Wheat phytotoxicity from arsenic and cadmium separately and together in solution culture and in a calcareous soil

The toxicity of two toxic elements, arsenic (As) and cadmium (Cd) (individually or in combination) on root elongation of wheat seedlings (Triticum aestivum, L.) were investigated both in hydroponics and in soils freshly spiked with the toxic elements. Median effective concentration (EC50) and non-observed effect concentration (NOEC) were used to investigate the toxic thresholds and potencies of the two elements. The EC50 for As was 0.97 μM in hydroponics and 196 mg kg−1 in soil, and 4.32 μM and 449 mg kg−1 for Cd, respectively. Toxic unit (TU) and additive index (AI) concepts were introduced to determine the combined outcomes, and different behaviors were obtained: synergism in solution culture (EC50mix = 0.36TUmix and AI: 1.76) and antagonism in soil experiments (EC50mix = 1.49TUmix and AI: −0.33). Furthermore, the data of soil bioavailable As and Cd cannot explain the discrepancy between the results derived from soil and hydroponics experiments.