A three-year in-situ study on the persistence of a combined amendment (limestone+sepiolite) for remedying paddy soil polluted with heavy metals.

In order to study the persistence of a combined amendment (LS, limestone+sepiolite) for remedying paddy soil polluted with the heavy metals Pb and Cd, a three-year in-situ experiment was conducted in a paddy soil near a mining area in southern Hunan, China. LS was applied at rates of 0, 2, 4, and 8g/kg (w/w); rice was subsequently planted for the three consecutive years of 2012 (first season), 2013 (second season), and 2014 (third season). Experimental results indicated that LS significantly increased soil pH values for all three seasons, and the enhancement ranked as follows: first season>second season>third season. Under the experimental conditions, the effect of LS on decreasing exchangeable concentrations of soil Pb and Cd was as follows: first season (97.6-99.8% for Pb and 88.3-98.9% for Cd)>second season (80.7-97.7% for Pb and 28.3-88.0% for Cd)>third season (32.6-97.7% for Pb and 8.3-71.4% for Cd); the effect of LS on reducing Pb concentrations in brown rice was: first season (73.5-81.2%)>third season (29.6-68.1%)>second season (0-9.7%), and that for reducing Cd concentrations in brown rice was third season (72.7-81.0%)>first season (56.1-66.8%)>second season (20.9-32.3%). For all three seasons, the effect of LS on reducing Cd content in brown rice was better than that for Pb. The highest translocation factors for Pb and Cd were from rice straw to husk, implying that the husk of rice plants was the main organ in which heavy metals accumulated. The effect of LS for decreasing soil exchangeable Cd content was relatively persistent, but that for Pb gradually decreased with time, implying that LS was more suitable for the long-term remediation of Cd-polluted soil than Pb-polluted soil.

Effect of calcium carbonate on cadmium and nutrients uptake in tobacco (Nicotiana tabacum L.) planted on contaminated soil.

In the present study, calcium carbonate (CaCO3) was applied to Cd-contaminated soil at rates of 0, 0.5 and 1.0 g kg(-1). The effect of CaCO3 on soil pH, organic matter, available Cd, exchangeable Cd and level of major nutrients in a tobacco field and on accumulation of various elements in tobacco plants was determined. The results showed that CaCO3 application significantly increased the pH level, available P and exchangeable Ca but decreased organic matter, available Cd, exchangeable Cd, available heavy metals (Fe, Mn, Zn and Cu) and available K in soil. Additionally, CaCO3 application substantially reduced Cd accumulation in tobacco roots, stems, upper leaves, middle leaves and lower leaves, with maximum decrease of 22.3%, 32.1%, 24.5%, 22.0% and 18.2%, respectively. There were large increase in total Ca and slight increases in total N and K but decrease to varying degrees in total Fe, Cu and Zn due to CaCO3 application. CaCO3 had little effect on total P and Mn levels in tobacco leaves.

[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.