The effects of biochars from rice residue on the formation of iron plaque and the accumulation of Cd, Zn, Pb, As in rice (Oryza sativa L.) seedlings

Abstract

h i g h l i g h t s" Rice biochar reduced Cd, Zn and Pb transport to rice shoots, though increased As. " Biochars derived from rice straw were more influential than from bran and husk. " Mechanisms for these effects were identified. " Biochar increased iron plaque formation, and its capacity to retain Cd and Pb. " Biochar also influenced the soil pore water solubility of Cd, Zn, Pb and As. A historically multi-metal contaminated soil was amended with biochars produced from different parts of rice plants (straw, husk and bran) to investigate how biochar can influence the mobility of Cd, Zn, Pb and As in rice seedlings (Oryza sativa L.). Rice shoot concentrations of Cd, Zn and Pb decreased by up to 98%, 83% and 72%, respectively, due to biochar amendment, though that of As increased by up to 327%. Biochar amendments significantly decreased pore water concentrations (C pw ) of Cd and Zn and increased that of As. For Pb it depended on the amendment. Porewater pH, dissolved organic carbon, dissolved phosphorus, silicon in pore water and iron plaque formation on root surfaces all increased significantly after the amendments. The proportions of Cd and Pb in iron plaque increased by factors 1.8-5.7 and 1.4-2.8, respectively; no increase was observed for As and Zn. Straw-char application significantly and noticeably decreased the plant transfer coefficients of Cd and Pb. This study, the first to investigate changes in metal mobility and iron plaque formation in rice plants due to amending a historically contaminated soil with biochar, indicates that biochar has a potential to decrease Cd, Zn and Pb accumulations in rice shoot but increase that of As. The main cause is likely biochar decreasing the C pw of Cd and Zn, increasing the C pw of As, and increasing the iron plaque blocking capacity for Cd and Pb.

Effects of Hybrid Giant Napier Biochar on Cadmium Migration in a Cabbage-Soil System Contaminated with Cadmium and Butachlor

“…This demonstrates that high-level biochar can inhibit the transportation of Cd from the underground part to the aboveground part, and accordingly reduce the accumulation of Cd in the aboveground part of cabbage. Similar results were also addressed by Zhang et al [20] and Zheng et al [23]. However, in some other studies, Cd bioaccumulation increased after applying biochar [11,19].…”

Mitigating heavy metal accumulation into rice (Oryza sativa L.) using biochar amendment — a field experiment in Hunan, China

“…Finally, there are also other studies showing that metal mobility is reduced in the presence of biochar due to adsorption on the biochar surface (especially on carboxylic and phenolic groups; Uchimiya et al 2011a, b). On the other hand, a probable increase in the silicon (Si) concentration of soil solution after biochar addition may also contribute to metal immobilization via the formation of silicate precipitates (Houben et al 2014;Zheng et al 2012;Gu et al 2011). A significant increase in Si concentration of soil pore water after biochar (made from rice straw) addition was obtained in our recent study ).…”

Effect of Biochars from Rice Husk, Bran, and Straw on Heavy Metal Uptake by Pot-Grown Wheat Seedling in a Historically Contaminated Soil

“…Decreases in Cd, Zn, and Pb concentrations and an increase in As concentration in rice plants grown in a multi-element contaminated soil under flooded conditions after biochar addition were also observed in previous studies by the authors . Studies showed that heavy metals were immobilized and As was mobilized in soils after biochar addition (Beesley et al 2010;Zheng et al 2012). Concentrations of Cd and Zn in soil pore water decreased significantly, whereas that of As increased markedly in a multi-element polluted soil amended with biochar under various soil moisture conditions (Beesley et al 2010).…”

“…"Biochars for metals in soil," BioResources 8(4), 5965-5982. 5966 2010; Zheng et al 2012). Concentrations of Cd and Zn in soil pore water decreased significantly, whereas that of As increased markedly in a multi-element polluted soil amended with biochar under various soil moisture conditions (Beesley et al 2010).…”