[Comparison of the Persistence of a Combined Amendment Stabilizing Pb, Cd, Cu and Zn in Polluted Paddy Soil]

A three-year in-situ experiment was conducted in a paddy soil near a mining area in southern Hunan in order to study the persistence of combined amendment of limestone+sepiolite (marked as LS) stabilizing Pb, Cd, Cu and Zn in polluted paddy soil. LS with ratios of 0, 2, 4, and 8 g·kg^-1 was applied once to the paddy soil, and rice was subsequently planted for three consecutive years of 2012 (first season), 2013 (second season), and 2014 (third season). The experimental results indicated that:①LS significantly increased soil pH values for all three seasons, and the enhancement ranked as follows:first season > second season > third season. ② LS obviously decreased the exchangeable contents of soil Pb, Cd and Zn for all three seasons, and the decreasing magnitude of exchangeable contents of soil heavy metals was 32.6%-97.7% for Pb, 8.3%-71.4% for Cd, and 10.9%-83.5% for Zn, respectively, in the third season; however, there was no significant decrease for Cu. The effects of LS decreasing exchangeable contents of soil heavy metals in three seasons followed the order of Pb > Zn > Cd > Cu. ③ LS decreased contents of Pb and Cd in brown rice in the third season by 26.7%-66.7% and 59.1%-80.3%, respectively, and the reduction trend increased with increasing LS application. Cu and Zn contents in brown rice did not decrease effectively. The effect of LS reducing contents of Pb, Cd, Cu and Zn in brown rice followed the order of Pb > Cd > Cu > Zn for the first season and the second season, but Cd > Pb > Zn > Cu for the third season. For all three seasons, the total effect of LS reducing heavy metal contents in brown rice followed the order of Pb > Cd > Cu > Zn. ④ The effect of LS stabilizing soil Pb and Cd emerged gradually with time. Therefore, LS was suitable for remedying soil polluted with Pb and Cd for a relatively long time because of its persistence.