Toxic metals in toenails as biomarkers of exposure: A review
Metadata
Show full item recordEditorial
Elsevier
Materia
Toenail Biomonitoring Toxic metals Exposure Biomarker
Date
2021-03-19Referencia bibliográfica
Inmaculada Salcedo-Bellido... [et al.]. Toxic metals in toenails as biomarkers of exposure: A review, Environmental Research, Volume 197, 2021, 111028, ISSN 0013-9351, [https://doi.org/10.1016/j.envres.2021.111028]
Sponsorship
FIS (Instituto de Salud Carlos III, State Secretary of R + D + I) PI12/00150 PI17CIII/00034 PI18/00287; FIS (European Union (ERDF/ESF, "Investing in your future") PI12/00150 PI17CIII/00034 PI18/00287 U; nited States Department of Health & Human Services National Institutes of Health (NIH) - USA NIH National Institute of Environmental Health Sciences (NIEHS) P42ES010349 P30ES009089Abstract
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.