University of Geneva, Sciences II, 30 Quai E.-Ansermet, 1221, Geneva 4, Switzerland.
University of Bordeaux, Allée Geoffroy Saint-Hilaire, 33615, Pessac, France.
Environ Res. 2022 May 15;208:112596. doi: 10.1016/j.envres.2021.112596. Epub 2021 Dec 28.
Estuaries are complex systems involving numerous biogeochemical gradients and processes that influence the behavior of trace metals. Lead (Pb), cadmium (Cd), and copper (Cu) speciation and partitioning were studied in the Gironde Estuary (SW France), using a multi-method approach in which data from innovative sensors and laboratory-based techniques were combined. For the first time in this system, the so-called dynamic fractions of the target metals (dissolved forms that are potentially bioavailable) were recorded on-board through voltammetry using unique antifouling gel-integrated microelectrode arrays (GIME) incorporated in a submersible sensing probe (TracMetal). Trace metals in the operationally defined dissolved <0.2 μm and <0.02 μm fractions, as well as complexed with suspended particles (collected after centrifugation) were quantified through sampling/laboratory-based techniques. High spatial resolution trace metal concentrations were monitored along the salinity gradient (S = 0.10 to S = 34.0) together with master bio-physicochemical parameters providing robust cruise-specific information on how well-known abiotic and biotic processes control the Gironde estuarine trace element partitioning, (i.e. conservative behavior, addition/removal). Combining conventional methods with GIME measurements showed: (i) the dominance of Cd dynamic species in the intra-estuarine total dissolved fraction (up to 90%), (ii) the importance of small colloids as trace metal carrier phases, desorbing and complexing dynamic fractions of Pb and Cu, and (iii) the potential influence of photo-redox processes remobilizing Pb under their dynamic forms (up to 80%). Data also suggest trace metal release/sorption by phytoplankton with an increase of dissolved Cu concentrations in the riverine branch, as well as Cu and Cd particulate concentrations showing higher levels towards productive coastal waters. This complete approach allowed to monitor key estuarine biogeochemical processes and highlighted the valuable use of the TracMetal to record subtle variations of potentially bioavailable dissolved metal fractions.
河口是一个复杂的系统，涉及许多生物地球化学梯度和过程，这些梯度和过程会影响痕量金属的行为。本研究采用多方法手段，结合创新传感器和实验室技术的数据，研究了法国西南部吉伦特河口（Gironde Estuary）中铅（Pb）、镉（Cd）和铜（Cu）的形态和分配。这是该系统中首次通过使用独特的防污凝胶集成微电极阵列（Gel-integrated microelectrode arrays，GIME）在潜水感应探头（TracMetal）上进行伏安法测量，记录下目标金属的所谓动态分数（具有潜在生物利用性的溶解形式）。通过采样/实验室技术，对操作定义的溶解 <0.2 μm 和 <0.02 μm 分数以及与悬浮颗粒络合的痕量金属（离心后收集）进行定量分析。沿盐度梯度（S=0.10 到 S=34.0）监测高空间分辨率痕量金属浓度，同时监测主要的生物物理化学参数，这些参数提供了有关生物地球化学过程如何控制吉伦特河口痕量元素分配的稳健的特定航次信息（即保守行为、添加/去除）。将常规方法与 GIME 测量相结合表明：（i）Cd 动态物种在河口内总溶解分数中占主导地位（高达 90%），（ii）小胶体作为痕量金属载体相的重要性，解吸和络合 Pb 和 Cu 的动态分数，以及（iii）光还原过程在其动态形式下重新迁移 Pb 的潜在影响（高达 80%）。数据还表明，浮游植物对痕量金属的释放/吸附作用导致河流分支中溶解 Cu 浓度增加，以及 Cu 和 Cd 颗粒浓度在生产力较高的沿海水域中更高。这种完整的方法可以监测关键的河口生物地球化学过程，并突出了 TracMetal 用于记录潜在生物利用性溶解金属分数细微变化的有价值的用途。
