Ashley-Martin et al. 2022 — Biomonitoring of inorganic arsenic species in pregnancy
This review from Health Canada scientists synthesises the evidence base for measuring inorganic arsenic (iAs) species during pregnancy, addressing both the value of speciated versus total arsenic measurement and the methodological challenges unique to the pregnant population. The authors document that physiological changes in pregnancy (increased glomerular filtration rate, plasma volume expansion of approximately 45%, hormonal changes that upregulate arsenic methylation) systematically alter arsenic biomarker profiles compared to non-pregnant adults, making pregnancy-specific reference values and correction factors essential. The review surveys nine common and emerging biological matrices (urine, blood, toenails, hair, meconium, placenta, cord blood, saliva, and others), evaluating each for half-life, detection rates, analytical methods, and suitability for iAs speciation in pregnant populations. A key finding is that while urinary DMA is the dominant species in pregnancy (averaging 71 to 89.7 percent of speciated arsenic, higher than the 60 to 80 percent in non-pregnant adults), the elevated %DMA partly reflects pregnancy-induced methylation efficiency rather than solely higher iAs intake, complicating interpretation in populations with seafood consumption.
Key numbers
Urinary arsenic species in pregnancy cohorts: mean %DMA 71.0 to 89.7 across Bangladesh, Spain, China, Mexico, Chile, and Canada studies; mean %MMA 4.8 to 7.8; %iAs 4.7 to 20.6. In non-pregnant adults: mean %DMA 60 to 80; %MMA 10 to 20. MIREC study (Canada, n=1,933 first trimester): 95th percentile total blood arsenic 2.32 µg/L (T1) and 2.77 µg/L (T3). Urinary iAs species detection rates highly variable across studies (LODs range from 0.02 to 0.89 µg/L for individual species). WHO drinking water guideline for iAs is 10 µg/L; most contemporary North American and European studies represent populations well below this threshold. At water iAs below 10 µg/L, food sources (rice, vegetables, seafood) become comparable contributors to iAs exposure relative to drinking water. Toenails and hair provide longer integration windows (months) than urine (days) or blood (hours), making them preferable for chronic exposure in low-exposure populations.
Methods (brief)
Narrative review with systematic literature identification; no meta-analytic pooling. Covers HPLC-ICP-MS as the primary validated method for urinary speciated arsenic; reviews hydride generation-cryotrapping-AAS as an alternative. Addresses creatinine vs specific gravity correction for urinary dilution, with specific gravity preferred in pregnancy. Documents that trivalent metabolites (MMA-III, DMA-III) are rarely quantifiable due to instability. Notes that total arsenic measurements are insufficient for epidemiological studies of pregnancy outcomes because arsenobetaine (low toxicity, from seafood) can dominate total arsenic and create exposure misclassification.
Implications
Certification: High value for prenatal and vulnerable-population exposure framing in HMT&C and courses. Establishes that iAs biomonitoring in pregnancy requires speciation (not total arsenic) and matrix-specific interpretation. Documents that rice, vegetables, and seafood are the primary dietary iAs exposure routes in low drinking-water-arsenic populations.
Courses: Core reference for modules on arsenic exposure assessment, speciation methodology, vulnerable population framing, and the distinction between iAs and tAs in exposure studies. The matrix comparison table (Table 2 in the paper) is directly teachable.
App: The dietary source framing (rice, vegetables, seafood as primary iAs contributors when drinking water is below 10 µg/L) directly supports ingredient-level iAs risk scoring in the app model.
Microbiome: Not addressed.