Inoculation of paddy soils with Rhodopseudomonas palustris enhanced heavy metal immobilisation

Abstract

To investigate the effect of microbial inoculum on soil heavy metal immobilisation, pot experiments were conducted with paddy soils contaminated by cadmium (Cd), lead (Pb), arsenic (As), and mercury (Hg), respectively. The results showed that the inoculation of Rhodopseudomonas palustris was more effective in the immobilisation of Pb and Cd in soils than the composite of R. palustris and Bacillus subtilis. Interestingly, a lower dosage of inoculum immobilised significantly more heavy metals than the higher dosage, potentially due to the competition of bacteria with limited nutrients. The heavy metal contents in rice grains also supported this finding, as less Pb and Cd were accumulated under the lower dosage. However, there were limited effects of microbial inoculations on the immobilisation of Hg and As. In general, our study indicated the effectiveness of R. palustris in immobilising Pb and Cd in soils and highlighted the importance of determining the optimal dosage of inoculum in bioremediation.

Keywords

• co-inoculation
• toxic element
• oryza sativa l.
• biosorbent
• contamination