Effect of iron application to prevent cadmium toxcity and heavy metal induced from sewage sludge, on plant growth and antioxidative enzyme activity in romaine lettuce (Lactuca sativa L. var. longifolia)

The aim of this study was to determine the effects of iron application, which was conducted to prevent cadmium and heavy metal toxicity resulting from sewage sludge application, on Romaine lettuce plant yield, enzyme activities in terms of SOD, CAT and APX, and MDA level as well as cadmium content in the soil and plant. The doses of 20 kg/ha Cd, 80 t/ha sewage sludge, 50 and 250 kg/ha iron were applied in the field experiment; and 100 mg/kg Cd, % 10 sewage sludge, and 100 and 500 mg/kg iron were applied in the pot experiment. Although, according to the results of the field experiment, the 20 kg/ha cadmium application on crop yield and yield criteria were not significantly effective, 100 mg/kg cadmium application significantly decreased plant development in the pot experiment. Though effect of iron application was not found to be significant in the pot experiment on crop yield decrease caused by cadmium application, Cd + 100 mg/kg iron application significantly prevented the decrease in plant height. APX and SOD activities in the field experiment and CAT activity and MDA level in the pot experiment significantly increased in response to cadmium application. On the contrary, additional sewage sludge application did not cause significant alteration on enzyme activities in both field and pot experiments. Increase in SOD and CAT activities and in MDA level under cadmium toxicity were decreased by iron and sewage sludge applications. In both experiment, additional cadmium application increased plant cadmium content and soil DTPA-Cd level. 50 kg/ha iron application in the field experiment and 500 mg/kg iron application in the pot experiment to Cd applied experimental soil caused decrease in soil DTPA-Cd levels. Nevertheless, sewage sludge + Cd application resulted in decrease of cadmium concentration in plant and soil as compared to sole application of Cd.These results pointed out that iron application could be beneficial to ameliorate the adverse effects of cadmium toxicity; municipal sewage sludge used in this experiment did not reveal a toxic effect due to low levels of heavy metal content and it might be beneficial to reduce cadmium toxicity because of its high organic matter content.