Keywords: 
• chemicals /
• algae infrared radiation /
• three-index method /
• technical improvement

Abstract: In previous acute toxicity tests by algae infrared radiation, the feasibility and stability of results was unsatisfactory, which is due to measuring temperature once each time in each cup, setting only two test groups, and applying single index (maximum of algae temperature difference). In order to solve these problems, an improved method was proposed. The algae temperature was measured three times in each cup during each test, three test groups were set, and three-index method was used instead of single index. The improved technology was applied to toxicity tests of both distilled water and aqueous solution of heavy metals. The results showed that the three-index method can control false results recurrence rate in 20%. When testing the toxicity of four kinds of coexisting heavy metals (0.066-0.156 mg·L^-1), the average recurrence rates(%)/reproducibility(%) of all the methods by measuring three algae temperature was 100%/100% whereas that of the method by measuring one algae temperature was 67%/100%. It is indicated that all the methods were effective when the concentration of heavy metals was within 0.066 mg·L^-1 and 0.156 mg·L^-1. During the toxicity test of single heavy metal (0.001-0.1 mg·L^-1), the average recurrence rates(%)/reproducibility(%) of the three-index method was 100%/100%, much higher than those of other methods. It is indicated that only the three-index method can be used to evaluate the toxicity of heavy metal within 0.001 mg·L^-1 and 0.1 mg·L^-1. During the toxicity test of five heavy metals (0.001-0.1 mg·L^-1), the average recurrence rates(%)/reproducibility(%) of the three-index method was 86.8%/100% on average. Overall, it is demonstrated that the three-index method can obtain better sensibility and stability in testing the acute toxicity of chemicals.