Biovolatilization of Arsenic as Arsines from Seawater

Abstract

Marine sources of arsenic to the atmosphere are normally dismissed as minor. Here we show that arsenic can be biovolatilized from seawater, and that biovolatilzation is based on organic arsenic species present in the seawater. Even though inorganic arsenic is in great excess in seawaters, it is trimethylarsine (TMA) that is the primary biovolatilized product, with dimethylarsine (DMA) also observed if dimethylarsinic acid (DMAA) is spiked into seawaters. With respect to budgets, 0.04% of the total arsenic in the seawater was biovolatilized over a 2-week incubation period. To test the environmental significance of this finding, wet deposition was analyzed for arsenic species at coastal locations, one of which was the origin of the seawater. It was found that the oxidized product of TMA, trimethylarsine oxide (TMAO), and to a less extent DMAA were widely present. When outputs for arsines (0.9 nmol/m/d) from seawater and inputs from wet deposition (0.3-0.5 nmol/m/d) were compared, they were of the same order of magnitude. These findings provide impetus to reexamining the global arsenic cycle, as there is now a need to determine the flux of arsines from the ocean to the atmosphere.

The Pedosphere as a Sink, Source, and Record of Anthropogenic and Natural Arsenic Atmospheric Deposition

“…Bedrock can become enriched or depleted in arsenic due to geotectonic processes for igneous intrusions, the depositional environment for sedimentary rocks, and subsequent effects of transformation on metamorphically derived parent material. , Sediment transport also mobilizes and redistributes arsenic through aeolian, fluvial, and subduction processes. , The arsenic content of any given soil horizon will be dependent on parent material contribution, with pedogenesis leading to further redistribution of arsenic within profiles through weathering, leaching, and sequestration (Figure ). If solubilization of arsenic occurs during weathering, arsenic can be lost from a profile to adjacent water bodies, through vertical and lateral flow. − Solubilization and mobility is highly affected by redox, with arsenic becoming more mobile under more reducing conditions, often driven by the microbial utilization of organic matter. , The dominant forms of arsenic in environmental media are inorganic, arsenate, and arsenite. , The oxidized form arsenate is less soluble due to its strong affinity to other elements, while the reduced form arsenite is more labile. , Inorganic arsenic (arsenate and arsenite) can be methylated and demethylated microbially, both in soils , and in aquatic systems. Inorganic arsenic and methylated oxyanions can be converted to their corresponding arsines. − The chemical formulas and abbreviations for the arsenic species commonly detected in soils, waters, and atmosphere, their interconversions, and biogeochemical cycling between the soil–water–air interfaces are given in Figure .…”

“…If solubilization of arsenic occurs during weathering, arsenic can be lost from a profile to adjacent water bodies, through vertical and lateral flow. − Solubilization and mobility is highly affected by redox, with arsenic becoming more mobile under more reducing conditions, often driven by the microbial utilization of organic matter. , The dominant forms of arsenic in environmental media are inorganic, arsenate, and arsenite. , The oxidized form arsenate is less soluble due to its strong affinity to other elements, while the reduced form arsenite is more labile. , Inorganic arsenic (arsenate and arsenite) can be methylated and demethylated microbially, both in soils , and in aquatic systems. Inorganic arsenic and methylated oxyanions can be converted to their corresponding arsines. − The chemical formulas and abbreviations for the arsenic species commonly detected in soils, waters, and atmosphere, their interconversions, and biogeochemical cycling between the soil–water–air interfaces are given in Figure . Biovolatilization is an arsenic loss mechanism from soil and seawaters but also a source to the Earth’s surface through redeposition of arsines oxidized in the atmosphere , (Figure ).…”

“…Inorganic arsenic and methylated oxyanions can be converted to their corresponding arsines. − The chemical formulas and abbreviations for the arsenic species commonly detected in soils, waters, and atmosphere, their interconversions, and biogeochemical cycling between the soil–water–air interfaces are given in Figure . Biovolatilization is an arsenic loss mechanism from soil and seawaters but also a source to the Earth’s surface through redeposition of arsines oxidized in the atmosphere , (Figure ). Whether arsine driven cycling causes loss or addition of arsenic to soil stores will vary due to bulk depositional settling and inherent microbial activity within soil profiles. , …”

“…Biovolatilization is an arsenic loss mechanism from soil and seawaters but also a source to the Earth’s surface through redeposition of arsines oxidized in the atmosphere , (Figure ). Whether arsine driven cycling causes loss or addition of arsenic to soil stores will vary due to bulk depositional settling and inherent microbial activity within soil profiles. , …”

Mercury distribution in surface soil of China is potentially driven by precipitation, vegetation cover and organic matter

“…1). Wet deposition associated with east Asian summer monsoon has been considered as a major contributor to the distribution of trace elements such as volatile element selenium [22] and arsenic [45,46].…”