Assessing the feasibility of using toenails as biomarkers for estimating inorganic arsenic exposure in Japanese adults.

Abstract

Background: Long-term exposure to inorganic arsenic (InAs) through arsenic (As)-contaminated drinking water poses serious health risks. However, epidemiological studies focusing on low-level dietary exposure to InAs are lacking. Furthermore, although toenail clippings are used as biomarkers for assessing As exposure in areas with contaminated drinking water, to date, no method has been developed for using toenails as a biomarker of long-term InAs exposure in individuals with lower exposure levels, e.g., from dietary sources including fish and seaweeds. Therefore, this study aimed to assess the feasibility of using toenails as biomarkers for estimating InAs exposure in Japanese adults.

Methods: Three sets of 7-day diet records and toenail clipping samples were collected from 39 healthy adult participants at intervals of 1-6 months over 4-8 months, spanning from June 2019 to March 2020. The analysis sample sets comprised 113 sample sets obtained from 38 subjects: 56 samples from 19 males and 57 samples from 19 females. The speciation of As species in the toenail samples was performed using high-performance liquid chromatography-inductively coupled plasma mass spectrometry. The sum of the InAs and monomethylarsonic acid (MMA) or sum of As species (sum-As) concentrations in toenail samples was used as an index of InAs exposure.

Results: The geometric mean (GM) concentration of InAs + MMA or sum-As in toenails was 0.180 µg As/g or 0.284 µg As/g. The estimated GM of daily dietary InAs exposure was 0.147 µg/kg/day. Log-transformed InAs + MMA or sum-As concentrations in toenails did not predict dietary InAs exposure levels from rice and hijiki consumption in both males and females. Similarly, toenail InAs + MMA or sum-As concentrations showed no correlation with dietary InAs exposure levels from rice or hijiki consumption.

Conclusions: Our findings indicate that human toenail clippings are not a suitable biomarker for assessing long-term InAs exposure levels in Japanese individuals based on the observed range of InAs and its metabolite concentrations in toenails.