Data from: Hitting reset on sediment toxicity: Sediment homogenization alters the toxicity of metal‐amended sediments

Laboratory testing of sediments frequently involves manipulation by amendment with contaminants and homogenization, which changes the physicochemical structure of sediments. These changes can influence the bioavailability of divalent metals, and field and mesocosm experiments have shown that laboratory-derived thresholds are often overly conservative. We assessed the mechanisms that lead to divergence between laboratory- and field-derived thresholds; specifically, we assessed the importance of slow equilibration to solid-phase ligands and vertical stratification. To mimic natural physicochemical conditions, we uniquely aged sediment with a flow-through exposure system. These sediments were then homogenized and compared, toxicologically, with freshly metal-amended sediments in a 28-d chronic toxicity bioassay with the amphipod Hyalella azteca. We assessed concentration–response relationships for 3 metals (copper, nickel, and zinc) and 5 geochemically distinct sediments. We observed minimal differences in growth and survival of H. azteca between aged and freshly spiked sediments across all sediments and metals. These trends suggest that a loss of toxicity observed during long-term sediment aging is reversed after sediment homogenization. By comparison with mesocosm experiments, we demonstrate that homogenizing sediment immediately before toxicity assays may produce artificially high toxicity thresholds. We suggest that toxicity assays with sediments that maintain vertical redox gradients are needed to generate field-relevant sediment metal toxicity thresholds.沉积物实验室测试常需通过添加污染物并均质化完成前处理，该操作会改变沉积物的理化结构。此类变化可影响二价金属的生物有效性，且野外与中宇宙实验均表明，实验室推导的阈值往往过于保守。本研究旨在解析实验室与野外推导阈值产生偏差的机制，重点评估了固相配体缓慢平衡以及垂直分层的重要性。为模拟自然理化环境，我们采用流水暴露体系对沉积物开展专属老化处理。随后将老化后的沉积物均质化，并与新鲜添加金属的沉积物，以端足类动物阿氏湖栖端足虫（Hyalella azteca）为受试生物开展为期28天的慢性毒性生物测定以进行毒理学对比。我们针对3种金属（铜、镍、锌）与5种地球化学特征迥异的沉积物，评估了浓度-响应关系。在所有沉积物与金属测试中，老化沉积物与新鲜添加金属沉积物中受试生物的生长与存活率差异极小。上述趋势表明，长期沉积物老化过程中出现的毒性损失，可在沉积物均质化后被逆转。通过与中宇宙实验对比，我们证实，在毒性测定前即刻对沉积物进行均质化处理，可能会人为推高毒性阈值。我们建议，采用能够维持垂直氧化还原梯度的沉积物开展毒性测定，方可生成贴合野外实际的沉积物金属毒性阈值。