Comparison of the Microtox test with the 96-hr LC50 test for the harpacticoid Nitocra spinipes.

A comparison between the static 96-hr LC50 test with the brackish water harpacticoid Nitocra spinipes and the Microtox (Beckman Instruments, Inc.) screening method has been done. The relationship between the two bioassays were evaluated for 16 pure and technical chemicals and 11 complex effluents from different types of industries. The correlation between the 96-hr LC50 values for Nitocra and the 5-, 15-, and 30-min effective concentration (EC50) for pure and technical chemicals had R2 values ranging between 0.751 and 0.796. A somewhat better correlation was shown between the two test methods for the complex effluents with R2 values ranging from 0.903 to 0.927. The sensitivity of the two tests for the actual types of samples were found to be in the same order of magnitude. Investigations concerning pretreatments of three chemicals (dibutyl phthalate, 1-octanol, and pentachlorophenol) fairly insoluble in water (less than 1000 mg/liter) have been done. Three solvents, acetone, dimethyl sulfoxide (DMSO), and propylene glycol, were studied with the Microtox system in a low concentration (500 mg/liter). Acetone exerted a slightly stimulatory effect and propylene glycol a slight reduction effect on bacterial luminescence.