Human toenails as a biomarker of exposure to elevated environmental arsenic

Abstract

A pilot study was conducted to determine the applicability of toenails as a biomarker of exposure to elevated environmental arsenic (As) levels. A total of 17 individuals were recruited for the pilot study: 8 residents living near to a former As mine, Devon, UK, forming the exposed group, plus 9 residents from Nottinghamshire, UK, with no anticipated As exposure who were used for comparison as a control group. All toenail samples were thoroughly washed prior to analysis and the wash solutions retained for As determination via ICP-MS to provide an indication of the background environmental As levels for each group. Total As was determined in washed toenail samples via ICP-MS following microwave assisted acid digestion. Concentrations of total As in the toenails of the exposed group were elevated, ranging from 858 to 25 981 µg kg⁻¹ (geometric mean = 5406 µg kg⁻¹), compared to the control group whose toenail As concentrations ranged from 73 to 273 µg kg⁻¹ (geometric mean = 122 µg kg⁻¹). Higher levels of exogenous As contamination were present on the toenails of the exposed group (geometric mean = 506 µg kg⁻¹) compared to the control group (geometric mean = 4.0 µg kg⁻¹) providing evidence of higher environmental As levels in the exposed group. Total As concentrations in toenail samples were positively correlated to environmental As levels (r = 0.60, p < 0.001). HPLC-ICP-MS analysis of aqueous toenail extracts revealed inorganic arsenite (As^III) to be the dominant species extracted (∼83%) with lesser amounts of inorganic arsenate (As^V) and organic dimethylarsinate (DMA^V) at ∼13% and ∼8.5%, respectively. Arsenic speciation in analysed toenail extracts from the two groups was comparable. The only notable difference between groups was the presence of small amounts (<1%) of organic methylarsonate (MA^V) in two toenail samples from the exposed group. Toenails are presented as a viable biomarker of exposure at sites with elevated environmental As, such as the former mining sites found throughout Devon and Cornwall, UK.