汚染土壌に生育したTriticum aestivumのカドミウムと鉛の固定化に及ぼす3種類の土壌改良の効果の違い

Differential effects of three amendments on the immobilisation of cadmium and lead for Triticum aestivum grown on polluted soil.

• Shengze Zhang
• Lingtong Quan
• Yanping Zhu
• Jin Yan
• Xiaoman He
• Jia Zhang
• Xiaoming Xu
• Zhubing Hu
• Feng Hu
• Yahua Chen
• Zhenguo Shen
• Yan Xia

抄録

汚染土壌中のカドミウム（Cd）と鉛（Pb）の固定化については、従来の化学的土壌改良剤や新規材料のバイオチャーが広く報告されている。しかし、それらの比較効果に関する情報は乏しい。本研究では，もみ殻バイオチャー（RHB）を，ハイドロキシアパタイト（HAP）や水和石灰（HDL）を含む2つの化学土壌改良材と比較し，重金属汚染土壌で生育したTriticum aestivum L.による植物の生育促進やCdの取り込み・移動を抑制する効果について検討した。RHBは対照および2種類の化学土壌改良材と比較して、小麦の生育を急速に改善した。HAP、HDLおよびRHB処理された植物は、根にCdおよびPbを保持し、それらの移動を制限した。RHB処理は、小麦の生育、収量促進、および小麦穀物中のカドミウムおよび鉛の低減に最も優れた効果を有していた。さらに、RHBとHAPで処理した土壌では、DTPA抽出カドミウム濃度が低下し、HAP処理した土壌で最大の低下が観察された。しかし，DTPA 抽出 Pb 濃度は，2 種類の化学的土壌改良剤を 40 日間施用しても有意な低下は認められず，RHB を 80 日間施用した土壌で最大の低下が認められた。いずれの処理においても，ポストハーベスト土壌中のカドミウムは，交換性，炭酸塩結合性，鉄-Mn酸化物の3種類のカドミウムが主に存在していたが，主な化学形態は鉄-Mn酸化物のカドミウムであった．また，3種類の土壌改良材を施用することで，交換性，有機物結合性カドミウムおよび有機物結合性鉛が減少した。HAPとRHBは土壌中のカドミウムの固定化と重金属の移動を減少させたが、HAPは汚染土壌中の小麦の生育を著しく阻害した。したがって、RHBは重金属汚染土壌で栽培された小麦の穀物中のカドミウムと鉛の生物蓄積を減少させる可能性を示した。

Conventional chemical soil amendments and novel material biochars have been widely reported for the immobilisation of cadmium (Cd) and lead (Pb) in polluted soil. However, information regarding their comparative effectiveness is poor. In the present study, rice husk biochar (RHB) was compared with two chemical soil amendments including hydroxyapatite (HAP) and hydrated lime (HDL) for their effectiveness to enhance plant growth and the reduction of Cd uptake and translocation by Triticum aestivum L. grown in heavy-metal-polluted soil. Compared with control and two chemical soil amendments, RHB rapidly improved wheat growth. The HAP, HDL, and RHB treated plants retained Cd and Pb in roots and restricted their translocation. The RHB treatment had the best effect on growth, yield promotion and the reduction of Cd and Pb in wheat grain. Furthermore, the soils treated with RHB and HAP showed lower DTPA-extracted Cd concentrations, and the maximum reduction was observed in HAP-amended soil. However, the DTPA-extracted Pb concentration was not significantly decreased after the application of two chemical soil amendments for 40 days; the maximum reduction was found in soil treated with RHB for 80 days. In all treatments, Cd in post-harvest soil was mainly present in exchangeable, carbonate bound, and Fe-Mn oxide Cd, while the dominant chemical form of Pb was Fe-Mn oxide Pb. Three soil amendments application decreased exchangeable and organic bound- Cd and Pb levels. HAP and RHB displayed significantly immobilisation for soil Cd and reduced translocation of heavy metal as well as its availability in soil, but the HAP had significant inhibition on growth of wheat in contaminated soil. Therefore, RHB shows a promising potential for the reduction of Cd and Pb bioaccumulation in grains from wheat grown on heavy-metal-polluted soils.