Nitrification inhibition test

The nitrification inhibition test AQC data for different batches of the test organism, Nitrosomonas, has given a range of EC50 values of 0.76 to 1.28 mg l-1. The plot of EC50 values for 3,5 dichlorophenol is given in Figure 3.1.4. 

If a substance is not readily biodegradable, this does not necessarily imply that the substance is toxic to microorganisms. Therefore, specific experiments on bacteria are carried out to obtain information on substance ecotoxicity. Examples are the respiratory inhibition test (e.g., OECD 209, [45]) and the nitrification inhibition test (ISO 9509, [46]), which are performed on a mixed microbial population representative of a sewage treatment plant s community, cell multiplication inhibition test on Pseudomonas putida (ISO 10712, [47]) and flash tests on luminescent bacteria Photobacterium phosphoreum [22] and Vibrio fischeri [24], which reduce their luminescence when exposed to toxic substances. 

The MTC values for the various effluents samples tested in the trial ranged from 5 to 48%. Effluents can exhibit a wide range of toxicities. Comparison of the results with nitrification and respiration inhibition tests where applicable showed that the MARA detected toxicity. 

Moreover, a substantial advantage of this microbial sensor over other existing tests for measuring the inhibition of nitrification is the very short measuring... 

ISO 9509, Water Quality - Toxicity Test for Assessing the Inhibition of Nitrification of Activated Sludge Microorganisms, International Organization for Standardization, Geneva, Switzerland, 2006. 

Rice and Pancholy studied the effects on nitrification of seven phenolic compounds (caffeic acid, chlorogenic acid, ferulic acid, isochlorogenic acid, isoquercitrin, myricetin and quercetin). They found with soil suspensions that Nitro somonas was much more susceptible to inhibition than Nitrobacter, and reported that the nitrification of ammonium by Nitro somonas was completely inhibited by ferulic acid at the extremely low concentration of 10 nil. Kov ever, since their procedure was based on a colorimetric test for the presence of nitrite, the possibility appears to exist that the result may have been due to the loss of nitrite rather than to inhibition of its formation. The other phenolic compounds tested v ere reported to cause inhibition of nitrification by Nitrosomonas at concentrations greater than 1 pM. 

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