pH值和硬度对两种氯酚类化合物对大型溞急性毒性的影响

以大型溞为研究对象,系统研究了pH值和硬度对2,4,6-三氯酚(2,4,6-TCP)和五氯酚(PCP)对大型溞急性毒性的影响.结果表明,pH值的影响非常显著.在实验pH值范围内(6~10),随pH值升高,两种氯酚对大型溞的急性毒性迅速降低,对不同pH值下两种氯酚在水中的形态分布与其毒性的相关性分析显示,pH值对毒性的影响机制与氯酚在水中的存在形态有密切关系,氯酚类物质的毒性主要由其分子态贡献,而pH值的升高促使分子态向离子态转化从而使其毒性降低.与pH值相比,硬度虽然对两种氯酚对大型溞急性毒性有一定的影响,但影响不显著.因此,在制定该类污染物的基准和标准时水体硬度的影响可以不作为关键因素考虑.

Effects of pH and water hardness on the acute toxicity of two chlorophenols to Daphnia Magna

Effects of pH and water hardness on the acute toxicities of 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) to Daphnia magna were evaluated. The results showed that pH had a significant effect on the acute toxicities of the two chlorophenols (CPs). In the tested pH range (pH6~10), the acute lethal toxicities of the two CPs were decreased with the increase of water pH, which were attributed to the speciation distribution of CPs in different pH.It had been reported that the toxicities of CPs were contributed by their unionized forms.The elevated solution pH will cause the transformation of their unionized fractions to ionic fractions, and hence decrease their toxicity. Compared with pH, the effect of water hardness on the acute toxicities of the two CPs to Daphnia magna had certain influence, but the impact was relatively insignificant. Therefore, the effect of water hardness was not an important factor in the determination of the water quality criteria and standards of CPs.