Allometry describes the disproportional scaling of physiological processes with the body size. This challenges the assumption of a direct relationship between metal concentrations in organisms and environmental levels, a premise commonly used in biomonitoring programs. However, deciphering the complex drivers of metal allometry is difficult because size and age often confound each other. In this study, we took advantage of a natural experiment provided by populations of oysters of known ages that exhibited substantial size variation within the same age cohorts. Using a stable metal isotope tracer technique, we examined the bioaccumulation of six metals (⁶⁰Ni, ⁶⁵Cu, ⁶⁸Zn, ¹⁰⁷Ag, ¹¹⁴Cd, ²⁰⁶Pb) under both dissolved and dietary exposures. Our results indicate that bioaccumulation efficiency primarily drives the allometric patterns of metal concentrations with age exerting a more pronounced influence than size. Older oysters showed a diminished bioaccumulation capacity, leading to negative correlations between the metal concentration and size. Meanwhile, indirect factors, such as growth dilution, played a minor role, and exposure duration had a negligible effect. This study enhances our understanding of the complex mechanisms governing metal bioaccumulation in marine organisms and provides critical insights into improving the interpretation of biomonitoring data.

中文翻译：

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自然实验显示老年牡蛎的金属含量较低：解开年龄、大小和生长影响

异速生长描述了生理过程与体型不成比例的缩放。这挑战了生物体内金属浓度与环境水平之间直接关系的假设，这是生物监测计划中常用的前提。然而，破译金属异速生长的复杂驱动因素是困难的，因为大小和年龄经常相互混淆。在这项研究中，我们利用了已知年龄的牡蛎种群提供的自然实验，这些牡蛎种群在同一年龄组中表现出很大的大小变化。使用稳定金属同位素示踪技术，我们检查了六种金属 （⁶⁰Ni、⁶⁵Cu、⁶⁸Zn、¹⁰⁷Ag、¹¹⁴Cd、²⁰⁶Pb） 在溶解和饮食暴露下的生物积累。我们的结果表明，生物积累效率主要驱动金属浓度的异速生长模式，年龄的影响比尺寸更明显。老牡蛎的生物积累能力降低，导致金属浓度和大小呈负相关。同时，生长稀释等间接因素起着次要作用，暴露持续时间的影响可以忽略不计。这项研究增强了我们对控制海洋生物中金属生物积累的复杂机制的理解，并为改进生物监测数据的解释提供了重要见解。