Methylmercury (MeHg) continues to pose a significant global health risk to wildlife and humans through fish consumption. Despite numerous advancements in understanding the mercury (Hg) cycle, questions remain about MeHg sources that accumulate in fish, particularly across transitional coastal areas, where harvest is prominent and Hg sources are numerous. Here we used a unique combination of Hg and nutrient isotopes, and otolith chemistry to trace the biogeochemical history of Hg and identify Hg sources that accumulated in an economically important fish species across Mobile Bay, Alabama (USA). Fish tissue Hg in our samples primarily originated from wet deposition within the watershed, and partly reflected legacy industrial Hg. Results also suggest that little Hg was lost through photochemical processes (<10% of fish tissue Hg underwent photochemical processes). Of the small amount that did occur, photodegradation of the organic form, MeHg, was not the dominant process. Biotic transformation processes were estimated to have been a primary driver of Hg fractionation (∼93%), with isotope results indicating methylation as the primary biotic fractionation process prior to Hg entering the foodweb. On a finer scale, individual lifetime estuarine habitat use influenced Hg sources that accumulated in fish and fish Hg concentrations, with runoff from terrestrial Hg sources having a larger influence on fish in freshwater regions of the estuary compared to estuarine regions. Overall, results suggest increases in Hg inputs to the Mobile Bay watershed from wet deposition, turnover of legacy sources, and runoff are likely to translate into increased uptake into the foodweb.

中文翻译：

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同位素和耳石化学提供了对南方比目鱼在盐度梯度上的汞生物地球化学历史的深入了解

甲基汞（MeHg）通过鱼类消费继续对野生动物和人类构成重大的全球健康风险。尽管在了解汞 (Hg) 循环方面取得了许多进展，但有关鱼类体内积累的甲基汞来源的问题仍然存在，特别是在过渡性沿海地区，这些地区的捕捞量很大且汞来源众多。在这里，我们使用汞和营养同位素的独特组合以及耳石化学来追踪汞的生物地球化学历史，并确定在美国阿拉巴马州莫比尔湾的一种重要经济鱼类中积累的汞来源。我们样本中的鱼组织汞主要来源于流域内的湿沉降，部分反映了遗留的工业汞。结果还表明，光化学过程中汞损失很少（<10% 的鱼组织汞经历了光化学过程）。在确实发生的少量物质中，有机形式甲基汞的光降解并不是主要过程。据估计，生物转化过程是汞分馏的主要驱动力（~93%），同位素结果表明甲基化是汞进入食物网之前的主要生物分馏过程。在更精细的尺度上，个体一生对河口生境的利用影响了鱼类中积累的汞来源和鱼类汞浓度，与河口地区相比，陆地汞来源的径流对河口淡水地区鱼类的影响更大。总体而言，结果表明，湿沉降、遗留源周转和径流导致莫比尔湾流域汞输入的增加可能会转化为食物网吸收的增加。