Luminescence biosensor design for toxicity assessment of heavy metals extracted from contaminated soils by biosurfactants

Abstract

Soil contamination, often by toxic compounds, is a major environmental challenge. In this research, a luminescence biosensor was developed for the detection and toxicity assessment of Zn2+, Cr6+, Ni2+ and Cu2+. Initially, the presented metals were extracted from the soil by combining two strong biosurfactants of saponin and rhamnolipid. The maximum extraction efficiency of the soil washing process was about 85 %, 68 %, 59 % and 55 % for Ni, Cr, Cu and Zn respectively at an optimum hydrophilic-lipophilic balance (HLB) value of 10.5. Immobilized Escherichia coli (E. coli) Luc was used as luminescent bacteria for the detection of heavy metals. The optimum aeration rate of the designed biosensor was 30 mL min(-1). The toxic effect of heavy metals on E. coli with Luc plasmid gene bacterium was determined for each heavy metal using the effective concentration (EC50). When the bioluminescence intensity (BL) decreased to half, the EC50 was determined to be (0.042, 0.125, 12 and 56) mg L-1 for Cu2+, Zn2+, Cr6+ and Ni2+ respectively. Therefore, the toxicity sensitivity of heavy metals is in the order of Cu2+ > Zn2+ > Cr6+ > Ni2+. From the obtained results it seems that the washing process using biosurfactants and designed biosensor is very useful for monitoring toxic heavy metals from cost and environmental point of view.