The influence of heavy metals on a mixed bacterial population of sewage origin in the chemostat

A reproducible mixed continuous bacterial population has been cultured in the chemostat at a low dilution rate. Four species originally isolated from activated sludge were used to provide an inoculum. The influence of cadmium, chromium, copper and lead as shock doses has been examined at concentrations of 50 mg l⁻¹ and the response of the population was found to vary for each metal. The most toxic metal was copper followed by cadmium, lead and chromium. Continuous doses of chromium and lead have been studied, the latter over a range of concentrations. It appears that concentrations of lead as low as 5 mg l⁻¹ cause modifications in the individual population sizes. Some of the species studied were found to be more resistant to heavy metal toxicity than others.