Assessment of urease inhibition assays for measuring toxicity of environmental samples

We evaluated the potential of free and immobilized urease for assaying toxicity of environmental samples. Free urease was sensitive to heavy metals and insensitive to organic toxicants. Toxicity of industrial wastewaters and process water, as determined via free urease assay, was correlated with the heavy metal content of these samples. High background (blank) absorbance was encountered in samples containing arnmonia. The background exceeded the linear range of the assay at ammonia nitrogen concentrations exceeding 8 mg/l. Immobilizing urease on glass beads was considered as a means of overcoming the problem of ammonia interference. Immobilized enzyme was unfortunately not sensitive to heavy metals. The potential of free urease for toxicity testing cannot be fully realized until a means of overcoming ammonia interference is developed.