Effect of DTPA on Cd solubility in soil--accumulation and subsequent toxicity to lettuce

In a controlled environment experiment, using Cd spiked soil, lettuce plants were grown under a range of DTPA levels and were subsequently harvested to determine levels of phytoaccumulation. Cadmium phytoaccumulation significantly increased with increasing soil Cd level (P<0.05) but unexpectedly decreased with increasing DTPA levels, despite the fact that solubility of Cd was increased in the soil. Cadmium translocation (from root to shoot) increased after DTPA application. Lettuce growth was inhibited by both Cd and DTPA (at and above 10 and 500 mg kg(-1) respectively), as a result of higher Cd mobility and subsequent toxicity which was caused by DTPA higher dosages. Metal solubility in the soil (ranged between 2.8 and 26.5 mg kg(-1)) was found to be significantly higher (P<0.01) as compared to control with increasing DTPA levels even after 3 months of DTPA application. Cadmium tissue concentration in all DTPA treatments was less than in the corresponding control treatment, indicating a negative effect of DTPA application on Cd uptake. In conclusion, lettuce was an unsuitable plant species for Cd accumulation, at least when associated with a DTPA chelator.