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

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.