Weakened fungus-assisted remediation of Cd(II) after addition of fibrous palygorskite.

Abstract

Aims: Rhodotorula mucilaginosa (Rho) has a strong ability to absorb heavy metals. In this study, the influences of fibrous palygorskite (Pal) on fungus-assisted remediation of Cd2+ was investigated.

Methods and results: Three sets of treatments were performed, i.e. Cd@Rho, Cd@Pal, and Cd@Rho + Pal. R. mucilaginosa removed Cd2+ via its extracellular polymeric substances and intracellular accumulation. The high sorption helped the fungus to resist the Cd2+ stress up to 200 mg l-1. In addition, the removal rate reached 17% at 50 mg l-1 level. In contrast, the sorption of Cd2+ by palygorskite was significantly lower (0.3%) than that of R. mucilaginosa. In the treatments of Cd@Rho + Pal, the removal rate declined from 24% to 5% when Cd2+ level increased from 50 to 100 mg l-1. This was attributed to the fact that palygorskite particles adhered to the cell surface, occupying adsorption sites for Cd2+. Although the Cd density on each cell declined, the cells showed limited relief due to the relatively high toxicity of Cd2+. Meanwhile, the P removal content also declined after addition of palygorskite. Moreover, the content of tryptophan and carotenoids, which can substantially resist heavy metal stress, were not significantly increased.

Conclusions: Therefore, the addition of fibrous palygorskite had an overall negative influence on fungus-assisted Cd remediation.