Atmospheric stability of arsines and the determination of their oxidative products in atmospheric aerosols (PM₁₀): evidence of the widespread phenomena of biovolatilization of arsenic

Abstract

Biovolatilisation of arsenic as their arsines in the form of AsH(3), and mono-, di and trimethylarsine has often been determined under laboratory conditions. Although environmental point sources such as landfill sites or hot springs have been characterised, only limited knowledge is available on how widespread the formation of volatile methylated arsenic compounds are in the environment. Here we studied the atmospheric stability of the different arsines and quantified their oxidation products in atmospheric particulate matter (PM(10)) in two locations in Argentina. The atmospheric half-life of the arsines range from 19 weeks for AsH(3) to 2 d for trimethylarsine (TMAs) at 20 degrees C in the dark, while during simulated daytime conditions the stability is reduced for all arsines and in particular for the methylated arsines by three orders of magnitude which suggests that TMAs can only be dispersed at night. At both locations the arsenic concentration was in all samples below 1 ng As m(-3), which is considered as rural background for arsenic. The oxidation products, i.e. methylarsonate (MA), dimethylarsinate (DMA) and trimethylarsine oxide (TMAO) were identified by using HPLC-ICP-MS/ES-MS in more than 90% of the 49 PM(10) samples taken from 8 sampling points at the two geographically different locations. TMAO was the predominate organoarsenicals in both locations (66 and 69%, respectively) while DMA was determined to be between 13 and 19% of all organoarsenicals at the two locations. The concentration of the organoarsenicals ranged from 4 to 60 pg As as TMAO m(-3), while the maximum concentration for DMA and MA were 16 and 6 pg As m(-3), respectively. No difference in terms of the concentration or distribution of the organoarsenicals in the PM(10) samples was identified as significant. Since the two locations were different in climate and industrial impact and sampled in different seasons, these data suggest that methylated arsenicals do occur as background chemicals in the environment. Due to the low atmospheric stability of the methylated arsines, it is suggested that biovolatilization of arsenic as methylated arsines is a widespread phenomenon. More studies however are necessary to identify the major sources and determine the flux of the volatilization process in order to determine whether or not the process has environmental significance.

Analytical approaches for arsenic determination in air: A critical review

“…The limits of detections provided by other authors for methylated As species (e.g. DMA and MMA) lie between 0.3-0.4 ng m -3 with HG-ICP-OES detection [128], and 1.16-1.97 ng m -3 with AFS detection [123], more than an order of magnitude than those reported by [74]. Therefore, their LODs do not allow them to detect organic arsenic species at the pg m -3 level.…”

“…In view of the results of Jakob et al [74], it can be found a possible reason for the apparent discrepancy with those other analytical methodologies that have not detected methylated As in PM samples. The limits of detections provided by other authors for methylated As species (e.g.…”

“…Jakob et al [74] have reported more recently an extraction method for methylated arsenic species from PM samples. These authors submitted PM10 samples from urban sites of Argentina to extraction with H 2 O 2 (30%), heating in a microwave oven.…”

“…In this case, Jakob et al [74] employed HPLC-ICP-MS for speciation of methylated As species. ICP-MS was operated in the collision cell mode with H 2 .…”

“…Therefore, their LODs do not allow them to detect organic arsenic species at the pg m -3 level. However, there may be other reasons to explain these discrepancies, rather than the analytical technique employed for detection, as the calibration graph employed for HPLC-ICP-MS is 5-30 µg l -1 [74], which is not very different with the different techniques: 1-10 µg l -1 with both HG-ICP-OES [128] and AFS [123]. One plausible reason is due to the natural origin of the methylated compounds.…”