Department of Environmental Health and Engineering, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA.
J Expo Sci Environ Epidemiol. 2023 Nov;33(6):945-953. doi: 10.1038/s41370-023-00560-y. Epub 2023 Jun 9.
Toenails are a promising matrix for chronic metal exposure assessment, but there are currently no standard methods for collection and analysis. Questions remain about sample mass requirements and the extent to which metals measured in this matrix are representative of chronic body burden.
This study proposes a method to maximize sample conservation for toenail metals analysis using inductively coupled plasma mass spectrometry (ICP-MS). We demonstrate the reliability of an ~25 mg toenail sample (typically 1-2 clippings) for metals analysis and evaluate the intra-individual variability of multiple metals in this matrix over time in men from the Gulf Long-term Follow-up (GuLF) Study.
Toenail samples from 123 GuLF Study participants were collected at two visits 3 years apart and analyzed for 18 elements using ICP-MS. Participants with samples exceeding 200 mg at the first visit (n = 29) were selected for triplicate sub-sample analysis. Kendall's coefficient of concordance (W) was used to assess sub-sample reliability and Spearman's correlation coefficients (ρ) were used to evaluate fluctuations in elemental concentrations over time.
Results were not reported for Cd, Co, Mo, Sb, and V (detected in <60% of the samples). There was strong agreement among triplicate samples (Kendall's W: 0.72 (Cu)-0.90 (Cu)) across all elements evaluated, moderate correlations of elemental concentrations (Spearman's ρ: 0.21-0.42) over 3 years for As, Ca, Cr, Fe, Pb, Mn, and Zn, and strong correlations (>0.50) for Se, Cu, and Hg.
This toenail reliability study found that a low-mass (~25 mg) toenail sample (1-2 clippings) is suitable for the determination of most elements using ICP-MS and helps to increase the analytical capacity of limited toenail biospecimens collected in cohort studies. The results highlight differences in the suitability of toenails for chronic metal exposure assessment by element and underscore the need to consider intra-person variability, especially when comparing results across studies. We also provide recommendations for analytical standardization and the partitioning of the total collected toenail sample into multiple analytic sub-samples for future studies using toenail biospecimen for multiple assays.
趾甲是评估慢性金属暴露的一种很有前途的基质，但目前尚无收集和分析的标准方法。关于样本质量要求以及该基质中测量的金属在多大程度上代表慢性体内负荷，仍存在一些问题。
本研究提出了一种使用电感耦合等离子体质谱法（ICP-MS）最大限度地保存趾甲金属分析样本的方法。我们证明了对于金属分析，使用~25mg 趾甲样本（通常为 1-2 个趾甲屑）的可靠性，并评估了 Gulf Long-term Follow-up（GuLF）研究中男性在一段时间内，该基质中多种金属的个体内变异性。
对 123 名 GuLF 研究参与者的趾甲样本进行了两次采集，两次采集时间相隔 3 年。使用 ICP-MS 分析了 18 种元素。在第一次采集时样本超过 200mg 的参与者（n=29）被选择进行三重复分样分析。采用肯德尔协调系数（W）评估分样可靠性，采用斯皮尔曼相关系数（ρ）评估元素浓度随时间的波动。
Cd、Co、Mo、Sb 和 V（在 <60%的样本中检测到）的结果未予报告。在所评估的所有元素中，三重复分样之间的结果具有很强的一致性（Kendall 的 W：0.72（Cu）-0.90（Cu）），3 年内元素浓度的相关性适中（Spearman 的 ρ：0.21-0.42），砷、钙、铬、铁、铅、锰和锌，以及硒、铜和汞的强相关性（>0.50）。
本趾甲可靠性研究发现，低质量（~25mg）趾甲样本（1-2 个趾甲屑）适合使用 ICP-MS 测定大多数元素，有助于增加在队列研究中收集的有限趾甲生物样本的分析能力。结果突出了不同元素的趾甲在评估慢性金属暴露方面的适用性，强调了在比较研究结果时需要考虑个体内变异性。我们还为分析标准化和将收集的总趾甲样本分为多个分析分样提供了建议，以供未来使用趾甲生物样本进行多种分析的研究使用。
