plant uptake of Ca increased with increasing Cu dose in nonleached samples, which likely contributed to the hormesis-like response observed in these samples, whereas Ca uptake in the leached samples was more consistent with that of the control except at the largest Cu doses for which Ca uptake decreased. Surprisingly, Al uptake in the most acidic soil was greater in leached than nonleached samples, which may have contributed to the greater toxicity exhibited in this soil than was predicted by Cu(2+) activity. These findings have implications for predicting trace metal toxicity in nutrient-stressed, acidic soils. Environ Toxicol Chem 2013;32:1800-1809. © 2013 SETAC.