MICROTESTING APPRAISAL OF ATP AND CELL RECOVERY TOXICITY END-POINTS AFTER ACUTE EXPOSURE OF SELENASTRUM-CAPRICORNUTUM TO SELECTED CHEMICALS

Employing microtesting procedures, intracellular ATP and cell recovery (96-h cell count determinations) were appraised as toxicity end-point responses after acute (4-h) exposure of the green alga Selenastrum capricornutum to metals (Cu2+, Co2+, Cd2+, Cr3+, Cr6+, Ni2+, Hg2+, Zn2+, B3+), sodium azide, and 4 organic compounds (sodium dodecyl sulphate, 2,4-dichloropbenol, phenol, tebuthiuron). Except for B3+, both end points were able to measure acute metal phytotoxicity effects at concentrations of 5 mg.L-1 or lower. The algal recovery test showed better metal toxicity discrimination than the ATP test on the basis of dose-response slope steepness and elevation differences. Both tests, however, supplied useful complementary information. While the ATP test reacted rapidly to chemical aggression, the recovery test offered pertinent insight into actual long-term consequences of acute exposure. With the nonmetals, both end-point responses were mitigated (sodium azide, sodium dodecyl sulphate, 2,4-dichlorophenol) or insensitive (phenol, tebuthiuron), suggesting low acute exposure risk to algae by these chemicals. Based on 4-h (ATP and cell recovery) EC50 to standard 96-h EC50 ratio values, the algal indicator was shown to have low tolerance to 6 chemicals (Cr3+, Cr6+, Hg2+, Cu2+, sodium dodecyl sulphate, 2,4-dichlorophenol). When compared to acute exposure bacterial assays, the acute exposure ATP and cell recovery microtests competed well in terms of overall sensitivity to a selection of chemicals. In general, this work demonstrates the utility that short-term algal exposure tests can provide for chemical toxicity investigations.