A novel respirometer for biological toxicity tests

A respirometer has been developed for microbial toxicity tests. The respirometer is based on luminescence quenching by molecular oxygen. The oxygen sensing film consists of luminescent ruthenium complex adsorbed on amorphous fumed silica and immobilized inside silicone rubber. The luminescence intensity depends on the oxygen concentration of sample in contact with sensing film. The inhibition effect of heavy metals on the respiration rate of microorganisms can be evaluated by monitoring the luminescence intensity of the sensing film. The toxicity of Cu 2+ , Zn 2+ , Ni 2+ , Cr 3+ , Pb 2+ and Hg 2+ on activated sludge was tested using the respirometer. The results indicated that the proposed method was sensitive to the heavy metals tested in this experiment. It was feasible to use the respirometer for microbial toxicity tests.

Determining oxygen consumption rate and asphyxiation point in Chanodichthys mongolicus using an improved respirometer chamber

Knowledge of oxygen consumption rates and asphyxiation points in fish is important to determine appropriate stocking and water quality management in aquaculture. The oxygen consumption rate and asphyxiation point in Chanodichthys mongolicus were detected under laboratory conditions using an improved respirometer chamber. The results revealed that more accurate estimates can be obtained by adjusting the volume of the respirometer chamber, which may avoid system errors caused by either repeatedly adjusting fish density or selecting different equipment specifications. The oxygen consumption rate and asphyxiation point of C. mongolicus increased with increasing water temperature and decreasing fish size. Changes in the C. mongolicus oxygen consumption rate were divided into three stages at water temperatures of 11-33~C： （I） a low temperature oxygen consumption rate stage when water temperature was 11-19~C, （2） the optimum temperature oxygen consumption rate stage when water temperature was 19-23~C, and （3） a high temperature oxygen consumption rate stage when water temperature was 〉27~C. The temperature quotients （Q10） obtained suggested that C. mongolicus preferred a temperature range of 19-23~C. At 19~C, C. mongolicus exhibited higher oxygen consumption rates during the day when the maximum values were observed at 10：00 and 14：00 than at night when the minimum occurred at 02：00.

Calibration of CO₂Trapping in Alkaline Solutions during Soil Incubation at Varying Temperatures Using a Respicond VI

Measurements of carbon dioxide (CO2)-evolution from soils are important in evaluating biomass and activity of soil microorganisms, as well as decomposition of soil organic matter. The Respicond VI is a fully computerized system allowing continuous measurement of CO2 evolution in short- and long-term soil incubation experiments in up to 96 incubation vessels. The measurement of CO2 evolution is based on the absorption of CO2 by an electrolyte (KOH solution) producing a change in the cell conductance measured using two electrodes. In this study, the Respicond VI was recalibrated yielding 174.5 mg CO2 as constant A expressing the theoretical maximum amount of CO2 absorbed in 10 ml 0.5 M KOH. This value of A corresponds to 34.9 mg CO2 ml-1 1 M KOH. The constant A does neither depend on the investigated incubation temperatures (5°C - 25°C) nor on the concentrations of the KOH solutions (0.5, 0.1, 0.05 M KOH). To eliminate any influence of changing incubation temperatures, either induced by uncertainties in temperature control or as a part of the experimental setup, on the conductance of KOH solution, a correction procedure was developed using a factor calculated from changing conductance of KOH solutions in incubation vessels without soil.