Fly-ash augmented soil enhances heavy metal accumulation and phytotoxicity in rice (Oryza sativa L.); A concern for fly-ash amendments in agriculture sector

Fly-ash (FA) utilization in the agriculture sector is very common practice due to presence of beneficial elements required for plant growth. However, presence of excessive amount of toxic metals in FA may be serious concern for agriculture. In the present study, the effects of FA on soil health, plant growth, toxic metal accumulation and antioxidant responses were investigated in rice (Oryza sativa L.), grown on soil amended with 50 % FA in natural condition. FA application resulted in reduction in soil enzymatic activities viz., dehydrogenase, acid phosphatase, beta-glucosidase and urease than garden soil (GS). FA amendments significantly decreased the root, shoot and panicle length and augmented sterility in rice. Interestingly, ICPMS analysis for metal accumulation revealed that the total accumulation of toxic metals, particularly Cd, Cr, Pb and As were 14-15 fold higher in roots and shoots and 4-20 fold higher in grains for the plants grown on FA amended soil than GS. The levels of nutrient elements viz., Mn, Co, Cu and Se were lesser in grains of FA treated soil than GS. Lipid peroxidation was increased in root and shoot of FA treated plants indicating oxidative stress. Activities of various antioxidant enzymes viz., SOD, APX, GPX, GR and their isozymes were correlated to each other and also increased against heavy metal induced toxicity. Human associated risk analysis revealed that the calculated maximum tolerable daily intake values for toxic metals (A mu g d(-1)) viz., Cr, As, Cd, Hg and Pb was beyond the safe limit in the rice grown in FA implicated soil. In conclusion, 50 % FA implication deteriorates the soil quality, rice production and elevates the toxic metals in grains, which may be a concern for safer rice consumption.