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 (EC(50)) and non-observed effect concentration (NOEC) were used to investigate the toxic thresholds and potencies of the two elements. The EC(50) for As was 0.97 microM in hydroponics and 196 mgkg(-1) in soil, and 4.32 microM and 449 mgkg(-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 (EC(50 mix)=0.36 TU(mix) and AI: 1.76) and antagonism in soil experiments (EC(50 mix)=1.49 TU(mix) 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.