Abstract：
We investigated how natural dissolved organic matter (DOM) of the Rio Negro (Amazon) affects acute copper (Cu) toxicity to local fish: the cardinal tetra (Paracheirodon axelrodi) and the dwarf cichlid (Apistogramma agassizii). It is established that Cu2+ complexation with DOM decreases Cu bioavailability (and thus toxicity) to aquatic organisms, as conceptualized by the Biotic Ligand Model (BLM). However, we also know that Rio Negro\'s DOM can interact with fish gills and have a beneficial effect on Na+ homeostasis, the main target of acute Cu toxicity in freshwater animals. We aimed to tease apart these potential protective effects of DOM against Cu-induced Na+ imbalances in fish. In the laboratory, we acclimated fish to Rio Negro water (10 mg L-1 DOC) and to a low-DOM water (1.4 mg L-1 DOC) with similar ion composition and pH (5.9). We measured 3-h Cu uptake in gills and unidirectional and net Na+ physiological fluxes across a range of Cu concentrations in both waters. Various DOM pre-acclimation times (0, 1 and 5 days) were evaluated in experiments with P. axelrodi. Copper exposure led to similar levels of net Na+ loss in the two fish, but with distinct effects on Na+ influx and efflux rates reflecting their different ionoregulation strategies. Rio Negro DOM protected against Cu uptake and toxicity in the two fish species. Both Cu uptake in fish gills and Na+ regulation disturbances were relatively well predicted by the modelled aqueous free Cu2+ ion concentration. These findings suggest that protection by DOM occurs mainly from Cu complexation under the tested conditions. The prevalence of this geochemical-type protection over a physiological-type protection agrees with the BLM conceptual framework, supporting the use of the BLM to assess the risk of Cu in these Amazonian waters.
摘要：
我们研究了里约内格罗（Amazon）的天然溶解有机物（DOM）如何影响对当地鱼类的急性铜（Cu）毒性：红衣主教四重奏（Parachirodonaxelrodi）和矮的丽鱼科鱼（Apistogrammaagassizii）。已确定Cu2与DOM的络合降低了Cu对水生生物的生物利用度（从而降低了毒性），由生物配体模型(BLM)概念化。然而,我们也知道RioNegro的DOM可以与鱼g相互作用，对Na+稳态有有益的影响，淡水动物急性Cu毒性的主要目标。我们旨在梳理DOM对Cu诱导的鱼类Na失衡的潜在保护作用。在实验室里,我们使鱼类适应了RioNegro水（10mgL-1DOC）和具有相似离子组成和pH（5.9）的低DOM水（1.4mgL-1DOC）。我们测量了s中3小时的Cu吸收以及两个水域中一系列Cu浓度的单向和净Na生理通量。在用P.axelrodi的实验中评估各种DOM预适应时间(0、1和5天)。铜暴露导致两条鱼的钠净损失水平相似，但对Na流入和流出速率有明显影响，反映了它们不同的离子调节策略。RioNegroDOM可防止两种鱼类对铜的吸收和毒性。通过模拟的水性游离Cu2离子浓度，可以相对较好地预测鱼ill中的Cu吸收和Na调节紊乱。这些发现表明，在测试条件下，DOM的保护主要来自Cu的络合。这种地球化学类型的保护相对于生理类型的保护的普遍性与BLM概念框架一致。支持使用BLM评估这些亚马逊水域中铜的风险。
