Changes in urinary arsenic methylation profiles in a 15-year interval after cessation of arsenic ingestion in Southwest Taiwan

BACKGOUND: Inorganic arsenic (iAs) is carcinogenic to humans. Methylated metabolites of arsenic (As) found in the urine could serve as potential tools for screening and early detection of cancer in populations exposed to As. Relatively little information is available regarding changes in As methylation profiles after cessation of As exposure. OBJECTIVE: We examined the changes in urinary arsenic (uAs) species profiles over 15 years in a cancer-free population that has ceased heavy and prolonged ingestion of As. METHODS: In 1989, a cohort study was carried out with 1,081 adults who resided in three villages in southwestern Taiwan where arseniasis was hyperendemic. After 15 years of follow-up, a subgroup of 205 cancer-free participants had completed all interviews and had uAs methylation data available. We used this group in our statistical analysis. Arsenic species were measured by high-performance liquid chromatography-hydride generation-atomic absorption spectrometry. RESULTS: We compared the initial analyses from 1989 with those performed 15 years later and found that the average differences for the proportion of urinary iAs, monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV) were -4.90%, -6.80%, and 11.69%, respectively. The elderly and those residents with longer periods of consuming high-As artesian well water exhibited greater changes (decreases) in %MMAV. CONCLUSION: The As methylation profiles indicate increased efficiency in As metabolism in residents after cessation of long-term exposure to high-level As. Moreover, the decreased %MMAV was more pronounced in the elderly cancer-free subcohort subjects.