Development of a free beta-galactosidase in vitro test for the assessment of heavy metal toxicity

The effect of heavy metals and organic compounds on the activity of the enz yme beta -galactosidase in a standardized bioassay has been evaluated, cons idering future applications in environmental monitoring. The tests were don e using a commercial extract of a hydrolase from the eukaryote yeast Kluyve romyces lactis and o-nitrophenyl-beta -D-galactopyranoside (ONPG) as substr ate. The enzyme was exposed to Cr(VI), Cd(II), Cu(II), Ni(II), Pb(II), Hg(I I), phenol, sodium dodecyl sulfate, methanol and pentachlorophenol for 5, 1 5, 30, and 60 min. According to the results, a 15 min exposure time was con sidered optimum for the performance of the assay. Results of tests with met als showed 1C(50) values ranging between 9.25mg/L for Cd(II) and 0.015mg/L for Hg(II), with an order of sensitivity of: Cd(II) < Ni(II) < Cr(VI) = Pb( II) < Cu(II) < Hg(II). Sensitivity to organic compounds ranged from 200 to 4000 mg/L, showing a higher specificity to heavy metals. The present in vit ro free enzyme test showed a similar behavior to other tests based on P-gal actosidase such as the MetPlate (TM). Furthermore, when compared to data fr om the literature on acute toxicity assays currently used in environmental assessment, test results show good agreement regarding the sensitivity to m etals. After standardization, the proposed test could be used as a rapid an d low-cost assay when evaluating biological effects of heavy metals in moni toring programs. (C) 2001 by John Wiley & Sons, Inc.