Response of a Rhizobium-based luminescence biosensor to Zn and Cu in soil solutions from sewage sludge treated soils

A luminescence based biosensor (Rhizotox-C) was used as an indicator of heavy metal pollution of soils. The response of the biosensor to increasing concentrations of total soil Zn, soil solution Zn, soil solution free Zn2+, total soil Cu and total soil solution Cu from soils of a long-term sewage sludge field experiment was investigated. The bioluminescence response of the Rhizotox-C biosensor declined as total soil Zn, soil solution Zn and free soil solution Zn2+ concentrations increased. The EC25 values for the biosensor for total soil Zn, soluble soil solution Zn and free soil solution Zn2+ were 164±43 mg kg−1 soil, 4±0.7 and 2±0.3 mg l−1, respectively. The EC50 values were 403±57 mg kg−1 soil, 16±3 and 6±1.0 mg l−1, respectively. The largest soil solution concentration of Cu was about 620 μg l−1, but this had no significant effect on luminescence. This corresponded to a total Cu concentration in bulk soil of about 349 mg kg−1.