Investigating the Occurrence and Environmental Significance of Methylated Arsenic Species in Atmospheric Particles by Overcoming Analytical Method Limitations

A novel analytical method has been developed for the determination of all five arsenic species known to exist in atmospheric particulate matter (PM), i.e., the inorganic arsenite iAs­(III) and arsenate iAs­(V), and the methylated methylarsonate (MA), dimethylarsinate (DMA) and trimethylarsine oxide (TMAO). Although the methylated species were first detected in PM in the late 1970s, most of the recent studies focus mainly on the two inorganic As species, ignoring TMAO in particular. In the present study, an HPLC (with an anion and cation exchange column connected in series)-arsine generation-ICP-MS system provided complete separation of all five As species and limits of detection from 10 to 25 pg As mL^–1. This method was applied to analyze water extracts of the inhalable fraction of atmospheric PM (PM₁₀, PM_2.5 and PM_2.1). 81 samples were collected, most during Saharan dust events, from a semirural area, and analyzed. The total water extractable arsenic ranged from 0.03 to 0.7 ng of As m^–3, values that are representative for remote areas. iAs­(V) was the most abundant species followed by TMAO, DMA, iAs­(III) and MA. None of the As species showed any particular trend with the presence or intensity of dust events, or seasonality, except for TMAO, which showed higher concentrations during the colder months