Toxicity of pure chemicals is assessed using respirometers by adding increasing concentrations of suspected toxic agents to active biomass cultures. The concentration at which oxygen uptake or gas production begins to decrease is known as the “threshold toxicant concentration.” Examples are shown below:
Anaerobic Toxicity Testing
This example shows the results of dosing an anaerobic culture with three concentrations of an industrial cleaning agent followed by respirometric measurement of methane production. The threshold toxic concentration was less than 80 mg/L of product and 600 mg/L produced a 50% decrease in methane production rate.
Aerobic Toxicity Testing
This example shows the results of respirometer tests in which three concentrations of cyanide were added to a aerobic test culture that received phenol as an organic substrate. The threshold toxic concentration of cyanide was 1 mg/L.