Department of Preventive Medicine and Public Health, University of Granada, Av. de La Investigación, 11, 18016, Granada, Spain; Instituto de Investigación Biosanitaria ibs. GRANADA, Spain; Consortium for Biomedical Research in Epidemiology & Public Health (CIBER en Epidemiología y Salud Pública - CIBERESP), Monforte de Lemos 5, 28029, Madrid, Spain.
Consortium for Biomedical Research in Epidemiology & Public Health (CIBER en Epidemiología y Salud Pública - CIBERESP), Monforte de Lemos 5, 28029, Madrid, Spain; Public Health & Preventive Medicine Teaching Unit, National School of Public Health, Carlos III Institute of Health, Monforte de Lemos 5, 28029, Madrid, Spain; Spanish Agency of Food Safety and Nutrition, Ministry of Consumer Affairs, Alcalá, 56, 28014, Madrid, Spain.
Environ Res. 2021 Jun;197:111028. doi: 10.1016/j.envres.2021.111028. Epub 2021 Mar 19.
Toenails have been used as biomarkers of exposure to toxic metals, but their validity for this purpose is not yet clear and might differ depending on the specific agent. To evaluate this issue, we reviewed the literature on: a) the time-window of exposure reflected by toenails; b) the reproducibility of toenail toxic-metal levels in repeated measures over time; c) their relationship with other biomarkers of exposure, and; d) their association with potential determinants (i.e. sociodemographic, anthropometric, or lifestyle characteristics) or with sources of exposure like diet or environmental pollution. Thus, we performed a systematic review, searching for articles that provided original data for levels of any of the following toxic metals in toenails: aluminum, beryllium, cadmium, chromium, mercury, nickel, lead, thallium and uranium. We identified 88 articles, reporting data from 67 different research projects, which were quite heterogeneous with regard to population profile, sample size and analytical technique. The most commonly studied metal was mercury. Concerning the time-window of exposure explored by toenails, some reports indicate that toenail cadmium, nickel and lead may reflect exposures that occurred 7-12 months before sampling. For repeated samples obtained 1-6 years apart, the range of intraindividual correlation coefficients of aluminum, chromium and mercury was 0.33-0.56. The correlation of toxic metal concentrations between toenails and other matrices was higher for hair and fingernails than for urine or blood. Mercury levels were consistently associated with fish intake, while other toxic metals were occasionally associated with specific sources (e.g. drinking water, place of residence, environmental pollution, and occupation). The most frequently evaluated health endpoints were cardiovascular diseases, cancer, and central nervous system diseases. Available data suggest that toenail mercury levels reflected long-term exposures and showed positive associations with fish intake. The lack of standardization in sample collection, quality control, analytical techniques and procedures - along with the heterogeneity and conflicting results among studies - mean it is still difficult to conclude that toenails are a good biomarker of exposure to toxic metals. Further studies are needed to draw solid conclusions about the suitability of toenails as biomarkers of exposure to toxic metals.
指甲已被用作暴露于有毒金属的生物标志物，但它们在这方面的有效性尚不清楚，而且可能因具体的金属而异。为了评估这个问题，我们回顾了以下方面的文献：a）指甲反映的暴露时间窗口；b）随着时间的推移，指甲中有毒金属水平的重复性；c）它们与其他暴露标志物的关系；以及 d）它们与潜在决定因素（即社会人口统计学、人体测量学或生活方式特征）或与饮食或环境污染等暴露源的关系。因此，我们进行了一项系统评价，搜索了提供以下任何一种有毒金属在指甲中水平的原始数据的文章：铝、铍、镉、铬、汞、镍、铅、铊和铀。我们确定了 88 篇文章，报告了 67 个不同研究项目的数据，这些项目在人口特征、样本量和分析技术方面差异很大。研究最多的金属是汞。关于指甲所探索的暴露时间窗口，一些报告表明，指甲中的镉、镍和铅可能反映了采样前 7-12 个月发生的暴露。对于相隔 1-6 年采集的重复样本，铝、铬和汞的个体内相关系数范围为 0.33-0.56。指甲与其他基质中有毒金属浓度的相关性在头发和指甲之间高于尿液或血液。汞水平与鱼类摄入量一直相关，而其他有毒金属偶尔与特定来源（如饮用水、居住地、环境污染和职业）相关。评估的健康终点最常见的是心血管疾病、癌症和中枢神经系统疾病。现有数据表明，指甲中的汞水平反映了长期暴露情况，并与鱼类摄入量呈正相关。由于缺乏样本采集、质量控制、分析技术和程序的标准化，再加上研究之间的异质性和相互矛盾的结果，因此仍难以得出指甲是有毒金属暴露的良好生物标志物的结论。需要进一步研究才能得出关于指甲作为有毒金属暴露生物标志物的适宜性的可靠结论。
