4,4’-DDT全生命周期暴露对大型溞(Daphnia magna)生长、生殖、心率、行为、存活及基因转录的影响

Whole-Life-Stage Exposure of 4,4’-DDT and Effects on Development,Reproduction,Heart Rate,Behavior,Survival and Gene Transcription of Daphnia magna

大型溞(Daphnia magna)慢性毒性测试的毒理学数据是美国环境保护局水质基准(water quality criteria,WQC)制定中非常重要的数据来源,用以推导能有效保护水生生物的化学污染物浓度阈值。以往的研究表明,在部分生命周期暴露的基础上得出的最低观察效应浓度(lowest observed effective concentration,LOEC)有时会高于在大型溞全生命周期暴露时的LOEC。因此,对于一些具有生物富集性和环境持久性的化学污染物而言,由部分生命周期测试的毒理学数据推导出的水质基准在全生命周期暴露后是否仍然会对水生生物产生毒性效应尚未明确。为此,本研究选取美国环境保护局WQC文件中的污染物4,4’-滴滴涕(4,4’-DDT)为受试化学污染物,其基准连续浓度(criteria continuous concentration,CCC)为测试浓度,开展模式生物大型溞全生命周期暴露实验,检测4,4’-DDT在大型溞不同生命阶段对其生长、生殖、心率、行为、存活及基因转录的影响。研究发现,美国环境保护局WQC文件制定的4,4’-DDT的CCC对大型溞全生命周期的生长、生殖、存活都没有产生显著性的影响,但是在不同生命阶段对于其心率和行为有显著性的毒性效应。基因转录结果表明,4,4’-DDT在生长阶段和死亡阶段分别显著性改变了大型溞与免疫功能和细胞信号传导功能相关代谢通路中基因的转录。此外,随着暴露时间的延长,其心率参数的LOEC从第21天的1 ng·L^(-1)降低至第32天的0.1 ng·L^(-1),说明即使在0.1 ng·L^(-1)暴露条件下仍然能够观察到4,4’-DDT对大型溞的毒性效应。因此在对一些持久性环境污染物作环境风险评估与环境基准制定时,全生命周期毒性测试也应得到适当的考虑。

Toxicological data deduced from chronic toxicity test of Daphnia magna is imperative in the establishment of the water quality criteria(WQC)of United States Environmental Protection Agency(US EPA),and in the calculation of concentration thresholds of contaminates to effectively protect aquatic organisms.However,previous studies revealed that compared with the partial-life-stage exposure,the whole-life-stage exposure of Daphnia magna decreased the lowest observed effective concentration(LOEC)of pollutants.Therefore,for those contaminates with bioaccumulation and environmental persistence,whether the pollutant with the criteria concentration deduced from partial-life-stage exposure test is toxic to aquatic organisms after the whole-life-stage exposure remains unknown.In order to investigate the question,this study selected 4,4’-DDT from the US EPA WQC document as a test pollutant and set its criterion continuous concentration(CCC)as test concentration to conduct the whole-life-stage exposure experiment to Daphnia magna,and to study its effects on growth,reproduction,heart rate,behavior,survival,and gene transcription of Daphnia magna at different life stages.The results demonstrated that 4,4’-DDT with the CCC set in the US EPA WQC had no significant impacts on growth,reproduction,survival after the whole-life-stage exposure,but the exposure caused significant effects on heart rate and behavior on different life stages.Gene transcription results indicated that 4,4’-DDT significantly altered the transcription of genes related to immune function and cell signaling function of Daphnia magna at the growth stage and the death stage,respectively.In addition,as exposure time prolonged,the LOEC of heart rate decreased from 1 ng·L^(-1) on day 21 st to 0.1 ng·L^(-1) on day 32 nd,which showed that 0.1 ng·L^(-1) of 4,4’-DDT has certain toxic effects to Daphnia magna.Therefore,in the environmental risk assessment and benchmarking derivation of some environmentally-persistent pollutants,the importance of the whole-life-stage exposure should be considered.