Micro-distribution of arsenic in toenail clippings using laser ablation inductively coupled plasma mass spectrometry: implications for biomonitoring.

Toenails are a common monitoring tool for arsenic exposure, but the risk of external contamination of toenails has cast doubt on its usefulness. The main objective of this study is to investigate the micro-distribution of arsenic through the dorsoventral plane of nail clippings to understand endogenous vs exogenous sources. We used laser-ablation inductively coupled plasma mass spectrometry to measure arsenic through a dorsoventral cross-section of the nail plate collected from reference (N = 17) and exposed individuals (N = 35). Our main results showed (1) bulk toenail concentrations measured using ICP-MS in this study ranged from 0.54 to 4.35 µg/g; (2) there was a double-hump pattern in arsenic concentrations, i.e., dorsal and ventral layers had higher arsenic than the inner layer; (3) the double-hump was more pronounced in the exposed group (ventral: 6.25 µg/g; inner: 0.75 µg/g; dorsal: 0.95 µg/g) than the reference group (ventral: 0.58 µg/g; inner: 0.15 µg/g; dorsal: 0.29 µg/g) on average; (4) the distribution was, in part, associated with different binding affinity of nail layers (i.e., ventral > dorsal > inner); (5) most individuals in the higher exposure group showed > 25% contamination in ventral and dorsal nail layers; and (6) there were no statistically significant correlations between LA-ICP-MS arsenic with either bulk toenail arsenic or urine arsenic from the same individuals. Our results on micro-distribution and binding affinity provide insight into the impact of external contamination on arsenic concentrations and show how LA-ICP-MS can access the protected inner nail layer to provide a more accurate result.

Cohort profile: health effects monitoring programme in Ndilǫ, Dettah and Yellowknife (YKHEMP).

PURPOSE: The Yellowknife Health Effects Monitoring Programme (YKHEMP) was established to examine the relationship of exposure to arsenic and other chemicals of potential concern such as antimony, cadmium, lead, manganese and vanadium and health outcomes. PARTICIPANTS: A total of 2037 individuals were recruited, including children (age 3-19) and adults (age 20+), residing in Dettah, NdilÇ« and Yellowknife, in the Northwest Territories, Canada, in two waves in Fall 2017 and Spring 2018. In Yellowknife, there were 891 (675 adults, 216 children), randomly selected participants with a participation rate of 64%. In addition, we also recruited a total of 875 (669 adults, 206 children) volunteer participants. A total of 225 (137 adults, 88 children) of the Yellowknives Dene First Nation (YKDFN), and 46 (33 adults, 13 children) of the North Slave Métis Alliance participated in the study. Each participant answered a lifestyle questionnaire as well as provided toenail clippings and urine for contaminant testing and saliva samples for testing of genetic polymorphisms associated with arsenic metabolism. Participants also provided consent to have their medical records reviewed by the research team for the past 5 years to allow for the investigation between exposure and health outcomes. FINDINGS TO DATE: The adult YKHEMP participants had lower urinary total arsenic but the children had higher inorganic arsenic than the general Canadian population. There was no difference in urinary total arsenic concentrations between adults and children, however, urinary inorganic arsenic concentrations were generally higher in children than in adults in all four YKHEMP sampling groups. The adult YKDFN participants had lower urinary total arsenic and inorganic arsenic concentrations compared with the random selected and volunteer participants. FUTURE PLANS: YKHEMP is designed as a prospective cohort study; the children participants will be re-examined in 2022 and both adult and children participants in 2027.