Development of an acid soil conditioning agent from lignin by ozone treatment III: improvement of ability of lignin to form an aluminum complex and to reduce aluminum toxicity after ozone treatment

Lignin prepared by a modified Klason method (KSL) was modified with ozone followed by alkaline treatments. The original and modified KSLs were subjected to a plant growth test with radish (Raphanus sativus L. var. radicula Pers.) in the presence of AlCl₃ (37.5 μM) to assess their ability to reduce aluminum toxicity. The formation of an aluminum complex with these KSLs was also examined by potentiometry. Neither the original nor alkaline-treated KSLs had an effect on aluminum toxicity or the formation of a complex, except for the alkaline-treated KSL at a maximal dose of 250 mg/l, which reduced aluminum toxicity. However, all the KSLs modified with ozone and alkali were effective at forming a complex and reducing aluminum toxicity. The dose of saponified ozone-treated KSLs required to reduce aluminum toxicity became lower and their water solubility increased as the ozone treatment was prolonged. These findings clearly show that water solubility and the ability to form a complex with and reduce the toxicity of aluminum were improved by ozone treatment of KSL.