Worms I, Simon D F, Hassler C S, Wilkinson K J
CABE (Analytical and Biophysical Environmental Chemistry), University of Geneva, 30, quai Ernest Ansermet, 1211 Geneva 4, Switzerland.
Biochimie. 2006 Nov;88(11):1721-31. doi: 10.1016/j.biochi.2006.09.008. Epub 2006 Sep 28.
An important challenge in environmental biogeochemistry is the determination of the bioavailability of toxic and essential trace compounds in natural media. For trace metals, it is now clear that chemical speciation must be taken into account when predicting bioavailability. Over the past 20 years, equilibrium models (free ion activity model (FIAM), biotic ligand model (BLM)) have been increasingly developed to describe metal bioavailability in environmental systems, despite the fact that environmental systems are always dynamic and rarely at equilibrium. In these simple (relatively successful) models, any reduction in the available, reactive species of the metal due to competition, complexation or other reactions will reduce metal bioaccumulation and thus biological effects. Recently, it has become clear that biological, physical and chemical reactions occurring in the immediate proximity of the biological surface also play an important role in controlling trace metal bioavailability through shifts in the limiting biouptake fluxes. Indeed, for microorganisms, examples of biological (transport across membrane), chemical (dissociation kinetics of metal complexes) and physical (diffusion) limitation can be demonstrated. Furthermore, the organism can employ a number of biological internalization strategies to get around limitations that are imposed on it by the physicochemistry of the medium. The use of a single transport site by several metals or the use of several transport sites by a single metal further complicates the prediction of uptake or effects using the simple chemical models. Finally, once inside the microorganism the cell is able to employ a large number of strategies including complexation, compartmentalization, efflux or the production of extracellular ligands to minimize or optimize the reactivity of the metal. The prediction of trace metal bioavailability will thus require multidisciplinary advances in our understanding of the reactions occurring at and near the biological interface. By taking into account medium constraints and biological adaptability, future bioavailability modeling will certainly become more robust.
环境生物地球化学中的一个重要挑战是确定天然介质中有毒和必需微量化合物的生物有效性。对于微量金属，现在很清楚，在预测生物有效性时必须考虑化学形态。在过去20年中，尽管环境系统总是动态的且很少处于平衡状态，但平衡模型（自由离子活性模型（FIAM）、生物配体模型（BLM））已越来越多地用于描述环境系统中的金属生物有效性。在这些简单（相对成功）的模型中，由于竞争、络合或其他反应导致金属的可用活性物种减少，都会降低金属的生物累积，进而降低生物效应。最近，很明显，在生物表面紧邻区域发生的生物、物理和化学反应，也通过限制生物摄取通量的变化在控制微量金属生物有效性方面发挥着重要作用。事实上，对于微生物，可以证明存在生物（跨膜运输）、化学（金属络合物的解离动力学）和物理（扩散）限制的例子。此外，生物体可以采用多种生物内化策略来克服介质物理化学对其施加的限制。几种金属使用单个运输位点或一种金属使用多个运输位点，进一步使使用简单化学模型预测摄取或效应变得复杂。最后，一旦进入微生物体内，细胞能够采用大量策略，包括络合、区室化、外排或产生细胞外配体，以最小化或优化金属的反应性。因此，预测微量金属的生物有效性将需要我们在理解生物界面及其附近发生的反应方面取得多学科进展。通过考虑介质限制和生物适应性，未来的生物有效性建模肯定会变得更加稳健。
