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 w
astewaters and process water, as determined via free urease assay, was
correlated with the heavy metal content of these samples. High backgr
ound (blank) absorbance was encountered in samples containing ammonia.
The background exceeded the linear range of the assay at ammonia nitr
ogen concentrations exceeding 8 mg/l. Immobilizing urease on glass bea
ds was considered as a means of overcoming the problem of ammonia inte
rference. Immobilized enzyme was unfortunately not sensitive to heavy
metals. The potential of free urease for toxicity testing cannot be fu
lly realized until a means of overcoming ammonia interference is devel
oped.