Toxicity of pure chemicals is assessed using respirometers by adding increasing concentrations to an active culture. The concentration at which oxygen uptake or gas production begins to decrease is known as the “threshold toxicant concentration.” Examples are shown below:
Aerobic Toxicity Testing
This example shows the results of dosing respirometer tests in which three concentrations of cyanide were added to a test culture that receive phenol as an organic substrate. The threshold toxic concentration of cyanide was 1 mg/L.
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 800 mg/L produced a 50% decrease in methane production rate.