研究表明，干旱条件会对水质产生不利影响，并使得包括杀虫剂在内的某些化学物质毒性变高，且更容易在鱼体内累积。

当中国的部分地区正在经历最为严重的旱情的时候，美国南部的部分地区则正在遭受自1887年以来最长的干旱期，发表在《综合环境评估与管理》（Integrated Environmental Assessment and Management）上的一篇最新研究表明，干旱条件会使得环境中的某些化学物质对鱼类和水生生物产生更高的毒性。

该研究发现，干旱条件会提高水中自然pH值的变化幅度。由于诸如氨等一些污染物会根据pH值的水平高低而对水生生物产生更高的毒性，这样就会造成危险。另外，逾75%的由世界卫生组织规定的基本药物以及大约三分之一的现代杀虫剂具有化合物的离子化基团。当扩散到环境中的时候，如果表面pH值很高，这些“弱碱”化合物会对鱼类产生更高的毒性。

“该研究表明，我们可能会低估或高估某些化学物质对鱼类的不良影响，”本研究的共同作者，美国德克萨斯州的贝勒大学（Baylor University）环境卫生科学主任Bryan Brooks博士说道。“对于使得某些化学物质毒性变高且更容易在鱼体内累积的现象来说，干旱条件，特别是受气候变化影响的那些干旱条件，如何影响水的pH值变化目前已经成为一个备受关注的领域。”

在两年的时间内，研究人员在不同的时期内从美国南部的23条溪流中，采集样本并测定一天内生态系统生产与呼吸如何溶解氧含量，以及磷与氮的含量和pH值如何变化。研究人员发现，在有史以来最为干旱的一年当中，水的pH值波动范围很极端，同时还伴有对水生生物更高的毒性。

“全球气候变化和降水类型变化引起的未来水资源短缺可能会对半干旱地区的溪流流量产生深远的影响，这会直接影响水资源管理，”共同作者Ted Valenti博士介绍道。“气候多变性对污染物危险度的累积影响作用的预测可能要求淡水系统的环境评估与管理方法的重大转变。”

原文出处：

Integrated Environmental Assessment and Management   DOI: 10.1002/ieam.202

Influence of drought and total phosphorus on diel pH in wadeable streams: Implications for ecological risk assessment of ionizable contaminants

Theodore W Valenti, Jason M Taylor, Jeffrey A Back, Ryan S King, Bryan W. Brooks

Climatological influences on site-specific ecohydrology are particularly germane in semi-arid regions where instream flows are strongly influenced by effluent discharges. Because many traditional and emerging aquatic contaminants (e.g., pharmaceuticals) are ionizable, we examined diel surface water pH patterns (i.e. change in pH over a 24?h period) at 23 wadeable streams in central Texas, USA, representing a gradient of nutrient enrichment during consecutive summers of 2006 and 2007. The years of our study were characterized by decidedly different instream flows, which likely affected production: respiration (P:R) dynamics and lead to distinctions in diel pH patterns between 2006 and 2007. Site-specific ambient water quality criteria for ammonia, aquatic toxicity of the model weak base pharmaceutical sertraline, and bioaccumulation of select weak base therapeutics were predicted using continuous water quality monitoring data from the sites. Drought conditions of 2006 significantly increased (p?<?0.05) diel pH changes compared to high instream flows of 2007 and the magnitude of diel pH variability was most pronounced at nutrient enriched sites in 2006. Differences in diel pH change patterns between 2006 and 2007 affected predictions of the environmental fate and effects for model weak base pharmaceuticals and ammonia. Overall, site-specific diel pH was more variable at some sites than the difference in mean surface water pH between the two summers. Diel pH variability affected regulatory criteria as 20% of the study sites in 2006 experienced greater than 5-fold differences in National Ambient Water Quality Criteria (NAWQC) for ammonia over 24-h periods. Our study emphasizes the potential uncertainty that diel pH variability may introduce in site-specific assessments and provides recommendations for environmental assessment of ionizable contaminants. Integr. Environ. Assess. Manag. 2011 SETAC.