Table2_Toxic elements in benthic lacustrine sediments of Utah’s Great Salt Lake following a historic low in elevation.xlsx

Terminal lakes (without outflow) retain elements and compounds that reach them through fluvial, point source or atmospheric deposition. If the lake sediment is exposed, some of these chemicals could become toxic dust particulates. The Great Salt Lake (GSL) in Utah is a terminal lake that experienced record-low lake elevation in 2021-22, exposing vast areas of playa. Here, we used inductively coupled plasma mass spectrometry to analyze the environmental chemistry of GSL shallow sediment during historic lows in spring, summer, and fall of 2021. Contaminants at the subsurface interface are most able to influence diffusion into the water column and uptake by benthic biota. We focused our analysis on copper, thallium, arsenic, mercury, lead, and zinc, which have been historically deposited in this region and are toxic when at high concentrations. We compared records of regional mining activity to understand the current contamination and assess relevant spatial and temporal gradients. We also used two different extraction methods (EPA 3050b and NH4AcO at pH=7) that can distinguish “environmentally available” vs. tightly associated and less available fractions. We observed consistent concentration of copper across sites indicating a larger relative impact of atmospheric deposition, with some evidence indicating further impacts of point sources. Arsenic, on the other hand, is maintained at high levels in submerged sediments and is likely geologically- and fluvially- derived. Thallium and mercury fluctuate seasonally and correlate with lake elevation. Lead and zinc levels are relatively low in GSL sites compared with freshwater input sites, indicating the deep brine layer may sequester these heavy metals, preventing their release into the water column. Overall, the concentrations of most metals in GSL sediments have declined from historic highs. However, each contaminant has distinct sources, seasonality, mobility and transmission. Complete recovery (if possible) may require many more decades and individual remediation strategies.

终端湖（无出水口）会留存经由河流、点源或大气沉降输入的各类元素与化合物。若湖底沉积物裸露，其中部分化学物质可能转化为有毒粉尘颗粒物。犹他州大盐湖（Great Salt Lake, GSL）即为一座终端湖，其在2021至2022年创下湖泊水位历史新低，裸露了大片干盐湖滩。本研究于2021年春、夏、秋三季，在该湖处于历史低水位期间，采用电感耦合等离子体质谱法（inductively coupled plasma mass spectrometry）对大盐湖浅层沉积物的环境化学特征开展分析。沉积物-水界面处的污染物最易扩散进入水体，并被底栖生物摄取。本研究重点关注了铜、铊、砷、汞、铅及锌这六种在该区域历史沉积且高浓度下具有毒性的污染物。研究人员通过对比区域采矿活动记录，以明晰当前污染状况，并评估相关的空间与时间梯度。本研究同时采用两种萃取方法：美国环保署标准方法3050b（EPA 3050b）与pH=7的乙酸铵（NH4AcO）萃取法，以此区分"环境可利用态"与"紧密结合且难溶出"的污染物组分。研究发现各采样点的铜浓度分布较为一致，表明大气沉降对其相对影响更大，同时部分证据显示点源亦存在额外影响。相较之下，砷在淹没沉积物中始终维持较高浓度，其来源大概率为地质作用与河流输入。铊与汞的浓度存在季节性波动，且与湖泊水位呈显著相关。相较于淡水输入点位，大盐湖采样点的铅与锌浓度相对较低，这表明深层卤水层可能固持了这些重金属，阻止其向水体释放。总体而言，大盐湖沉积物中多数金属的浓度已较历史峰值有所下降。但各类污染物的来源、季节性特征、迁移性及传播路径均存在显著差异。若要实现完全修复（若可行），则可能需要数十年之久，且需制定针对性的修复策略。