Toxic metals in toenails as biomarkers of exposure: A review

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 issue, we reviewed literature on: a) time-window reflected by toenails; b) reproducibility toenail toxic-metal levels in repeated measures over time; c) relationship with other exposure, and; d) association potential determinants (i.e. sociodemographic, anthropometric, or lifestyle characteristics) sources like diet environmental pollution. Thus, performed a systematic review, searching articles that provided original data any following metals toenails: aluminum, beryllium, cadmium, chromium, mercury, nickel, lead, thallium uranium. We identified 88 articles, reporting from 67 different research projects, which were quite heterogeneous regard population profile, sample size analytical technique. The most commonly studied metal was mercury. Concerning explored toenails, some reports indicate nickel lead may reflect exposures occurred 7–12 months before sampling. For samples obtained 1–6 years apart, range intraindividual correlation coefficients chromium mercury 0.33–0.56. concentrations between toenails matrices higher hair fingernails than urine blood. Mercury consistently associated fish intake, while occasionally (e.g. drinking water, place residence, pollution, occupation). frequently evaluated health endpoints cardiovascular diseases, cancer, central nervous system diseases. Available suggest long-term showed positive associations intake. lack standardization collection, quality control, techniques procedures – along heterogeneity conflicting results among studies mean it still difficult conclude are good biomarker metals. Further needed draw solid conclusions about suitability