Toxicity of heavy metals for microorganisms isolated from slow sand filter schmutzdecke

Abstract

This paper describes the susceptibility of three species of environmental bacteria isolated from the schmutzdecke of biologically active slow sand filters to cadmium, chromium and lead. The microorganisms, all identified as members of the genus Pseudomonas, were grown in tryptic soy broth with various concentrations of the selected heavy metals. The mean generation times (MGT) of the bacteria were compared to evaluate the toxic effects of the heavy metals. All three species tolerated high doses of heavy metals and the MGTs increased exponentially as the heavy metal concentrations increased; 12 mg I^‐1 was die highest dose tested and the bacteria continued to grow albeit at very slow rates. In dilute media, the toxic effects of heavy metals were enhanced, illustrating the protection effect of organic matter and heavy metal complex formation. Growth studies of the isolated microorganisms on half‐strength tryptic soy agar containing 6 mg I^‐1 heavy metals also proved useful in determining toxidty.

Keywords:

• Biomass
• bacterial species
• growth curves
• mean generation time
• organic matter
• chemical complexes