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Generation of Substantially Metal-Reduced but Aldehyde-Rich Aerosol for E-Cigarette Toxicity Studies

When e-liquid is aerosolized in an e-cigarette for inhalation by the user, the aerosol becomes contaminated by a mixture of toxicants, including metals ...

Columbia University

Iron oxides control the mobility of a host of contaminants in aquifer systems, and the microbial reduction of iron oxides in the subsurface is linked to high levels of arsenic in groundwater that affects greater than 150 million people globally. Paired observations of groundwater and solid-phase aquifer composition are critical to understand spatial and temporal trends in contamination and effectively manage changing water resources, yet field-representative mineralogical data are sparse across redox gradients relevant to arsenic contamination. We characterize iron mineralogy using X-ray absorption spectroscopy across a natural gradient of groundwater arsenic contamination in Vietnam. Hierarchical cluster analysis classifies sediments into meaningful groups delineating weathering and redox changes, diagnostic of depositional history, in this first direct characterization of redox transformations in the field. Notably, these groupings reveal a signature of iron minerals undergoing active reduction before the onset of arsenic contamination in groundwater. Pleistocene sediments undergoing postdepositional reduction may be more extensive than previously recognized due to previous misclassification. By upscaling to similar environments in South and Southeast Asia via multinomial logistic regression modeling, we show that active iron reduction, and therefore susceptibility to future arsenic contamination, is more widely distributed in presumably pristine aquifers than anticipated.

Aquifer-Scale Observations of Iron Redox Transformations in Arsenic-Impacted Environments to Predict Future Contamination.

Assessing human exposure to commonly used, highly toxic, but non-persistent organophosphates (OPs) is challenging because these toxicants are readily biotransformed into dialkyl phosphates (DAPs) and other metabolites. Growing hair accumulates toxicants and their metabolites, which makes hair a valuable non-invasively sampled matrix that can be used to retrospectively examine chemical exposure. However, the efficient quantification of hydrophilic DAP compounds in hair is challenging due to complex hair matrix effects. To improve upon existing methods, we first examined the acid dissociation constants (pKa) of DAPs and amino acids (major components in hair) and identified the best pH conditions for minimizing matrix effects. We hypothesized that under basic pH conditions DAPs and amino acids would be negatively charged and have weak interactions favorable to DAP dissociation from the matrix. To test this, we compared the efficiency of various pH conditions of suitable solvents to extract six DAPs from hair samples, and we quantified these DAPs using liquid chromatography-tandem mass spectroscopy (LC-MS/MS). As expected, a basic extraction (methanol with 2% NHOH) approach had the highest extraction efficiency and yielded satisfactory recoveries for all six DAPs (72%-152%) without matrix effects. Additionally, the alkaline extract can be directly injected into the LC-MS/MS. This relatively rapid and simple procedure allowed us to process up to 90 samples per week with reproducible results. To our knowledge, this is the first method to quantify all six DAPs simultaneously in hair using LC-MS/MS with electrospray ionization (ESI) in negative ion mode. Finally, we demonstrated the feasibility of measuring DAP levels in hair samples from patients affected with amyotrophic lateral sclerosis (ALS), a neurodegenerative disease potentially linked to OP exposure. Due to our optimized solvent extraction process, the method we have developed is compatible with the rapidity and sensitivity needed for hair analysis applied to population biomonitoring.

Article	Year
Aquifer-Scale Observations of Iron Redox Transformations in Arsenic-Impacted Environments to Predict Future Contamination. Environmental science & technology letters\| PubMed ID: 33604397	2020
Rapid LC-MS/MS quantification of Organophosphate non-specific metabolites in hair using alkaline extraction approach. Journal of chromatography. B, Analytical technologies in the biomedical and life sciences\| PubMed ID: 36774786	2023

Khue N. Nguyen

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