Rare earth elements (REEs) are a natural resource of vital economic interest. While REE mining and processing are known for severe environmental issues, REEs are also by-products of other mining processes (e.g. uranium). Here, we provide an in-depth assessment of REE distribution across a lake system impacted by adjacent uranium mining over a long period (Bow Lake, Ontario, Canada). We observed a robust REE-U correlation with a consistent La/U ratio of 2.0 ± 0.2 and La concentrations up to 2200 µg g⁻¹. Selective extraction results demonstrated that 80–94% of REEs were acid extractible, while 3–8% of REEs were extracted by an alkaline solution (i.e. bound to natural organic matter). Analysis of specific REE patterns, together with a strong REE-P correlation, suggest that (co)precipitation with P mineral would be an important mechanism sequestrating REEs into Bow Lake sediments. Moreover, we identified three sources of particles delivering REEs into the lake with unique REE patterns: mine tailings, U ores and Precambrian bedrock. Negative Sm anomalies were detected in three soil samples and associated with the Precambrian bedrock. We also detected positive Gd and La anomalies in the sediments. Lanthanum anomalies were strongly correlated with U authigenic accumulation and thus associated with microbial processes requiring La, such as methanotrophy. This research demonstrates that lake sediments adjacent to U mining could represent ecological risks given that La and other REE concentrations largely exceed the maximum permissible concentrations. Water and sediment quality criteria are therefore required as both primary REE mining and extraction of REEs as by-products from legacy metallurgical tailings are increasing.

稀土元素 (REE) 是具有重要经济利益的自然资源。虽然 REE 开采和加工以严重的环境问题而著称，但 REE 也是其他开采过程（例如铀）的副产品。在这里，我们对受邻近铀矿开采影响的湖泊系统（加拿大安大略省弓湖）的 REE 分布进行了深入评估。我们观察到稳健的 REE-U 相关性，La/U 比值一致为 2.0 ± 0.2，La 浓度高达 2200 µg g ^-1. 选择性提取结果表明，80-94% 的 REE 可被酸提取，而 3-8% 的 REE 被碱性溶液提取（即与天然有机物结合）。对特定 REE 模式的分析以及强烈的 REE-P 相关性表明，与 P 矿物的（共）沉淀将是将 REE 封存到 Bow Lake 沉积物中的重要机制。此外，我们确定了三种以独特的 REE 模式将 REE 输送到湖中的颗粒来源：尾矿、U 矿石和前寒武纪基岩。在三个土壤样品中检测到负 Sm 异常，并与前寒武纪基岩有关。我们还在沉积物中检测到正 Gd 和 La 异常。镧异常与 U 自生积累密切相关，因此与需要 La 的微生物过程有关，如甲烷营养。该研究表明，鉴于 La 和其他 REE 浓度大大超过最大允许浓度，U 矿附近的湖泊沉积物可能代表生态风险。因此，水和沉积物质量标准是必需的，因为主要的 REE 开采和 REE 作为来自遗留冶金尾矿的副产品的提取正在增加。