Abstract:Single and joint toxicity of toluene, ethylbenzene and xylene on Neocaridina denticulata sinensis was examined using the semi-static bioassay. In the single acute toxicity experiments, the 96h LC50 value of TEX was 13.8, 10.4, 11.3 mg/L, respectively, and the sequence of toxicity was in order of ethylbenzene>xylene>toluene. On the basis of the equal toxicity solution method (ETS), the binary action of binary of toluene, ethylbenzene and xylene in different toxic unit ratios (4:1, 3:2, 2:3, 1:4) on Neocaridina denticulata sinensis was analyzed. The results showed that the joint action between toluene and ethylbenzene, ethylbenzene and xylene, and toluene and xylene was strictly in conformity with the model of additivity. On the basis of the toxic unit method (TU) and the mixture toxicity index method (MTI), the ternary action of toluene, ethylbenzene and xylene by two different ways of combination (in toxic unit ratio 1:1:1 and in concentration ratio 1:1:1) on Neocaridina denticulata sinensis weas evaluated. The 96h LC50 value of the ternary mixtures was 11.6 and 10.7 mg/L, respectively, which was quite similar to the results in the single action so that could be also regarded as the medium toxicity toxicant. Besides, the results demonstrated that the joint action was considered as partial addition after a 48-h exposure and synergism after a 96-h exposure. Thus, the joint toxicity of the ternary mixtures turned out to be related to the exposure time, from partial addition to synergism. However, synergism observed was not significant, which meant that the joint action was close to additivity. In conclusion, the joint action of the binary and ternary mixtures of toluene, ethylbenzene and xylene on Neocaridina denticulata sinensis can be mainly assumed to be additive action. Therefore, when establishing the water quality guideline or criteria, controlling water pollution, and assessing aquatic ecosystem risk of toluene, ethylbenzene and xylene in the future, the additive action can be safely recommended.