Abstract
Effect of humic acid on heavy-metal toxicity to Escherichia coli was investigated. The toxicity was evaluated as growth inhibition, namely an increase in generation or lag phase time, or a decrease in O.D. at stationary phase. With five metals (Co2+, Ni2+, Cd2+, Cu2+, Cr6+), an approximately linear relationship was observed between these parameters and metal concentration. The slope of such straight line obtained with each metal decreased clearly except with Cu2+ when E. coli was incubated in the culture medium containing humic acid together with a metal. That is to say, the toxicity of heavy metals was reduced with the humic acid. Gel filtration chromatography of a mixture of each metal and the humic acid showed that these metals had affinity for the humic acid under the growth conditions of E. coli.
