Freezing concentration in AODs toxicity test

Abstract

Freezing of water solution to amplify concentration of impurities in the water is part of AODs (Aquatic Organisms Environmental Diagnostic-stream) toxicity test procedure. The quality of AODs test solution determined the bioassay results of the concentrated solution resulted from freezing. Making the test solution for AODs by freezing concentration technique needs to be reviewed and adjusted since the freezing procedure of AODs is different from the country where the AOD method was first developed. The research objective was to evaluate the freezing performance of sample solution of AODs toxicity test at a certain speed of rotary evaporator i.e. 60-70 rpm, the quality of isopropyl alcohol at a cooling temperature of −15°C to −20°C, room temperature of 25°C. Efficiency recovery of solute was calculated at 180%, 320%, 560%, 1000% and 1800% freezing concentration. Evaluation of AODs freezing techniques was conducted ex-situ in the laboratory, on water samples taken from 5 locations in the Gadjah Wong stream. The research resulted in some important information for freezing concentration standardization procedure. The higher the volume ratio of the concentration, the longer the time of freezing process at a fixed rotational speed. It took between 15 minutes to 2 hours to have a final volume of 100 ml solution from various volume ratios. There were differences in recovery efficiency of solute at various freezing concentrations and with various solute concentrations in the river water samples. The higher the solute concentration level in the river water sample, the lower the recovery efficiency of the solute. High solute concentration usually represents the river water quality in dry season. Pretty good recovery efficiency (80-100%) only achieved in a solution with a low freezing concentration (180%, 320% and 560%). Good recovery efficiency of solute was resulted in low solute concentration and low TDS or EC concentrations in the river water samples. The freezing concentration techniques performance does not contradict with previous other expert’s research and successfully represent the sample test solution for standardization of AODs method.