Effects of Cd-resistant bacteria and calcium carbonate + sepiolite on Cd availability in contaminated paddy soil and on Cd accumulation in brown rice grains

A pot experiment was conducted to evaluate the effects of combined application of cadmium (Cd)-resistant bacteria (J) and calcium carbonate + sepiolite (G) on both Cd bioavailability in contaminated paddy soil and on Cd accumulation in rice plants. Adding the mixture (J + G) to the soils significantly increased soil pH, decreased extractable Cd contents, and increased Fe/Mn-oxide Cd and organic-bound Cd contents. The applying of J + G, J and G decreased Cd contents in various rice tissues (roots, stems and leaves, husks, and brown rice grains) to different degrees. Compared with those of the CK, Cd contents decreased by 17.8%–53.3% in the roots, 12.3%–27.4% in the stems and leaves, 25.4%–44.6% in the husks, and 28.8%–55.7% in the brown rice grains for the application of J + G; Cd contents decreased by 8.2%–28.5% in the roots, 11.5%–32.0% in the husks, and 27.8%–45.9% in the brown rice grains for the application of J; Cd contents decreased by 12.9%–26.5% in the roots, in the stems and leaves decreased by 4.6%–34.1% in the stems and leaves, 60.2%–79.7% in the husks, and 35.7%–47.6% in the brown rice grains for the application of G. The alone application of bacteria (J) could reduce the bioavailability of Cd in soil and the contents of Cd in brown rice grains to some extent. Moreover, when the bacteria were applied in combination with mineral (J + G), it was a more effective method than the alone application of J or G to reduce the soil Cd bioavailability. Under all the tested conditions, applications of J4+G4 (320 mL kg−1 of J + 8 g kg−1 of G) resulted in the greatest reduction in Cd contents in brown rice grains. Overall, the results indicated that the combination of Cd-resistant bacteria and mineral material could effectively reduce Cd bioavailability in paddy soils and inhibit Cd accumulation in brown rice grains.